Name: high-resolution respirometry to assess mitochondrial function in permeabilized and intact cells
Uploaded: 2017-02-08T13:00:00.000+00:00
Duration: 8 min 33 s
Description: Watch this Scientific Journal Video about High-resolution Respirometry to Assess Mitochondrial Function in Permeabilized and Intact Cells at JoVE.com

This study was supported by the Swiss National Science Foundation (Grant n&#186; 32003B_127619).

1. Cell Culture
<ol>
	<li>Culture human hepatoma HepG2 cells6 in 25 cm2 cell culture flasks in Dulbecco&#39;s Modified Eagle&#39;s medium (DMEM) containing 10% heat-inactivated fetal bovine serum (FBS) and 1% penicillin-streptomycin at 37 &#176;C in an incubator (5% CO2, 95% air) (seeding density: 1 x 106 cells per 25 cm2 cell culture flask, incubation time in the 37 &#176;C incubator: 48 hr, cell density at confluency: 4-5 x 106 cells per 25 cm2 cell culture flask).</li>
	<li>Perform the experiments when cells are 90% to 95% confluent.</li>
</ol>
2. High-resolution Respirometry Calibration of Polarographic Oxygen Sensors
<ol>
	<li>Pipette 2.1 ml of respiration buffer into an oxygraph chamber and stir the buffer continuously using a magnetic stirring bar present in the chamber (700 rpm) at 37 &#176;C for 1 hr until a stable oxygen flux signal of the polarographic oxygen sensor is obtained. 
	NOTE: Polarographic oxygen electrodes within each oxygraph chamber measure oxygen concentration and calculate oxygen consumption (flux) within each chamber. The oxygen concentration and oxygen consumption rates (flux) are displayed real-time online in a computer using software for data acquisition and analysis.</li>
	<li>Perform an air calibration of the polarographic oxygen sensor according to the manufacturer&#39;s protocols14. 
	NOTE: Calibration of polarographic oxygen sensors in respiration media and oxygen concentration in the media at air saturation experimental temperature is performed only once daily in the morning. Afterwards the media can be removed from the chambers and cells resuspended in a fresh respiration media are added to an oxygraph chamber and respiratory rates are measured. After the first experiment, the chamber can be washed and additional series of experiments can be performed in the same chamber without further calibrations.</li>
</ol>
3. Trypsinization of Adherent Cells, Counting Cells
<ol>
	<li>On the day of the experiment, aspirate the DMEM from the 25 cm2 cell culture flask.</li>
	<li>Rinse the cell culture monolayer in the culture flask with 5 ml of phosphate buffered saline (PBS).</li>
	<li>Pipette 0.5 ml of 25 mg/ml of trypsin solution (prewarmed to 37 &#176;C in a 37 &#176;C water bath) into the cell monolayer in the culture flask and incubate for 5 min at 37 &#176;C in an incubator (5% CO2, 95% air).</li>
	<li>Pipette 5 ml of DMEM containing 10% FBS into the detached cells in the cell culture flask and suspend the cells by pipetting.</li>
	<li>Transfer resuspended cells to a 15 ml centrifuge tube and centrifuge for 5 min at 350 x g at room temperature and decant the supernatant.</li>
	<li>Resuspend the cell pellet in 1 ml of respiration buffer13 (Table 1).</li>
	<li>Count the cells using a cell counter and resuspend them in the respiration buffer to a final density of 1 x 106 cells/ml. Since cellular respiration rates will be normalized to cell number, count the cells with an accurate and precise cell counter.</li>
</ol>
4. High-resolution Respirometry
<ol>
	<li>After air calibration (performed only once daily, steps 2.1-2.2), aspirate the respiration medium from a chamber of the oxygraph and add 2.1 ml of cell suspension (1 x 106 cells/ml) from step 3.7 to the chamber.</li>
	<li>Close the oxygraph chamber by insertion of the stopper.</li>
	<li>Stir the cells continuously using a magnetic stirring bar present in the chamber (700 rpm) at 37 &#176;C and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved. 
	NOTE: The oxygen concentration and oxygen flux signal are displayed real-time online in a computer using software for data acquisition and analysis14.</li>
	<li>Afterwards, inject substrates and inhibitors for mitochondrial respiration through the titanium injection ports of the stoppers using the following protocols.</li>
</ol>
5. Digitonin Titration in Intact Cells by Respirometry
<ol>
	<li>Prepare an oxygraph chamber containing cell suspension (1 x 106/ml) following the procedure described in steps 4.1 to 4.3 of the protocol.</li>
	<li>Inject 2 &#181;l of 0.2 mM rotenone (0.2 &#181;M) &#39;CAUTION&#39; into the oxygraph chamber containing cell suspension through the titanium injection port of the chamber stopper using a syringe and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved. 
	NOTE: All the injections in the following steps are performed through the titanium injection ports of stoppers using syringes. Addition of rotenone is optional (it prevents reverse electron flow) and can be omitted for digitonin titration experiments, see step 6.3.</li>
	<li>Inject 20 &#181;l of 1 M succinate (10 mM) into the oxygraph chamber and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved.</li>
	<li>Inject 10 &#181;l of 0.5 M ADP (2.5 mM) into the oxygraph chamber and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved.</li>
	<li>Inject 2 &#181;l of 2 mM digitonin (2 &#181;M) into the oxygraph chamber and record cellular respiration for 2-5 min until a stable oxygen signal is achieved.</li>
	<li>Again inject 2 &#181;l of 2 mM digitonin into the oxygraph chamber and record cellular respiration for 2-5 min until a stable oxygen signal is achieved. 
	NOTE: Stepwise addition of digitonin to the cells will induce an increase in cellular oxygen consumption and the oxygen flux signal will increase.</li>
	<li>Continue injecting 2-4 &#181;l of 2 mM digitonin stepwise (2-4 &#181;M each step) into the chamber. After each step, record cellular respiration for 2-5 min until a stable oxygen flux signal is achieved. 
	NOTE: Stop injecting digitonin when the oxygen flux signal reaches a maximal level and further injections of digitonin do not increase the respiration rate. The readers should determine optimal digitonin concentration in their laboratories using their own reagents and use obtained optimal digitonin concentration in the steps 6.2 and 7.2 of the following protocols for their experiments.</li>
</ol>
6. Evaluation of the Mitochondrial Outer Membrane Integrity: Cytochrome C
<ol>
	<li>Prepare an oxygraph chamber containing cell suspension (1 x 106/ml) following the procedure described in steps 4.1 to 4.3 of the protocol.</li>
	<li>Inject 2 &#181;l of 8 mM digitonin (8 &#181;M) into the oxygraph chamber containing the cell suspension (1 x 106/ml) and permeabilize the cells for 5 min.</li>
	<li>Inject 20 &#181;l of 1 M succinate (10 mM) into the oxygraph chamber and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved.</li>
	<li>Inject 10 &#181;l of 0.5 M ADP (2.5 mM) into the oxygraph chamber and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved. 
	NOTE: Addition of ADP to the cells will stimulate complex I and induce an increase in oxygen consumption, and oxygen flux signal will increase and stabilize.</li>
	<li>Inject 5 &#181;l of 4 mM cytochrome c (10 &#181;M) into the oxygraph chamber and record cellular respiration for 5-10 min until a stable oxygen flux signal is achieved.</li>
	<li>Finally inject 1 &#181;l of 4 mg/ml oligomycin (2 &#181;g/ml) and record cellular respiration until a stable oxygen flux signal is achieved.</li>
</ol>
7. Maximal ADP-stimulated Respiration (State 3) of Permeabilized HepG2 Cells
<ol>
	<li>Prepare an oxygraph chamber containing cell suspension (1 x 106/ml) following the procedure described in steps 4.1 to 4.3 of the protocol.</li>
	<li>Inject 2 &#181;l of 8 mM digitonin (8 &#181;M) into the oxygraph chamber containing the cell suspension and permeabilize the cells for 5 min.</li>
	<li>Inject 12.5 &#181;l of 0.8 M of malate (5 mM) and 10 &#181;l of 2 M of glutamate (10 mM) into the oxygraph chamber. Record cellular respiration until a stable oxygen flux signal is achieved.</li>
	<li>Inject 10 &#181;l of 0.5 M ADP (2.5 mM) into the oxygraph chamber and record cellular respiration until the oxygen flux signal increases and stabilizes. 
	NOTE: Addition of ADP to the cells will induce an increase in oxygen consumption and the oxygen flux signal will increase.</li>
	<li>Inject 2 &#181;l of 0.2 mM rotenone (0.2 &#181;M) &#39;CAUTION&#39; into the oxygraph chamber and record cellular respiration until the oxygen flux signal decreases and stabilizes.</li>
	<li>Afterwards, inject 20 &#181;l of 1 M succinate (10 mM) into the oxygraph chamber and record cellular respiration until the oxygen flux signal increases and stabilizes.</li>
	<li>Then, inject 2 &#181;l of 5 mM antimycin A (5 &#181;M) &#39;CAUTION&#39; into the oxygraph chamber and record cellular respiration until the oxygen flux signal decreases and stabilizes.</li>
	<li>Then inject 2.5 &#181;l of 0.8 mM ascorbate (1 mM) and immediately after inject 2.5 &#181;l of 0.2 mM TMPD (0.25 mM) into the oxygraph chamber and record cellular respiration until the oxygen flux signal increases and stabilizes.</li>
	<li>Finally inject 10 &#181;l of 1 M sodium azide (5 mM) &#39;CAUTION&#39; into the oxygraph chamber and record cellular respiration until the oxygen flux signal decreases and stabilizes.</li>
</ol>
8. Oxygen Consumption of Intact Cells
<ol>
	<li>Prepare an oxygraph chamber containing cell suspension (1 x 106/ml) following the procedure described in steps 4.1 to 4.3 of the protocol.</li>
	<li>Inject 1 &#181;l of 4 mg/ml oligomycin (2 &#181;g/ml) into the oxygraph chamber containing cell suspension and record cellular respiration until a stable oxygen flux signal is achieved.</li>
	<li>Afterwards inject 1 &#181;l of 0.2 mM of FCCP (0.1 &#181;M) &#39;CAUTION&#39; into the oxygraph chamber and record cellular respiration until the oxygen flux signal increases and stabilizes.</li>
	<li>Inject 3 &#181;l of 0.2 mM of FCCP (0.4 &#181;M) into the oxygraph chamber and record cellular respiration until the oxygen flux signal increases further and stabilizes.</li>
	<li>Titrate FCCP in 0.1 to 0.3 &#181;M steps by injecting 1-3 &#181;l of 0.2 to 1 mM FCCP (0.1 to 2 &#181;M final concentration in the chamber) into the oxygraph chamber until the oxygen flux signal reaches its maximal levels and no further increases and then starts declining. 
	NOTE: Stop injecting FCCP when the oxygen signal reaches a maximal level and starts declining.</li>
	<li>Then, inject 2 &#181;l of 0.2 mM rotenone (0.2 &#181;M) and 2 &#181;l of 5 mM antimycin A (5 &#181;M) into the chamber. Record respiration until the oxygen flux signal decreases and stabilizes.</li>
</ol>

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The authors have nothing to disclose.

The objective of the present protocol was to use high-resolution respirometry to measure mitochondrial respiratory chain complexes&#39; (I-IV) respiratory rates, maximal mitochondrial electron transport system capacity and mitochondrial outer membrane integrity.
There are some critical steps within the present protocol. First, cellular oxygen consumption rates are usually normalized to the number of cells (pmol/[sec x number of cells]). Therefore, before monitoring cellular oxygen consumption,...

Mitochondria fulfill important roles in cellular energy metabolism, especially by using oxygen to produce adenosine triphosphate (ATP). They are implicated in cell death and in several human diseases. Mitochondrial oxidative phosphorylation (OXPHOS) combines electron transport along the electron transport chain with oxygen consumption and ATP synthesis. The mitochondrial tricarboxylic acid (TCA) cycle is involved in the conversion of proteins, carbohydrates and fats into energy rich compounds as nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FADH2). Electrons of the NADH and FADH2 are then transferred to the respiratory electron transport chain protein complexes (I to IV) located in the inner mitochondrial membrane. In addition, two other redox pathways can transfer electrons to electron transport chain: i) mitochondrial electron-transferring flavoprotein (ETF) which is located on the matrix face of the inner mitochondrial membrane, and supplies electrons from fatty acid &#946;-oxidation; and ii) mitochondrial glycerophosphate dehydrogenase which oxidizes glycerophosphate to dihydroxyacetone phosphate and feeds electrons to the mitochondrial electron transport chain. Complex IV (the ultimate electron acceptor) transfers the electrons to one oxygen molecule, converting oxygen to two molecules of water. Moving of the electrons from respiratory electron transport chain complex I to IV is coupled with proton flow from the mitochondrial matrix to the intermembrane space which establishes an electrochemical gradient across the mitochondrial inner membrane. Afterwards, mitochondrial complex V (ATP synthase) shuttles the hydrogen ions back into the mitochondrial matrix and synthesizes ATP molecules. OXPHOS function can be assessed in vivo and in vitro using various techniques and various mitochondrial respiration states can be obtained. In isolated mitochondria the following respiratory states can be measured: i) basal mitochondrial respiration (state 1), ii) oxygen consumption after the addition of specific substrates of the mitochondrial respiratory chain complexes (state 2), iii) maximal mitochondrial oxygen consumption after the addition of saturating concentrations of adenosine diphosphate (ADP) (state 3) and, iv) resting respiration after ADP consumption (converted to ATP) (state 4). In intact cells the following respiratory states can be measured: i) basal cellular oxygen consumption in the presence of endogenous substrates and ADP, ii) basal cellular oxygen consumption in the presence of oligomycin (oligomycin-insensitive respiration) and oligomycin-sensitive respiration (ATP turnover), iii) FCCP uncoupled respiration, and iv) non-mitochondrial respiration after the addition of antimycin A and rotenone. In permeabilized cells, specific substrates of the electron transport chain complexes and ADP can be added and maximal complex-dependent respiratory rates such as complex I-, II- and IV-dependent respiratory rates can be measured.
Measurements of cellular respiration provide important insights into mitochondrial respiratory capacity specific to complexes I-IV, mitochondrial integrity and energy metabolism1,2,3. One of the devices which enable measurements of mitochondrial oxygen consumption with high accuracy, resolution and sensitivity is the high-resolution oxygraph4. The high-resolution oxygraph device contains two chambers with injection ports and each chamber is equipped with a polarographic oxygen sensor. Cellular or isolated mitochondrial suspensions are stirred continuously in the respirometer. To assess mitochondrial function, substrates and inhibitors for mitochondrial complex activity can be added following standard protocols. Substrates and inhibitors can be titrated by injection into the chambers of the oxygraph, and oxygen consumption rates are calculated using software and expressed as picomoles per second per number of cells. High-resolution respirometry offers several advantages over traditional and conventional polarographic oxygen electrode devices including increased sensitivity and the ability to work with small numbers of biological samples such as intact or permeabilized cells. In addition, each device contains two chambers, and respiratory rates can be recorded simultaneously for comparisons of oxygen concentrations. The high-resolution oxygraph also has the advantage of reduced leakage of oxygen from the device chambers compared to traditional polarographic oxygen electrode devices. Another device recently developed to measure cellular oxygen consumption is the 96-well extracellular flux analyzer5. The extracellular flux analyzer is equipped with fluorescence instead of polarographic sensors. The advantages of the extracellular flux analyzer compared to the high-resolution oxygraph are i) it is a largely automated device, ii) it is possible to measure oxygen consumption in 24- and 96-well plates for high-throughput screening, therefore requiring lower amounts of biological samples, and iii) additional measurement of cellular glycolytic flux is possible. The disadvantages of the extracellular flux analyzer in comparison to the high-resolution oxygraph are i) the high costs of the device and of consumables such as fluorescent plates, which are non-reusable, and ii) only four compounds per assay/well are injectable, therefore the system is not feasible for substrate-uncoupler-inhibitor titration protocols.
In the present study, we use high-resolution respirometry to determine mitochondrial respiration. For cellular oxygen consumption experiments, the cells are permeabilized to allow the entry of exogenous ADP and oxidizable mitochondrial substrates for feeding electrons into complexes of the respiratory system. This approach allows the dissection of individual mitochondrial complexes respiratory capacities, which is a distinct advantage compared to intact cells (many substrates are cell-impermeant). However, cell membrane permeabilization will disrupt the barrier between the cytosol and extracellular space and medium (wash out of cytosolic solutes) and the composition of the intracellular space is equilibrated with the extracellular medium. One of the disadvantages of permeabilized cells over intact cells is that the mitochondrial outer membrane can be damaged if excessive amounts of detergent are employed during cell permeabilization. In intact cells, basal, coupled and uncoupled respiration of intact cells can be measured. This method evaluates oxygen consumption of intact cells without the addition of exogenous substrates and ADP, reproducing the respiratory function in the integrated cell and also providing information on maximal mitochondrial electron transport capacity6,7. One of the advantages of intact cells over permeabilized cells is that cellular environment is not disrupted and mitochondria are in contact with the whole components of the cells. In order to permeabilize the cellular plasma membrane, detergents such as digitonin have been used8. However, mitochondrial outer membrane integrity can be compromised if excessive amounts of digitonin are employed. To confirm that mitochondrial outer membrane integrity is not compromised in permeabilized cells, digitonin titration is performed to determine the optimal concentration for cellular permeabilization. For these experiments, cells are resuspended in respiration medium and digitonin concentration is titrated by respirometry in the presence of mitochondrial substrates and ADP, and respiration rates are measured. Respiration of intact, non-permeabilized cells is not stimulated in the presence of mitochondrial substrates and ADP. However, subsequent stepwise digitonin titration would yield gradual permeabilization of plasma membranes, and optimal digitonin concentration is obtained. This is shown by the increase of respiration up to full permeabilization. Mitochondrial quality and outer membrane integrity can be verified by adding exogenous cytochrome c2,9. Cytochrome c is a 12 kDa electron carrying protein of the mitochondrial electron transport chain 10,11,12. It is localized in the mitochondrial intermembrane space, and is involved in oxygen consumption, carrying electrons from complex III to complex IV. Once the mitochondrial outer membrane is damaged, cytochrome c is released, and mitochondrial oxygen consumption is reduced. Upon addition of exogenous cytochrome c, any augmentation in mitochondrial respiration is indicative of a disrupted mitochondrial outer membrane.
In permeabilized cells, substrates and inhibitors of mitochondrial complex activity are added following various protocols3,9. For example in order to investigate mitochondrial complex-driven respiratory rates, the following protocol can be used. After permeabilization of the cells, first complex I is stimulated by the substrates malate and glutamate, which generate NADH as a substrate to the respiratory chain and provoke the activation of complex I. Afterwards, ADP is added for conversion to ATP (state 3, active complex I-dependent respiration). After a stable signal is reached, rotenone (mitochondrial complex I inhibitor) is administered to inhibit complex I. Rotenone is followed by succinate to FADH2 and to activate complex II (state 3, active complex II-dependent respiration). In order to measure complex IV-dependent respiration, first complex III-dependent respiration is inhibited by adding antimycin A (mitochondrial complex III inhibitor). Afterwards, complex IV-dependent respiration is stimulated by administering ascorbate and tetramethylphenylendiamine (TMPD). TMPD can auto-oxidize in the respiration buffer, therefore the maximal complex IV-dependent respiration rate (State 3) is calculated by subtracting respiration rates before and after the addition of sodium azide, an inhibitor of mitochondrial complex IV. The respiration experiments can be carried out in two chambers of an oxygraph in parallel-one serving as a control (unstimulated cells), the other containing the stimulated cells. Obviously, the cells can be pre-treated in various ways, e.g., with drugs affecting mitochondrial functions, before their oxygen consumption is measured in the oxygraph chamber. This protocol allows functional examination of the individual mitochondrial respiratory chain complexes. In addition, one can measure maximal ADP-stimulated respiration (state 3) of permeabilized cells, using exogenous fatty acid in the form of palmitate. In this protocol, concentrated stocks of sodium palmitate are conjugated with ultra fatty acid free bovine serum albumin (BSA) (6:1 molar ratio palmitate:BSA). Afterwards, cells first are permeabilized with digitonin and mitochondrial respiration is assessed by the addition of carnitine and palmitate followed by addition of ADP (state 3, maximal respiration). Then, oligomycin is added to mimic state 4 (state 4o) and respiratory control ratio (RCR value) is calculated as state 3/state 4o. &#946;-oxidation promotes production of acetyl CoA (which enters in the TCA cycle) and generation of FADH2 and NADH, the electrons of which are passed to the electron transport chain by electron-transferring flavoprotein and &#946;-hydroxyacyl-CoA dehydrogenase. Mitochondria are at the center of fatty acid metabolism and described palmitate-BSA protocol can be used by researchers examining fatty acid oxidation. In intact cells, activators and inhibitors of mitochondrial complex activity are added following a different protocol6,9. For these experiments, first oxygen consumption of non-permeabilized cells in the absence of exogenous substrates is measured (phosphorylating respiration rate). Then, the non-phosphorylating respiration rate is measured after the addition of oligomycin, which is an inhibitor of mitochondrial ATP synthase. Afterwards, the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) is administrated at various concentrations and the maximal mitochondrial uncoupled respiratory rate is measured. Protonophores such as FCCP can induce an augmentation in proton permeability of the inner membrane, allowing passive movement of protons to dissipate the chemiosmotic gradient. An increase in proton permeability uncouples oxidative respiration (no ATP production) and induces an increase in oxygen consumption. Afterwards, rotenone and antimycin A are added to inhibit mitochondrial respiration, and non-mitochondrial respiration is subtracted from all other respiratory rates.
The oxygen consumption rates can be expressed as IO2 [pmol x sec-1 x 10-6 cells] (oxygen flow per million cells) which is calculated by dividing volume-specific oxygen flux (in the closed oxygen chamber), JV,O2 [pmol x sec-1 x ml-1] by cell concentration in the cell chamber (number of cells per volume [106 cells&#8729;ml1])15. Cell-mass specific oxygen flux, JO2 [pmol x sec-1 x mg-1], is flow per cell, IO2 [pmol x sec-1 x 10-6 cells], divided by mass per cell [mg&#8729;106 cells]; or volume-specific flux, JV, O2 [pmol x sec-1 x ml-1], divided by mass per volume [mg&#8729;ml1]. JO2 is the oxygen flux per cell protein, dry weight or cell volume.
In the present study using high-resolution respirometry, we describe protocols to determine i) optimum digitonin concentration for complete cellular plasma membrane permeabilization (digitonin titration assay), ii) mitochondrial outer membrane integrity using exogenous cytochrome c, iii) mitochondrial respiratory chain complexes I, II and IV maximal respiratory rates in digitonin-permeabilized HepG2 cells in the presence of exogenous ADP and mitochondrial respiratory chain substrates, and iv) basal, coupled and maximal uncoupled respiration (maximal electron transport capacity) of intact cells without the addition of exogenous substrates and ADP, reproducing the respiratory function in the integrated cell.

<table><tbody><tr><td>ADP</td><td>Sigma</td><td>A 4386</td><td>Chemical</td></tr><tr><td>Antimycin A</td><td>Sigma</td><td>A 8674</td><td>Chemical, dissolve in ethanol</td></tr><tr><td>Ascorbate</td><td>Merck</td><td>1.00127</td><td>Chemical</td></tr><tr><td>BSA</td><td>Sigma</td><td>A 6003</td><td>Chemical</td></tr><tr><td>FCCP</td><td>Sigma</td><td>C 2920</td><td>Chemical, dissolve in ethanol</td></tr><tr><td>Countess automated cell counter&amp;nbsp;</td><td>Thermo Fisher Scientific</td><td>n/a</td><td>Automated cell counting instrument</td></tr><tr><td>Cytochrome c</td><td>Sigma</td><td>C 7752</td><td>Chemical</td></tr><tr><td>Digitonin</td><td>Sigma</td><td>D 5628</td><td>Chemical, dissolve in DMSO</td></tr><tr><td>DMEM</td><td>Gibco</td><td>31966021</td><td>Medium</td></tr><tr><td>EGTA</td><td>fluka</td><td>3779</td><td>Chemical</td></tr><tr><td>FBS</td><td>Gibco</td><td>26010-074</td><td>Medium component</td></tr><tr><td>Glutamate</td><td>Sigma</td><td>G 1626</td><td>Chemical</td></tr><tr><td>Hepes</td><td>Sigma</td><td>H 7523</td><td>Chemical</td></tr><tr><td>KCl</td><td>Merck</td><td>1.04936</td><td>Chemical</td></tr><tr><td>KH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;</td><td>Merck</td><td>1.04873</td><td>Chemical</td></tr><tr><td>K-lactobionate</td><td>Sigma</td><td>L 2398</td><td>Chemical</td></tr><tr><td>MgCl&lt;sub&gt;2&lt;/sub&gt;</td><td>Sigma</td><td>M 9272</td><td>Chemical</td></tr><tr><td>O2k-Core: Oxygraph-2k&amp;nbsp;</td><td>Oroboros Instruments</td><td>10000-02</td><td>High-resolution respirometry instrument</td></tr><tr><td>Oligomycin</td><td>Sigma</td><td>O 4876</td><td>Chemical, dissolve in ethanol</td></tr><tr><td>Penicillin-streptomycin</td><td>Gibco</td><td>15140122</td><td>Chemical</td></tr><tr><td>Sodium azide</td><td>Sigma</td><td>S2002</td><td>Chemical</td></tr><tr><td>Rotenone</td><td>Sigma</td><td>R 8875</td><td>Chemical, dissolve in ethanol</td></tr><tr><td>Succinate</td><td>Sigma</td><td>S 2378</td><td>Chemical</td></tr><tr><td>Taurine</td><td>Sigma</td><td>T 8691</td><td>Chemical</td></tr><tr><td>TMPD</td><td>Sigma</td><td>T 3134</td><td>Chemical</td></tr><tr><td>Trypsin</td><td>Sigma</td><td>T 4674</td><td>Chemical</td></tr></tbody></table>

high-resolution respirometry to assess mitochondrial function in permeabilized and intact cells

A high-resolution oxygraph is a device for measuring cellular oxygen consumption in a closed-chamber system with very high resolution and sensitivity in biological samples (intact and permeabilized cells, tissues or isolated mitochondria). The high-resolution oxygraph device is equipped with two chambers and uses polarographic oxygen sensors to measure oxygen concentration and calculate oxygen consumption within each chamber. Oxygen consumption rates are calculated using software and expressed as picomoles per second per number of cells. Each high-resolution oxygraph chamber contains a stopper with injection ports, which makes it ideal for substrate-uncoupler-inhibitor titrations or detergent titration protocols for determining effective and optimum concentrations for plasma membrane permeabilization. The technique can be applied to measure respiration in a wide range of cell types and also provides information on mitochondrial quality and integrity, and maximal mitochondrial respiratory electron transport system capacity.

Determination of Optimum Digitonin Concentration for Cellular Permeabilization: Digitonin Titration Experiment
Digitonin titration is performed to determine the optimal concentration for permeabilization of HepG2 cells. For these experiments, digitonin is titrated in intact cells in the presence of rotenone, succinate (mitochondrial complex II substrate) and a saturating amount of ADP (to induce complex II-dependent state 3), and r...

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High-resolution Respirometry to Assess Mitochondrial Function in Permeabilized and Intact Cells

High-resolution respirometry is used to determine mitochondrial oxygen consumption. This is a straightforward technique to determine mitochondrial respiratory chain complexes&#39; (I-IV) respiratory rates, maximal mitochondrial electron transport system capacity, and mitochondrial outer membrane integrity.

A high-resolution oxygraph is a device for measuring cellular oxygen consumption in a closed-chamber system with very high resolution and sensitivity in ...

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41.3K Views.  University of Bern.  Hoge-resolutie respirometrie wordt gebruikt om mitochondriale zuurstofconsumptie bepalen. Dit is een eenvoudige techniek om mitochondriale ademhalingsketen complexen (I-IV) ademhalingssnelheid, maximale mitochondriale elektronentransport systeemcapaciteit en buitenste mitochondriale membraan integriteit te bepalen. 

Video: High-resolution Respirometry to Assess Mitochondrial Function in Permeabilized and Intact Cells

Assessing Mitochondrial Function in Sciatic Nerve by High-Resolution Respirometry

Mitochondrial dysfunction in peripheral nerves accompanies several diseases associated with peripheral neuropathy, which can be triggered by multiple causes, including autoimmune diseases, diabetes, infections, inherited disorders, and tumors. Assessing mitochondrial function in mouse peripheral nerves can be challenging due to the small sample size, a limited number of mitochondria present in the tissue, and the presence of a myelin sheath. The technique described in this work minimizes these challenges by using a unique permeabilization protocol adapted from one used for muscle fibers, to assess sciatic nerve mitochondrial function instead of isolating the mitochondria from the tissue. By measuring fluorimetric reactive species production with Amplex Red/Peroxidase and comparing different mitochondrial substrates and inhibitors in saponin-permeabilized nerves, it was possible to detect mitochondrial respiratory states, reactive oxygen species (ROS), and the activity of mitochondrial complexes simultaneously. Therefore, the method presented here offers advantages compared to the assessment of mitochondrial function by other techniques.

High-resolution respirometry coupled to fluorescence sensors determines mitochondrial oxygen consumption and reactive oxygen species (ROS) generation. The present protocol describes a technique to assess mitochondrial respiratory rates and ROS production in the permeabilized sciatic nerve.

Mitochondrial dysfunction in peripheral nerves accompanies several diseases associated with peripheral neuropathy, which can be triggered by multiple ...

Biochemistry

Preparation and Respirometric Assessment of Mitochondria Isolated from Skeletal Muscle Tissue Obtained by Percutaneous Needle Biopsy

Respirometric profiling of isolated mitochondria is commonly used to investigate electron transport chain function. We describe a method for obtaining samples of human Vastus lateralis, isolating mitochondria from minimal amounts of skeletal muscle tissue, and plate based respirometric profiling using an extracellular flux (XF) analyzer. Comparison of respirometric profiles obtained using 1.0, 2.5 and 5.0 &#956;g of mitochondria indicate that 1.0 &#956;g is sufficient to measure respiration and that 5.0 &#956;g provides most consistent results based on comparison of standard errors. Western blot analysis of isolated mitochondria for mitochondrial marker COX IV and non-mitochondrial tissue marker GAPDH indicate that there is limited non-mitochondrial contamination using this protocol. The ability to study mitochondrial respirometry in as little as 20 mg of muscle tissue allows users to utilize individual biopsies for multiple study endpoints in clinical research projects.

Methods for biopsy of Vastus lateralis, preparation of purified mitochondria, and respirometric profiling are described. The use of small muscle volume makes this technique suitable for clinical research applications.

Respirometric profiling of isolated mitochondria is commonly used to investigate electron transport chain function. We describe a method for obtaining ...

Medicine

Multi-parameter Measurement of the Permeability Transition Pore Opening in Isolated Mouse Heart Mitochondria

The mitochondrial permeability transition pore (mtPTP) is a non specific channel that forms in the inner mitochondrial membrane to transport solutes with a molecular mass smaller than 1.5 kDa. Although the definitive molecular identity of the pore is still under debate, proteins such as cyclophilin D, VDAC and ANT contribute to mtPTP formation. While the involvement of mtPTP opening in cell death is well established1, accumulating evidence indicates that the mtPTP serves a physiologic role during mitochondrial Ca2+ homeostasis2, bioenergetics and redox signaling 3.
mtPTP opening is triggered by matrix Ca2+ but its activity can be modulated by several other factors such as oxidative stress, adenine nucleotide depletion, high concentrations of Pi, mitochondrial membrane depolarization or uncoupling, and long chain fatty acids4. In vitro, mtPTP opening can be achieved by increasing Ca2+ concentration inside the mitochondrial matrix through exogenous additions of Ca2+ (calcium retention capacity). When Ca2+ levels inside mitochondria reach a certain threshold, the mtPTP opens and facilitates Ca2+ release, dissipation of the proton motive force, membrane potential collapse and an increase in mitochondrial matrix volume (swelling) that ultimately leads to the rupture of the outer mitochondrial membrane and irreversible loss of organelle function.
Here we describe a fluorometric assay that allows for a comprehensive characterization of mtPTP opening in isolated mouse heart mitochondria. The assay involves the simultaneous measurement of 3 mitochondrial parameters that are altered when mtPTP opening occurs: mitochondrial Ca2+ handling (uptake and release, as measured by Ca2+ concentration in the assay medium), mitochondrial membrane potential, and mitochondrial volume. The dyes employed for Ca2+ measurement in the assay medium and mitochondrial membrane potential are Fura FF, a membrane impermeant, ratiometric indicator which undergoes a shift in the excitation wavelength in the presence of Ca2+, and JC-1, a cationic, ratiometric indicator which forms green monomers or red aggregates at low and high membrane potential, respectively. Changes in mitochondrial volume are measured by recording light scattering by the mitochondrial suspension. Since high-quality, functional mitochondria are required for the mtPTP opening assay, we also describe the steps necessary to obtain intact, highly coupled and functional isolated heart mitochondria.

A spectrofluorometric protocol for the measurement of the mitochondrial permeability transition pore opening in isolated mouse heart mitochondria is presented here. The assay involves the simultaneous measurement of mitochondria Ca2+ handling, mitochondrial membrane potential and mitochondrial volume. The procedure for obtaining high-quality and functional heart mitochondria is also described.

The mitochondrial permeability transition pore (mtPTP) is a non specific channel that forms in the inner mitochondrial membrane to transport solutes with ...

Isolation of Intact Mitochondria from Skeletal Muscle by Differential Centrifugation for High-resolution Respirometry Measurements

Mitochondria are involved in cellular energy metabolism and use oxygen to produce energy in the form of adenosine triphosphate (ATP). Differential centrifugation at low- and high-speed is commonly used to isolate mitochondria from tissues and cultured cells. Crude mitochondrial fractions obtained by differential centrifugation are used for respirometry measurements. The differential centrifugation technique is based on the separation of organelles according to their size and sedimentation velocity. The isolation of mitochondria is performed immediately after tissue harvesting. The tissue is immersed in an ice-cold homogenization medium, minced using scissors and homogenized in a glass homogenizer with a loose-fitting pestle. The differential centrifugation technique is efficient, fast and inexpensive and the mitochondria obtained by differential centrifugation are pure enough for respirometry assays. Some of the limitations and disadvantages of isolated mitochondria, based on differential centrifugation, are that the mitochondria can be damaged during the homogenization and isolation procedure and that large amounts of the tissue biopsy or cultured cells are required for the mitochondrial isolation.

Here, a quadriceps muscle specimen is taken from an anaesthetized pig and mitochondria are isolated by differential centrifugation. Then, the respiratory rates of mitochondrial respiratory chain complexes I, II and IV are determined using high-resolution respirometry.

Mitochondria are involved in cellular energy metabolism and use oxygen to produce energy in the form of adenosine triphosphate (ATP). Differential ...

High-resolution Respirometry to Measure Mitochondrial Function of Intact Beta Cells in the Presence of Natural Compounds

High-resolution respirometry allows for the measurement of oxygen consumption of isolated mitochondria, cells and tissues. Beta cells play a critical role in the body by controlling blood glucose levels through insulin secretion in response to elevated glucose concentrations. Insulin secretion is controlled by glucose metabolism and mitochondrial respiration. Therefore, measuring intact beta cell respiration is essential to be able to improve beta cell function as a treatment for diabetes. Using intact 832/13 INS-1 derived beta cells we can measure the effect of increasing glucose concentration on cellular respiration. This protocol allows us to measure beta cell respiration in the presence or absence of various compounds, allowing one to determine the effect of given compounds on intact cell respiration. Here we demonstrate the effect of two naturally occurring compounds, monomeric epicatechin and curcumin, on beta cell respiration under the presence of low (2.5 mM) or high glucose (16.7 mM) conditions. This technique can be used to determine the effect of various compounds on intact beta cell respiration in the presence of differing glucose concentrations.

The goal of this protocol is to measure the effect of glucose-mediated changes to mitochondrial respiration in the presence of natural compounds on intact 832/13 beta cells using high-resolution respirometry.

High-resolution respirometry allows for the measurement of oxygen consumption of isolated mitochondria, cells and tissues. Beta cells play a critical role ...

Determining Respiration in Human Sperm Cells by High-Resolution Respirometry

High-Resolution Respirometry to Assess Mitochondrial Function in Human Spermatozoa

Semen quality is often studied by routine semen analysis, which is descriptive and often inconclusive. Male infertility is associated with altered sperm mitochondrial activity, so the measurement of sperm mitochondrial function is an indicator of sperm quality. High-resolution respirometry is a method of measuring the oxygen consumption of cells or tissues in a closed-chamber system. This technique can be implemented to measure respiration in human sperm and provides information about the quality and integrity of the sperm mitochondria. High-resolution respirometry allows the cells to move freely, which is an a priori advantage in the case of sperm. This technique can be applied with intact or permeabilized spermatozoa and allows for the study of intact sperm mitochondrial function and the activity of individual respiratory chain complexes. The high-resolution oxygraph instrument uses sensors to measure the oxygen concentration coupled with sensitive software to calculate the oxygen consumption. The data are used to calculate respiratory indices based on the oxygen consumption ratios. Consequently, the indices are the proportions of two oxygen consumption rates and are internally normalized to the cell number or protein mass. The respiratory indices are an indicator of sperm mitochondrial function and dysfunction.

Author Spotlight: Advancing Male Infertility Research by Unraveling Sperm Metabolism and Mitochondrial Function 

The analysis of sperm mitochondrial function by high-resolution respirometry permits the measurement of the oxygen consumption of freely moving spermatozoa in a closed-chamber system. The technique can be applied to measure respiration in human spermatozoa, which provides information on sperm mitochondrial characteristics and integrity.

Semen quality is often studied by routine semen analysis, which is descriptive and often inconclusive. Male infertility is associated with altered sperm ...

Measuring Mitochondrial Substrate Flux in Recombinant Perfringolysin O-Permeabilized Cells

Mitochondrial substrate flux is a distinguishing characteristic of each cell type, and changes in its components such as transporters, channels, or enzymes are involved in the pathogenesis of several diseases. Mitochondrial substrate flux can be studied using intact cells, permeabilized cells, or isolated mitochondria. Investigating intact cells encounters several problems due to simultaneous oxidation of different substrates. Besides, several cell types contain internal stores of different substrates that complicate results interpretation. Methods such as mitochondrial isolation or using permeabilizing agents are not easily reproducible. Isolating pure mitochondria with intact membranes in sufficient amounts from small samples is problematic. Using non-selective permeabilizers causes various degrees of unavoidable mitochondrial membrane damage. Recombinant perfringolysin O (rPFO) was offered as a more appropriate permeabilizer, thanks to its ability to selectively permeabilize plasma membrane without affecting mitochondrial integrity. When used in combination with microplate respirometry, it allows testing the flux of several mitochondrial substrates with enough replicates within one experiment while using a minimal number of cells. In this work, the protocol describes a method to compare mitochondrial substrate flux of two different cellular phenotypes or genotypes and can be customized to test various mitochondrial substrates or inhibitors.

In this work, we describe a modified protocol to test mitochondrial respiratory substrate flux using recombinant perfringolysin O in combination with microplate-based respirometry. With this protocol, we show how metformin affects mitochondrial respiration of two different tumor cell lines.

Mitochondrial substrate flux is a distinguishing characteristic of each cell type, and changes in its components such as transporters, channels, or ...

High-Resolution Respirometry to Assess Bioenergetics in Cells and Tissues Using Chamber- and Plate-Based Respirometers

High-resolution respirometry (HRR) allows monitoring oxidative phosphorylation in real-time for analysis of individual cellular energy states and assessment of respiratory complexes using diversified substrate-uncoupler-inhibitor titration (SUIT) protocols. Here, the usage of two high-resolution respirometry devices is demonstrated, and a basic collection of protocols applicable for the analysis of cultured cells, skeletal and heart muscle fibers, and soft tissues such as the brain and liver are presented. Protocols for cultured cells and tissues are provided for a chamber-based respirometer and cultured cells for a microplate-based respirometer, both encompassing standard respiration protocols. For comparative purposes, CRISPR-engineered HEK293 cells deficient in mitochondrial translation causing multiple respiratory system deficiency are used with both devices to demonstrate cellular defects in respiration. Both respirometers allow for comprehensive measurement of cellular respiration with their respective technical merits and suitability dependent on the research question and model under study.

Assessing oxidative phosphorylation using high-resolution respirometers has become an integral part of the functional analysis of mitochondria and cellular energy metabolism. Here, we present protocols for the analysis of cellular energy metabolism using chamber and microplate-based high-resolution respirometers and discuss the key benefits of each device.

High-resolution respirometry (HRR) allows monitoring oxidative phosphorylation in real-time for analysis of individual cellular energy states and ...

High-Resolution Fluoro-Respirometry of Equine Skeletal Muscle

Mitochondrial function-oxidative phosphorylation and the generation of reactive oxygen species-is critical in both health and disease. Thus, measuring mitochondrial function is fundamental in biomedical research. Skeletal muscle is a robust source of mitochondria, particularly in animals with a very high aerobic capacity, such as horses, making them ideal subjects for studying mitochondrial physiology. This article demonstrates the use of high-resolution respirometry with concurrent fluorometry, with freshly harvested skeletal muscle mitochondria, to quantify the capacity to oxidize substrates under different mitochondrial states and determine the relative capacities of distinct elements of mitochondrial respiration. Tetramethylrhodamine methylester is used to demonstrate the production of mitochondrial membrane potential resulting from substrate oxidation, including calculation of the relative efficiency of the mitochondria by calculating the relative membrane potential generated per unit of concurrent oxygen flux. The conversion of ADP to ATP results in a change in the concentration of magnesium in the reaction chamber, due to differing affinities of the adenylates for magnesium. Therefore, magnesium green can be used to measure the rate of ATP synthesis, allowing the further calculation of the oxidative phosphorylation efficiency (ratio of phosphorylation to oxidation [P/O]). Finally, the use of Amplex UltraRed, which produces a fluorescent product (resorufin) when combined with hydrogen peroxide, allows the quantification of reactive oxygen species production during mitochondrial respiration, as well as the relationship between ROS production and concurrent respiration. These techniques allow the robust quantification of mitochondrial physiology under a variety of different simulated conditions, thus shedding light on the contribution of this critical cellular component to both health and disease.

Horses have an exceptional aerobic exercise capacity, making equine skeletal muscle an important tissue for both the study of equine exercise physiology as well as mammalian mitochondrial physiology. This article describes techniques for the comprehensive assessment of mitochondrial function in equine skeletal muscle.

Mitochondrial function-oxidative phosphorylation and the generation of reactive oxygen species-is critical in both health and disease. Thus, measuring ...

High-Resolution Analysis of Mitochondrial Function in Human PBMCs

High-Resolution Fluorespirometry to Assess Dynamic Changes in Mitochondrial Membrane Potential in Human Immune Cells

Peripheral mononuclear cells (PBMCs) exhibit robust changes in mitochondrial respiratory capacity in response to health and disease. While these changes&#160;do not always reflect what occurs in other tissues, such as skeletal muscle, these cells are an accessible and valuable source of viable mitochondria from human subjects. PBMCs are exposed to systemic signals that impact their bioenergetic state. Thus, expanding our tools to interrogate mitochondrial metabolism in this population will elucidate mechanisms related to disease progression. Functional assays of mitochondria are often limited to using respiratory outputs following maximal substrate, inhibitor, and uncoupler concentrations to determine the full range of respiratory capacity, which may not be achievable in vivo. The conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP) by ATP-synthase results in a decrease in mitochondrial membrane potential (mMP) and an increase in oxygen consumption. To provide a more integrated analysis of mitochondrial dynamics, this article describes the use of high-resolution fluorespirometry to measure the simultaneous response of oxygen consumption and mitochondrial membrane potential (mMP) to physiologically relevant concentrations of ADP. This technique uses tetramethylrhodamine methylester (TMRM) to measure mMP polarization in response to ADP titrations following maximal hyperpolarization with complex I and II substrates. This technique can be used to quantify how changes in health status, such as aging and metabolic disease, affect the sensitivity of mitochondrial response to energy demand in PBMCs, T-cells, and monocytes from human subjects.

Author Spotlight: New Insights into PBMC Mitochondrial Responses Using Fluorespirometry

Methods for studying mitochondrial bioenergetics under physiologically relevant substrate concentrations in immune cells are limited. We provide a detailed protocol that uses high-resolution fluorespirometry to assess changes in the response of the mitochondrial membrane potential to energy demand in human T-cells, monocytes, and peripheral mononuclear cells.

High-resolution Respirometry to Assess Mitochondrial Function in Permeabilized and Intact Cells

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