The studies were supported by NIH HL75503 to KP.

All experiments performed on animals were as approved by the Institutional Animal Care and Use Committee of the University of Tennessee Health Science Center.
1. Tubing for Perfusing Rat Lung Preparations
<ol>
	<li>Prepare a tubing system with Tygon tubing (#18) for blood perfusion as shown in Figure 1. Connect pressure transducers (P23XL) and place the tubing on the microscope stage.</li>
	<li>Set water bath temperature to 37 &#176;C.</li>
	<li>Connect the lung inlet and outlet temporarily with Tygon tubing.</li>
</ol>
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/51552/51552fig1highres.jpg" width="500" /> 
Figure 1.&#160;Blood perfusion tubing. The schematic shows the tubing setup used for circulating blood through the isolated lung preparation. Also indicated are associated components through which the tubing is routed. A schematic of the heart and lung is included to show sites of connection between the tubing and pulmonary artery (PA), and left atrial (LA) cannula (blue dashed lines).
2. Preparation of Isolated Rat Lungs
<ol>
	<li>Anesthetize rats (male Sprague-Dawley Rats; 250-300 g) with ketamine (80-100 mg/kg) and with xylazine (5-10 mg/kg). After ensuring a surgical plane of anesthesia, place the animal in a supine position.</li>
	<li>Perform tracheostomy, insert a tracheal cannula (PE-90) and secure with surgical suture.</li>
	<li>Infuse heparin (100-200 U) into the heart by cardiac puncture (21 G butterfly needle), wait for 60 sec and exsanguinate blood (~12-15 ml blood).</li>
	<li>Prepare two cannulas (Tygon tubing, 3 mm diameter; 4 cm long; flared at one end) and fill with saline.</li>
	<li>Perform a thoracotomy. Make an incision (3 mm) on the right ventricle and slide the flared end of a cannula into the incision toward the pulmonary artery. Secure cannula to pulmonary artery with surgical sutures.</li>
	<li>Incise (3 mm) the apex of the left ventricle and slide the flared end of the second cannula into the incision. Guide the cannula into the left atrium. Secure cannula to the left ventricle with an umbilical tape (2 mm width).</li>
	<li>Dissect any connective tissue, and remove the lung and heart together with the attached cannulas. Place lung and heart on a petri dish. Reposition the lung so that the diaphragmatic surface is on top. The three cannulas should face the same direction.</li>
	<li>Place the lung preparation on a stage that can be manipulated in the X-Y directions. Any stage that comes with a microscope can be modified to hold the tubing or a custom-made stage built, if needed.</li>
</ol>
3. Blood Perfusion of Isolated Rat Lungs
<ol>
	<li>Mix the exsanguinated blood with an equal volume albumin (5%) solution and add to the reservoir. Start the peristaltic pump and set flow rate to 14 ml/min. Allow blood to fill the tubing.</li>
	<li>With the shunt open, remove the temporary lung inlet-outlet connector. Attach the pulmonary artery and left atrial cannula to the lung inlet and outlet, respectively. Ensure that there are no air bubbles in the tubing.</li>
	<li>Connect the tracheal cannula to a third pressure transducer (P23XL). Inflate lungs with 30% oxygen via the tracheal cannula and maintain pressure at 5 cm H2O.</li>
	<li>Close the shunt with a clamp to begin lung perfusion. Maintain pulmonary artery and left atrial pressures at ~10 and 3 cm H2O respectively.</li>
</ol>
4. Preparing Lung for Microvascular Infusion
<ol>
	<li>Raise the rear end of the extension tubing for the catheter above the level of the lung and secure.</li>
	<li>Prepare an infusion catheter by inserting about 30 cm of a 40 cm long PE10 tubing into a ~30 cm long PE90 tubing. Connect the exposed end of the PE10 tubing to a needle (30 G) attached to a syringe (1 cc).</li>
	<li>Insert the catheter combination into the raised rear end of the extension tubing. Guide the catheter combination through the left atrium and into the lung until it meets resistance. Then, push the PE10 catheter alone further into the lung until it meets resistance. Note that applying excessive force while inserting the catheter will injure the lung.</li>
	<li>Fill the 1 cc syringe with Ringer&#8217;s solution and attach to a syringe pump. Set infusion rate to 10 &#181;l/min.</li>
	<li>Infusion site will become pale compared to rest of the lung.</li>
	<li>Moisten the lung with saline and cover the lung with plastic wrap with a hole large enough to leave the infusion site uncovered.</li>
	<li>Swab some stopcock grease on the bottom of an O-ring (custom-made) and place a glass coverslip (#1.5, 22 mm diameter) on the bottom of the O-ring. Gently position the O-ring with the coverslip on the infusion site. Secure the O-ring with a standard test-tube holder. The coverslip/O-ring combination does not distort the alveolar structures underneath it, as recently reported15.</li>
	<li>Position an objective (20X) of a fluorescence microscope above the O-ring and focus on the lung surface.</li>
</ol>
5. Imaging Fluorescent Dextran Transit Through Microvessels
<ol>
	<li>Prepare the microscope for imaging FITC florescence.</li>
	<li>Select a region to be imaged and acquire images at the rate of 1/minute using image acquisition software.</li>
	<li>Begin infusion of FITC-dextran 20 kD (0.5 mg/ml) using the syringe pump. Fluorescence in blood vessels will gradually increase and reach a maximum. Continue infusion for 60 min.</li>
	<li>Then switch to Ringer&#8217;s infusion to wash off luminal fluorescence. Maintain infusion for over 10 min. Continue image acquisition at 1/min during wash-off.</li>
</ol>
6. Image Analysis
<ol>
	<li>Open the image acquisition file.</li>
	<li>Place regions of interest over microvessels within the image frame.</li>
	<li>Play the image file frame-by-frame and record the fluorescence intensity at each region of interest for all frames.</li>
	<li>Plot the change in fluorescence intensity for each region of interest as a function of time.</li>
	<li>Quantify the maximum fluorescence intensity and the residual fluorescence intensity after 10 min of washoff.</li>
	<li>Calculate the ratio of maximum to residual fluorescence intensity at each region of interest to get the permeability index for microvessels associated with that region of interest.</li>
</ol>

<ol>
	<li>Ware, L. B., Matthay, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+acute+respiratory+distress+syndrome.">The acute respiratory distress syndrome.</a> N Engl J Med. 342, 1334-1349 (2000).</li><li>Matthay, M. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+acute+respiratory+distress+syndrome.">The acute respiratory distress syndrome.</a> J Clin Invest. 122, 2731-2740 (2012).</li><li>Bhattacharya, J., Matthay, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+and+repair+of+the+alveolar-capillary+barrier+in+acute+lung+injury.">Regulation and repair of the alveolar-capillary barrier in acute lung injury.</a> Annu Rev Physiol. 75, 593-615 (2013).</li><li>Parthasarathi, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Connexin+43+mediates+spread+of+Ca2+-dependent+proinflammatory+responses+in+lung+capillaries.">Connexin 43 mediates spread of Ca2+-dependent proinflammatory responses in lung capillaries.</a> J Clin Invest. 116, 2193-2200 (2006).</li><li>Parthasarathi, K., Bhattacharya, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localized+Acid+instillation+by+a+wedged-catheter+method+reveals+a+role+for+vascular+gap+junctions+in+spatial+expansion+of+Acid+injury.">Localized Acid instillation by a wedged-catheter method reveals a role for vascular gap junctions in spatial expansion of Acid injury.</a> Anat Rec (Hoboken). 294, 1585-1591 (2011).</li><li>Gorin, A. B., Stewart, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+permeability+of+endothelial+and+epithelial+barriers+to+albumin+flux.">Differential permeability of endothelial and epithelial barriers to albumin flux.</a> J Appl Physiol Respir Environ Exerc Physiol. 47, 1315-1324 (1979).</li><li>Boutoille, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FITC-albumin+as+a+marker+for+assessment+of+endothelial+permeability+in+mice:+comparison+with+125I-albumin.">FITC-albumin as a marker for assessment of endothelial permeability in mice: comparison with 125I-albumin.</a> Exp Lung Res. 35, 263-271 (2009).</li><li>Thorball, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=FITC-dextran+tracers+in+microcirculatory+and+permeability+studies+using+combined+fluorescence+stereo+microscopy,+fluorescence+light+microscopy+and+electron+microscopy.">FITC-dextran tracers in microcirculatory and permeability studies using combined fluorescence stereo microscopy, fluorescence light microscopy and electron microscopy.</a> Histochemistry. 71, 209-233 (1981).</li><li>Stevens, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Functional+and+molecular+heterogeneity+of+pulmonary+endothelial+cells.">Functional and molecular heterogeneity of pulmonary endothelial cells.</a> Proc Am Thorac Soc. 8, 453-457 (2011).</li><li>Ofori-Acquah, S. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heterogeneity+of+barrier+function+in+the+lung+reflects+diversity+in+endothelial+cell+junctions.">Heterogeneity of barrier function in the lung reflects diversity in endothelial cell junctions.</a> Microvasc Res. 75, 391-402 (2008).</li><li>Kandasamy, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+imaging+reveals+endothelium-mediated+leukocyte+retention+in+LPS-treated+lung+microvessels.">Real-time imaging reveals endothelium-mediated leukocyte retention in LPS-treated lung microvessels.</a> Microvasc Res. 83, 323-331 (2012).</li><li>Kandasamy, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipopolysaccharide+induces+endoplasmic+store+Ca2+-dependent+inflammatory+responses+in+lung+microvessels.">Lipopolysaccharide induces endoplasmic store Ca2+-dependent inflammatory responses in lung microvessels.</a> PloS One. 8, (2013).</li><li>Qiao, R. L., Bhattacharya, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Segmental+barrier+properties+of+the+pulmonary+microvascular+bed.">Segmental barrier properties of the pulmonary microvascular bed.</a> J Appl Physiol. 71, 2152-2159 (1991).</li><li>Parthasarathi, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+connexin43+mediates+acid-induced+increases+in+pulmonary+microvascular+permeability.">Endothelial connexin43 mediates acid-induced increases in pulmonary microvascular permeability.</a> Am J Physiol Lung Cell Mol Physiol. 303, (2012).</li><li>Wu, Y., Perlman, C. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+methods+for+assessing+alveolar+mechanics.">In situ methods for assessing alveolar mechanics.</a> J Appl Physiol 1985. 112, 519-526 (2012).</li><li>Kuebler, W. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+signaling+mechanism+between+gas+and+blood+compartments+of+the+lung.">A novel signaling mechanism between gas and blood compartments of the lung.</a> Journal Clin Invest. 105, 905-913 (2000).</li></ol>

The authors have nothing to disclose.

The isolated blood-perfused lung preparation coupled with real time imaging provides a simple tool for determination of permeability changes in single lung microvessels. We applied this method to define permeability changes in response to infusions of LPS. Our data clearly suggest that LPS infusion caused an increase in microvascular permeability. Further, the data also indicate that permeability changes induced by LPS were similar in both venules and capillaries. Thus, a major advantage of this technique is the ability ...

Increased microvascular permeability in lungs leads to development of alveolar edema and compromised gas exchange and is a major characteristic of acute lung injury (ALI)1-3. Thus, estimates of vascular permeability are important in defining the extent of lung injury and efficacy of proposed therapeutic interventions. Gravimetric analysis such as blood free lung wet-to-dry ratio and microvascular filtration coefficient are widely used methods to estimate permeability4,5. Other methods include quantifying the retention of radioactive or fluorescent probes in lung tissue6-8. However, the above methods require postexperiment processing of lung tissue samples toward elucidating the permeability data. Moreover, since one animal can be only used for a single treatment protocol, large animal numbers may be needed for a complete study. A common characteristic of the above methods is that they determine the mean vascular permeability for all blood vessels within the tissue sample. However, it is well established that pulmonary micro- and macro-vessels are phenotypically different9. Hence, permeability responses may be heterogeneous among the various vessel segments as well9,10. Thus, quantifying mean permeability of all pulmonary vessels in a tissue sample may not adequately reflect this heterogeneity.
In the isolated blood-perfused lung preparation, blood vessels on the lung surface can be visualized by an upright microscope4,11,12. This enables characterizing responses in single vessels and thus, addressing any heterogeneity in the responses13. In addition, by utilizing fluorescence imaging of microvessels, fluorescence based assays can be incorporated. Further, a left atrial microcatheter can be used to deliver agents and fluorescence probes into blood vessels11,14. The microcatheter limits the delivery to a small lung region, thus exposing only the blood vessels within the region to the infused agents and fluorophores. This allows multiple small regions within the same lung to be used for separate experiments, leading to an overall reduction in animals needed for a study.
Real time imaging enables capture of dynamic changes in vascular and extravascular fluorescence of single microvessels of the isolated lung preparation. Thus, for each microvessel within an image field, changes in fluorescence during infusion of fluorophores and washoff can be recorded, and quantified offline14. Using values of maximum and residual vascular fluorescence, a permeability index for each microvessel within the imaging field can be determined. To determine permeability changes in response to inflammatory or injurious agents, the desired agent can be administered first and then the permeability index determined. In addition, the image field can be set anywhere within the lung region infused by the microcatheter, thus enabling a high degree of flexibility in selecting the desired vascular network. Thus, the isolated blood-perfused lung preparation in tandem with real time imaging provides an attractive experimental model to quantify permeability in single lung microvessels.

<table border="0" cellpadding="0" cellspacing="0" width="740">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Tygon Tubing</td>
			<td style="width:108px;">Fisher Scientific</td>
			<td style="width:119px;"></td>
			<td style="width:297px;">#18</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Pressure Transducer</td>
			<td style="width:108px;">Data Sciences International</td>
			<td style="width:119px;">P23XL</td>
			<td>Need quantity 3</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Butterfly Needle</td>
			<td style="width:108px;">Greiner Bio-One</td>
			<td align="right" style="width:119px;">450081</td>
			<td>21G</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Peristaltic pump</td>
			<td style="width:108px;">Cole Parmer</td>
			<td style="width:119px;">Masterflex L/S</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">PE-90 tubing</td>
			<td style="width:108px;">Becton Dickinson</td>
			<td align="right" style="width:119px;">427421</td>
			<td>30 cm needed</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">PE-10 tubing</td>
			<td style="width:108px;">Becton Dickinson</td>
			<td align="right" style="width:119px;">427401</td>
			<td>40 cm needed</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Syringe Pump</td>
			<td style="width:108px;">Braintree Scientific</td>
			<td style="width:119px;">BS8000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">O-ring</td>
			<td style="width:108px;"></td>
			<td style="width:119px;"></td>
			<td>Custom made with a 20 mm diamter hole&#160; and a handle&#160; to secure o-ring to holder</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Upright fluorescence microscope</td>
			<td style="width:108px;">Olympus America</td>
			<td style="width:119px;">BX61WI</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Image Acquisition Software</td>
			<td style="width:108px;">Molecular Devices</td>
			<td style="width:119px;">Metamorph</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">FITC Dextran 20KD</td>
			<td style="width:108px;">Sigma Aldrich</td>
			<td style="width:119px;"></td>
			<td>0.5 mg/ml (A dextran of different molecular size can be selected, if trial experiments indicate its suitability based on the calculated permeability index values)&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Lipopolysaccharide</td>
			<td style="width:108px;">Sigma Aldrich</td>
			<td style="width:119px;"></td>
			<td>Serotype 0111:B4</td>
		</tr>
	</tbody>
</table>

quantifying single microvessel permeability in isolated blood-perfused rat lung preparation

The isolated blood-perfused lung preparation is widely used to visualize and define signaling in single microvessels. By coupling this preparation with real time imaging, it becomes feasible to determine permeability changes in individual pulmonary microvessels. Herein we describe steps to isolate rat lungs and perfuse them with autologous blood. Then, we outline steps to infuse fluorophores or agents via a microcatheter into a small lung region. Using these procedures described, we determined permeability increases in rat lung microvessels in response to infusions of bacterial lipopolysaccharide. The data revealed that lipopolysaccharide increased fluid leak across both venular and capillary microvessel segments. Thus, this method makes it possible to compare permeability responses among vascular segments and thus, define any heterogeneity in the response. While commonly used methods to define lung permeability require postprocessing of lung tissue samples, the use of real time imaging obviates this requirement as evident from the present method. Thus, the isolated lung preparation combined with real time imaging offers several advantages over traditional methods to determine lung microvascular permeability, yet is a straightforward method to develop and implement.

An isolated blood-perfused lung preparation connected to the perfusion tubing and related equipment is shown in Figure 2. For demonstration purposes, we used a Sprague Dawley rat, though the procedures described herein can be used with any rat species. Infusions through a left atrial microcatheter reach only a small region of the lung. The infused region can be identified by the infusion-induced discoloration (Figure 3). The lung preparation as positioned for real-time imaging is shown i...

Watch this Scientific Journal Video about Quantifying Single Microvessel Permeability in Isolated Blood-perfused Rat Lung Preparation at JoVE.com

Quantifying Single Microvessel Permeability in Isolated Blood-perfused Rat Lung Preparation

The isolated blood-perfused lung preparation makes it feasible to visualize microvessel networks on the lung surface. Here we describe an approach to quantify permeability of single microvessels in isolated lungs using real time fluorescence imaging.

The isolated blood-perfused lung preparation is widely used to visualize and define signaling in single microvessels. By coupling this preparation with ...

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9.4K Views.  The University of Tennessee Health Science Center. The isolated blood-perfused lung preparation makes it feasible to visualize microvessel networks on the lung surface. Here we describe an approach to quantify permeability of single microvessels in isolated lungs using real time fluorescence imaging.

Video: Quantifying Single Microvessel Permeability in Isolated Blood-perfused Rat Lung Preparation

Standardized Preparation of Single-Cell Suspensions from Mouse Lung Tissue using the gentleMACS Dissociator

The preparation of single-cell suspensions from tissues is an important prerequisite for many experiments in cellular research. The process of dissociating whole organs requires specific parameters in order to obtain a high number of viable cells in a reproducible manner. The gentleMACS Dissociator optimizes this task with a simple, practical protocol. The instrument contains pre-programmed settings that are optimized for the efficient but gentle dissociation of a variety of tissue types, including mouse lungs. In this publication the use of the gentleMACS Dissociator on lung tissue derived from mice is demonstrated.

Dissociating cells from specific tissue types requires specific parameters for tissue agitation to obtain a high volume of viable, culturable cells. The Miltenyi gentleMACS dissociator optimizes this task with a simple, practical protocol. In this publication the use of this apparatus on lung tissue is explained.

The preparation of single-cell suspensions from tissues is an important prerequisite for many experiments in cellular research. The process of ...

Characterization of the Isolated, Ventilated, and Instrumented Mouse Lung Perfused with Pulsatile Flow

The isolated, ventilated and instrumented mouse lung preparation allows steady and pulsatile pulmonary vascular pressure-flow relationships to be measured with independent control over pulmonary arterial flow rate, flow rate waveform, airway pressure and left atrial pressure. Pulmonary vascular resistance is calculated based on multi-point, steady pressure-flow curves; pulmonary vascular impedance is calculated from pulsatile pressure-flow curves obtained at a range of frequencies. As now recognized clinically, impedance is a superior measure of right ventricular afterload than resistance because it includes the effects of vascular compliance, which are not negligible, especially in the pulmonary circulation. Three important metrics of impedance - the zero hertz impedance Z0, the characteristic impedance ZC, and the index of wave reflection RW - provide insight into distal arterial cross-sectional area available for flow, proximal arterial stiffness and the upstream-downstream impedance mismatch, respectively. All results obtained in isolated, ventilated and perfused lungs are independent of sympathetic nervous system tone, volume status and the effects of anesthesia. We have used this technique to quantify the impact of pulmonary emboli and chronic hypoxia on resistance and impedance, and to differentiate between sites of action (i.e., proximal vs. distal) of vasoactive agents and disease using the pressure dependency of ZC. Furthermore, when these techniques are used with the lungs of genetically engineered strains of mice, the effects of molecular-level defects on pulmonary vascular structure and function can be determined.

The following protocol outlines the process of isolating, ventilating and instrumenting mouse lungs to measure steady or pulsatile pulmonary vascular pressure-flow relationships in order to quantify the effects of blood flow, airflow, airway changes and vascular changes on right ventricular afterload.

The isolated, ventilated and instrumented mouse lung preparation allows steady and pulsatile pulmonary vascular pressure-flow relationships to be measured ...

The ex vivo Isolated Skeletal Microvessel Preparation for Investigation of Vascular Reactivity

The isolated microvessel preparation is an ex vivo preparation that allows for examination of the different contributions of factors that control vessel diameter, and thus, perfusion resistance1-5. This is a classic experimental preparation that was, in large measure, initially described by Uchida et al.15 several decades ago. This initial description provided the basis for the techniques that was extensively modified and enhanced, primarily in the laboratory of Dr. Brian Duling at the University of Virginia6-8, and we present a current approach in the following pages. This preparation will specifically refer to the gracilis arteriole in a rat as the microvessel of choice, but the basic preparation can readily be applied to vessels isolated from nearly any other tissue or organ across species9-13. Mechanical (i.e., dimensional) changes in the isolated microvessels can easily be evaluated in response to a broad array of physiological (e.g., hypoxia, intravascular pressure, or shear) or pharmacological challenges, and can provide insight into mechanistic elements comprising integrated responses in an intact, although ex vivo, tissue. The significance of this method is that it allows for facile manipulation of the influences on the integrated regulation of microvessel diameter, while also allowing for the control of many of the contributions from other sources, including intravascular pressure (myogenic), autonomic innervation, hemodynamic (e.g., shear stress), endothelial dependent or independent stimuli, hormonal, and parenchymal influences, to provide a partial list. Under appropriate experimental conditions and with appropriate goals, this can serve as an advantage over in vivo or in situ tissue/organ preparations, which do not readily allow for the facile control of broader systemic variables. 
The major limitation of this preparation is essentially the consequence of its strengths. By definition, the behavior of these vessels is being studied under conditions where many of the most significant contributors to the regulation of vascular resistance have been removed, including neural, humoral, metabolic, etc. As such, the investigator is cautioned to avoid over-interpretation and extrapolation of the data that are collected utilizing this preparation. The other significant area of concern with regard to this preparation is that it can be very easy to damage cellular components such as the endothelial lining or the vascular smooth muscle, such that variable source of error can be introduced. It is strongly recommended that the individual investigator utilize appropriate measurements to ensure the quality of the preparation, both at the initiation of the experiment and periodically throughout the course of a protocol.

The ex vivo Isolated Skeletal Microvessel Preparation for Investigation of Vascular Reactivity

An ex vivo preparation is described for isolation of the largest gracilis muscle resistance arterioles for interrogation of both vascular responses to vasoactive stimuli and the assessment of basic structural properties via passive wall mechanics.

The isolated  microvessel preparation is an ex vivo preparation that allows for examination of the different contributions of  factors that control vessel ...

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 ...

Measuring the Osmotic Water Permeability Coefficient (Pf) of Spherical Cells: Isolated Plant Protoplasts as an Example

Studying AQP regulation mechanisms is crucial for the understanding of water relations at both the cellular and the whole plant levels. Presented here is a simple and very efficient method for the determination of the osmotic water permeability coefficient (Pf) in plant protoplasts, applicable in principle also to other spherical cells such as frog oocytes. The first step of the assay is the isolation of protoplasts from the plant tissue of interest by enzymatic digestion into a chamber with an appropriate isotonic solution. The second step consists of an osmotic challenge assay: protoplasts immobilized on the bottom of the chamber are submitted to a constant perfusion starting with an isotonic solution and followed by a hypotonic solution. The cell swelling is video recorded. In the third step, the images are processed offline to yield volume changes, and the time course of the volume changes is correlated with the time course of the change in osmolarity of the chamber perfusion medium, using a curve fitting procedure written in Matlab (the &#8216;PfFit&#8217;), to yield Pf.

Measuring the Osmotic Water Permeability Coefficient Pf of Spherical Cells: Isolated Plant Protoplasts as an Example

Measuring the osmotic water permeability coefficient (Pf) of cells can help understand the regulatory mechanisms of aquaporins (AQPs). Pf determination in spherical plant cell protoplasts presented here involves protoplasts isolation and numerical analysis of their initial rate of volume change as a result of an osmotic challenge during constant bath perfusion.

Studying AQP regulation mechanisms is crucial for the understanding of water relations at both the cellular and the whole plant levels. Presented here is ...

Single-channel Analysis and Calcium Imaging in the Podocytes of the Freshly Isolated Glomeruli

Podocytes (renal glomerular epithelial cells) are known to regulate glomerular permeability and maintain glomerular structure; a key role for these cells in the pathogenesis of various renal diseases has been established since podocyte injury leads to proteinuria and foot process effacement. It was previously reported that various endogenous agents may cause a dramatic overload in intracellular Ca2+ concentration in podocytes, presumably leading to albuminuria, and this likely occurs via calcium-conducting ion channels. Therefore, it appeared important to study calcium handling in the podocytes both under normal conditions and in various pathological states. However, available experimental approaches have remained somewhat limited to cultured and transfected cells. Although they represent a good basic model for such studies, they are essentially extracted from the native environment of the glomerulus. Here we describe the methodology of studying podocytes as a part of the freshly isolated whole glomerulus. This preparation retains the functional potential of the podocytes, which are still attached to the capillaries; therefore, podocytes remain in the environment that conserves the major parts of the glomeruli filtration apparatus. The present manuscript elaborates on two experimental approaches that allow 1) real-time detection of calcium concentration changes with the help of ratiometric confocal fluorescence microscopy, and 2) the recording of the single ion channels activity in the podocytes of the freshly isolated glomeruli. These methodologies utilize the advantages of the native environment of the glomerulus that enable researchers to resolve acute changes in the intracellular calcium handling in response to applications of various agents, measure basal concentration of calcium within the cells (for instance, to evaluate disease progression), and assess and manipulate calcium conductance at the level of single ion channels.

Changes in the intracellular calcium levels in the podocytes are one of the most important means to control the filtration function of glomeruli. Here we explain a high-throughput approach that allows detection of real-time calcium handling and single ion channels activity in the podocytes of the freshly isolated glomeruli.

Podocytes (renal glomerular epithelial cells) are known to regulate glomerular permeability and maintain glomerular structure; a key role for these cells ...

Microperfusion Technique to Investigate Regulation of Microvessel Permeability in Rat Mesentery

Experiments to measure the permeability properties of individually perfused microvessels provide a bridge between investigation of molecular and cellular mechanisms regulating vascular permeability in cultured endothelial cell monolayers and the functional exchange properties of whole microvascular beds. A method to cannulate and perfuse venular microvessels of rat mesentery and measure the hydraulic conductivity of the microvessel wall is described. The main equipment needed includes an intravital microscope with a large modified stage that supports micromanipulators to position three different microtools: (1) a beveled glass micropipette to cannulate and perfuse the microvessel; (2) a glass micro-occluder to transiently block perfusion and enable measurement of transvascular water flow movement at a measured hydrostatic pressure, and (3) a blunt glass rod to stabilize the mesenteric tissue at the site of cannulation. The modified Landis micro-occlusion technique uses red cells suspended in the artificial perfusate as markers of transvascular fluid movement, and also enables repeated measurements of these flows as experimental conditions are changed and hydrostatic and colloid osmotic pressure difference across the microvessels are carefully controlled. Measurements of hydraulic conductivity first using a control perfusate, then after re-cannulation of the same microvessel with the test perfusates enable paired comparisons of the microvessel response under these well-controlled conditions. Attempts to extend the method to microvessels in the mesentery of mice with genetic modifications expected to modify vascular permeability were severely limited because of the absence of long straight and unbranched microvessels in the mouse mesentery, but the recent availability of the rats with similar genetic modifications using the CRISPR/Cas9 technology is expected to open new areas of investigation where the methods described herein can be applied.

The modified Landis technique enables paired measurement of the hydraulic conductivity of individual microvessels in the mesentery of normal and genetically modified rats under control and test conditions using microperfusion techniques. It provides a convenient method to evaluate mechanisms that regulate microvessel permeability and transvascular exchange under physiological conditions.

Experiments to measure the permeability properties of individually perfused microvessels provide a bridge between investigation of molecular and cellular ...

Isolation of CD146+ Resident Lung Mesenchymal Stromal Cells from Rat Lungs

Mesenchymal stromal cells (MSCs) are increasingly recognized for their therapeutic potential in a wide range of diseases, including lung diseases. Besides the use of bone marrow and umbilical cord MSCs for exogenous cell therapy, there is also increasing interest in the repair and regenerative potential of resident tissue MSCs. Moreover, they likely have a role in normal organ development, and have been attributed roles in disease, particularly those with a fibrotic nature. The main hurdle for the study of these resident tissue MSCs is the lack of a clear marker for the isolation and identification of these cells. The isolation technique described here applies multiple characteristics of lung resident MSCs (L-MSCs). Upon sacrifice of the rats, lungs are removed and rinsed multiple times to remove blood. Following mechanical dissociation by scalpel, the lungs are digested for 2-3 hr using a mix of collagenase type I, neutral protease and DNase type I. The obtained single cell suspension is subsequently washed and layered over density gradient medium (density 1.073 g/ml). After centrifugation, cells from the interphase are washed and plated in culture-treated flasks. Cells are cultured for 4-7 days in physiological 5% O2, 5% CO2 conditions. To deplete fibroblasts (CD146-) and to ensure a population of only L-MSCs (CD146+), positive selection for CD146+ cells is performed through magnetic bead selection. In summary, this procedure reliably produces a population of primary L-MSCs for further in vitro study and manipulation. Because of the nature of the protocol, it can easily be translated to other experimental animal models.

Isolation of CD146+ Resident Lung Mesenchymal Stromal Cells from Rat Lungs

This protocol describes an isolation technique for obtaining primary lung resident mesenchymal stromal cells from rats, through the use of enzymatic digestion, density gradient separation, plastic adherence and CD146+ magnetic bead selection.

Mesenchymal stromal cells (MSCs) are increasingly recognized for their therapeutic potential in a wide range of diseases, including lung diseases. Besides ...

The Mouse Isolated Perfused Kidney Technique

The mouse isolated perfused kidney (MIPK) is a technique for keeping a mouse kidney under ex vivo conditions perfused and functional for 1 hr. This is a prerequisite for studying the physiology of the isolated organ and for many innovative applications that may be possible in the future, including perfusion decellularization for kidney bioengineering or the administration of anti-rejection or genome-editing drugs in high doses to prime the kidney for transplantation. During the time of the perfusion, the kidney can be manipulated, renal function can be assessed, and various pharmaceuticals administered. After the procedure, the kidney can be transplanted or processed for molecular biology, biochemical analysis, or microscopy.
This paper describes the perfusate and the surgical technique needed for the ex vivo perfusion of mouse kidneys. Details of the perfusion apparatus are given and data are presented showing the viability of the kidney&#39;s preparation: renal blood flow, vascular resistance, and urine data as functional, transmission electron micrographs of different nephron segments as morphological readouts, and western blots of transport proteins of different nephron segments as molecular readout.

The mouse isolated perfused kidney (MIPK) is a technique for keeping a mouse kidney under ex vivo conditions perfused and functional for 1 hr. The buffers and surgical technique are described in detail.

The mouse isolated perfused kidney (MIPK) is a technique for keeping a mouse kidney under ex vivo conditions perfused and functional for 1 hr. This is a ...

An Improved Chemotaxis Assay for the Rapid Identification of Rhizobacterial Chemoattractants in Root Exudates

Chemotaxis identification is very important for the research and application of rhizosphere growth-promoting bacteria. We established a straightforward method to quickly identify the chemoattractants that could induce the chemotactic movement of rhizosphere growth-promoting bacteria on sterile glass slides via simple steps. Bacteria solution (OD600 = 0.5) and sterile chemoattractant aqueous solution were added dropwise on the glass slide at an interval of 1 cm. An inoculating loop was used to connect the chemoattractant aqueous solution to the bacterial solution. The slide was kept at room temperature for 20 min on the clean bench. Finally, the chemoattractant aqueous solution was collected for bacterial counting and microscopic observation. In this study, through multiple comparisons of experimental results, the method overcame multiple shortcomings of traditional bacterial chemotaxis methods. The method reduced the error of plate counting and shortened the experimental cycle. For the identification of chemoattractant substances, this new method can save 2-3 days compared to the traditional method. Additionally, this method allows any researcher to systematically complete a bacterial chemotaxis experiment within 1-2 days. The protocol can be considered a valuable resource for understanding plant-microbe interactions.

Here, we present an improved chemotaxis assay protocol. The goal of this protocol is to reduce the steps and costs of traditional bacterial chemotaxis methods and to serve as a valuable resource for understanding plant-microbe interactions.

Chemotaxis identification is very important for the research and application of rhizosphere growth-promoting bacteria. We established a straightforward ...