This work was supported by the Deutsche Forschungsgemeinschaft (KFO 196 &#8220;Signaltransduktion bei adaptativen und maladaptiven kardialen Remodelling-Prozessen&#8221;, FR 1638/1-2) and by the DZHK (German Centre for Cardiovascular Research, a part of the German Centres of Health Research, which is a BMBF (German Ministry of Education and Research) initiative).

NOTE: The basic steps of the isolation procedure are shown in Figure&#160;1. All steps are described in detail in the following protocol. Papillary muscle isolation, mounting in organ bath chamber, acquisition and analysis is performed in a consecutive and compulsory timescale.
All animal experiments were performed in accordance with German legislation on protection of animals and were approved by the Ethics Review Board of University of Heidelberg.
1. Preparation of Instrumentation
<ol>
	<li>For contractility measurements use a multichambered organ bath setup. Components of an ex vivo contractility organ bath setup are shown in Figure 2. 
	NOTE: To minimize the amount of time between the preparation of the papillary muscle and the beginning of the experimental protocol, set up equipment and prepare buffers prior to collecting experimental tissue.This provides the greatest amount of time that the tissue remains viable to conduct experiments.</li>
	<li>Start up computer and data acquisition equipment. Turn on organ bath heat (preset to 32 &#176;C) and allow units to preset temperature.</li>
	<li>Prepare the acquisition equipment. Start recording data as mentioned in the software manual.</li>
	<li>Check and conduct calibration (if necessary) on each channel and zero all channels to standardize the electric signal supplied from the respective force transducer (associated with that channel) to a 2-g force supplied by a certified weight.</li>
	<li>Turn on gas supply (95% O2/5% CO2) to organ bath chambers. Continuously gas all chambers during the entire protocol measurements.</li>
</ol>
2. Preparation of Buffers and Physiological Solutions
<ol>
	<li>Prepare a Krebs-Henseleit buffer solution to achieve final concentrations of 119 mM NaCl; 25 mM NaHCO3; 4.6 mM KCl; 11mM glucose; 1 mM Na-pyruvate; 1.5 mM CaCl2; 1.64 mM MgSO4; 1.18 mM KH2PO4 and adjust pH to 7.4 (see Table 1 Physiological solution).</li>
	<li>Prepare separate Krebs-Henseleit buffer solution to use during isolation as described in step 2.1 with additional 30mM 2,3-Butanedione monoxime (BDM) and 50 IE Heparin/ml. Cool solution to 4&#176;C (see Table 1 Preparation solution). For ischemia simulation, prepare ischemia-solution as described in Table 1.</li>
	<li>For the protocol of the Ca2+-dependent contractility, add Ca2+ to the Krebs-Henseleit buffer solution to requested final concentration. 
	NOTE: prepare these solutions directly before its usage and gass with carbogen to avoid precipitation of Calciumcarbonate. Prewarm solution to 32&#176;C before using.</li>
</ol>
3. Preparation of the Gassing Tube and Dissection Dish used during the Papillary Excision Procedure
<ol>
	<li>Connect a soft gassing tube (external diameter 2-4 mm) to the gas connection (100% oxygen, carbogen alternatively) with expert working.</li>
	<li>Create a closed ring of the gassing tube fitting inside the dissection dish. Puncture the gassing tube several times that a continuous bubbling is assured. This gassing tube can be used several times.</li>
	<li>Prepare dissection dish with a silicon elastomer at the bottom (0.5 cm thick), so that pins can be stuck into it. This dish can be used several times.</li>
</ol>
4. Isolation of Left Anterior Papillary Muscle from Mice
NOTE: Before starting the isolation of the papillary muscle, check that the gas lines are clear of blockages.
<ol>
	<li>Prepare organ bath setup as mentioned in the protocol section 1-3 before starting the preparation of the papillary muscles. Prepare all solutions at the day of the experiment.</li>
	<li>Sacrifice the mouse (approximately 8-12 weeks old) by cervical dislocation according to expert working and institutional guidelines.</li>
	<li>Fix the animal in dorsal position by fixing forepaws and hind paws on a dissection board, open the thorax lateral on both sides by cutting through the ribs with sharp bone scissors, then cut the diaphragm with a transversal cut. Remove the pericardium. Now the heart and the aorta are accessible.</li>
	<li>Fix the heart with blunt forceps on the vascular truncus close to the heart and separate the heart quickly with scissors from the lungs and the surrounding tissue.</li>
	<li>Transfer the beating heart to a Petri dish filled with cooled preparation solution gassed with oxygen (step 2.2). Allow the heart to beat and stimulate heart contractions softly via touching the cardiac apex with forceps.</li>
	<li>As soon the heart is completely exsanguinous, transfer it to the dissection dish filled with cooled preparation solution (step 2.2) and gassed with O2. From this step on use a stereomicroscope.</li>
	<li>Fix the heart with a small pin through the right ventricle so that the heart is seen from dorsal (right ventricle is situated on the right side from the operator&#8217;s view).</li>
	<li>Using microsurgical scissors separate both atria on the atrioventricular level, cut connecting tissue from the ventricles and discard. Perform a cut through the ventricular wall from the AV-valve-level to the apex of the heart avoiding any mechanical pressure.</li>
	<li>Open the ventricle and fix the left-sided free wall with forceps, thus having a look at both left ventricular papillary muscles.</li>
	<li>Slightly cut away the ventricular tissue lateral on both sides of the left anterior papillary muscle preserving a part of the valvular sail on the papillary muscle preparation and avoid touching or stretching the papillary muscle as much as possible. Dissect the remaining ventricular wall tissue from the papillary muscle.</li>
	<li>Attach silk threads (7/0, metric 0.5) on both sides of the papillary muscle preparation, one on the valvular sail and one on the muscular part. Fix the preparation in the organ bath chamber filled with organ bath solution and gassed with carbogen, as temperature 32 &#176;C is suggested.</li>
</ol>
5. Equilibration and Stimulation of the Papillary Muscle
<ol>
	<li>Stimulate the papillary muscle preparation with rectangular pulses (duration of 2 ms and current of 100 mA) at stimulation frequency of 1 Hz immediately after the fixation in the organ bath.</li>
	<li>Ensure a frequent change of the organ bath solution, either by continuous change or by frequent manual change (every 5 min) according to the setup of the organ bath type used.</li>
	<li>Gradually increase the pretension until maximal twitch force in reached. Maximal twitch force is reached when the increase of the pretension is not followed by a further augmentation in the twitch force.</li>
	<li>After 45-60 min of equilibration, start the experimental protocol.</li>
</ol>
6. Suggested Experimental Protocols for Contractility Measurements
NOTE: The experimental protocol outlined below comprises standard maneuvers to characterize cardiac contractility under physiological and pathophysiological conditions. In the representative section we describe these protocols in detail also showing representative results (see also Table 2).
<ol>
	<li>Recording and analysis of the experimental protocols
	<ol>
		<li>For recording, use a suitable software with adequate temporal resolution (acquisition rate &#8805; 1kHz).</li>
		<li>Analyze parameters including twitch force amplitude (height), time to peak tension (TTP) and half maximal relaxation time (R50/TFall, respectively) as mentioned in the software program (as example Chart 5.5 of ADInstruments, see Figure 4).</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Endoh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+Ca2++signaling+and+Ca2++sensitizers.">Cardiac Ca2+ signaling and Ca2+ sensitizers.</a> Circ J. 12 (12), 1915-1925 (2008).</li><li>Bers, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium+cycling+and+signaling+in+cardiac+myocytes.">Calcium cycling and signaling in cardiac myocytes.</a> Annu Rev Physiol. 70, 23-49 (2008).</li><li>Bers, D., Despa, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Na/K-ATPase&#8212;an+integral+player+in+the+adrenergic+fight-or+flight+response.">Na/K-ATPase&#8212;an integral player in the adrenergic fight-or flight response.</a> Trends Cardiovasc Med. 19, 111-118 (2009).</li><li>Bers, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+excitation&#8211;contraction+coupling.">Cardiac excitation&#8211;contraction coupling.</a> Nature. 415, 198-205 (2002).</li><li>Pieske, B., 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=al.+Ca(2+)-dependent+and+Ca(2+)-independent+regulation+of+contractility+in+isolated+human+myocardium.">al. Ca(2+)-dependent and Ca(2+)-independent regulation of contractility in isolated human myocardium.</a> Basic Res Cardiol. 92, 75-86 (1997).</li><li>Corbin, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sildenafilcitrate+does+not+affect+cardiac+contractility+in+human+or+dog+heart.">Sildenafilcitrate does not affect cardiac contractility in human or dog heart.</a> Curr Med ResOpin. 19 (8), 747-752 (2003).</li><li>Romero-Vecchione, E., Vasquez, J., Rosa, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+negative+inotropic+effect+of+cocaine+in+rat+ventricle+strip.">Direct negative inotropic effect of cocaine in rat ventricle strip.</a> Acta Cient Venez. 47 (1), 17-23 (1996).</li><li>N&#228;bauer, 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=Positive+inotropic+effects+in+isolated+ventricular+myocardium+from+nonfailing+and+terminally+failing+human+hearts.">Positive inotropic effects in isolated ventricular myocardium from nonfailing and terminally failing human hearts.</a> Eur J Clin Invest. 18 (6), 600-606 (1988).</li><li>Gao, W. D., Perez, N. G., Marban, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calcium+cycling+and+contractile+activation+in+intact+mouse+cardiac+muscle.">Calcium cycling and contractile activation in intact mouse cardiac muscle.</a> J Physiol. 507, 175-184 (1998).</li><li>Bluhm, W. F., Kranias, E. G., Dillmann, W. H., Meyer, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phospholamban:+a+major+determinant+of+the+cardiac+force-frequency+relationship.">Phospholamban: a major determinant of the cardiac force-frequency relationship.</a> Am J Physiol Heart Circ Physiol. 278 (1), H249-H255 (2000).</li><li>Redel, A., Baumgartner, W., Golenhofen, K., Drenckhahn, D., Golenhofen, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+activity+and+force-frequency+relationship+of+isolated+mouse+papillary+muscle:+effects+of+extracellular+calcium+concentration,+temperature+and+contraction+type.">Mechanical activity and force-frequency relationship of isolated mouse papillary muscle: effects of extracellular calcium concentration, temperature and contraction type.</a> Pflugers Arch. 445 (2), 297-304 (2002).</li><li>Uhl, S., Mathar, I., Vennekens, R., Freichel, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adenylyl+cyclase-mediated+effects+contribute+to+increased+Isoprenaline-induced+cardiac+contractility+in+TRPM4+deficient+mice.">Adenylyl cyclase-mediated effects contribute to increased Isoprenaline-induced cardiac contractility in TRPM4 deficient mice.</a> JMCC. 74, 307-317 (2014).</li><li>Allen, D. G., Jewell, B. R., Wood, E. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+of+the+contractility+of+mammalian+myocardium+at+low+rates+of+stimulation.">Studies of the contractility of mammalian myocardium at low rates of stimulation.</a> J Physiol. 254 (1), 1-17 (1976).</li><li>Pieske, B., Maier, L. S., Schmidt-Schweda, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sarcoplasmic+reticulum+Ca2++load+in+human+heart+failure.">Sarcoplasmic reticulum Ca2+ load in human heart failure.</a> Basic Res Cardiol. 97, 163-171 (2002).</li><li>Koch-Weser, J., Blinks, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Influence+of+the+Interval+between+Beats+on+Myocardial+Contractility.">The Influence of the Interval between Beats on Myocardial Contractility.</a> Pharmacol Rev. 15, 601-652 (1963).</li><li>Bocalini, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myocardial+remodeling+after+large+infarcts+in+rat+converts+post+rest-potentiation+in+force+decay.">Myocardial remodeling after large infarcts in rat converts post rest-potentiation in force decay.</a> Arq Bras Cardiol. 98 (3), 243-251 (2012).</li><li>Juggi, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+ischemia-reperfusion+on+the+post-rest+inotropy+of+isolated+perfused+rat+heart.">Effect of ischemia-reperfusion on the post-rest inotropy of isolated perfused rat heart.</a> J Cell Mol Med. 6 (4), 621-630 (2002).</li><li>Lakatta, E. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Beyond+Bowditch:+the+convergence+of+cardiac+chronotropy+and+inotropy.">Beyond Bowditch: the convergence of cardiac chronotropy and inotropy.</a> Cell Calcium. 35 (6), 629-624 (2004).</li><li>Taylor, D. G., Parilak, L. D., LeWinter, M. M., Knot, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+of+the+rat+left+ventricle+force+and+Ca2++-frequency+relationships:+similarities+to+dog+and+human.">Quantification of the rat left ventricle force and Ca2+ -frequency relationships: similarities to dog and human.</a> Cardiovasc Res. 61 (1), 77-86 (2004).</li><li>Schmidt, U., Hajjar, R. J., Gwathmey, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+force-interval+relationship+in+human+myocardium.">The force-interval relationship in human myocardium.</a> J Card Fail. 1 (4), 311-321 (1995).</li><li>Rossman, E. I., Petre, R. E., Chaudhary, K. W., Piacentino, V. 3. r. d., Janssen, P. M., Gaughan, J. P., Houser, S. R., Margulies, K. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Abnormal+frequency-dependentresponses+represent+the+pathophysiologic+signature+of+contractile+failure+inhuman+myocardium.">Abnormal frequency-dependentresponses represent the pathophysiologic signature of contractile failure inhuman myocardium.</a> JMCC. 36 (1), 33-42 (2004).</li><li>Moran, A. E., Forouzanfar, M. H., Roth, G. A., Mensah, G. A., Ezzati, M., Murray, C. J., Naghavi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+trends+in+ischemic+heart+disease+mortality+in+21+world+regions,+1980+to+2010:+the+Global+Burden+of+Disease+2010+stud.">Temporal trends in ischemic heart disease mortality in 21 world regions, 1980 to 2010: the Global Burden of Disease 2010 stud.</a> Circulation. 129 (14), 1483-1492 (1980).</li><li>Lee, J. A., Allen, D. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Changes+in+intracellular+free+calcium+concentration+during+long+exposures+to+simulated+ischemia+in+isolated+mammalian+ventricular+muscle.">Changes in intracellular free calcium concentration during long exposures to simulated ischemia in isolated mammalian ventricular muscle.</a> Circ Res. 71 (1), 58-69 (1992).</li></ol>

The authors declare that they have no competing financial interests.

In this manuscript we describe a method to investigate contractility of murine papillary muscle in vitro which can be used to answer several scientific questions related to heart physiology and pathology in mice as well as to support the analysis of transgenic lines and the discovery of new pharmaceutical approaches to treat heart dysfunctions. We illustrate the use of this method to assess physiological, pathological and pharmacological properties of cardiac muscle contractility (see Fig 3). Ad...

The investigation of proteins like ion channels referring their role for cardiac contractility is essential to discover different pathomechanisms and to establish new therapeutic strategies for cardiac diseases such as ischemia and heart failure.
Contractile function of mammalian cardiomyocytes is known to be modulated by various ion channels, transporters and other proteins. Action potential evoked activation of voltage dependent sarcolemmal L-type Ca2+ channels leads to Ca2+ influx from extracellular space and subsequently to Ca2+-induced Ca2+ release (CICR)1, which triggers cellular contraction2. Ca2+-signaling plays a central role in cardiac contractility and adaptation to physiological or pathological stress. Catecholamines activate cardiac &#946;-adrenergic receptors, thus stimulating adenylyl cyclase (AC) which synthesizes cAMP. Being activated, protein kinase A (PKA) phosphorylates different intracellular and membrane associated proteins like L-type Ca2+ channels, phospholamban and ryanodine receptors resulting in modification of Ca2+ transients and cardiac contractility1,3,4. cAMP is degraded by phosphodiesterase (PDE). Activation of Gs-coupled receptors other than &#946;-adrenoceptors also leads to accumulation of cAMP.
The technique of contractility measurements in isolated ventricular muscle strips is well established for larger mammalian species5-8. Based on the possibility of gene targeting in mice it is important to establish methods to analyze murine cardiac physiology. However, existing data about the physiological properties of isolated muscle preparations in mice differ depending on experimental conditions9-12.
The described method is used to analyze cardiac contractility of left ventricular papillary muscle preparations in vitro. Investigation of cardiac contractility is performed in the absence of influences modifying cardiac contractility in vivo, like blood pressure, neurohumoral stimulation and physical or metabolic stress. The beating rate of the contracting muscle preparation can be rigorously defined and changed arbitrarily. Twitch force can be analyzed in the context of specific stimuli such as calcium concentration, beating frequency or temperature. In addition, this method can be used to investigate different signaling pathway components and to compare cardiac performance of genetically modified mouse models by controlling experimental conditions mentioned above.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>S7653</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma-Aldrich</td>
			<td>S5761&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>P9333</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>D9434&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium pyruvate</td>
			<td>Sigma-Aldrich</td>
			<td>P5280&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium chloride dihydrate</td>
			<td>Sigma-Aldrich</td>
			<td align="right">223506</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium sulfate heptahydrate</td>
			<td>Sigma-Aldrich</td>
			<td align="right">230391</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td>Sigma-Aldrich</td>
			<td>P 5655</td>
			<td></td>
		</tr>
		<tr>
			<td>2,3-Butanedione monoxime</td>
			<td>Sigma-Aldrich</td>
			<td>B0753</td>
			<td></td>
		</tr>
		<tr>
			<td>Forskolin</td>
			<td>Sigma-Aldrich</td>
			<td>F3917</td>
			<td>Hazard statement H312, solve in DMSO</td>
		</tr>
		<tr>
			<td>3-?Isobutyl-?1-?methylxanthine</td>
			<td>Sigma-Aldrich</td>
			<td>I5879</td>
			<td>Hazard statement H 302, solve in DMSO</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide (DMSO)</td>
			<td>Sigma-Aldrich</td>
			<td>D2650</td>
			<td></td>
		</tr>
		<tr>
			<td>Isoprenaline hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>I5627</td>
			<td>Hazard statement H 315-H319-H335</td>
		</tr>
		<tr>
			<td>Sodium Heparine 250.000 IE/10ml</td>
			<td>ratiopharm</td>
			<td>PZN 3874685</td>
			<td></td>
		</tr>
		<tr>
			<td>Histamine dihydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>H7250</td>
			<td>Hazard statement H 315-H 317-H319- H334-H335</td>
		</tr>
	</tbody>
</table>

contractility measurements on isolated papillary muscles for the investigation of cardiac inotropy in mice

Papillary muscle isolated from adult mouse hearts can be used to study cardiac contractility during different physiological/pathological conditions. The contractile characteristics can be evaluated independently of external influences such as vascular tonus or neurohumoral status. It depicts a scientific approach between single cell measurements with isolated cardiac myocytes and in vivo studies like echocardiography. Thus, papillary muscle preparations serve as an excellent model to study cardiac physiology/pathophysiology and can be used for investigations like the modulation by pharmacological agents or the exploration of transgenic animal models. Here, we describe a method of isolating the murine left anterior papillary muscle to investigate cardiac contractility in an organ bath setup. In contrast to a muscle strip preparation isolated from the ventricular wall, the papillary muscle can be prepared in toto without damaging the muscle tissue severely. The organ bath setup consists of several temperature-controlled, gassed and electrode-equipped organ bath chambers. The isolated papillary muscle is fixed in the organ bath chamber and electrically stimulated. The evoked twitch force is recorded using a pressure transducer and parameters such as twitch force amplitude and twitch kinetics are analyzed. Different experimental protocols can be performed to investigate the calcium- and frequency-dependent contractility as well as dose-response curves of contractile agents such as catecholamines or other pharmaceuticals. Additionally, pathologic conditions like acute ischemia can be simulated.

The protocol of this manuscript for contractility measurements of isolated murine papillary muscle preparations is tuned to optimal conditions to achieve reproducible experimental results under physiological conditions. To define optimal experimental conditions we performed pilot experiments varying organ bath temperature and extracellular calcium concentration (see also12). The protocol described here was performed with an extracellular calcium concentration of 1.5 mM and a temperature of 32 &#176;C.
<p c...

Watch this Scientific Journal Video about Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice at JoVE.com

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

Murine left ventricular papillary muscle can be used to investigate cardiac contractility in vitro. This article describes in detail the isolation and experimental protocols to study cardiac contractile characteristics.

Papillary muscle isolated from adult mouse hearts can be used to study cardiac contractility during different physiological/pathological conditions. The ...

contractility-measurements-on-isolated-papillary-muscles-for

Research

JoVE Journal

Biology

14.9K Views.  Universität Heidelberg. Murine left ventricular papillary muscle can be used to investigate cardiac contractility in vitro. This article describes in detail the isolation and experimental protocols to study cardiac contractile characteristics.

Video: Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca2+-activated K+ (BK) channels. The protocol may also be used to study the structure-function relationship for other ion channels and neurotransmitter receptors1. BK channels are widely expressed in different tissues and have been implicated in many physiological functions, including regulation of smooth muscle contraction, frequency tuning of inner hair cells and regulation of neurotransmitter release2-6. BK channels are activated by membrane depolarization and by intracellular Ca2+ and Mg2+ 6-9. Therefore, the protocol is designed to control both the membrane voltage and the intracellular solution. In this protocol, messenger RNA of BK channels is injected into Xenopus laevis oocytes (stage V-VI) followed by 2-5 days of incubation at 18&deg;C10-13. Membrane patches that contain single or multiple BK channels are excised with the inside-out configuration using patch clamp techniques10-13. The intracellular side of the patch is perfused with desired solutions during recording so that the channel activation under different conditions can be examined. To summarize, the mRNA of BK channels is injected into Xenopus laevis oocytes to express channel proteins on the oocyte membrane; patch clamp techniques are used to record currents flowing through the channels under controlled voltage and intracellular solutions.

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

Ionic current of BK channels is recorded using patch clamp techniques. BK channels are expressed in Xenopus oocytes by injecting messenger RNA. The intracellular solution during patch clamp recordings is controlled by a perfusion system.

The protocol presented here is designed to study the activation of the large conductance, voltage- and Ca2+-activated K+ (BK) channels. The protocol may ...

Bioengineering Human Microvascular Networks in Immunodeficient Mice

The future of tissue engineering and cell-based therapies for tissue regeneration will likely rely on our ability to generate functional vascular networks in vivo. In this regard, the search for experimental models to build blood vessel networks in vivo is of utmost importance 1. The feasibility of bioengineering microvascular networks in vivo was first shown using human tissue-derived mature endothelial cells (ECs) 2-4; however, such autologous endothelial cells present problems for wide clinical use, because they are difficult to obtain in sufficient quantities and require harvesting from existing vasculature. These limitations have instigated the search for other sources of ECs. The identification of endothelial colony-forming cells (ECFCs) in blood presented an opportunity to non-invasively obtain ECs 5-7. We and other authors have shown that adult and cord blood-derived ECFCs have the capacity to form functional vascular networks in vivo 7-11. Importantly, these studies have also shown that to obtain stable and durable vascular networks, ECFCs require co-implantation with perivascular cells. The assay we describe here illustrates this concept: we show how human cord blood-derived ECFCs can be combined with bone marrow-derived mesenchymal stem cells (MSCs) as a single cell suspension in a collagen/fibronectin/fibrinogen gel to form a functional human vascular network within 7 days after implantation into an immunodeficient mouse. The presence of human ECFC-lined lumens containing host erythrocytes can be seen throughout the implants indicating not only the formation (de novo) of a vascular network, but also the development of functional anastomoses with the host circulatory system. This murine model of bioengineered human vascular network is ideally suited for studies on the cellular and molecular mechanisms of human vascular network formation and for the development of strategies to vascularize engineered tissues.

Here, we describe a methodology to deliver human cord blood-derived endothelial colony-forming cells (ECFCs) and bone marrow-derived mesenchymal stem cells (MSCs), embedded in a collagen/fibronectin gel, subcutaneously into immunodeficient mice. This cell/gel combination generates a human vascular network that connects with the mouse vasculature.

The future of tissue engineering and cell-based therapies for tissue regeneration will likely rely on our ability to generate functional vascular networks ...

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 ...

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

Described here is a method to measure contractility of isolated skeletal muscles. Parameters such as muscle force, muscle power, contractile kinetics, fatigability, and recovery after fatigue can be obtained to assess specific aspects of the excitation-contraction coupling (ECC) process such as excitability, contractile machinery and Ca2+ handling ability. This method removes the nerve and blood supply and focuses on the isolated skeletal muscle itself. We routinely use this method to identify genetic components that alter the contractile property of skeletal muscle though modulating Ca2+ signaling pathways. Here, we describe a newly identified skeletal muscle phenotype, i.e., mechanic alternans, as an example of the various and rich information that can be obtained using the in vitro muscle contractility assay. Combination of this assay with single cell assays, genetic approaches and biochemistry assays can provide important insights into the mechanisms of ECC in skeletal muscle.

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

We describe a method to directly measure muscle force, muscle power, contractile kinetics and fatigability of isolated skeletal muscles in an in vitro system using field stimulation. Valuable information on Ca2+ handling properties and contractile machinery of the muscle can be obtained using different stimulating protocols.

 
Described here is a method to measure contractility of isolated skeletal muscles. Parameters such as muscle force, muscle power, contractile kinetics, ...

Intravital Microscopy of the Microcirculation in the Mouse Cremaster Muscle for the Analysis of Peripheral Stem Cell Migration

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to nonmarrow tissue have not been completely clarified. We describe here the technique of intravital microscopy applied to the mouse cremaster microcirculation for analysis of peripheral bone marrow stem cell migration in vivo. Intravital microscopy of the M. cremaster has been previously introduced in the field of inflammatory research for direct observation of leucocyte interaction with the vascular endothelium. Since sufficient peripheral stem and progenitor cell migration includes similar initial steps of rolling along and firm adhesion at the endothelial lining it is conceivable to apply the M. cremaster model for the observation and quantification of the interaction of intravasculary administered stem cells with the endothelium. As various chemical components can be selectively applied to the target tissue by simple superfusion techniques, it is possible to establish essential microenvironmental preconditions, for initial stem cell recruitment to take place in a living organism outside the bone marrow.

Intravital microscopy of the mouse M. cremaster microcirculation offers a unique and well-standardized in vivo model for the analysis of peripheral bone marrow stem cell migration.

In the era of intravascular cell application protocols in the context of regenerative cell therapy, the underlying mechanisms of stem cell migration to ...

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 ...

Analysis of the Gap Junction-dependent Transfer of miRNA with 3D-FRAP Microscopy

Small antisense RNAs, like miRNA and siRNA, play an important role in cellular physiology and pathology and, moreover, can be used as therapeutic agents in the treatment of several diseases. The development of new, innovative strategies for miRNA/siRNA therapy is based on an extensive knowledge of the underlying mechanisms. Recent data suggest that small RNAs are exchanged between cells in a gap junction-dependent manner, thereby inducing gene regulatory effects in the recipient cell. Molecular biological techniques and flow cytometric analysis are commonly used to study the intercellular exchange of miRNA. However, these methods do not provide high temporal resolution, which is necessary when studying the gap junctional flux of molecules. Therefore, to investigate the impact of miRNA/siRNA as intercellular signaling molecules, novel tools are needed that will allow for the analysis of these small RNAs at the cellular level. The present protocol describes the application of three-dimensional fluorescence recovery after photobleaching (3D-FRAP) microscopy to elucidating the gap junction-dependent exchange of miRNA molecules between cardiac cells. Importantly, this straightforward and non-invasive live-cell imaging approach allows for the visualization and quantification of the gap junctional shuttling of fluorescently labeled small RNAs in real time, with high spatio-temporal resolution. The data obtained by 3D-FRAP confirm a novel pathway of intercellular gene regulation, where small RNAs act as signaling molecules within the intercellular network.

Here, we describe the application of three-dimensional fluorescence recovery after photobleaching (3D-FRAP) for the analysis of the gap junction-dependent shuttling of miRNA. In contrast to commonly applied methods, 3D-FRAP allows for the quantification of the intercellular transfer of small RNAs in real time, with high spatio-temporal resolution.

Small antisense RNAs, like miRNA and siRNA, play an important role in cellular physiology and pathology and, moreover, can be used as therapeutic agents ...

A Simple and Efficient Method for In Vivo Cardiac-specific Gene Manipulation by Intramyocardial Injection in Mice

Gene manipulation specifically in the heart significantly potentiate the investigation of cardiac disease pathomechanisms and their therapeutic potential. In vivo cardiac-specific gene delivery is commonly achieved by either systemic or local delivery. Systemic injection via tail vein is easy and efficient in manipulating cardiac gene expression by using recombinant adeno-associated virus 9 (AAV9). However, this method requires a relatively high amount of vector for efficient transduction, and may result in nontarget organ gene transduction. Here, we describe a simple, efficient, and time-saving method of intramyocardial injection for in vivo cardiac-specific gene manipulation in mice. Under anesthesia (without ventilation), the pectoral major and minor muscles were bluntly dissected, and the mouse heart was quickly exposed by manual externalization through a small incision at the fourth intercostal space. Subsequently, adenovirus encoding luciferase (Luc) and vitamin D receptor (VDR), or short hairpin RNA (shRNA) targeting VDR, was injected with a Hamilton syringe into the myocardium. Subsequent in vivo imaging demonstrated that luciferase was successfully overexpressed specifically in the heart. Moreover, Western blot analysis confirmed the successful overexpression or silencing of VDR in the mouse heart. Once mastered, this technique can be used for gene manipulation, as well as injection of cells or other materials such as nanogels in the mouse heart.

A Simple and Efficient Method for In Vivo Cardiac-specific Gene Manipulation by Intramyocardial Injection in Mice

Here we present a protocol for cardiac-specific gene manipulation in mice. Under anesthesia, the mouse hearts were externalized through the fourth intercostal space. Subsequently, adenoviruses encoding specific genes were injected with a syringe into the myocardium, followed by protein expression measurement via in vivo imaging and Western blot analysis.

Gene manipulation specifically in the heart significantly potentiate the investigation of cardiac disease pathomechanisms and their therapeutic potential. ...

Analyzing the &alpha;-Actinin Network in Human iPSC-Derived Cardiomyocytes Using Single Molecule Localization Microscopy

The maturation of iPSC-derived cardiomyocytes is a critical issue for their application in regenerative therapy, drug testing and disease modeling. Despite the development of multiple differentiation protocols, the generation of iPSC cardiomyocytes resembling an adult-like phenotype remains challenging. One major aspect of cardiomyocytes maturation involves the formation of a well-organized sarcomere network to ensure high contraction capacity. Here, we present a super resolution-based approach for semi-quantitative analysis of the &#945;-actinin network in cardiomyocytes. Using photoactivated localization microscopy a comparison of sarcomere length and z-disc thickness of iPSC-derived cardiomyocytes and cardiac cells isolated from neonatal tissue was performed. At the same time, we demonstrate the importance of proper imaging conditions to obtain reliable data. Our results show that this method is suitable to quantitatively monitor the structural maturity of cardiac cells with high spatial resolution, enabling the detection of even subtle changes of sarcomere organization.

Analyzing the &#945;-Actinin Network in Human iPSC-Derived Cardiomyocytes Using Single Molecule Localization Microscopy

The formation of a proper sarcomere network is important for the maturation of iPSC-derived cardiomyocytes. We present a super resolution-based approach that allows for the quantitative evaluation of the structural maturation of stem cell derived cardiomyocytes, to improve culture conditions promoting cardiac development.

The maturation of iPSC-derived cardiomyocytes is a critical issue for their application in regenerative therapy, drug testing and disease modeling. ...

Dissection of the Endolymphatic Sac from Mice

The study of mutant mouse models of human hearing and balance disorders has unraveled many structural and functional changes which may contribute to the human phenotypes. Although important progress has been done in the understanding of the development and function of the neurosensory epithelia of the cochlea and vestibula, limited knowledge is available regarding the development, cellular composition, molecular pathways and functional characteristics of the endolymphatic sac. This is, in large part, due to the difficulty of visualizing and microdissecting this tissue, which is an epithelium comprised of only one cell layer. The study presented here describes an approach to access and microdissect the endolymphatic sac from the wild-type mouse inner ear at different ages. The result of a similar dissection is shown in a pendrin-deficient mouse model of enlargement of the vestibular aqueduct. A transgenic mouse with a fluorescent endolymphatic sac is presented. This reporter mouse can be used to readily visualize the endolymphatic sac with limited dissection and determine its size. It can also be used as an educational tool to teach how to dissect the endolymphatic sac. These dissection procedures should facilitate further characterization of this understudied part of the inner ear.

This study describes how to dissect the endolymphatic sac from the inner ear of the mouse at different ages. The result of a similar dissection is shown in an Slc26a4-null mouse model of enlargement of the endolymphatic sac. A transgenic mouse with a fluorescent reporter expressed in the endolymphatic sac is presented as a model to readily visualize the endolymphatic sac, and educational tool.

The study of mutant mouse models of human hearing and balance disorders has unraveled many structural and functional changes which may contribute to the ...

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

Podsumowanie

Przeglądaj więcej filmów

Rozdziały w tym wideo

Patch Clamp and Perfusion Techniques for Studying Ion Channels Expressed in Xenopus oocytes

Bioengineering Human Microvascular Networks in Immunodeficient Mice

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

Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles

Intravital Microscopy of the Microcirculation in the Mouse Cremaster Muscle for the Analysis of Peripheral Stem Cell Migration

The Mouse Isolated Perfused Kidney Technique

Analysis of the Gap Junction-dependent Transfer of miRNA with 3D-FRAP Microscopy

A Simple and Efficient Method for In Vivo Cardiac-specific Gene Manipulation by Intramyocardial Injection in Mice

Analyzing the α-Actinin Network in Human iPSC-Derived Cardiomyocytes Using Single Molecule Localization Microscopy

Dissection of the Endolymphatic Sac from Mice