Isolated while heart calorimetry: energetics of length-dependent activation.
Myocardial energy expenditure measured by whole heart calorimetry has in the past been used to demonstrate that the thermal accompaniment of contractile activity is indicative of both force-related and force-independent activities. A mechanical technique for demonstrating the length dependence of activation in the right ventricular papillary muscle has been extended to the intact but isolated whole left ventricle of the heart. A functional relationship between the degree of length-dependent activation and force-independent energy expenditure has been observed. Potentiation of isovolumic cardiac mechanical activity by inotropic stimulation with extracellular calcium is thermally more economic than similar potentiation by length-dependent activation, particularly at large ventricular volumes (long muscle fiber lengths). A hypothesis is formulated that explains both the current myothermic observations and the aequorin calcium transients observed by Allen and Kurihara. Important analytic limitations of whole heart calorimetry are acknowledged.
D000818:Animals; D001833:Body Temperature Regulation; D002118:Calcium / Q000494:pharmacology; D002151:Calorimetry; D004734:Energy Metabolism; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D011817:Rabbits; D013268:Stimulation, Chemical; D013314:Stress, Mechanical; D014336:Troponin / Q000378:metabolism; D019209:Troponin C
D014336:Troponin; D019209:Troponin C; D002118:Calcium