Discrepancy between left ventricular mechanoenergetics and mitochondrial respiratory function in canine acute failing hearts

In canine excised cross-circulated hearts, we induced three different types of acute failure (time-dependently deteriorated, calcium (Ca²⁺) overloaded, and capsaicin-induced) to investigate the relation between left ventricular mechanoenergetics and myocardial subcellular (mitochondrial) energetics. First, we measured left ventricular pressure and volume and coronary arteriovenous oxygen content difference and blood flow. We analyzed these data by using the framework of the E_max (a contractility index)-PVA (pressure-volume area; total mechanical energy)-V_O2 (oxygen consumption per beat) relation. All acute failing hearts demonstrated similar changes in mechanoenergetics, that is, decreased E_max and decreasedV_O2 for the excitation-contraction coupling (presumably Ca²⁺ handling). We then examined the mitochondrial respiratory function by measuring their oxygen consumption for ATP synthesis polarographically. As indexes of the function, respiratory control index (RCI) and State III O₂ consumption were obtained with succinate as substrate. RCI and State III O₂ consumption behaved differently among the three different types of acute cardiac failure. We conclude that the left ventricular mechanoenergetics do not directly reflect changes in mitochondrial energetics in different types of acute failing.