Mechanoenergetic studies in isolated mouse hearts

We tested the feasibility of an isolated, balloon-in-ventricle, isovolumically contracting, crystalloid-perfused mouse heart preparation (n = 10) for studies of cardiac mechanoenergetics using the end-systolic pressure-volume relation (ESPVR) and myocardial oxygen consumption (VO2)-pressure-volume area (PVA) framework employed in larger species. The intraventricular balloon method was shown to be accurate for measurement of left ventricular volume, especially at relatively higher volumes. The ESPVR demonstrated contractility-dependent curvilinearity. Average slope of the ESPVR was 1,299 +/- 369 (SD) mmHg.g.ml(-1), with a volume intercept of 0.018 +/- 0.006 ml. The VO2-PVA relation was well fitted by a straight line, with average slope and V-O2 intercept of 3.57 +/- 1.31 x 10(-5) ml O-2.mmHg(-1).ml(-1) and 0.92 +/- 0.21 x 10(-3) ml O-2.beat(-1).g(-1), respectively. Decreasing perfusate Ca2+ concentration resulted in a decrease in the slope of the ESPVR, a decrease in the V-O2 intercept of the V-O2-PVA relation, but no significant change in its slope. Hearts from hypothyroid (n = 8) mice demonstrated similar mechanoenergetic changes. We conclude that delineation of the ESPVR and the V-O2-PVA relation is feasible in the mouse heart. Our method should allow an assessment of cardiac mechanoenergetics as sophisticated as that previously possible only in larger hearts.