997-86 Intracellular Calcium Transients Underlie Mechanical Restitution in Whole Rat Hearts

Abstract

Mechanical restitution describes the recovery of myocardial contractility during the interval between heart beats. Although restitution has been widely studied, much of the understanding about restitution of the whole heart has been inferred from isolated muscle studies. We investigated whether results from isolated muscle regarding intracellular calcium transients underlying mechanical restitution could be substantiated in the whole heart. Therefore, we obtained restitution curves for left ventricular pressure and, simultaneously, for intracellular calcium transients in isolated rat hearts (pressure and calcium plotted as a function of extrasystolic intervals). Intracellular calcium transients were assessed by surface fluorometry after Indo-1-loading. Restitution curves were generated by computer-controlled pacing protocols. We found that, similar to isolated muscle, restitution curves for both pressure and intracellular calcium transients in the whole heart followed similar monoexponential functions. Moreover, interval-dependent changes in pressure were strongly correlated to interval-dependent changes in the amplitude of intracellular calcium transients (correlation by linear regression: r = 0.92, P = 0.00). Thus, for the first time, the results from isolated muscle regarding intracellular calcium transients underlying mechanical restitution could be substantiated in the whole heart.