Influence of paired stimulation on the electro-mechanical dissociation during low calcium perfusion of isolated rat hearts

Abstract

It is demonstrated that during electro-chemical dissociation of the isolated rat hearts, perfused according to the Langendorff method with a modified Tyrode solution, with very low calcium concentration, contractions may reappear, after transposing every second impulse of a regular train of stimuli, to an earlier moment (paired stimulation). The contractions increase in size during shortening of this distance and become optimal during paired stimulation with maximal fusion. Evidence is presented that the spacing of the two successive stimuli of each pair is of major importance in evoking this phenomenon. We assume that this stimulation pattern causes an increase of intracellular calcium concentration. The effect of increase in calcium concentration in the perfusion fluid on this relation between spacing of stimuli and contract ion is compatible with this hypothesis.