The isometric twitch of rabbit papillary muscle: reflection of the cellular calcium movements?

The cycling of the activator-Ca of the myocardium is mediated by the sarcolemma (SL) and the sarcoplasmic reticulum (SR). Both the extent and the time course of the release as well as of the removal of the activator-Ca by the SL differ from that by the SR. The visualization of these differences in the isometric myograms of isolated myocardium (Bogdanov et al. 1979; Günther et al. 1986; King and Bose 1983; Malecot et al. 1986) prompted the conclusion that distinct cellular Ca movements determine distinct parts of the isometric contraction-relaxation cycle. To test this hypothesis the effects of Ca, isoprenaline and ouabain on the isometric contraction-relaxation cycle of rabbit papillary muscles were re-evaluated. The similarities and differences in the effects of the interventions on the twitch measures could be explained by their effects on the cellular Ca movements.