PROPAGATION OF EXCITATION-CONTRACTION COUPLING INTO VENTRICULAR MYOCYTES

This paper examines the [Ca2+](i) transient in isolated rat heart cell s using a laser scanning confocal microscope and the calcium indicator fluo-3. We find that the depolarization-evoked [Ca2+](i) transient is activated synchronously near the surface and in the middle of the hea rt cell with similar kinetics of activation. The time of rise of the t ransient did not depend on whether the sarcoplasmic reticulum (SR) Ca- release was abolished (by thapsigargin and ryanodine). The synchrony o f activation and the similarity of levels of [Ca2+](i) at the peripher al and deeper myoplasm (regardless of the availability of SR Ca-releas e) shows that sarcolemmal Ca channels and SR Ca-release channels are d istributed throughout the rat heart cell and that the propagation of t he action potential into the interior of the cell is rapid. In additio n, the activation of calcium release from the SR by CICR is rapid (<<2 ms) when compared to the time-course of calcium influx via the sarcol emmal Ca channel.