Propagation of excitation-contraction coupling into ventricular myocytes

This paper examines the [Ca2+]i transient in isolated rat heart cells 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 heart cell with similar kinetics of activation. The time of rise of the transient did not depend on whether the sarcoplasmic reticulum (SR) Ca-release was abolished (by thapsigargin and ryanodine). The synchrony of activation and the similarity of levels of [Ca2+]i at the peripheral and deeper myoplasm (regardless of the availability of SR Ca-release) shows that sarcolemmal Ca channels and SR Ca-release channels are distributed throughout the rat heart cell and that the propagation of the action potential into the interior of the cell is rapid. In addition, 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 sarcolemmal Ca channel.