The study demonstrates that a single sarcolemmal Ca2+ channel opening can trigger a Ca2+ spark, providing fundamental insights into the local control theory of cardiac excitation-contraction coupling.
Ca2+ sparks, the elementary events underlying excitation-contraction (E-C) coupling, occur when sarcoplasmic reticulum (SR) Ca2+ release channels open. They are activated locally by Ca2+ influx through sarcolemmal (SL) Ca2+ channels. By measuring the probability of spark occurrence under conditions in which their probability of occurrence is low, we address two important questions raised by our recent work: (1) When a Ca2+ spark is triggered, how many SL Ca2+ channels (at a minimum) contribute to its activation? (2) What is the relation between the subcellular local Ca2+, produced by the opening of SL Ca2+ channels and the consequent SR Ca2+ release? By comparing the voltage dependence of Ca2+ sparks in rat ventricular myocytes with the Ca2+ current, we show that the opening of a single SL Ca2+ channel can trigger a Ca2+ spark. Furthermore, we deduce that the probability of SR Ca2+ release depends of the square of the local Ca2+i produced by SL Ca2+ channel openings. These results are discussed with respect to the properties of Ca2+-induced Ca2+-release (CICR) and the local control theory of excitation-contraction coupling.
Santana et al. (1996) studied this question.