Relation Between the Sarcolemmal Ca 2+ Current and Ca 2+ Sparks and Local Control Theories for Cardiac Excitation-Contraction Coupling

• Published in: Circulation research 1996-01, Vol.78 (1), p.166-171
• Main Authors: Santana, L.F., Cheng, H., Gómez, A.M., Cannell, M.B., Lederer, W.J.
• Format: Article
• Language: English
• Subjects: Animals; Calcium; Electrophysiology; Ion Transport; Life Sciences; Models, Theoretical; Myocardial Contraction; Rats; Sarcolemma
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.78.1.166

Abstract Ca 2+ sparks, the elementary events underlying excitation-contraction (E-C) coupling, occur when sarcoplasmic reticulum (SR) Ca 2+ release channels open. They are activated locally by Ca 2+ influx through sarcolemmal (SL) Ca 2+ 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 Ca 2+ spark is triggered, how many SL Ca 2+ channels (at a minimum) contribute to its activation? (2) What is the relation between the subcellular local [Ca 2+ ] i produced by the opening of SL Ca 2+ channels and the consequent SR Ca 2+ release? By comparing the voltage dependence of Ca 2+ sparks in rat ventricular myocytes with the Ca 2+ current, we show that the opening of a single SL Ca 2+ channel can trigger a Ca 2+ spark. Furthermore, we deduce that the probability of SR Ca 2+ release depends of the square of the local [Ca 2+ ] i produced by SL Ca 2+ channel openings. These results are discussed with respect to the properties of Ca 2+ -induced Ca 2+ release (CICR) and the local control theory of excitation-contraction coupling.