Relation between the sarcolemmal Ca2+ current and Ca2+ sparks and local control theories for cardiac excitation-contraction coupling

• Published in: Circulation research 1996, Vol.78 (1), p.166-171
• Main Authors: SANTANA, L. F, CHENG, H, GOMEZ, A. M, CANNELL, M. B, LEDERER, W. J
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Calcium - physiology; Electrophysiology; Fundamental and applied biological sciences. Psychology; Heart; Ion Transport; Models, Theoretical; Myocardial Contraction - physiology; Rats; Sarcolemma - physiology; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.res.78.1.166

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.