Relation between the sarcolemmal Ca2+ current and Ca2+ sparks and local control theories for 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
L F
LF
Department of Physiology, University of Maryland at Baltimore School of Medicine 21201, USA.
Cheng
H
H
Gómez
A M
AM
Cannell
M B
MB
Lederer
W J
WJ
D000818:Animals; D002118:Calcium / Q000502:physiology*; D004594:Electrophysiology; D017136:Ion Transport; D008962:Models, Theoretical; D009200:Myocardial Contraction / Q000502:physiology*; D051381:Rats; D012508:Sarcolemma / Q000502:physiology*
D002118:Calcium