Mechanism of calmodulin inhibition of cardiac sarcoplasmic reticulum Ca2+ release channel (ryanodine receptor).
The functional effects of calmodulin (CaM) on single cardiac sarcoplasmic reticulum Ca(2+) release channels (ryanodine receptors) (RyR2s) were determined in the presence of two endogenous channel effectors, MgATP and reduced glutathione, using the planar lipid bilayer method. Single-channel activities, number of events, and open and close times were determined at varying cytosolic Ca(2+) concentrations. CaM reduced channel open probability at <10 micro M Ca(2+) by decreasing channel events and mean open times and increasing mean close times. At >10 micro M Ca(2+), CaM was less effective in inhibiting RyR2. CaM decreased mean open times but increased channel events, without significantly affecting mean close times. A series of voltage pulses was applied to the bilayer from +50 to -50 mV and from -50 mV to +50 mV to rapidly increase and decrease open channel-mediated sarcoplasmic reticulum lumenal to cytosolic Ca(2+) fluxes. CaM decreased the duration of the open events after the voltage switch from -50 mV to +50 mV. In parallel experiments, a Ca(2+)-insensitive calmodulin mutant was without effect on RyR2 activity. The results are discussed in terms of a possible role of CaM in the termination of cardiac sarcoplasmic reticulum Ca(2+) release.
Xu
Le
L
Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260, USA.
Meissner
Gerhard
G
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D008051:Lipid Bilayers / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*
D002147:Calmodulin; D008051:Lipid Bilayers; D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium