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Am J Physiol Cell Physiol 294: C1288-C1297, 2008. First published March 5, 2008; doi:10.1152/ajpcell.00033.2008
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RECEPTORS AND SIGNAL TRANSDUCTION

Calmodulin in adult mammalian skeletal muscle: localization and effect on sarcoplasmic reticulum Ca2+ release

George G. Rodney

Department of Organizational Systems & Adult Health, University of Maryland School of Nursing, Baltimore, Maryland

Submitted 23 January 2008 ; accepted in final form 28 February 2008

Calmodulin is a ubiquitous Ca2+ binding protein that binds to ryanodine rectors (RyR) and is thought to modulate its activity. Here we evaluated the effects of recombinant calmodulin on the rate of occurrence and spatial properties of Ca2+ sparks as an assay of activation in saponin-permeabilized mouse myofibers. Control myofibers exhibited a time-dependent increase and subsequent decrease in spark frequency. Recombinant wild-type calmodulin prevented the time-dependent appearance of Ca2+ sparks and decreased the derived Ca2+ flux from the sarcoplasmic reticulum during a spark by ~37%. A recombinant Ca2+-insensitive form of calmodulin resulted in an instantaneous increase in spark frequency as well as an increase in the derived Ca2+ flux by ~24%. Endogenous calmodulin was found to primarily localize to the Z-line. Surprisingly, removal of endogenous calmodulin did not alter the time dependence of Ca2+ spark appearance. These results indicate that calmodulin may not be essential for RyR1-dependent Ca2+ release in adult mammalian skeletal muscle.

ryanodine receptor; calcium sparks; calcium-induced calcium release; calcium signaling; calcium imaging


Address for reprint requests and other correspondence: G. G. Rodney, Dept. of Organizational Systems & Adult Health, Univ. of Maryland School of Nursing, 655 W. Lombard St., Rm. 778, Baltimore, MD 21201 (e-mail: Rodney{at}son.umaryland.edu)






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