Ca2+ activation of RyR1 is not necessary for the initiation of skeletal-type excitation-contraction coupling

Jennifer J. O'Brien, Wei Feng, Paul D. Allen, S. R. Wayne Chen, Isaac N Pessah, Kurt G. Beam

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

Although an elevation in myoplasmic Ca2+ can activate the skeletal muscle ryanodine receptor (RyR1), the function of this Ca2+ activation is unclear because extracellular Ca2+ influx is unnecessary for skeletal-type EC coupling. To determine whether Ca2+ activation of RyR1 is necessary for the initiation of skeletal-type EC coupling, we examined the behavior of RyR1 with glutamate 4032 mutated to alanine (E4032A-RyR1) because this mutation had been shown to dramatically reduce activation by Ca2+. Proc. Natl. Acad. Sci. USA. 98:2865-2870). Analysis after reconstitution into planar lipid bilayers revealed that E4032A-RyR1 was negligibly activated by 100 μM Ca2+ (Po too low to be measured). Even in the presence of both 2 mM caffeine and 2 mM ATP, Po remained low for E4032A-RyR1 (ranging from <0.0001 in 100 μM free Ca2+ to 0.005 in 2 mM free Ca2+). Thus, the E4032A mutation caused a nearly complete suppression of activation of RyR1 by Ca2+. Depolarization of E4032A-RyR1-expressing myotubes elicited L-type Ca2+ currents of approximately normal size and myoplasmic Ca2+ transients that were skeletal-type, but about fivefold smaller than those for wild-type RyR1. The reduced amplitude of the Ca2+ transient is consistent either with the possibility that Ca2+ activation amplifies Ca2+ release during EC coupling, or that the E4032A mutation generally inhibits activation of RyR1. In either case, Ca2+ activation of RyR1 does not appear to be necessary for the initiation of Ca2+ release during EC coupling in skeletal muscle.

Original languageEnglish (US)
Pages (from-to)2428-2435
Number of pages8
JournalBiophysical Journal
Volume82
Issue number5
StatePublished - 2002

ASJC Scopus subject areas

  • Biophysics

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    O'Brien, J. J., Feng, W., Allen, P. D., Wayne Chen, S. R., Pessah, I. N., & Beam, K. G. (2002). Ca2+ activation of RyR1 is not necessary for the initiation of skeletal-type excitation-contraction coupling. Biophysical Journal, 82(5), 2428-2435.