Modulation of sarcoplasmic reticulum Ca2+ release in skeletal muscle expressing ryanodine receptor impaired in regulation by calmodulin and S100A1
Naohiro Yamaguchi, et al.
11/30/2013
Am J Physiol Cell Physiol
Yamaguchi N, Prosser BL, Ghassemi F, Xu L, Pasek DA, Eu JP, Hernández-Ochoa EO, Cannon BR, Wilder PT, Lovering RM, Weber D, Melzer W, Schneider MF, Meissner G. Modulation of sarcoplasmic reticulum Ca2+ release in skeletal muscle expressing ryanodine receptor impaired in regulation by calmodulin and S100A1. Am J Physiol Cell Physiol 300: C998–C1012, 2011. First published February 2, 2011; doi:10.1152/ajpcell.00370.2010.—In vitro, calmodulin (CaM) and S100A1 activate the skeletal muscle ryanodine receptor ion channel (RyR1) at submicromolar Ca2+ concentrations, whereas at micromolar Ca2+ concentrations, CaM inhibits RyR1. One amino acid substitution (RyR1-L3625D) has previously been demonstrated to impair CaM binding and regulation of RyR1. Here we show that the RyR1- L3625D substitution also abolishes S100A1 binding. To determine the physiological relevance of these findings, mutant mice were generated with the RyR1-L3625D substitution in exon 74, which encodes the CaM and S100A1 binding domain of RyR1. Homozygous mutant mice (Ryr1D/D) were viable and appeared normal. However, single RyR1 channel recordings from Ryr1D/D mice exhibited impaired activation by CaM and S100A1 and impaired CaCaM inhibition. Isolated flexor digitorum brevis muscle fibers from Ryr1D/D mice had depressed Ca2+ transients when stimulated by a single action potential. However, during repetitive stimulation, the mutant fibers demonstrated greater relative summation of the Ca2+ transients. Consistently, in vivo stimulation of tibialis anterior muscles in Ryr1D/D mice demonstrated reduced twitch force in response to a single action potential, but greater summation of force during high-frequency stimulation. During repetitive stimulation, Ryr1D/D fibers exhibited slowed inactivation of sarcoplasmic reticulum Ca2+ release flux, consistent with increased summation of the Ca2+ transient and contractile force. Peak Ca2+ release flux was suppressed at all voltages in voltage-clamped Ryr1D/D fibers. The results suggest that the RyR1-L3625D mutation removes both an early activating effect of S100A1 and CaM and delayed suppressing effect of CaCaM on RyR1 Ca2+ release, providing new insights into CaM and S100A1 regulation of skeletal muscle excitation-contraction coupling.