Defects in ryanodine receptor calcium release in skeletal muscle from postmyocardial infarcted rats

Defective calcium (Ca2+) signaling and impaired contractile function have been observed in skeletal muscle secondary to impaired mycocardial function. However, the molecular basis for these muscle defects have not been identified. In this study, we evaluated the alterations of the ryanodine-sensitive Ca2+ release channels (RyR1) by analyzing global and local <LF>Ca2+ signaling in a rat postmycocardial infarction (PMI) <LF>model of myocardial overload. Ca2+ transients, measured with multiphoton imaging in individual fibers within a whole extensor digitorum longus (EDL) muscle, exhibited significantly reduced amplitude and a prolonged time course in PMI. Spatio-temporal properties of spontaneous Ca2+ sparks in fibers isolated from PMI EDL muscles were also significantly altered. In addition, RyR1 from PMI skeletal muscles were PKA-hyperphosphorylated and depleted of the FK506 binding protein (FKBP12). These data show that PMI skeletal muscles exhibit altered local Ca2+ signaling, assocated with hyperphosphorylation of RyR1. The observed changes in Ca2+ signaling may contribute to defective excitation-contraction coupling in muscle that can attribute to the reduced exercise capacity in PMI, out of proportion to the degree of cardiac dysfunction.