Impaired interaction between skeletal ryanodine receptors in malignant hyperthermia

Abstract

Functional coupling between clustered membrane receptors has been identified as a novel mechanism to improve signaling performance in a number of physiological processes. The potential role of defective inter-receptor coupling in the pathogenesis of disease, however, has not previously been explored. Ryanodine receptors (RyRs), the primary calcium release channel of muscle, usually form ordered two-dimensional arrays in the sarcoplasmic reticulum membranes. Mutations in RyRs are known to cause a number of severe diseases both in skeletal muscle and in heart. Here we present a model demonstrating how impaired functional coupling between neighboring mutant RyR1_R615C channels may contribute to the pharmacogenetic skeletal muscle sensitivity, malignant hyperthermia (MH). We find that purified RyR1_R615C from MH susceptible porcine skeletal muscle shows significantly reduced oligomerization when compared to RyR1_WT, indicating a potential loss of intrinsic intermolecular control. The MH-triggering volatile anesthetic, halothane, activates RyR1_R615C and RyR1_WT to a similar extent, using [³H]ryanodine binding as a measure of activation. Modeling RyR1 array function with parameters modified to simulate the loss of functional inter-RyR coupling recapitulates the MH molecular phenotype-RyR1 channels leaky to Ca²⁺ at rest and long open-times following exposure to halothane. Our work suggests that a defect in inter-RyR1 coupling is a novel direction for research into the pathogenesis of MH.