Malignant hyperthermia (MH) is a pharmacogenetic disease of skeletal muscle. The long term objectives are to understand exactly how mutations of the ryanodine receptor (RyR1) and the L-type Ca2+ channel (alpha1DHPR) alter the process of excitation contraction coupling, and to define how pharmacologic agents and exposure to persistent ubiquitous environmental contaminants, such as polychlorinated biphenyls (PCBs), influence the phenotypic penetrance of human MH. HYPOTHESIS I: Mutations in RyR1 and the alpha1DHPR associated with human MH influence the ability of the alpha1DHPR and FKBP12 to interact with and regulate the function of RyR1. These changes lead to a common pattern of dysfunction of antegrade and retrograde signaling among these proteins upon exposure to MH triggering agents. The specific aims are 1) to create and express mutated cDNAs with RyR1 MH mutations Arg163Cys, Gly341Arg, Arg614Cys, Val2168Met, Arg2163Cys, and Arg2458His and the alpha1DHPR mutation, Arg1086His, in null skeletal myotubes and elucidate the effect of these mutations on macroscopic Ca2+ fluxes, [3H]ryanodine-binding, single-channel gating kinetics and the structural integrity of the FKBP12/RyR1 complex, and 2) to create four transgenic mouse lines (RyR1 Gly341Arg, Arg614Cys, Arg2458His and alpha1DHPR Arg1086His), each expressing one of these mutated proteins and measure their responses to halogenated volatile anesthetics and depolarizing neuromuscular blockers in vivo, and their responses to clinical in vitro contracture tests (IVCT). HYPOTHESIS II: The normal variation in concentrations of persistent ubiquitous environmental contaminants which are prevalent in human tissues can significantly influence the phenotypic penetrance of human MH mutations. The specific aims are 1) to define the mechanisms by which specific PCB congeners modify molecular events, and establish how these changes influence the MH phenotype by heightening the sensitivity and maximum response to pharmacologic agents, and 2) to administer relevant levels of environmental contaminants to transgenic mice carrying one of the MH mutations and determine changes in the ease with which animals show signs and symptoms of the syndrome, and/or changes the severity of their response to fixed doses of triggering agents.