DESCRIPTION: Voltage-gated Na+ channels are heteromultimeric integral membrane proteins that are responsible for the initial phase of the action potential in most excitable cells. A variety of inherited diseases of skeletal muscle (hyperkalemic periodic paralysis, paramyotonia congentia) and cardiac muscle (congenital long QT syndrome) are now known to be caused by genetic mutations in two human Na+ channel a-subunit genes: SCN4A and SCN5A encoding the skeletal muscle and cardiac isoforms, respectively. This proposal is a competing renewal of RO1-NS32387 and outlines experiments aimed at defining the molecular basis of these human disorders, and to elucidate relationships between the structure and function of voltage-gated Na+ channels. Mutant Na+ channels will be expressed heterologously in a cultured mammalian cell system, and studied by detailed electrophysiological analyses. As an extension of this work, they also will exploit the mutant expression system to evaluate the pharmacology of disease causing Na+ channel alleles. This is based on preliminary evidence that allele-specific differences exist among the various SCN4A and SCN5A mutations in local anesthetic/antiarrhythimic drug affinity, and that knowledge of these differences may assist in development of therapeutic strategies. In this endeavor, they will correlate pharmacological responses to specific genotypes. Defining allele-specific pharmacology in Na+ channel diseases may have direct therapeutic implications by identifying compounds that act beneficially to correct the underlying functional defect in the channel and thus provide for more rationale drug treatment of these disorders. Ongoing efforts to define the molecular basis of charge movement in voltage-gated Na+ channels will continue and the role of D1/S6 in fast inactivation will be evaluated. A third area of investigation will be to define structural determinants of Na+ channel a-b1 subunit interactions. These studies will provide information regarding the structure and function of mammalian Na+ channels.