Electrophysiological Properties of Novel Mutations in CLC-1 Chloride Channel of Korean Patients with Myotonia Congenita

Abstract

Myotonia Congenita is a genetic disease that displays the symptom of muscle stiffness and impaired muscle relaxation caused by hyperexcitability of the plasma membrane. There are two types of Myotonia Congenita; Autosomal dominant Myotonia Congenital (Thomsen's disease) and autosomal recessive generalized Myotonia (Becker's myotonia) are caused by mutations in the skeletal muscle chloride channel, ClC-1.ClC-1, the member of a large family of anion channels, is voltage-gated chloride channel. It is abundantly expressed in human skeletal muscle. In skeletal muscle, the voltage-gated chloride channels contribute to stabilize the resting membrane potential and control electrical excitability. ClC-1 channels contain double-barreled structure which consists of two identical protopores. Each pore is voltage dependent and functions independently.When mutations in the gene for ClC-1 underlie Myotonia Congenita, it can affect normal function of the channel and damage the specialized property of independently working double pores. Since Mytonia Congenital was first diagnosed, a number of mutations widely displayed in the protein have been revealed so far. Here, nine mutants (p.M128I, p.S189C, p.M373L, p.P480S, p.G523D, p.M609K, p.T310M, p.R317X, p.R47W, A298T and p.G355R) from Korean patients who suffer from Myotonia Congenita were reported in 2009. We studied the functional changes of each mutant by using patch clamp method. We observed remarkably reduced chloride conductance from most of mutants. Mutants, p.M128I, and p.G523D showed steady-opened current pattern compared to WT. Furthermore, open probability of mutants was slightly or markedly altered and this clearly indicates the modification of pore property.