Muscle sodium channel inactivation defect in paramyotonia congenita with the thr1313met mutation.

Mutations of the skeletal muscle sodium (Na) channel have been reported in families with paramyotonia congenita (PC), an autosomal dominant disorder with cold and/or exercise induced stiffness and myotonia. Functional consequences of specific Na channel mutations responsible for PC have not been described. Patch clamp recording of single Na channels were made in cultured myotubes at 22 and 34 degrees C from a PC patient with the thr1313met mutation. Cell-attached and outside-out recordings of mutant PC channels contained long duration and late openings. The mean open time was increased and the ensemble average showed a prolonged inward Na current. This membrane depolarization could cause repetitive action potentials and the clinical syndrome.