Sodium flux in myotonic muscular dystrophy

Abstract

Intact human intercostal muscle fibers were removed by biopsy from 4 normal and 4 myotonic dystrophy patients. These preparations remained in good physiological condition in-vitro and were used to study the washout of 22Na with which they had been loaded in the cold. The aim of the experiments was to learn whether abnormalities of membrane electrogenesis and accumulation of intrafiber sodium reported in myotonic dystrophy arise from failure of the active transport mechanism for Na or from an increase in membrane permeability. Normal and diseased specimens were compared with and without oua-bain on the assumption that the glycoside would not affect cells already lacking a Na pump. Consistently, the myotonic fibers showed qualitatively normal pump flux of Na, but it was found, in agreement with earlier workers, that they contained about twice normal Na concentration, tt is suggested that the pump is normal but there is increased permeability with entry of Na into a readily exchangeable and an inex-changeable pool.