POSSIBLE ROLE OF APAMIN-SENSITIVE K-DYSTROPHY( CHANNELS IN MYOTONIC)

Myotonic muscular dystrophy is a genetic disease characterized mainly by muscle atrophy and myotonia, a repetitive electrical activity of mu scle. In the present study, the possible role of apamin-sensitive K+ c hannels in the genesis of myotonia was investigated. Apamin is a pepti de from bee venom that specifically blocks small conductance Ca2+-acti vated K+ channels. The injection of a small amount of apamin (20-30 mu l, 10 mu mol/L) into the thenar muscle of myotonic dystrophy patients decreased the basal electrical activity during the electromyogram in the 6 patients studied. Myotonic discharges after muscle percussion we re more difficult to trigger and of smaller intensity and duration. In 2 controls and in 2 patients with generalized myotonia, as well as in 1 patient with myotonia congenita (where the defect is in chloride ch annels), apamin had no effect. These results suggest that apamin-sensi tive K+ channels participate in the mechanism that generates myotonia in myotonic dystrophy. (C) 1994 John Wiley & Sons, Inc.