The effects of the increase of arterial potassium upon the excitability of normal and dystrophic myotonic muscles in man.

Progressively increasing concentrations of potassium chloride were administered intra-arterially to patients affected with dystrophia myotonica (Steinert's disease) and to healthy volunteers before and after parenteral taurine treatment. Changes in the excitability of thenar eminence muscles were related to plasma potassium concentrations. A rise in the plasma potassium brought about a parallel increase of muscular excitability in normal individuals whilst in dystrophic myotonic patients it was associated with a two-phase phenomenon: the severity of myotonia first decreased and then, at higher plasma potassium levels, greatly worsened with the occurrence of spontaneous myotonic discharges. The administration of taurine, a membrane-stabilizing drug, considerably lowered the excitability of both normal and dystrophic myotonic muscles. The effects of potassium and taurine on muscular membrane conductance may explain the observed changes in muscular excitability.