Alteration of muscle and red cell sodium and potassium in 20,25-diazacholesterol-induced myotonia

Myotonia was induced in rats by a single oral dose of 20,25-diazacholesterol. Myotonia as determined by electromyography developed in 12 days, and was maintained for 20 days. Accompanying the myotonia there was a significant decrease in intracellular sodium that, when compared with controls, was most marked in white glycolytic muscles such as white vastus lateralis [24.6 (se ± 4.3) percentage of decrease (P < 0.005)], and the paraspinal muscles [18.0 (se ± 4.4) percentage of decrease (P < 0.01)], and least in red oxidative muscles such as soleus (3.8 (se ± 4.4) percentage of decrease, not significant). No change in intracellular potassium was observed. The changes in muscles are probably the result of a decreased membrane permeability for sodium. No alteration in serum, or red cell sodium, potassium, or chloride was observed, and (Na⁺ + K⁺)ATPase of the red cells remained constant.