Effect of Chronic K⁺ Deficiency on Contractile Properties of Soleus Muscle in Rats: Evidence of Sex Differences

Alterations in skeletal muscle function of chronically K(+)-depleted male and female rats were investigated in isolated soleus muscles. 2. By 16 weeks K+ deficiency, plasma K+ concentrations in both male and female rats were reduced to approximately 2 mEq/L, which was accompanied by an approximate 50% reduction in muscle K+ content and a marked increase in muscle Na+ content. These changes were similar in both males and females. 3. Plasma creatine phosphokinase activity progressively increased with time in K(+)-depleted male rats, whereas only a slight increase was observed in female rats. 4. Maximum isometric twitch tension (Pt) and tetanic tension (Po) of K(+)-depleted soleus muscles from male rats was markedly suppressed; this was not seen for soleus muscles obtained from female rats. 5. After exposure to insulin in low-K+ solution, the contractile tension of soleus from the K(+)-depleted male rats was suppressed to a greater extent. 6. All alterations in muscle function during chronic K+ depletion were restored to normal after 2 weeks K+ repletion. 7. The results suggest that there is a preponderance for male over female rats in developing alterations in skeletal muscle function during chronic K+ deficiency. The changes may be associated with abnormalities of muscle membrane permeability and cellular function.