CNS control of active sodium transport in muscle during progressive hypokalemia in the rat.

The degree of plasma hypokalemia was graded with the duration of a potassium deficient diet. The intracellular Na+ and K+ contents ([Na]i and [K]i) of the innervated soleus muscle of hypokalemic rats were determined and plotted as a function of plasma K+ concentration following a potassium deficient diet during 1-8 weeks. The progression of plasma hypokalemia was highly correlated with both [Na]i accumulation and [K]i loss in the muscle. Denervation of muscles in the hypokalemic rat resulted in a rapid activation of the Na-pump in the denervated soleus muscle regardless of the degree of plasma hypokalemia. This pump activation in the denervated muscle was chronically maintained throughout the hypokalemia. Restoration of a normal, K+ containing, diet for 4 days in hypokalemic rats resulted in a complete recovery of normal Na+ and K+ contents in both the innervated muscle and plasma, while the [Na]i and [K]i in the denervated muscle was unaffected. The relationship between the CNS-induced inhibition of the muscle Na-pump and the plasma K+ levels in hypokalemic rats is discussed.