The relation of the electrolyte composition of plasma and skeletal muscle.

Darrow and his associates (1, 2) have recently obtained evidence that a correlation exists between the concentration of serum bicarbonate, muscle potassium, and intracellular sodium from a study on rats subjected to procedures designed to produce a deficit of one of the ions sodium, chloride, or potassium. Thus, the serum bicarbonate concentration was found to vary directly with the intracellular sodium and inversely with muscle potassium when renal adjustment was attained in the presence of a deficiency of sodium, chloride, or potassium. As an example, when a potassium deficiency was induced by maintaining rats on a diet low in potassium, or by the repeated injection of desoxycorticosterone acetate (DCA), the loss of muscle potassium and gain of intracellular sodium were found to be accompanied by an elevation of the serum bicarbonate concentration. In addition, the elevated serum bicarbonate concentration was found to be associated with a decreased serum chloride concentration. Several years ago one of the present authors (E. M.) and others (3) noted that dogs subjected to repeated injections of DCA exhibited a striking reduction of muscle potassium, a gain of intracellular sodium, and a slight decrease of the plasma chloride concentration. In this latter study there was found to be a tendency toward an increased plasma bicarbonate concentration (not reported at the time, but see below) ; however, there appeared to be no clear relationship between the changes of the muscle sodium and potassium and the plasma bicarbonate level. In this respect the observations on dogs with potassium deficiency differed from those on rats. The experiments included in this paper represent further studies on dogs and rats with potassium deficiency induced by the administration of DCA or by maintaining the animals on a diet low in potassium. They were undertaken for the following purposes: (1) to observe and compare the relationship of the electrolyte composition of plasma and skeletal muscle of dogs and rats, and (2) to observe the influence of altering the dietary