RELATION OF MUSCLE ELECTROLYTE TO ALTERATIONS IN SERUM POTASSIUM AND TO THE TOXIC EFFECTS OF INJECTED POTASSIUM CHLORIDE

Abstract

The usual range of muscle K in adult rats is 47 to 50 mM. per 100 g. of fat-free solids. Muscle K levels as low as 44 mM. may occur even though the conc. of K and Na in the serum and the amt. of Na in the muscle remain normal. Increases in muscle K above 50 mM. produced by injecting KC1 are transitory in normal intact animals and return to high normal levels (49 mM.) within 60-90 mins. after the last inj. and to low normal levels (45 mM.) 18 hrs. after the last inj. Such transitory increases in muscle K are accompanied invariably by a shift of Na out of the cell and have not been demonstrated except in the presence of an increased conc. of serum K. With the fall in muscle K which follows the transitory rise, the serum K conc. and muscle Na return towards normal levels. Significant increases in muscle K occurred without evidence of K poisoning in animals in which the serum conc. of K, was not elevated above 10 meq. per liter. Increases in muscle K in animals whose muscle has previously been rendered deficient in K (i.e., from 29 to 44 mM. per 100 gs. of fat-free solids) remain fixed at least for 17 hrs. after the last inj. of KC1. The tolerance of animals with low muscle K to the toxic effects of injected K is appreciably greater than the tolerance of animals with normal muscle K. The slower rise in serum K concs. in the former is probably due to to the greater capacity of the skeletal muscle to take up K from extracellular fluid. The toxic effects of injected K are directly related to the elevation in conc. of serum K and only indirectly to that of muscle K. Within the range of muscle K between 29 and 55 mM. per 100 g. of fat-free solids found in these expts. there is a reciprocal relationship between muscle K and the intracellular Na of the muscle. About 1 mM. of Na may be interchanged for 2 mM. of K.