NET POTASSIUM MOVEMENT BETWEEN RESTING MUSCLE AND PLASMA IN MAN IN THE BASAL STATE AND DURING THE NIGHT 1

Abstract

Net movement of K between forearm tissues (mainly muscle) and plasma was measured by the Fick principle: the product of plasma flow through the forearm (measured by dye-dilution) and the difference in concentration of K in arterial and venous plasma defines the quantity of K taken up by (or released from) forearm tissues per unit time. There is net movement of K out of resting forearm muscle into plasma in the late morning hours in fasted subjects. From 1 A.M. to 10 A.M. no net movement occurs. From 10 A.M. to 1 P.M. the mean A-V difference in 21 subjects was -0.23 meq/l. The net loss in 15 subjects averaged 0.88 ueq/ minute/100 g muscle, or about 0.5%/hour of intracellular K. This diurnal variation in K movement from muscle is strikingly similar to the diurnal variation in urinary excretion of K. The constancy of arterial plasma concentration of K in the late morning hours in spite of greatly increased urinary excretion may be explained by the simultaneous movement of K from muscle into extracellular fluid.