EFFECT OF EXTRACELLULAR POTASSIUM CONCENTRATION ON THE SODIUM-POTASSIUM PUMP RATE IN HUMAN-LYMPHOCYTES

1. The purpose of this study was to determine whether physiological ch anges in extracellular free [K+] cause significant changes in the Na+- K+ pump rate and intracellular free [Na+]. 2. The Na+-K+ pump rate was measured in human lymphocytes by determining ouabain-sensitive Rb-86( +) influx at several concentrations of K+. The Na+-K+ pump rate increa sed within the physiological range of extracellular free [K+] (K-1/2=1 .5 mmol/l). 3. To test the hypothesis that elevation of extracellular free [K+] reduces intracellular free [Na+] rapidly, which in turn then slows the pump rate during experimental incubations, lymphocyte intra cellular free [Na+] was measured using the fluorochrome sodium-binding benzofuran isophthalate, With larger elevations of extracellular free [K+], intracellular free [Na+] dropped more rapidly, Thus previous di screpancies among determinations of K-1/2 may be the result of variati ons in incubation times, which can skew the pump rates measured during incubations in various extracellular free [K+] values, Steady-state i ntracellular free [Na+] varied inversely with extracellular free [K+].