POTASSIUM AND SODIUM EXCRETION AND POTASSIUM HOMEOSTASIS DURING ACUTE HYPOKALEMIA.

Abstract

Decreased potassium and increased sodium excretion were observed in dogs acutely potassium-depleted by hemodialysis. Potassium excretion at constant blood pH varied directly with plasma [K+]. When filtered Na load and urine flow were constant during K+ depletion, increase in Na excretion was equivalent to decrease in K+ excretion, suggesting close coupling between transtubular movements of the two ions. Large changes in plasma [K+] (30%) and K+ excretion (50%) were produced with removal of a relatively small amount (estimated 3%) of total body K+. Plasma [K+] decrease during depletion was rapidly decelerated by movement of intracellular K+ into the extracellular fluid (ECF). When ECF [K+] stabilized, further decrease in K+ excretion ceased despite continued reduction of total body K+. It appears: 1) that tubular secretion of K+ is directly and rapidly responsive to reduction in ECF [K+]; 2) that low ECF [K+] may simultaneously impair contraluminal K+ uptake and Na extrusion, reducing K+ excretion and Na reabsorption during acute hypokalemia. Stoichiometry of changes suggests a 1:1 coupling between K+ secretion and moiety of Na reabsorption in the distal nephron.