Renal Potassium Handling in Aging Rats

Abstract

Aging is often related to electrolyte disorders. This study was designed to evaluate the renal capacity for K⁺ handling of aging rats submitted to both extreme situations of K⁺ depletion and K⁺ loading. Aging rats were submitted to metabolic assessment, measurement of plasma aldosterone and determination of Na⁺,K⁺–ATPase and H⁺,K⁺–ATPase activity in the inner medullary collecting duct (IMCD). During K⁺ depletion, aging rats showed low values of urine K⁺ excretion. After 2 weeks of dietary K⁺ restriction, the plasma K⁺ levels of these animals reached 2.9±0.1 mEq/l without acid–base disorders. During K⁺ loading, aging rats showed a significant increase in urinary K⁺ excretion, with plasma K⁺ remaining at normal levels (4.7±0.1 mEq/l). Plasma aldosterone levels were low in control aging rats but K⁺ intake modulated the levels of this hormone, with K⁺ depletion reducing it and K⁺ loading significantly increasing it. Na⁺,K⁺–ATPase activity increased only in the initial portion of the IMCD of aging rats after 2 weeks of K⁺ depletion. In the distal portion of the IMCD, Na⁺,K⁺–ATPase activity did not change. H⁺,K⁺–ATPase remained unchanged in both the proximal and distal portions of the IMCD of aging rats. During K⁺ loading, there was no change in Na⁺,K⁺–ATPase or H⁺,K⁺–ATPase activity in the proximal or distal portions of the IMCD of aging rats. This study suggests that the senescent kidney responded to K⁺ conservation and excretion under the two extremes of low and high K⁺ intake.