Effects of aging and potassium depletion on renal collecting tubule K⁺-controlling ATPases

The effects of aging and potassium depletion (KD) on renal cortical and medullary collecting tubule (CCT and MCT) K⁺-controlling ATPase activities, Na⁺,K⁺-ATPase and H⁺,K⁺-ATPase, were performed in 4 and 30 month-old male Fischer 344 × Brown-Norway F1 (F344 × BNF1) rats. Following KD, which was induced by a K⁺-deficient diet for 7 days, both animal age groups had comparable levels of hypokalaemia, but the decreased fractional excretion of K⁺ (FE_K⁺) was more prominent in the old-age group. The aged animals had a 37% lower basal Na⁺,K⁺-ATPase activity in MCT (P < 0.05), but marked increases in basal H⁺,K⁺-ATPase activity in both CCT and MCT (P < 0.001) were noted. Potassium depletion resulted in 28% (P < 0.05) and 66% (P < 0.01) increases in CCT and MCT Na⁺,K⁺-ATPase activities, respectively, in the young-age group. In the old-age group, KD caused a 125% (P < 0.001) increase in MCT Na⁺,K⁺-ATPase activity, but had no effect on CCT Na⁺,K⁺-ATPase activity. The collecting tubule H⁺,K⁺-ATPase activity was increased in both the young and old-age KD groups. The increase of magnitude in the latter was much higher than in the former. In response to KD, the more prominent rises in CCT and MCT H⁺,K⁺-ATPase activities (with an increased percentage in MCT Na⁺,K⁺-ATPase activity) was observed in the old-age animals when compared with the younger ones. This could result in an increased K⁺ reabsorption, leading to the lower value of FE_K⁺. Thus, the K⁺-controlling mechanisms in the renal collecting tubule of aging rats are still intact and effective in coping with KD.