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 x Brown-Norway F1 (F344 x 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+ (FEK+) 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 FEK+. Thus, the K+-controlling mechanisms in the renal collecting tubule of aging rats are still intact and effective in coping with KD.