Renal brush-border Na+-H+ exchange activity in the aging rat.

Amiloride-sensitive Na+-H+ exchange activity in brush-border membrane vesicles isolated from male rat proximal tubules was decreased in the senescent rat (24 mo) compared with the young adult (6 mo). There was no significant loss in Na+-H+ exchange activity in the kidneys of animals between 6 and 18 mo of age. Amiloride-insensitive Na+ uptake and the rate of pH gradient dissipation were not altered during aging. The decrease in sodium-dependent phosphate transport preceded the decline in Na+-H+ exchange activity by at least 6 mo. Sodium-dependent glucose transport was not significantly altered during aging. Thus various renal plasma membrane transport functions were affected differently in the aging rat. The decrease in Na+-H+ exchange activity during aging contrasted with the increase in exchange activity reported previously in acute ablation models of chronic renal failure.