Increased Na⁺-H⁺ exchange in brush border vesicles from dogs with renal failure

In the remnant kidney model of chronic renal failure, absolute reabsorption of Na⁺ in the proximal tubule of the remaining nephrons is increased over normal. Absolute proximal tubular reabsorption of bicarbonate and proximal tubular H⁺ excretion per nephron have also been shown to be increased over normal in this model of renal disease. Na⁺ uptake in membrane vesicles isolated from the brush border membrane of remnant kidneys of dogs with chronic renal failure is increased over uptake in membrane vesicles isolated from kidneys of normal dogs. In the present studies an amiloride-sensitive, electroneutral Na⁺-H⁺ exchanger was identified in canine renal brush border membrane vesicles. Na⁺ uptake in membrane vesicles in the presence of an initial H⁺ gradient (intravesicular pH < extravesicular pH) was increased in membrane vesicles isolated from the remnant kidneys of dogs with chronic renal failure over that in membrane vesicles from kidneys of normal dogs. This increase was abolished by amiloride. It is possible that the alterations in Na⁺ and bicarbonate reabsorption and H⁺ excretion in the remnant kidney model of chronic failure can be explained on the basis of increased activity of the Na⁺-H⁺ exchanger in the renal brush border membrane.