Effect of hypokalemia on the abundance of HK alpha(1) and HK alpha(2) protein in the rat kidney

An H+-K+-adenosinetriphosphatase (H+-K+-ATPase) contributes to potassium reabsorption by the collecting ducts of the rat kidney. mRNAs for two isoforms of the H+-K+-ATPase, HK alpha(1) and HK alpha(2), have been found in the rat kidney. To evaluate whether the HK alpha(1) and HK alpha(2) proteins are present in the rat kidney, microsomes enriched in HK alpha(1) or HK alpha(2) were isolated using the MiniMac magnetic separation system with antibodies directed against either HK alpha(1) (HK 12.18) or HK alpha(2) (AS 31.7). Immunoblots of rat kidney microsomal protein isolated with HK 12.18 revealed a band similar to 94 kDa in size that comigrated with the G1 fraction of the stomach. Immunoblots of rat kidney microsomal protein isolated with AS 31.7 revealed a band slightly greater than 94 kDa that comigrated with a band obtained from rat colonic microsomal protein. To examine the effect of perturbations in potassium metabolism, the abundance of the HK alpha(1) and HK alpha(2) isoforms was compared in rats fed a normal or potassium-deficient diet. A low-potassium diet increased the abundance of HK alpha(2), whereas that of HK alpha(1) was not altered. These data suggest that HK alpha(2) might be the isoform responsible for potassium conservation by the kidney.