Chronic hypokalemia enhances expression of the H+-K+-ATPase alpha(2)-subunit gene in renal medulla

Recent molecular and physiological studies suggested that at least two H+-K+-adenosinetriphosphatase (H+-K+-ATPase) isozymes are expressed in the rat kidney and that these ion pumps respond to changes in dietary potassium balance. We used Northern analysis and in situ hybridization to analyze the expression of mRNA encoding the ''colonic'' isoform of the H+-K+-ATPase alpha-subunit (HK alpha 2) in normal and potassium-deprived (2 wk) rats. Control rats exhibited low levels of HK alpha 2 mRNA in the cortical and medullary thick ascending limb, distal convoluted tubule, connecting segment, and the entire collecting duct. The potassium-deprived rats expressed approximately fivefold higher levels of HK alpha 2 mRNA in the outer and inner medulla compared with controls, as well as hypertrophy and increased in situ hybridization signal in the intercalated cells of the inner stripe of the outer medullary collecting duct and the proximal inner medullary collecting duct. In contrast, renal cortical expression of HK alpha 2 mRNA was low and comparable in the two groups. Our results suggest that enhanced expression of the HK alpha 2 subunit gene in the renal medulla contributes to potassium conservation during chronic hypokalemia.