Renal Adaptive Responses of HK alpha2 Gene(HK alpha 2a, HK alpha 2b) to the Changes of Potassium(K) Diet

Ahn, Kyu Youn; Kim, Bo Young; Lee, Seung Won; Kim, Kyung Keun; Park, Sung Sik

Abstract

Recent molecular and physiological studies suggested that at least two H/K-ATPase isozymes are expressed in the rat kidney, and two distinct isoforms(HK alpha 2a, 2b) are resulted from alternative splicing of the 5-end of HK alpha 2 in distal colon by sequence analysis. Northern analysis and in situ hybridization(ISH) were carried out to analyze the expression of HK alpha 2a. and HK alpha 2b, mRNAs in rat kidney according to the changes of K-diet. Isoform specific 32P-labeled cDNA(for Northern) or digoxigenin labeled cRNA(for ISH) probes were used. Northern analysis demonstrated that HK a z. mRNA is abundantly expressed in normal(group 1: normal diet 2W) renal cortex, modestly in normal outer medulla, and weakly in normal inner medulla. The potassium-deprived rats(group 2: K-free diet 1W, and group 4: K-free diet 2W) expressed 40N lower levels in cortex and 2-4 fold higher levels of HKalpha 2a. mRNA in outer and inner medulla compared to normal rat. The potassium loading rats after potassium-deprivation(group 3: normal diet 1W after K-free diet 1W, and group 5: normal diet 1W after K-free diet 2W showed almost normal levels of HK alpha 2a. mRNA. HK alpha 2b, mRNA was not detected in any tissues of groups. By ISH, mRNA for HK alpha 2, was detected in the thick ascending limb, distal convoluted tubule, and the entire collecting duct. All groups exhibited comparable cellular patterns of labeling. Signal intensity of group 2 and 4 was less in cortical collecting duct(CCD), especially principal cells and much higher in the inner stripe of the outer medullary collecting duct(OMCDi) and the proximal inner medullary collecting duct(IMCD) compared to group 1. Group 3 and 5 exhibited signal intensity of group l. These results indicate that chronic hypokalemia enhances expression of HK alpha 2a, gene in OMCDi and proximal IMCD, decreases in CCD, and restores at normal levels in potassium-loading after potassium-deprivation and suggest that this isoform plays an important role in potassium balance by these segments accordiog to the changes of K-diet.