Effects of Chronic Hypokalemia on Rat Distal Colon

Ahn, Kyu Youn; Heo, Tag; Lee, Seung Won; Park, Sung Sik

Abstract

Recent molecular and physiological studies suggested that at least two distinct H/K-ATPase activities are present in the mammalian colon. Potassium (K+) balance is achieved by the control of urinary K+ excretion and by the control of K+ absorption from the digestive tract. The colon also participates substantively in the regulation of systemic K+ homeostasis. Northern analysis and in situ hybridization (ISH) for analyzing the expression of mRNA encoding the colonic H/K-ATPase a subunit and EM study for morphologic adaptations were carried out in normal and potassium-deprived (2 weeks) rats. Northern analysis demonstrated that colonic H/K-ATPase a subunit mRNA is abundantly expressed in normal rat distal colon. Abundance of colonic H/K-ATPase a subunit mRNA in potassium-deprived rat distal colon was not significantly increased compared to controls. By ISH, mRNA for colonic H/K-ATPase a subunit was detected in the surface epithelial cells, Goblet cells, and upper third of the intestinal gland. Both groups exhibited comparable cellular patterns of labeling and signal intensity. The surface epithelial cells exhibited a mixture of hybridization signal intensity. Most cells had intense hybridization signal for colonic H/K-ATPase a subunit mRNA and some cells had moderate, and a few cells had weak. Occasionally, strong hybridization signal was detected in the lower portion of the intestinal gland. EM study demonstrated that two types of surface columnar epithelial cells were present in normal distal colon and included type 1 cells with more abundant vesicles in supranuclear cytoplasm and type 2 cells with moderate amount of vesicles. In potassium-deprived distal colon, type 2 cells were only present in surface columnar epithelial cells. Others were not significant differences between two groups. These results suggest that two (or more) H/K-ATPase a subunit isoforms are present in rat distal colon, and colonic H/K-ATPase asubunit gene does not significantly contribute to potassium conservation during chronic hypokalemia in spite of abundant expression of this gene.