Pc. Sangan et al., REGULATION OF COLONIC H-K-ATPASE IN LARGE-INTESTINE AND KIDNEY BY DIETARY NA DEPLETION AND DIETARY K DEPLETION, American journal of physiology. Cell physiology, 41(2), 1997, pp. 685-696
Active K absorption in the rat distal colon is energized by an apical
membrane H-K-ATPase, whereas K absorption in the distal collecting duc
t is generally believed to be modulated by a related renal H-K-ATPase.
Experiments were performed to establish the mechanism(s) by which die
tary Na depletion (with resulting elevated aldosterone levels) and K d
epletion stimulate K absorption. A colonic H-K-ATPase-specific cDNA pr
obe and a polyclonal antibody were utilized to measure mRNA (Northern
blot analyses) and protein (Western blot and immunofluorescence studie
s) abundance in the distal and proximal colon and renal collecting duc
ts and cortex of dietary Na- and K-depleted rats. Dietary Na depletion
, but not K depletion, upregulated H-K-ATPase-specific mRNA and protei
n expression in the distal and proximal colon; Na depletion also stimu
lated H-K-ATPase activity in the distal colon. In contrast to the dist
al colon, H-K-ATPase-specific protein level in the outer medulla was e
nhanced by dietary K depletion, but not by Na depletion. This study es
tablishes that 1) dietary Na depletion stimulates colonic H-K-ATPase a
ctivity most likely by a transcriptional process and 2) the regulation
of colonic H-K-ATPase expression by dietary Na depletion and dietary
Ti depletion is not identical in the large intestine and differs in th
e kidney from the colon, suggesting the presence of two (or more) H-K-
ATPase isoforms in the rat colon.