Regulation of colonic H-K-ATPase in large intestine and kidney by dietary Na depletion and dietary K depletion

Abstract

Active K absorption in the rat distal colon is energized by an apical membrane H-K-ATPase, whereas K absorption in the distal collecting duct is generally believed to be modulated by a related renal H-K-ATPase. Experiments were performed to establish the mechanism(s) by which dietary Na depletion (with resulting elevated aldosterone levels) and K depletion stimulate K absorption. A colonic H-K-ATPase-specific cDNA probe and a polyclonal antibody were utilized to measure mRNA (Northern blot analyses) and protein (Western blot and immunofluorescence studies) abundance in the distal and proximal colon and renal collecting ducts and cortex of dietary Na- and K-depleted rats. Dietary Na depletion, but not K depletion, upregulated H-K-ATPase-specific mRNA and protein expression in the distal and proximal colon; Na depletion also stimulated H-K-ATPase activity in the distal colon. In contrast to the distal colon, H-K-ATPase-specific protein level in the outer medulla was enhanced by dietary K depletion, but not by Na depletion. This study establishes that 1) dietary Na depletion stimulates colonic H-K-ATPase activity most likely by a transcriptional process and 2) the regulation of colonic H-K-ATPase expression by dietary Na depletion and dietary K depletion is not identical in the large intestine and differs in the kidney from the colon, suggesting the presence of two (or more) H-K-ATPase isoforms in the rat colon.

The α-Subunit of the Colonic H+,K+-ATPase Assembles with β1-Na+,K+-ATPase in Kidney and Distal Colon

“…However, ␤ 1 was detected in the immunoprecipitated sample of renal medulla from control rats when as much as 35 mg of proteins were used in the immunoprecipitation experiment (data not shown). This observation agrees with data reported previously by our laboratory (6) and others (7,8) that the abundance of HK␣ 2 is very low in renal medulla of control rats. Surprisingly, a ␤ 1 -subunit was not detected, as well, when the immunoprecipitation experiments were performed using up to 1 mg of membranes from control distal colon or the distal colon harvested from rats with chronic hypokalemia (Fig.…”

Cloning and Expression of a Chloride-dependent Na+-H+ Exchanger

“…The rats were allowed free access to water. One group of rats was fed a sodium-free diet for 7 days, as described previously (16), to produce a secondary increase in serum aldosterone levels (17).…”

“…Colonic mRNA was isolated from a purified colonic epithelial cell preparation, as described previously (16). Northern blot hybridization was also performed using mRNA isolated from colonic epithelial cells of normal mice and from a segment of sigmoid colon obtained at operation for diverticulitis with the 32 P-labeled 189-bp novel portion of the open reading frame of Cl-NHE cDNA as a probe.…”

Ouabain-sensitive H,K-ATPase Functions as Na,K-ATPase in Apical Membranes of Rat Distal Colon

“…The colonic H,K-ATPase is a member of the gene family of P-type ATPases, which include ouabain-sensitive Na,K-ATPase, gastric parietal cell H,K-ATPase that is ouabain-insensitive, and ATP1AL1 (2)(3)(4)(5)(6). Colonic H,K-ATPase consists of ␣ (HKc␣) and ␤ (HKc␤) 1 subunits, which have been identified and characterized, and is up-regulated by dietary sodium depletion and aldosterone (7)(8)(9).…”