REGULATION OF H-K+-ATPASE EXPRESSION IN KIDNEY()

It is now widely accepted that proton secretion by the collecting duct is mediated, in part, by an H+-K+-adenosinetriphosphatase (H+-K+-ATPa se). Controversy persists regarding which H+-K+-ATPase isoform is expr essed in kidney. Several laboratories have reported preliminarily the amplification from kidney of stomach and/or colon-identical products u sing gastric or colonic-specific primers in the polymerase chain react ion (PCR). We have developed highly specific probes for the catalytic subunit using reverse transcriptase-PCR with gastric- or colonic-speci fic primers. The resulting cDNAs were verified by sequencing and were then used in Northern analysis of whole kidney total RNA obtained from one of the following three groups of rats: 1) controls, 2) chronic hy pokalemia, or 3) chronic metabolic acidosis. Probes for both the colon ic and gastric alpha-subunit H+-K+-ATPase isoforms hybridized to whole kidney total RNA derived from potassium-replete control rats. A marke d elevation of colonic mRNA abundance, but not gastric message, was ob served in response to chronic hypokalemia induced by dietary potassium deprivation. Elevation of either gastric or colonic mRNA was not obse rved with chronic metabolic acidosis. Under the conditions of the pres ent study, it appears that the mRNA encoding the colonic alpha-isoform of the H+-K+-ATPase in kidney is upregulated by chronic hypokalemia b ut not by chronic metabolic acidosis. The observation that the gastric H+-K+-ATPase alpha-isoform does not appear to be regulated in either condition suggests that this isoform is expressed constitutively in ki dney.