DIFFERENTIAL REGULATION OF PUTATIVE K-ATPASE BY LOW-K+ DIET AND CORTICOSTEROIDS IN RAT DISTAL COLON AND KIDNEY()

K+ homeostasis depends on K+ absorption in digestive and renal epithel ia. Recently, a cDNA encoding for a putative K+-adenosinetriphosphatas e (ATPase) alpha-subunit has been characterized. We studied its expres sion by ribonuclease protection assay and in situ hybridization in the distal colon and the kidney of rats in various physiological states. In the distal colon of control rats, high expression of the colonic pu tative K+-ATPase mRNA was restricted to the surface epithelial cells. A low-K+ diet did not modify this expression, adrenalectomy decreased it, and aldosterone or dexamethasone treatment for 2 days restored nor mal levels. In the kidney of control rats, levels of K+-ATPase mRNA we re very low. A low-K+ diet revealed a clear mRNA expression, which is consistent with a recent report [J. A. Kraut, F. Starr, G. Sachs, and M. Reuben. Am. J. Physiol. 268 (Renal Fluid Electrolyte Physiol. 37): F581-F587, 1995]. This expression was restricted to the outer medullar y collecting duct, presumably in principal cells. Changes in corticost eroid status did not influence the renal expression. Our results, toge ther with previous studies on K-+ absorption and K+-ATPase activity, s uggest that more than a single molecular form of K+-ATPase is likely t o be responsible for the regulation of K+ absorption in the colon and distal nephron.