Cellular localization and regulation of chif in kidney and colon. Capurro, Claudia, Nathalie Coutry, Jean-Pierre Bonvalet, Brigitte Escoubet, Haim Garty, and Nicolette Farman. Institut National de la Sant et de la Recherche Medicale, 1U246 and 2U426, Institut Federatif de Recherches "Cellules Epitheliales", Faculte de Medecine Xavier Bichat, BP 416-75870 PARIS Cedex 18- France, Dept. of Membrane Research & Biophysics. The Weizmann Institute of Science, Rehovot, Israel
APStracts 3:0096C, 1996.
CHIF is a novel cDNA recently cloned from a rat distal colon cDNA library of dexamethasone-treated animals. While its expression in Xenopus oocytes evokes a potassium channel activity similar to that induced by Isk (minK), its cellular role is not clear. CHIF exhibits significant homologies with proteins that are putatively regulatory (phospholemman, [gamma] subunit of Na+-K+-ATPase, Mat-8) while it differs from the small conductance potassium channel Isk. We have studied the tissue-specificity of CHIF expression in rat by in situ hybridization. CHIF is selectively present in the distal parts of the nephron (medullary and papillary collecting ducts, and end-portions of cortical collecting tubule) and in the epithelial cells of the distal colon. No expression of CHIF was found in renal proximal tubule, loop of Henle and distal tubule, proximal colon, small intestine, lung, choroid plexus, salivary glands or brain. To gain some insights into CHIF function, we have investigated, using in situ hybridization and RNAse protection assay, whether CHIF mRNA expression could be altered in some situations. In the distal colon corticosteroid hormones, sodium restriction, low potassium diet, and metabolic acidosis, significantly increased CHIF mRNA expression. In the kidney, metabolic acidosis was the only condition that showed an increase in CHIF mRNA expression. Some of these treatments also altered the expssion of the colonic H+-K+-ATPase mRNA. In summary, CHIF mRNA is selectively expressed in the medullary collecting duct of the kidney and in the epithelium of the distal colon; its expression varies differently in these two target tissues after alterations in corticosteroid status, potassium depletion and metabolic acidosis. The precise cell-specific functions of CHIF remain to be established. 

Received 20 November 1995; accepted in final form 15 March 1996.
APS Manuscript Number C699-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96