NA+ H+ EXCHANGERS, NHE-1 AND NHE-3, OF RAT INTESTINE - EXPRESSION ANDLOCALIZATION/

Na-H exchange (NHE) is one of the major non-nutritive Na absorptive pa thways of the intestine and kidney. Of the four NHE isoforms that have been cloned, only one, NHE-3, appears to be epithelial specific. We h ave examined the regional and cellular expression of NHE-3 in the rat intestine. NHE-3 message in the small intestine was more abundant in t he villus fractions of the small intestine than in the crypts. Analysi s of NHE-3 mRNA distribution in the gut by in situ hybridization demon strated epithelial cell specificity, as well as expression preferentia l to villus cells. NHE-1 message, in contrast, was ubiquitous, with sl ightly greater expression exhibited in the differentating crypt and lo wer villus cells of the small intestine. Isoform-specific NHE-3 fusion protein antibody identified a 97-kD membrane protein in the upper vil lus cells of the small intestine, which was exclusively localized in t he apical membrane. In contrast, antibody previously developed against the COOH-terminal region of human NHE-1 (McSwine, R. L., G. Babnigg, M. W. Musch, E. B. Chang, and M. L. Villereal, manuscript submitted fo r publication) identified a 11O-kD basolateral membrane protein. These data suggest that unlike NHE-1, which probably serves a ''housekeepin g'' function, NHE-3 may be involved in vectorial Na transport by the i ntestine.