Interaction of syntaxins with the amiloride-sensitive epithelial sodium channel

Amiloride-sensitive sodium channels mediate sodium entry across the apical membrane of epithelial cells in variety of tissues. The rate of Na+ entry i s controlled by the regulation of the epithelial sodium channel (ENaC) comp lex. Insertion/retrieval of the ENaC complex into the apical membrane as we ll as direct kinetic effects at the single channel level are recognized mec hanisms of regulation. Recent data suggest that the syntaxin family of targ eting proteins interact with and functionally regulate a number of ion chan nels. and pumps. To evaluate the role of these proteins in regulating ENaC activity, we co-expressed rat ENaC cRNA (alpha, beta, gamma subunits) with syntaxin 1A or 3 cRNAs in Xenopus oocytes. Basal ENaC currents were inhibit ed by syntaxin 1A and stimulated by syntaxin 3, Both syntaxin IA and syntax in 3 could be co-immunoprecipitated with ENaC subunit proteins, suggesting physical interaction, interestingly, immunofluorescence data suggest that w ith either syntaxin isoform the ENaC-associated epifluorescence on the oocy te surface is enhanced. These data indicate that (i) both syntaxin isoforms increase the net externalization of the ENaC channel complex, (ii) that th e functional regulation is isoform specific, and (iii) suggest that ENaC ma y be regulated through mechanisms involving protein-protein interactions.