CARBOXYLMETHYLATION OF THE BETA-SUBUNIT OF XENAC REGULATES CHANNEL ACTIVITY

The action of aldosterone to increase apical membrane permeability in responsive epithelia is thought to be due to activation of sodium chan nels. Aldosterone stimulates methylation of a 95-kDa protein in apical membrane of A6 cells, and we have previously shown that methylation o f a 95-kDa protein in the immunopurified Na+ channel complex increases open probability of these channels in planar lipid bilayers. We repor t here that aldosterone stimulates carboxylmethylation of the beta sub unit of xENaC in A6 cells. In vitro translated beta subunit, but not a lpha or gamma, serves as a substrate for carboxylmethylation. Carboxyl methylation of ENaC reconstituted in planar lipid bilayers leads to an increase in open probability only when beta subunit is present. When the channel complex is immunoprecipitated from A6 cells and analyzed b y Western blot with antibodies to the three subunits of xENaC, all thr ee subunits are recognized as constituents of the complex. The results suggest that Na+ channel activity in A6 cells is regulated, in part, by carboxylmethylation of the beta subunit of xENaC.