Carboxyl methylation activates purified renal amiloride-sensitive Na+ channels in planar lipid bilayers

The early increase in luminal membrane Na+ permeability by aldosterone in Na(+)-reabsorbing epithelia is attributed to an increase in the open probability (and number) of preexisting amiloride-sensitive Na+ channels. Carboxyl methylation reactions are involved, but the mechanism of action is unknown. We report that the 90-95-kDa polypeptide subunit of a purified renal Na+ channel protein can be specifically carboxymethylated and that this biochemical reaction, in the presence of guanosine 5'-3-O-(thio)triphosphate, leads directly to an increase in channel activity. Further, we show that protein kinase A-mediated phosphorylation can synergistically activate these channels. We suggest that renal Na+ channels have multiple biochemical regulatory inputs and that post-translational modifications underlie the increases in luminal membrane Na+ channel activity produced by aldosterone and vasopressin in Na(+)-reabsorbing epithelia.