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+ chann els, Carboxyl methylation reactions are involved, but the mechanism of action is unknown. We report that the 90-95-kDa polypeptide subunit o f a purified renal Na+ channel protein can be specifically carboxymeth ylated and that this biochemical reaction, in the presence of guanosin e 5'-3-O-(thio)triphosphate, leads directly to an increase in channel activity. Further, we show that protein kinase A-mediated phosphorylat ion can synergistically activate these channels. We suggest that renal Na+ channels have multiple biochemical regulatory inputs and that pos t-translational modifications underlie the increases in luminal membra ne Na+ channel activity produced by aldosterone and vasopressin in Na-reabsorbing epithelia.