Functional Analyses of a N-Terminal Splice Variant of the α Subunit of the Epithelial Sodium Channel

The amiloride-sensitive epithelial sodium channel (ENaC) is the limiting step for sodium absorption in epithelial cells of the distal nephron, distal colon, airways and excretory ducts of several glands. In vivo and in vitro studies showed that the α subunit of ENaC is necessary for the expression of functional channels. Using RT-PCR strategy, a novel N-terminal splice variant has been identified which deletes 49 amino acids in the N-terminal region of the mouse αENaC subunit. In oocytes expressing the αENaC splice variant, together with β and γENaC subunits, amiloride-sensitive currents were less than 20% of values obtained with the wild type ENaC. The single channel conductance and the ionic selectivity were similar and there was only a minor decrease in the level of expression of the protein at the oocyte surface. These findings indicate that the deleted sequence in the N-terminal part of the mouse and rat αENaC subunit might play a role in the regulation of the activity of expressed ENaC channels.