title: Arginine vasopressin and forskolin regulate apical cell surface expression of epithelial Na+ channels in A6 cells.
abstract: Both arginine vasopressin (AVP) and forskolin regulate vectorial Na+ transport across high-resistance epithelia by increasing the Na+ conductance of the apical membrane mediated by amiloride-sensitive Na+ channels. Pretreatment of A6 cells with brefeldin A partially inhibited the increase in Na+ transport in response to forskolin, suggesting recruitment of Na+ channels from an intracellular pool. The activation of Cl- secretion was not affected. Apical cell surface expression of Na+ channels was examined following activation of transepithelial Na+ transport across the epithelial cell line A6 by AVP or forskolin. Apical cell surface radioiodinated Na+ channels were immunoprecipitated to quantify the biochemical pool of Na+ channels at the apical plasma membrane and to determine whether an increment in the biochemical pool of Na+ channels expressed at the apical cell surface is a potential mechanism by which AVP and forskolin increase apical membrane Na+ conductance. The activation of Na+ transport across A6 cells by AVP was accompanied by a significant increase in the biochemical pool of Na+ channels at the apical plasma membrane within 5 min after addition of hormone, which was sustained for at least 30 min. The increase in apical cell surface expression of Na+ channels was also observed 30 min after application of forskolin. No changes in the oligomeric subunit composition of the channel were noted. Brefeldin A inhibited the forskolin-stimulated increase in apical cell surface expression of Na+ channels. These results suggest that AVP and forskolin regulate Na+ transport, in part, via rapid recruitment of Na+ channels to the cell surface, perhaps from a pool of channels in the subapical cytoplasm.
authors.affiliation: Department of Medicine, University of Pennsylvania.
authors.forename: T R
authors.initials: TR
authors.lastname: Kleyman
authors.forename: S A
authors.initials: SA
authors.lastname: Ernst
authors.forename: B
authors.initials: B
authors.lastname: Coupaye-Gerard
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000494:pharmacology*; D020126:Brefeldin A; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology*; D003517:Cyclopentanes / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism*; D015222:Sodium Channels / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D003517:Cyclopentanes; D015222:Sodium Channels; D001127:Arginine Vasopressin; D005576:Colforsin; D020126:Brefeldin A; D000584:Amiloride