title: Calcium rapidly down-regulates human renal epithelial sodium channels via a W-7-sensitive mechanism.
abstract: Increases in intracellular calcium (Ca(2+)) inhibit renal sodium (Na(+)) absorption in cortical collecting ducts, but the precise mechanism is unclear. We, therefore, studied the effects of raising intracellular Ca(2+) (using 10 µmol/L A23187, a Ca(2+) ionophore) on wild-type and Liddle-mutated human epithelial Na(+) channels (hENaC) expressed in Xenopus oocytes, using the dual-electrode voltage clamp technique. A23187 decreased amiloride-sensitive Na(+) current by 55% in oocytes expressing wild-type hENaC, an effect prevented by co-exposure to 50 μmol/L W-7 (to inhibit the Ca(2+)/calmodulin complex). By contrast, co-exposure to 50 μmol/L calphostin (to inhibit protein kinase C) or 5 μmol/L KN-62 (to inhibit Ca(2+)/calmodulin-dependent protein kinase II) had no effect on the decrease in amiloride-sensitive Na(+) current elicited by A23187 alone. Whereas A23187 reduced amiloride-sensitive Na(+) current in oocytes expressing wild-type hENaC, it had no similar effect in those expressing Liddle-mutated hENaCs, suggesting that the activity of individual Na(+) channels in situ was unchanged by the rise in intracellular Ca(2+). These data suggest that the A23187-induced rise in intracellular Ca(2+) inhibited wild-type hENaC through a W-7-sensitive mechanism, which likely reflected enhanced removal of Na(+) channels from the cell membrane by endocytosis. We, therefore, propose that Na(+) absorption in cortical collecting duct cells is inhibited by Ca(2+), possibly when complexed with calmodulin.
authors: Leeds Institute of Biomedical and Clinical Sciences, St James's University Teaching Hospital, Level 7, Clinical Sciences Building, Beckett Street, Leeds, LS9 7TF, UK.
authors: Gerard G
authors: GG
authors: Robins
authors: Geoffrey I
authors: GI
authors: Sandle
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D053503:Epithelial Sodium Channels / Q000737:chemistry* / Q000378:metabolism*; D005260:Female; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009865:Oocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000378:metabolism; D013449:Sulfonamides / Q000494:pharmacology*; D014982:Xenopus laevis
chemical_list: D004791:Enzyme Inhibitors; D053503:Epithelial Sodium Channels; D013449:Sulfonamides; C017967:W 7; D012964:Sodium; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium