Activators of epithelial Na+ channels inhibit cytosolic feedback control. Evidence for the existence of a G protein-coupled receptor for cytosolic Na+.
We have previously shown that epithelial Na+ channels in mouse mandibular gland duct cells are controlled by cytosolic Na+ and Cl-, acting, respectively, via Go and Gi proteins. Since we found no evidence for control of epithelial Na+ channels by extracellular Na+ ([Na+]o), our findings conflicted with the long-held belief that Na+ channel activators, such as sulfhydryl reagents, like para-chloromercuriphenylsulfonate (PCMPS), and amiloride analogues, like benzimidazolylguanidinium (BIG) and 5-N-dimethylamiloride (DMA), induce their effects by blocking an extracellular channel site which otherwise inhibits channel activity in response to increasing [Na+]o. Instead, we now show that PCMPS acts by rendering epithelial Na+ channels refractory to inhibition by activated G proteins, thereby eliminating the inhibitory effects of cytosolic Na+ and Cl- on Na+ channel activity. We also show that BIG, DMA, and amiloride itself, when applied from the cytosolic side of the plasma membrane, block feedback inhibition of Na+ channels by cytosolic Na+, while leaving inhibition by cytosolic Cl- unaffected. Since the inhibitory effects of BIG and amiloride are overcome by the inclusion of the activated alpha-subunit of Go in the pipette solution, we conclude that these agents act by blocking a previously unrecognized intracellular Na+ receptor.
Komwatana
P
P
Department of Physiology, University of Sydney, NSW 2006, Australia.
Dinudom
A
A
Young
J A
JA
Cook
D I
DI
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000838:Anions; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects* / Q000502:physiology; D004848:Epithelium / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006146:Guanidines / Q000494:pharmacology; D008297:Male; D051379:Mice; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018987:Salivary Ducts / Q000166:cytology; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology; D013439:Sulfhydryl Reagents / Q000494:pharmacology
D000838:Anions; D006146:Guanidines; D011956:Receptors, Cell Surface; D015222:Sodium Channels; D013439:Sulfhydryl Reagents; C039465:5-dimethylamiloride; C032996:2-benzimidazolylguanidine; D002731:4-Chloromercuribenzenesulfonate; D000584:Amiloride; D019204:GTP-Binding Proteins