Activators of epithelial Na+ channels inhibit cytosolic feedback control. Evidence for the existence of a G protein-coupled receptor for cytosolic Na+

• Published in: The Journal of membrane biology Vol. 162; no. 3; pp. 225 - 232
• Main Authors: Komwatana, P, Dinudom, A, Young, J A, Cook, D I
• Format: Journal Article
• Language: English
• Published: United States 01.04.1998
• Subjects: 4-Chloromercuribenzenesulfonate - pharmacology; Amiloride - analogs & derivatives; Amiloride - pharmacology; Animals; Anions; Cells, Cultured; Cytosol - metabolism; Epithelial Cells - drug effects; Epithelial Cells - physiology; Epithelium - physiology; GTP-Binding Proteins - metabolism; Guanidines - pharmacology; Male; Mice; Receptors, Cell Surface - metabolism; Salivary Ducts - cytology; Sodium Channels - drug effects; Sodium Channels - physiology; Sulfhydryl Reagents - pharmacology
• ISSN: 0022-2631; 1432-1424
• DOI: 10.1007/s002329900360

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.