Potassium channels in cultured bovine adrenal medullary cells: effects of high K, veratridine and carbachol on 86rubidium efflux.
To investigate the K permeability mechanism(s) in cultured bovine adrenal medullary cells, we measured the effects of high K, veratridine and carbachol on 86Rb efflux from the 86Rb preloaded cells. In non-stimulated cells, the basal efflux of 86Rb into Krebs-Ringer phosphate buffer containing 5.6 mM K proceeded gradually at the rate of 0.7% of cell 86Rb per min. High K caused a rapid 86Rb efflux; it was considerably reduced in Ca free medium. Mn, Co and Mg strongly inhibited high K-induced 45Ca influx and 86Rb efflux. Veratridine induced a sustained 86Rb efflux; it was inhibited by tetrodotoxin and abolished in Na free sucrose medium, but little affected in Ca free medium. Carbachol evoked a rapid and transient efflux of 86Rb; it amounted to 16.9% of cell 86Rb during 1 min. Carbachol-induced 86Rb efflux was inhibited by hexamethonium and d-tubocurarine. Nicotine caused 86Rb efflux, but muscarine had no effect. Carbachol-induced 86Rb efflux was substantially reduced in Na free sucrose medium, but little affected in Ca free medium. Mn, Co and Mg strongly reduced carbachol-induced 45Ca influx, but they did not appreciably alter carbachol-induced 22Na influx and 86Rb efflux. These results suggest that adrenal medullary cells have, at least, three distinct types of K permeability mechanisms: (1) basal K efflux, (2) Ca dependent K efflux, and (3) Na dependent K efflux. It seems that nicotine receptors mediate K efflux by increasing Na influx via nicotinic receptor-associated ionic channels rather than Ca influx via voltage dependent Ca channels.
D000313:Adrenal Medulla / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D012413:Rubidium / Q000493:pharmacokinetics*; D014701:Veratridine / Q000494:pharmacology*; D014702:Veratrine / Q000031:analogs & derivatives*
D002413:Cations, Divalent; D007473:Ion Channels; D014701:Veratridine; D002217:Carbachol; D014702:Veratrine; D012413:Rubidium; D011188:Potassium