title: Regulation of alpha-bungarotoxin sites in chromaffin cells in culture by nicotinic receptor ligands, K+, and cAMP.
abstract: Previous work had shown that incubation with the nicotinic antagonist d-tubocurarine resulted in a marked increase in alpha-bungarotoxin (alpha-BGT) binding in adrenal medullary chromaffin cells in culture; the possible molecular mechanisms involved in up-regulating the alpha-BGT sites were investigated. To determine whether changes in the extracellular K+ concentration could influence the number of toxin binding sites, the chromaffin cells were incubated in the presence of 2-50 mM K+; this resulted in an increase in alpha-BGT binding similar to that observed with the nicotinic antagonist. This enhanced binding was maximal with 20 mM K+ and was not due simply to a generalized ion effect, inasmuch as incubation of the cells with a concentration of Na+ of equivalent osmolarity did not alter alpha-BGT binding. Carbachol and the agonist nicotine completely prevented the K+-induced increase in the binding sites. In contrast to the marked up-regulation of the nicotinic alpha-BGT sites by K+, this agent did not increase the acetylcholine-induced release of [3H]noradrenaline from chromaffin cells in culture, further supporting the contention that the nicotinic alpha-BGT site and the functional nicotinic receptor are distinct. The increases in toxin binding due to K+ and d-tubocurarine were partially additive, suggesting that d-tubocurarine and K+ may share a common pathway, but only to a small degree. The calcium channel agonist BAY K 8644 and antagonist D600 had no effect on alpha-BGT binding either alone or in the presence of K+ or d-tubocurarine. On the other hand, forskolin, an activator of adenylate cyclase, and dibutyryl cAMP, an analog of cAMP, partially prevented the K+ and the d-tubocurarine-induced increases in toxin binding. These results suggest an involvement of cAMP in both the nicotinic antagonist-induced and K+-induced up-regulation of the sites. The observation that several mechanisms exist for the fine regulation of the nicotinic alpha-BGT binding sites in adrenal chromaffin cells could imply that this nicotinic receptor population plays a role in this tissue.
authors: Department of Pharmacology, McGill University, Montreal, Quebec, Canada.
authors: S
authors: S
authors: Geertsen
authors: R
authors: R
authors: Afar
authors: J M
authors: JM
authors: Trifaró
authors: M
authors: M
authors: Quik
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000502:physiology*; D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002038:Bungarotoxins / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D004789:Enzyme Activation; D005711:Gallopamil / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014403:Tubocurarine / Q000494:pharmacology; D064569:alpha7 Nicotinic Acetylcholine Receptor
chemical_list: D002038:Bungarotoxins; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D064569:alpha7 Nicotinic Acetylcholine Receptor; D005576:Colforsin; D005711:Gallopamil; D003994:Bucladesine; D009538:Nicotine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002217:Carbachol; D000262:Adenylyl Cyclases; D011188:Potassium; D014403:Tubocurarine; D009638:Norepinephrine