title: Co-existence of muscarinic and nicotinic receptors and their functional interaction in mouse Beta-TC6 cells.
abstract: Mouse Beta-TC6 insulinoma cells possessing nicotinic receptor [Ohtani, M., Oka, T., Badyuk, M., Xiao, Y., Kellar, KJ., Daly, JW., 2006. Mouse beta-TC6 insulinoma cells: high expression of functional alpha3beta4 nicotinic receptors mediating membrane potential, intracellular calcium, and insulin release. Mol. Pharmacol. 69, 899-907.] also expressed M(3) and M(4) muscarinic receptors. Carbamylcholine, a mixed muscarinic/nicotinic receptor agonist, or oxotremorine M, a selective muscarinic agonist, elicited an elevation of cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and release of insulin. The maximal [Ca(2+)](i) response induced by carbamylcholine was larger than that of oxotremorine M or that of nicotine, suggesting that carbamylcholine enhanced the [Ca(2+)](i) response by stimulating two types of receptor. M(3) and M(4) muscarinic receptor antagonists inhibited the [Ca(2+)](i) responses to carbamylcholine and oxotremorine M, suggesting the involvement of these muscarinic receptors in the regulation of [Ca(2+)](i). In addition, pretreatment with carbamylcholine inhibited the [Ca(2+)](i) responses to oxotremorine M or nicotine, indicating that the effect of carbamylcholine on [Ca(2+)](i) was mediated by both muscarinic and nicotinic receptors. A phospholipase C (PLC) inhibitor U73122, a protein kinase C (PKC) inhibitor chelerythrine and a phospholipase A(2) (PLA(2)) inhibitor AACOCF(3) inhibited the [Ca(2+)](i) response to carbamylcholine or oxotremorine M, while these inhibitors did not block the effect of nicotine. Carbamylcholine induced a smaller extent of insulin secretion than oxotremorine M, suggesting that concomitant stimulation of muscarinic and nicotinic receptors by carbamylcholine resulted in the negative type of the receptor interaction.
authors.affiliation: Chemical Biology, National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ohtani
authors.forename: John W
authors.initials: JW
authors.lastname: Daly
authors.forename: Takami
authors.initials: T
authors.lastname: Oka
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D051379:Mice; D018721:Muscarinic Agonists / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D007328:Insulin; D018721:Muscarinic Agonists; D018727:Muscarinic Antagonists; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D002118:Calcium