In various gastrointestinal smooth muscles, two different muscarinic receptor subtypes, <$E roman M sub 2> and <$E roman M sub 3>, are expressed; these receptors are the target for the parasympathetic neurotransmitter acetylcholine. Although the number of <$E roman M sub 2> receptors is much greater than that of <$E roman M sub 3> receptors, the functional role of the former receptor subtype has yet to be fully defined, since pharmacological analyses of the contractile responses to acetylcholine and other muscarinic agonists have revealed that such responses are mediated extensively by the minor <$E roman M sub 3> subtype. The <$E roman M sub 3> receptor links to <$E roman Ca sup 2+> store release, and the released <$E roman Ca sup 2+> ions may contribute to the contraction. However, many studies indicated the importance of <$E roman Ca sup 2+> influx through voltage-gated <$E roman Ca sup 2+> channels, rather than <$E roman Ca sup 2+> release, in muscarinic contractions, since the contractile responses are markedly inhibited by <$E roman Ca sup 2+> channel blockers. The major <$E roman M sub 2> receptors link to the opening of cationic channels leading to the membrane depolarization, which in turn activates voltage-gated <$E roman Ca sup 2+> channels. Thus, there should be somewhere a point of contact between the <$E roman M sub 3>- and <$E roman M sub 2>-mediated signal transductions, as if <$E roman M sub 3> receptor stimulation is connected with membrane depolarization. Our electrophysiological and pharmacological findings suggest

that the <$E roman M sub 2>-mediated cationic channel opening and a resulting increase in the membrane electrical activity are the primary mechanism for mediating the contractile response to muscarinic agonists. Such an allosteric interaction between <$E roman M sub 2> and <$E roman M sub 3> receptors that <$E roman M sub 3> activation intensifies the <$E roman M sub 2>/cation channel pathway may account at least in part for the failure of many previous analyses to detect the <$E roman M sub 2> participation in the contractile responses to full agonists.

  Якщо, ви не знайшли інформацію про автора(ів) публікації, маєте бажання виправити або відобразити більш докладну інформацію про науковців України запрошуємо заповнити "Анкету науковця"