title: Presynaptic muscarinic receptors inhibiting active acetylcholine release in the bullfrog sympathetic ganglion.
abstract: 1 The effects of bethanechol and atropine on the release of acetylcholine (ACh) from bullfrog sympathetic preganglionic nerve terminals were examined electrophysiologically. 2 Bethanechol (1 mM) caused no depolarization of sympathetic preganglionic nerve terminals, whereas carbachol or ACh in the same concentration induced marked depolarizations of these terminals. 3 Bethanechol (10 microM) depressed the amplitude of fast excitatory postsynaptic potentials (e.p.s.ps) recorded in Ca2+-high Mg2+ solution, without depolarizing ganglion cells. The quantal content measured from these fast e.p.s.ps by the variance method showed a significant reduction. 4 Amplitudes of both miniature e.p.s.ps and ACh-potentials induced by iontophoresis of ACh were not affected by addition of bethanechol (10 microM). 5 The depressant effect of bethanechol (10 microM) on fast e.ps.ps disappeared in the presence of atropine (3 microM). 6 Atropine (3 microM) increased the quantal content measured from fast e.p.s.ps recorded in low Ca2+-high Mg2+ solution. 7 The depressant effect of bethanechol (10 microM) on fast e.p.s.ps was unaffected by alpha-adrenoceptor blocking agents (phenoxybenzamine (10 microM) or phentolamine (10 microM). 8 These results suggest that presynaptic nerve terminals in bullfrog sympathetic ganglia possess a muscarinic receptor which inhibits active release of ACh.
mesh_terms: D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D001626:Bethanechol Compounds / Q000494:pharmacology; D004594:Electrophysiology; D005728:Ganglia, Sympathetic / Q000378:metabolism*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009045:Motor Endplate / Q000187:drug effects; D009411:Nerve Endings / Q000187:drug effects; D011892:Rana catesbeiana; D011950:Receptors, Cholinergic / Q000502:physiology*; D011976:Receptors, Muscarinic / Q000502:physiology*
chemical_list: D001626:Bethanechol Compounds; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D001285:Atropine; D000109:Acetylcholine