Acetylcholine elicits metabolically mediated M2-muscarinic hyperpolarization in isolated rabbit sympathetic neurons.
Topically applied acetylcholine elicited a hyperpolarizing (ACh-HP) response in about 2/3 of the principal neurons of rabbit superior cervical ganglia isolated in a culture medium for several days. Membrane changes responsible for the ACh-HP were multiple and varied with the level of membrane potential (Vm): At, or less negative than, resting Vm (about -60 mV), membrane conductance (Gm) was increased; at Vm more negative than -70 mV, Gm either increased, decreased, or remained unchanged. The effect of altering extracellular K+ and Ca2+ concentrations suggest that a Ca2(+)-dependent increase in K+ conductance contributes to ACh-HP; however, drugs reported to block such channels (D-tubocurarine at 30 microM or apamin at 200 nM) shortened duration of the ACh-HP but did not depress peak amplitude. The ACh-HP was depressed by the M2-muscarinic antagonist AF-DX 116 and blocked by an intracellular administration of guanosine-5'-o-(2-thiodiphosphate) (GDP-beta-S) or by preincubation with pertussis toxin. Intracellularly injected inositol-1,4,5-triphosphate (IP3) elicited a hyperpolarization associated with an increase in Gm at any Vms. Activators of protein kinase C applied extracellularly, 1,2-oleoylacetylglycerol (OAG) or phorbol-12,13-dibutyrate (Pb(Bu)2) elicited a hyperpolarization with a decrease in Gm at Vms more negative than -50 mV and a reversal potential close to Ec1. In the presence of Li+, ACh-HP was smaller after a repetitive stimulation with ACh. These results suggest that, in these neurons, ACh can directly activate M2-muscarinic receptors coupled to GTP-binding proteins, which leads to both an increase in Ca2(+)-sensitive K+ conductance mediated by the intracellular messenger IP3 and a decrease in a conductance, possibly Gc1, through another phosphatidylinositide pathway.
Department of Physiology, Tokyo Medical College, Japan.
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Mochida
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001030:Apamin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D005728:Ganglia, Sympathetic / Q000187:drug effects* / Q000502:physiology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010276:Parasympatholytics / Q000494:pharmacology; D037342:Pertussis Toxin; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits; D011976:Receptors, Muscarinic / Q000145:classification / Q000187:drug effects* / Q000502:physiology; D013873:Thionucleotides / Q000494:pharmacology; D014403:Tubocurarine / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010276:Parasympatholytics; D011976:Receptors, Muscarinic; D013873:Thionucleotides; D010566:Virulence Factors, Bordetella; D006153:Guanosine Diphosphate; D001030:Apamin; C023427:guanosine 5'-O-(2-thiodiphosphate); D015544:Inositol 1,4,5-Trisphosphate; D008094:Lithium; D037342:Pertussis Toxin; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; D014403:Tubocurarine