A physiologically-evoked M1-muscarinic depolarization in guinea-pig inferior mesenteric ganglion neurons.
The possibility of physiologically-evoked muscarinic excitatory synaptic potentials was examined in the inferior mesenteric ganglion (IMG) with intracellular microelectrodes in vitro. Three types of depolarizing responses were evoked concurrently by colonic distension: (1) fast nicotinic excitatory postsynaptic potentials (EPSPs); (2) an 'intermediate' time course depolarization and (3) a long time course potential that persisted throughout the period of distension. After hexamethonium was superfused over the ganglia the long time course potential was observed in 91% of IMG neurons. Intermediate time course of depolarizations were observed in 100% of IMG neurons and correlated with each propulsive contraction of the distal colon. The intermediate depolarizations had an average amplitude of 1.8 +/- 0.1 mV (n = 175 individual events; 27 preparations) with an average duration of 11.9 +/- 0.8 sec (n = 28 individual events). The intermediate time course synaptic potentials were accompanied by an increase in input resistance of 15% (n = 6). Superfusion of atropine (1 microM; n = 6) on the IMG or the M1-selective antagonist pirenzepine (1 microM; n = 5) abolished the intermediate time course synaptic potentials during distension. Superfusion of the M2-selective antagonist AF-DX 116 (1 microM; n = 4) had no effect. In all preparations examined, distension-induced intermediate time course depolarizations were blocked by tetrodotoxin (TTX) (3 microM). Pressure ejection of carbachol (1 mM, 60-100 ms pulses) evoked depolarizations of similar amplitude (6.5 +/- 0.7 mV; n = 18) and duration to the intermediate depolarizations observed during propulsive contractions.(ABSTRACT TRUNCATED AT 250 WORDS)
Anthony
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Department of Pharmacology, University of Arizona, College of Medicine, Tucson 85724.
Kreulen
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D000200:Action Potentials; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003106:Colon / Q000294:innervation*; D005260:Female; D005728:Ganglia, Sympathetic / Q000502:physiology*; D005769:Gastrointestinal Motility; D006168:Guinea Pigs; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology*; D010890:Pirenzepine / Q000031:analogs & derivatives / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D013314:Stress, Mechanical
D006584:Hexamethonium Compounds; D011976:Receptors, Muscarinic; D018738:Hexamethonium; D010890:Pirenzepine; D001285:Atropine; D002217:Carbachol; C048593:otenzepad