Kinetic analysis of acetylcholine-induced current in isolated frog sympathetic ganglion cells.
1. Kinetic properties of activation and inactivation phases of the ACh-gated nicotinic current were investigated in isolated frog sympathetic ganglion cells using "concentration-clamp" technique under voltage-clamp conditions. This technique combines internal perfusion with a rapid change of the external solution within a few milliseconds. 2. The dose-response curve for the peak current induced by ACh showed a sigmoidal increase, in which the apparent dissociation constant Kd and Hill coefficient were 2.6 x 10(-5) M and 2.0, respectively. 3. The current-voltage relationship of ACh-induced currents were linear at potentials more negative than the reversal potential (EACh) of -5.5 +/- 1.3 mV (mean +/- SE) but showed a slight inward rectification at positive potentials over +20 mV. Since this current could be generated predominantly by an increase of Na+ and K+ conductances, the value of EACh was close to the theoretical potential, -1.3 mV, for the total amount of both Na+ and K+ or Cs+ in the extracellular and intracellular solutions. 4. There was no difference between the dose-response curves of ACh- and nicotine-induced currents. The ACh-induced current was suppressed in a competitive manner by the nicotinic antagonists, d-tubocurarine and hexamethonium, but muscarine did not induce any response, indicating that the ACh-gated current might be mediated by the nicotinic ACh receptor-ionophore complex. 5. There was a latent period of the order of milliseconds in the ACh receptor activation phase before attaining exponential increase of activation process.(ABSTRACT TRUNCATED AT 250 WORDS)
Akaike
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N
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Tokutomi
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N
Kijima
H
H
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009474:Neurons / Q000502:physiology*; D009538:Nicotine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011892:Rana catesbeiana
D009538:Nicotine; D000109:Acetylcholine