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)
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
N
N
Akaike
N
N
Tokutomi
H
H
Kijima
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