Journal of Neurophysiology, Vol 61, Issue 2 283-290, Copyright © 1989 by APS
Kinetic analysis of acetylcholine-induced current in isolated frog sympathetic ganglion cells
N. Akaike, N. Tokutomi and H. Kijima
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
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)
