Inhibition of nicotinic acetylcholine response by atropine in frog isolated sympathetic neurons.
The effect of atropine on nicotinic acetylcholine (ACh) response was studied in frog isolated sympathetic ganglion cells using a 'concentration clamp' technique which combines intra-cellular perfusion with a rapid external solution change within 3 ms. When atropine (more than 6 x 10(-7) M) was simultaneously applied to neurons with ACh (6 x 10(-6) M), the current amplitude was instantaneously reduced in a dose-dependent fashion. Further decreases in the current amplitude were observed in a time-dependent manner during about 20 min after the start of drug-application. Thereafter the current amplitude gradually restored toward the control level in the following 90-120 min in spite of the continuous presence of atropine. However, because d-tubocurarine greatly inhibited the 'restored' current, the last-mentioned is suggested to be also mediated by nicotinic ACh receptor-ionophore complex. Therefore, the inhibitory action of atropine on the peak amplitude of ACh response was examined at 15-20 min after adding the agent. It was dose-dependent but not voltage-dependent. Respective concentrations of atropine and d-tubocurarine causing half the maximum inhibition (IC50) of the peak current evoked by ACh (6 x 10(-6) M) were 1.8 x 10(-5) M and 1.8 x 10(-6) M. Thus, the inhibitory potency was 10 times less than that of d-tubocurarine, an antagonist of nicotinic ACh receptors. The blockade of ACh response by d-tubocurarine was competitive while that by atropine was non-competitive. The current elicited by ACh consisted of two (fast and slow) exponential components plus a steady-state one in the control period.(ABSTRACT TRUNCATED AT 250 WORDS)
Sadoshima
J
J
Research Institute of Angiocardiology and Cardiovascular Clinic, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Oyama
Y
Y
Akaike
N
N
D000109:Acetylcholine / Q000494:pharmacology*; D000320:Adrenergic Fibers / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009433:Neural Inhibition / Q000187:drug effects*; D018733:Nicotinic Antagonists; D011892:Rana catesbeiana / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000502:physiology*; D014403:Tubocurarine / Q000494:pharmacology
D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D001285:Atropine; D000109:Acetylcholine; D014403:Tubocurarine