Patch clamp experiments on nicotinic acetylcholine receptor-ion channels in bullfrog sympathetic ganglion cells.
Nicotinic acetylcholine-receptor ion channels (AChR channels) were studied in bullfrog sympathetic ganglion cells cultured for 1 day to 3 weeks, using a patch clamp technique. Microsuperfusion of ACh (2-10 microM) to the ganglion cell under the whole cell clamp produced an inward current at membrane potentials negative to -60 mV, which had a fast onset and decay. This rapid ACh-induced current was accompanied by a large current fluctuation, decreased and increased in amplitude by membrane depolarization and hyperpolarization, respectively, and blocked by d-tubocurarine. Thus, this current must be induced by the nicotinic action of ACh, but not by a muscarinic effect to activate a slow cation-selective current. At depolarized levels more than -50 mV, ACh induced an additional inward current which was slow in time course, accompanied by no or decreased current fluctuation and increased in amplitude by membrane depolarization. Accordingly, this slow ACh-induced current could result from the suppression of a voltage-dependent K+ current (M-current: Brown and Adams 1980) by the muscarinic action of ACh. Fluctuation analysis of the rapid ACh-induced current at potentials negative to -50 mV revealed the elementary conductance of 14 pS and a power spectral density distribution of the double Lorentzian function which yielded the time constants of 5.4 and 62.5 ms at -60 to -80 mV. The variance of either component was independent of the mean current.
Department of Physiology, Saga Medical School, Japan.
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K
Kuba
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Tanaka
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Kumamoto
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Minota
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001001:Anura; D004553:Electric Conductivity; D004560:Electricity; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*
D011978:Receptors, Nicotinic; D000109:Acetylcholine