Properties of the nicotinic-receptor-activated current in adrenal chromaffin cells of the guinea-pig.
Properties of acetylcholine(ACh)- and nicotine-induced currents were studied in the guinea-pig chromaffin cell, using the whole-cell and cell-attached versions of the patch-clamp technique. Bath application of ACh or nicotine, but not muscarine, produced an inward current associated with an increase in current noise at a membrane potential of -70 mV. Low concentrations of both agonists produced a sustained inward current whereas high concentrations produced a transient, then a sustained inward current. Nicotine was about twice as potent as ACh in inducing the inward current. Hexamethonium (6 microM) inhibited the ACh-induced current but not in a competitive manner. By contrast, atropine (6 microM) inhibited the ACh-induced current more strongly with increasing concentrations of ACh. The nicotinic-receptor-activated current ("nicotinic current") showed inward rectification and, when Cs+ was used instead of K+ in the pipette solution, the polarity of the current changed at around -5 mV and a negative slope occurred between +10 mV and +30 mV. The nicotinic channel had a unit conductance of 33 pS. During the initial 20-30 min of whole-cell voltage-clamp recording, the time course of the agonist-induced desensitization was markedly facilitated. Addition of 5 mM MgATP in the pipette solution at least partly prevented this facilitation of the desensitization. The frequency of activation of the nicotinic receptor and the extracellular Ca2+ were not primary factors in the acceleration of rate of desensitization.
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
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Inoue
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Kuriyama
D000109:Acetylcholine / Q000494:pharmacology; D000311:Adrenal Glands / Q000166:cytology / Q000502:physiology*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002838:Chromaffin System / Q000166:cytology / Q000502:physiology*; D004553:Electric Conductivity; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D006168:Guinea Pigs; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D008297:Male; D011950:Receptors, Cholinergic / Q000502:physiology; D011978:Receptors, Nicotinic / Q000502:physiology*
D006584:Hexamethonium Compounds; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D018738:Hexamethonium; D001285:Atropine; D000109:Acetylcholine