Acetylcholine-induced membrane potential changes in endothelial cells of rabbit aortic valve.
1. Using a microelectrode technique, acetylcholine (ACh)-induced membrane potential changes were characterized using various types of inhibitors of K+ and Cl- channels in rabbit aortic valve endothelial cells (RAVEC). 2. ACh produced transient then sustained membrane hyperpolarizations. Withdrawal of ACh evoked a transient depolarization. 3. High K+ blocked and low K+ potentiated the two ACh-induced hyperpolarizations. Charybdotoxin (ChTX) attenuated the ACh-induced transient and sustained hyperpolarizations; apamin inhibited only the sustained hyperpolarization. In the combined presence of ChTX and apamin, ACh produced a depolarization. 4. In Ca2+-free solution or in the presence of Co2+ or Ni2+, ACh produced a transient hyperpolarization followed by a depolarization. In BAPTA-AM-treated cells, ACh produced only a depolarization. 5. A low concentration of A23187 attenuated the ACh-induced transient, but not the sustained, hyperpolarization. In the presence of cyclopiazonic acid, the hyperpolarization induced by ACh was maintained after ACh removal; this maintained hyperpolarization was blocked by Co2+. 6. Both NPPB and hypertonic solution inhibited the membrane depolarization seen after ACh washout. Bumetanide also attenuated this depolarization. 7. It is concluded that in RAVEC, ACh produces a two-component hyperpolarization followed by a depolarization. It is suggested that ACh-induced Ca2+ release from the storage sites causes a transient hyperpolarization due to activation of ChTX-sensitive K+ channels and that ACh-activated Ca2+ influx causes a sustained hyperpolarization by activating both ChTX- and apamin-sensitive K+ channels. Both volume-sensitive Cl- channels and the Na+-K+-Cl- cotransporter probably contribute to the ACh-induced depolarization.
Department of Pharmacology, Nagoya City University Medical School, Nagoya, Japan. mohashi@med.nagoya-cu.ac.jp
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D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001021:Aortic Valve / Q000187:drug effects* / Q000502:physiology; D001030:Apamin / Q000494:pharmacology; D002034:Bumetanide / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D018999:Charybdotoxin / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D018118:Chloride Channels / Q000037:antagonists & inhibitors; D003035:Cobalt / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004727:Endothelium / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D007211:Indoles; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects*; D009532:Nickel / Q000494:pharmacology; D009579:Nitrobenzoates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D011817:Rabbits; D014665:Vasodilator Agents / Q000494:pharmacology*
D002614:Chelating Agents; D018118:Chloride Channels; D004232:Diuretics; D007211:Indoles; D007476:Ionophores; D009579:Nitrobenzoates; D026902:Potassium Channel Blockers; D014665:Vasodilator Agents; D002034:Bumetanide; D018999:Charybdotoxin; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D001030:Apamin; D000001:Calcimycin; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D003035:Cobalt; D004533:Egtazic Acid; D009532:Nickel; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium; C000543:cyclopiazonic acid