January 1999, Volume 126, Issue 1, Pages 19 - 26

Original Article

Acetylcholine-induced membrane potential changes in endothelial cells of rabbit aortic valve Masuo Ohashi1,3, Kohichi Satoh2 & Takeo Itoh1 1Department of Pharmacology, Nagoya City University Medical School, Nagoya 467-8601, Japan     2Department of 2nd Internal Medicine, Nagoya City University Medical School, Nagoya 467-8601, Japan     3Author for correspondence at: Department of Pharmacology, Nagoya City University Medical School, Mizuho-ku, Nagoya 467-8601, Japan. E-mail: mohashi@med.nagoya-cu.ac.jp

Keywords

endothelial cell;   aortic valve;   acetylcholine;   potassium channel;   chloride channel

Abstract

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.

Received 26 May 1998; Revised 15 September 1998; Accepted 5 October 1998

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