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(Hypertension. 2000;35:379.)
© 2000 American Heart Association, Inc.

Scientific Contributions

Sympathetic Control of Arterial Membrane Potential by ATP-Sensitive K⁺-Channels

Kenichi Goto; Koji Fujii; Isao Abe; Masatoshi Fujishima

From the Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.

Correspondence to Koji Fujii, MD, PhD, Second Department of Internal Medicine, Kyushu University Hospital, Maidashi 3-1-1, Higashi-ku, Fukuoka, 812-8582, Japan. E-mail fujii{at}intmed2.med.kyushu-u.ac.jp

Abstract—Stimulation of perivascular nerve terminals leads to a release of various neurotransmitters such as norepinephrine, epinephrine, acetylcholine, nitric oxide, and calcitonin gene-related peptide (CGRP). Because some of these substances have been shown to cause smooth muscle hyperpolarization by direct or endothelium-dependent mechanisms, we hypothesized that the liberation of 1 or more of these transmitters may lead to neurogenic hyperpolarization in arterial muscle cells. The present study was designed to determine the presence or absence of neurogenic hyperpolarization and, if present, its underlying mechanisms in isolated rat mesenteric resistance arteries, through the use of conventional microelectrode techniques. The experiments were performed under the combined blockade of -adrenoceptors and purinoceptors with phentolamine and suramin to eliminate depolarizing responses to nerve stimulation. Under these conditions, perivascular nerve stimulation (5 Hz, 30 seconds) evoked smooth muscle hyperpolarization (-3.3±0.3 mV, n=15), which was abolished by tetrodotoxin, indicating the neurogenic origin of the response. This neurogenic hyperpolarization was resistant to atropine, nitro-L-arginine, or CGRP8-37, a CGRP antagonist, but was abolished by guanethidine and ß-blocker propranolol. This hyperpolarization was also abolished by glibenclamide, an ATP-sensitive K⁺ channel (K_ATP) blocker, but was unaffected by apamin, a Ca²⁺-activated K⁺ channel blocker. In separate experiments, exogenous norepinephrine caused glibenclamide-sensitive hyperpolarization in the presence of phentolamine. On the other hand, norepinephrine-induced depolarization in the absence of phentolamine was enhanced by propranolol. These findings suggest that neurally released catecholamines cause membrane hyperpolarization through the activation of K_ATP by ß-adrenoceptors. Such hyperpolarization may play an important role in the control of arterial membrane potential by opposing -adrenergic depolarization.

Key Words: receptors, adrenergic, beta • nervous system, sympathetic • potassium • membranes • hyperpolarization • muscle, smooth, vascular • rats

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