title: Inhibitory effect of tetrabutylammonium ions on endothelium/nitric oxide-mediated vasorelaxation.
abstract: Apart from the well-described K+ channel blocking effects in vascular smooth muscle cells, monovalent quaternary ammonium ions may also interact with endothelial cells in the endothelium-intact mammalian arteries. The present study was aimed to examine the effect of tetrabutylammonium ions on endothelium-dependent and -independent relaxation in the rat isolated aortic rings. Pretreatment with tetrabutylammonium concentration dependently reduced the endothelium-dependent relaxation induced by acetylcholine, cyclopiazonic acid and ionomycin. Tetrabutylammonium also inhibited endothelium-independent relaxation induced by hydroxylamine or nitroprusside. Pretreatment of endothelium-denuded rings with tetrabutylammonium did not affect relaxation induced by NS1619 or by diltiazem. In contrast, tetrabutylammonium significantly reduced the pinacidil- or cromakalim-induced relaxation. Tetrabutylammonium also inhibited the acetylcholine- but not nitroprusside-induced increase of tissue content of cyclic GMP in the aortic rings. The present study indicates that tetrabutylammonium ions could inhibit endothelial and exogenous nitric oxide-mediated aortic relaxation while it had no effect on relaxation induced by activation of Ca2+-activated K+ channels (by NS1619) or by inhibition of voltage-gated Ca2+ channels (by diltiazem). The inhibitory effect on pinacidil- and cromakalim-induced relaxation suggests that tetrabutylammonium ions also inhibit ATP-sensitive K+ channels in aortic smooth muscle cells.
authors.affiliation: Department of Physiology, Chinese University of Hong Kong, People's Republic of China. yu-huang@cuhk.edu.hk
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.forename: J P
authors.initials: JP
authors.lastname: Bourreau
authors.forename: H Y
authors.initials: HY
authors.lastname: Chan
authors.forename: C W
authors.initials: CW
authors.lastname: Lau
authors.forename: J W
authors.initials: JW
authors.lastname: Wong
authors.forename: X
authors.initials: X
authors.lastname: Yao
mesh_terms: D000818:Animals; D002412:Cations; D006152:Cyclic GMP / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D066298:In Vitro Techniques; D009569:Nitric Oxide / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D015221:Potassium Channels / Q000819:agonists / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology*; D051381:Rats; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology
chemical_list: D002412:Cations; D020030:Nitric Oxide Donors; D015221:Potassium Channels; D000644:Quaternary Ammonium Compounds; D009569:Nitric Oxide; C009405:tetrabutylammonium; D006152:Cyclic GMP