title: Venoconstriction to endothelin-1 in humans: role of calcium and potassium channels.
abstract: Recent studies in vitro have suggested that there may be an interaction between endothelin-1 and ATP-sensitive K+ channels in vascular smooth muscle. Here we have investigated whether agents acting on membrane Ca2+ and K+ channels modulate endothelin-1-induced venoconstriction in vivo in human subjects. In a series of studies, six healthy subjects received, on separate occasions, local infusions into dorsal hand veins of endothelin-1 coinfused with 1) the ATP-sensitive K+ channel opener, cromakalim; 2) the dihydropyridine Ca2+ antagonist, nicardipine; 3) a control vasodilator, hydralazine; and 4) saline placebo. Endothelin-1 caused local venoconstriction with a maximum reduction in vein size of 66 +/- 4% at 60 min (P = 0.0001 vs. basal). Cromakalim prevented endothelin-1-induced venoconstriction (9 +/- 10% maximum constriction; P = 0.68 vs. basal). By contrast, nicardipine, in a dose sufficient to block depolarization-induced constriction caused by K+ infusion, had only a partial effect on endothelin-1-induced venoconstriction (35 +/- 8% maximum constriction; P = 0.001 vs. basal; P = 0.02 vs. endothelin-1), whereas a 10-fold higher dose of nicardipine had no additional effect and hydralazine had no effect. In further studies, cromakalim, but not nicardipine, reversed endothelin-1-induced venoconstriction. Cromakalim did not prevent constriction induced by norepinephrine. Although calcium entry through dihydropyridine-sensitive Ca2+ channels may account in part for the vasoconstrictor action of endothelin-1 in humans, the abolition of endothelin-1 responses by a K+ channel opener suggests additional mechanisms of action for endothelin-1.
authors.affiliation: Department of Medicine, Western General Hospital, University of Edinburgh, United Kingdom.
authors.forename: W G
authors.initials: WG
authors.lastname: Haynes
authors.forename: D J
authors.initials: DJ
authors.lastname: Webb
mesh_terms: D000328:Adult; D001578:Benzopyrans / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D019806:Cromakalim; D003971:Diastole / Q000187:drug effects; D016232:Endothelins / Q000008:administration & dosage / Q000494:pharmacology*; D006225:Hand / Q000294:innervation; D006801:Humans; D006830:Hydralazine / Q000494:pharmacology; D007262:Infusions, Intravenous; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009529:Nicardipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D011758:Pyrroles / Q000494:pharmacology; D013599:Systole / Q000187:drug effects; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology; D014680:Veins / Q000187:drug effects / Q000502:physiology*
chemical_list: D001578:Benzopyrans; D015220:Calcium Channels; D016232:Endothelins; D015221:Potassium Channels; D011758:Pyrroles; D014665:Vasodilator Agents; D019806:Cromakalim; D006830:Hydralazine; D009529:Nicardipine; D011188:Potassium; D009638:Norepinephrine