Changes in intracellular free Ca2+ concentration by activation of alpha-adrenoceptors in rat tail artery.
Changes in intracellular free Ca2+ concentration ([Ca2+]i) by activation of alpha 1- and alpha 2-adrenoceptors were microfluorometrically measured in rat tail arteries loaded with the Ca2(+)-sensitive fluorescent dye fura-2. Under the normal condition (1.8 mM Ca2+), stimulation with the selective alpha 1-adrenoceptor agonist phenylephrine very rapidly raised [Ca2+]i to the peak concentration, plateauing at this level, whereas the stimulation with the selective alpha 2-adrenoceptor agonist UK-14,304 gradually increased [Ca2+]i. In Ca2(+)-free solution, the stimulation of alpha 1-adrenoceptors caused a transient increase in [Ca2+]i, whereas the stimulation of alpha 2-adrenoceptors had no effect. These results directly prove that alpha 1-adrenoceptor activation induces both the release of intracellular Ca2+ and the influx of extracellular Ca2+, whereas activation of alpha 2-adrenoceptors evokes only the influx of extracellular Ca2+. Plotting the increase in [Ca2+]i against the developed contraction revealed that it was always linearly related regardless of the type of alpha-adrenoceptor stimulated. Therefore, the intracellular mechanisms after the increase in [Ca2+]i are probably common to the vasocontractile responses mediated by alpha 1- and alpha 2-adrenoceptors.
Abe
K
K
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
Saito
H
H
Matsuki
N
N
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D001572:Benzofurans; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000378:metabolism*; D016257:Fura-2; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012039:Regional Blood Flow / Q000187:drug effects; D013623:Tail / Q000098:blood supply; D014661:Vasoconstriction / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D001572:Benzofurans; D011810:Quinoxalines; D010656:Phenylephrine; D000068438:Brimonidine Tartrate; D002118:Calcium; D016257:Fura-2