Alpha-adrenoceptor subtypes and Ca2+ mobilization in the rabbit ear artery.
The mobilization of cellular and extracellular Ca2+ pools by selective alpha 1-adrenoceptor (phenylephrine) and alpha 2-adrenoceptor (xylazine) agonists as well as noradrenaline was evaluated in rabbit ear artery. Noradrenaline and phenylephrine possess full intrinsic activity for both types of Ca2+ mobilization whereas xylazine up to 1 mM had only a limited contractile effect, being more effective in inducing extracellular Ca2+-dependent response. However, extracellular Ca2+ was mobilized by xylazine in a concentration 20 times higher than that required to stimulate pre-junctional alpha 2-adrenoceptors. Noradrenaline (5 microM) and xylazine (1 mM) induced cellular and extracellular Ca2+-dependent contractions which were prazosin-sensitive and yohimbine-resistant. Xylazine-induced contractile activity, particularly that dependent upon the extracellular Ca2+ pool, was markedly reduced by selective adrenergic denervation with 6-hydroxydopamine, but the actions of noradrenaline were unaffected. These results suggest that: (1) rabbit ear artery contain post-junctional alpha 1-adrenoceptor but not alpha 2-adrenoceptors; (2) stimulation of these alpha 1-adrenoceptors can account for the overall contractile activity of exogenously added noradrenaline and (3) stimulation of alpha 1-adrenoceptors results in mobilization of cellular as well as extracellular Ca2+ pools.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004347:Drug Interactions; D006892:Hydroxydopamines / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology; D016627:Oxidopamine; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D014661:Vasoconstriction / Q000187:drug effects; D014991:Xylazine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
D006892:Hydroxydopamines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D014991:Xylazine; D015016:Yohimbine; D016627:Oxidopamine; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin