ALPHA ADRENERGIC-RECEPTORS IN BEEF AORTIC MEMBRANES CHARACTERIZED BY [H-3] DIHYDROERGOCRYPTINE BINDING

  • 1 January 1980
    • journal article
    • research article
    • Vol. 246  (2) , 237-250
Abstract
.alpha.-Adrenergic receptors of beef vascular smooth muscle membranes were identified and characterized using [3H] dihydroergocryptine as a radioligand. Under experimental conditions [3H] dihydroergocryptine binds rapidly and in saturable fashion to isolated beef aortic membranes, specific binding reaching equilibrium in 5 min at 37.degree. C. Scatchard analysis of the binding data indicates a single population of binding sites with the Kd of 10.4 nM and maximum number of binding sites equaling 156 f[femto]mol/mg membrane protein. The identity of [3H] dihydroergocryptine binding sites with the .alpha.-receptor was established by the competition studies. Catecholamines inhibited binding in the following order: (-) epinephrine > (-) norepinephrine > (.+-.) norepinephrine > (-) isoproterenol. .alpha.-Adrenergic antagonists (prazosin, phentolamine, ergotamine, dihydroergocryptine, yohimbine) are potent inhibitors of binding; the .beta.-adrenergic antagonist propranolol showed a weak affinity for the binding sites. The high affinity [3H] dihydroergocryptine binding sites evidently are identical to the vascular (.alpha.1) adrenergic receptor.

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