Classification of bovine aortic alpha-1 adrenoceptors by the criteria of ligand affinity and molecular mass.

[3H]Prazosin bound to a single class of alpha-1 adrenoceptors in bovine aortic membranes with a Kd of 25 pM. Digitonin solubilized 30% of the receptors as assayed by specific [3H] prazosin binding. The rank order potency of displacing ligands was the same for both membrane-bound and soluble alpha-1 adrenoceptors [prazosin greater than phentolamine greater than yohimbine and (-)-epinephrine = (-)-norepinephrine much greater than (+)-norepinephrine]. Prazosin had a significantly lower affinity for the soluble receptor, whereas the other adrenergic ligands had the same affinity for both forms of the receptor. The alpha-1 adrenoceptor was affinity-labeled with 2-[4-(4-azido-3-[125I]iodobenzoyl)piperazin-1-yl]-4-amino-6,7- dimethoxyquinazoline and analyzed by reducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The molecular mass of the receptor binding subunit in both bovine aorta and rat liver was found to be 86,000 MW. It is concluded from this study that bovine aortic alpha-1 adrenoceptors have pharmacologic and biochemical characteristics similar to those in other tissues.