Arylazide photoaffinity probe for α₂-adrenoceptors

An arylazide photoaffinity probe for α₂-adrenoceptors has been developed and characterized. The compound, 3-methyl-6-chloro-9-azido-1H-2,3,4,5-tetrahydro-3-benzazepine (SKF 102229), had a K_i for the human platelet α₂-adrenoceptor of ~40 nM. Upon exposure to ultraviolet light, SKF 102229 irreversibly blocked the binding of [³H]yohimbine to both membrane bound and solubilized, partially purified, receptors. The extent of α₂-adrenoceptor blockade was dependent upon both the length of exposure to ultraviolet light and the concentration of SKF 102229. Typically, a 60% decrease in α₂-adrenoceptor number is obtained following 8 min of photolysis in the presence of 100 nM SKF 102229. The pharmacologic characteristics of the irreversible blockade produced by SKF 102229 were those of an α₂-adrenoceptor. Thus, photodependent, irreversible blockade of α₂-adrenoceptors by SKF 102229 was prevented by the concomitant presence of phentolamine or p-aminoclonidine but not by prazosin. Given its specificity and efficient blockade of the ligand binding site, SKF 102229 should prove useful for studies of the structure and function of α₂-adrenoceptors.