Biochemical characterization of histamine H1 receptors in bovine adrenal medulla

Bovine adrenal medullary membranes display high affinity and saturable binding to [3H]mepyramine, a selective H1 antagonist, with Kd of 1.5 +/- 0.1 nM and Bmax of 694 +/- 12 fmol/mg protein. [3H]Azidobenzpyramine, an azidobenzamide derivative of mepyramine, was synthesized and used to photolabel the high affinity mepyramine binding sites. Following photolysis, a protein component with an approximate molecular weight of 53-58 kDa was shown to be covalently labeled, as judged by gel filtration and SDS/PAGE; labeling being greatly reduced in the presence of excess unlabeled mepyramine. These results indicate that bovine adrenal medulla expresses a large number of H1 receptors, which are pharmacologically and biochemically indistinguishable from the H1 receptor of many other tissues of various species.