Identification and characterization of beta-adrenergic receptors were attempted in particulate membrane fractions derived from isolated ciliary processes (CP) of rabbit eyes. High-affinity binding sites for 125I-hydroxybenzylpindolol (125I-HYP), a beta-adrenergic antagonist, were identified in particulate membrane fractions of homogenized CP that were recovered from discontinuous sucrose density gradients. Adenylate cyclase activity was recovered in the same fraction as the 125I-HYP binding sites. The dissociation constant of 125I-HYP for the high affinity site is 0.25 nM, with a minimum capacity of about 35 fmol/mg of protein. Adrenergic agonists and antagonists, including timolol, 1-alprenolol, d,1-propranolol, 1-isoproterenol, 1-epinephrine, and phentolamine, were examined for their ability to displace 125I-HYP from its binding site. The results were consistent with the identification of the high-affinity 125I-HYP binding sites as beta-adrenergic receptors. This is the first report which identifies by ligand binding techniques beta-adrenergic receptors in CP exclusive of iridial or other uveal tissue and supports the possibility of direct action of beta-adrenergic agents on the formation of aqueous humor.
