Human retinal pigment epithelial cells possess beta 2-adrenergic receptors

Beta-adrenergic receptors on cultured human retinal pigment epithelium were demonstrated by the binding of [125I]cyanopindolol. Its pharmacologic specificity was also examined. Specific [125I]cyanopindolol binding was saturable, with a dissociation constant of 130 pM and a receptor density of 12 fmol per one-half million cells, which is equivalent to 14,000 receptor sites per retinal pigment epithelial cell. Agonists competed for specific [125I]cyanopindolol binding, with the following rank order of potencies: (-)-isoproterenol > (-)-epinephrine > (-)-norepinephrine. Beta 2-selective antagonist ICI-118551 was approximately 3 log orders more potent than the beta 1-selective antagonist, betaxolol. These receptors were also coupled to an adenylate cyclase. These results suggest strongly that cultured human retinal pigment epithelial cells possess beta 2-adrenergic receptors. The potential significance of these findings with regard to retinal pigment epithelial functions is discussed herein.