Characterization of alpha-2D adrenergic receptor subtypes in bovine ocular tissue homogenates
Bylund, D.B.; Iversen, L.J.; Matulka, W.J.; Chacko, D.M.
Journal of Pharmacology and Experimental Therapeutics 281(3): 1171-1177
1997
ISSN/ISBN: 0022-3565 PMID: 9190850 Document Number: 483667
The alpha-2 adrenergic receptors are known to be present in the mammalian eye and to mediate the effects of alpha-2 agonists used in the treatment of glaucoma. Little is known, however, regarding the relative densities of the three alpha-2 subtypes in the various tissues of the eye. We used receptor binding experiments with the radioligand (3H)RX821002 to characterize the alpha-2 adrenergic receptors in three tissues of the bovine eye, the ciliary body, retinal pigment epithelium/choriocapillaris and iris. The K-D values in the three tissues were similar (0.12-0.14 nM), and the B-max values ranged from 100 fmol/mg of protein for the ciliary body and retinal pigment epithelium/choriocapillaris to 200 fmol/mg of protein for the iris. The pharmacological characteristics of the alpha-2 receptors in all three tissues of the bovine eye, as assessed by competition studies, were essentially identical and were similar to the characteristics of the alpha-2A/D receptors of the bovine neurosensory retina. The correlation coefficients between the logarithms of the K-i values for the three tissues and the neurosensory retina for nine adrenergic agents were .98 to .99. We conclude that the alpha-2 adrenergic receptors in the ciliary body, iris and retinal pigment epithelium/choriocapillaris of the bovine eye are mainly alpha-2D.