Characterization of Alpha-2D Adrenergic Receptor Subtypes in Bovine Ocular Tissue Homogenates
- Departments of 1Pharmacology (D.B.B., L.J.I., W.J.M.) and2Ophthalmology (D.M.C.), University of Nebraska Medical Center, Omaha, Nebraska
Abstract
The alpha-2 adrenergic receptors are known to be present in the mammalian eye and to mediate the effects ofalpha-2 agonists used in the treatment of glaucoma. Little is known, however, regarding the relative densities of the threealpha-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. TheK D values in the three tissues were similar (0.12–0.14 nM), and the B maxvalues 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 thealpha-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 theK 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.
Footnotes
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Send reprint requests to: David B. Bylund, Ph.D., Department of Pharmacology, University of Nebraska Medical Center, 600 South 42nd Street, Box 986260, Omaha, NE 68198-6260.
- Abbreviation:
- RPE
- retinal pigment epithelium
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- Received June 13, 1996.
- Accepted February 3, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
