ALPHA-2-ADRENERGIC RECEPTORS IN THE BOVINE RETINA PRESENCE OF ONLY THE ALPHA-2D SUBTYPE

Purpose. To identify and characterize the alpha-2 adrenergic receptor subtypes present in the bovine neurosensory retina. Methods. Radioliga nd saturation and inhibition binding assays were performed with the an tagonist radioligands [H-3]RX821002 and [H-3]rauwolscine. Results. [H- 3] RX821002 bound to a single class of receptors with the characterist ics of an alpha-2 adrenergic receptor with an affinity (K-D) of 0.16 n M and a receptor density (B-max) of 1500 fmol/mg protein. Correlation of the affinities (pK(i) values) for nine antagonists in the bovine ne urosensory retina with the alpha-2D receptor of the bovine pineal gave a correlation coefficient of 0.99. The correlation coefficients for t he alpha-2A (0.84), alpha-2B (0.36), and alpha-2C (0.39) subtypes were much lower. The presence of a minor population of alpha-2B or alpha-2 C receptors was excluded. Conclusions. A high density of alpha-2D adre nergic receptors is present in the bovine neurosensory retina. Neither the alpha-2B nor the alpha-2C subtype is detectable.