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: Radioligand saturation and inhibition binding assays were performed with the antagonist radioligands [3H]RX821002 and [3H]rauwolscine.

Results: [3H]RX821002 bound to a single class of receptors with the characteristics of an alpha-2 adrenergic receptor with an affinity (KD) of 0.16 nM and a receptor density (Bmax) of 1500 fmol/mg protein. Correlation of the affinities (pKi values) for nine antagonists in the bovine neurosensory retina with the alpha-2D receptor of the bovine pineal gave a correlation coefficient of 0.99. The correlation coefficients for the 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-2C receptors was excluded.

Conclusions: A high density of alpha-2D adrenergic receptors is present in the bovine neurosensory retina. Neither the alpha-2B nor the alpha-2C subtype is detectable.