Characterization of alpha2 adrenergic receptor subtypes in human ocular tissue homogenates.

PURPOSE: To determine the predominant alpha2 adrenergic receptor subtypes present in the human eye.

METHODS

Saturation- and competition-receptor- binding experiments were performed with the radioligand [3H]RX821002 in human ciliary body, retinal pigmented epithelium-choriocapillaris, iris, and neurosensory retina. The affinities of various adrenergic antagonists in these ocular tissues were compared with their affinities for the cloned alpha2A, alpha2B, and alpha2C adrenergic receptor subtypes.

RESULTS

The density of alpha2 adrenergic receptors was highest in the iris (440 femtomoles/mg protein), lowest in the neurosensory retina (14 femtomoles/mg protein), and intermediate in the other two tissues (approximately 90 fmol/mg protein). The drug affinities in all four human ocular tissues were highly correlated (correlation coefficients between 0.94 and 0.97) with the affinities for the human alpha2A adrenergic receptor subtype and poorly correlated (correlation coefficients between 0.15 and 0.66) with the alpha2B and alpha2C subtypes.

CONCLUSIONS

In agreement with previous studies in several animal species, the alpha2 adrenergic receptors in the human ciliary body, retinal pigmented epithelium-choriocapillaris, iris, and neurosensory retina are predominately of the alpha2A subtype.