Characterization of alpha2 adrenergic receptor subtypes in human ocular tissue homogenates.
OBJECTIVE
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.
Bylund
D B
DB
Department of Pharmacology, University of Nebraska Medical Center, Omaha 68198-6260, USA. dbylund@unmc.edu
Chacko
D M
DM
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D001667:Binding, Competitive; D002829:Choroid / Q000187:drug effects / Q000378:metabolism; D002924:Ciliary Body / Q000187:drug effects / Q000378:metabolism; D005123:Eye / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D019329:Idazoxan / Q000031:analogs & derivatives / Q000494:pharmacology; D007498:Iris / Q000187:drug effects / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000187:drug effects / Q000378:metabolism; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000378:metabolism
C547768:ADRA2A protein, human; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; C058525:2-methoxyidazoxan; D019329:Idazoxan