Cultured human trabecular meshwork cells express functional alpha 2A adrenergic receptors.
OBJECTIVE
For the treatment of glaucoma, alpha-2 adrenergic receptor (alpha 2-AR) agonists are thought to lower intraocular pressure primarily by decreasing aqueous humor production. Effects on the outflow pathways, however, also may occur. To begin to examine this possibility, the authors characterized the alpha 2-AR subtypes present in cultures of human trabecular meshwork (HTM) cells using both immunofluorescence microscopy and functional measures of alpha 2-AR activation.


METHODS
For immunofluorescence microscopy, subtype-specific polyclonal antibodies that recognize each of the human alpha 2-AR subtypes (alpha 2A, alpha 2B, alpha 2C) were used. Functional studies involved the inhibition of forskolin-stimulated cyclic adenosine monophosphate (cAMP) production, the stimulation of mitogen-activated protein (MAP) kinase activity, and the stimulation of mitotic activity as reflected by the expression of proliferating cell nuclear antigen (PCNA).


RESULTS
From the immunofluorescence microscopy, there was evidence for the presence of the alpha 2A subtype, but not alpha 2B or alpha 2C subtype, on HTM cells. The administration of the alpha 2-agonist, dexmedetomidine, to HTM cells resulted in a 90% inhibition of forskolin-stimulated cAMP formation, a twofold stimulation of MAP kinase activity, and a threefold increase in the expression of PCNA. Additionally, preincubation of cells with either of the alpha 2-AR-selective antagonists, rauwolscine or atipamezole, reversed the functional effects of dexmedetomidine.


CONCLUSIONS
Functional alpha 2A-ARs are present on HTM cells where they may affect the outflow pathway during the treatment of glaucoma with alpha 2-AR agonists.
Stamer
W D
WD
Department of Pharmacology/Toxicology, University of Arizona, Tucson 85721, USA.
Huang
Y
Y
Seftor
R E
RE
Svensson
S S
SS
Snyder
R W
RW
Regan
J W
JW
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000328:Adult; D000368:Aged; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002478:Cells, Cultured; D005576:Colforsin / Q000037:antagonists & inhibitors / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D008856:Microscopy, Fluorescence; D008875:Middle Aged; D008938:Mitosis; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D014129:Trabecular Meshwork / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018809:Proliferating Cell Nuclear Antigen; D018341:Receptors, Adrenergic, alpha-2; D005576:Colforsin; D000242:Cyclic AMP; D017871:Calcium-Calmodulin-Dependent Protein Kinases