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channels in pigmented ciliary
epithelial cells
Departments of 1 Physiology and 3 Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104; and 2 Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, Connecticut 06510
Purines regulate intraocular pressure. Adenosine activates
Cl
channels of nonpigmented ciliary epithelial cells
facing the aqueous humor, enhancing secretion. Tamoxifen and ATP
synergistically activate Cl channels of pigmented ciliary
epithelial (PE) cells facing the stroma, potentially reducing net
secretion. The actions of nucleotides alone on Cl channel
activity of bovine PE cells were studied by electronic cell sorting,
patch clamping, and luciferin/luciferase ATP assay. Cl
channels were activated by ATP > UTP, ADP, and UDP, but not by 2-methylthio-ATP, all at 100 µM. UTP triggered ATP release. The second messengers Ca2+, prostaglandin (PG)E2,
and cAMP activated Cl channels without enhancing effects
of 100 µM ATP. Buffering intracellular Ca2+
activity with
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid
or blocking PGE2 formation with indomethacin
inhibited ATP-triggered channel activation. The Rp stereoisomer
of 8-bromoadenosine 3',5'-cyclic monophosphothioate inhibited protein
kinase A activity but mimicked 8-bromoadenosine 3',5'-cyclic
monophosphate. We conclude that nucleotides can act at >1 P2Y
receptor to trigger a sequential cascade involving Ca2+,
PGE2, and cAMP. cAMP acts directly on Cl
channels of PE cells, increasing stromal release and potentially reducing net aqueous humor formation and intraocular pressure.
aqueous humor formation; P2Y receptors; adenosine 3',5'-cyclic monophosphate; prostaglandins; calcium
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