PGE(2), Ca(2+), and cAMP mediate ATP activation of Cl(-) channels in pigmented ciliary epithelial cells.
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 microM. UTP triggered ATP release. The second messengers Ca(2+), prostaglandin (PG)E(2), and cAMP activated Cl(-) channels without enhancing effects of 100 microM ATP. Buffering intracellular Ca(2+) activity with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid or blocking PGE(2) 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 Ca(2+), PGE(2), and cAMP. cAMP acts directly on Cl(-) channels of PE cells, increasing stromal release and potentially reducing net aqueous humor formation and intraocular pressure.
Fleischhauer
J C
JC
Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Mitchell
C H
CH
Peterson-Yantorno
K
K
Coca-Prados
M
M
Civan
M M
MM
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002417:Cattle; D048429:Cell Size / Q000187:drug effects; D018118:Chloride Channels / Q000502:physiology*; D002924:Ciliary Body / Q000166:cytology / Q000502:physiology*; D000242:Cyclic AMP / Q000502:physiology*; D015232:Dinoprostone / Q000502:physiology*; D004847:Epithelial Cells / Q000502:physiology / Q000648:ultrastructure; D008156:Luciferases / Q000737:chemistry; D009711:Nucleotides / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010858:Pigmentation / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D014544:Uridine Triphosphate / Q000494:pharmacology
D018118:Chloride Channels; D009711:Nucleotides; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D008156:Luciferases; D015232:Dinoprostone; D002118:Calcium; D014544:Uridine Triphosphate