PGE2, Ca, and cAMP mediate ATP activation of Cl channels in pigmented ciliary epithelial cells

Fleischhauer, Johannes C., Claire H. Mitchell, Kim Peterson-Yantorno, Miguel Coca-Prados, and Mortimer M. Civan. PGE2, Ca21, and cAMP mediate ATP activation of Cl channels in pigmented ciliary epithelial cells. Am J Physiol Cell Physiol 281: C1614–C1623, 2001.— 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 mM. UTP triggered ATP release. The second messengers Ca21, prostaglandin (PG)E2, and cAMP activated Cl channels without enhancing effects of 100 mM ATP. Buffering intracellular Ca21 activity with 1,2-bis(2-aminophenoxy)ethane-N,N,N9,N9tetraacetic acid or blocking PGE2 formation with indomethacin inhibited ATP-triggered channel activation. The Rp stereoisomer of 8-bromoadenosine 39,59-cyclic monophosphothioate inhibited protein kinase A activity but mimicked 8-bromoadenosine 39,59-cyclic monophosphate. We conclude that nucleotides can act at .1 P2Y receptor to trigger a sequential cascade involving Ca21, 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.