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L. M. Highstrom, D. F. Woodward, W. D. Stamer; Characterization of Prostaglandin EP4 Receptors in Human Conventional Outflow Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):809.
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Prostaglandin EP4 receptors are expressed by both trabecular meshwork (TM) and Schlemm’s canal (SC) cells of the conventional outflow pathway. Activation of EP4 receptors in monkeys efficaciously lowers intraocular pressure, while having no effect on aqueous secretion or uveoscleral outflow. We hypothesize that prostaglandin EP4 receptors regulate human conventional outflow.
To test this idea, cAMP accumulation was used as an indicator of receptor activation in primary cultures of confluent and mature human TM and SC cells that were treated with increasing concentrations of a selective EP4 agonist (3,7-dithiaPGE1) with or without forskolin (FSK). HEK 293 cells stably transfected with prostaglandin EP4 and EP2 receptors were used as controls. Intracellular cAMP accumulation was measured using a PKA binding assay and data were analyzed using GraphPad statistical analysis software.
Treatment with 3,7-dithiaPGE1 resulted in a dose-related increase in cAMP accumulation in both SC (EC50=9.76 x 106, n=4) and TM (EC50=8.66 x 107, n=6) cells. By comparison, 3,7-dithiaPGE1 treatment increased cAMP accumulation in both EP4 HEK 293 cells (EC50=2.85 x 1010, n=4) and EP2 HEK293 cells (EC50=3.9 x 107, n=4), exhibiting a 1000 fold difference in relative potency. Interestingly, other studies showed that 3,7-dithiaPGE1 treatment affects cAMP accumulation in FSK-pretreated SC cells in a dose-dependent manner at concentrations corresponding to prostaglandin EP4 receptor activity (n=4).
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