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G. M. Sumida, W. Stamer; Sphingosine-1-Phosphate Receptor Antagonist Increases Outflow Facility. Invest. Ophthalmol. Vis. Sci. 2010;51(13):152.
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Sphingosine 1-phosphate (S1P) decreases outflow facility in both porcine and human perfused eyes and the S1P1 and S1P3 receptors are expressed by cells that populate the conventional outflow pathway, namely trabecular meshwork (TM) and Schlemm’s canal (SC) endothelial cells. Using S1P receptor antagonists, the aim of this study was to determine the relative involvement of the receptor subtypes in the S1P-mediated effects on outflow facility.
Porcine eyes in organ-culture were perfused at 15 mmHg constant pressure to obtain a baseline facility. Anterior chamber contents were then exchanged with 50 µM antagonist or antagonist + 5 µM S1P and further perfused. Control eyes were exchanged with media and S1P alone and normalized facilities (facility /baseline facility) were used to compare the treatment groups. 10 µM antagonists pre-incubated with TM and SC primary cells prior to S1P treatment (0.1, 1, and 10 µM) were used to block S1P-induced MLC phosphorylation. Phospho-MLC was detected via immunoblot analysis with β-actin used as a loading control.
W146 (S1P1 receptor antagonist) failed to block the S1P-induced decrease in outflow facility. Similarly, VPC23019 (S1P1,3 receptor antagonist) also did not block the decrease in outflow facility, but interestingly, anterior chamber exchange with media containing VPC23019 (1.52 ± 0.23, n=4) increased facility compared to media exchange (1.17 ± 0.21, n=7) after 1 hr of perfusion (mean normalized facility ± SD, p < 0.05). In both cultured TM and SC cells, W146 enhanced S1P-induced phosphorylation of MLC in all experiments (n=3). Responses with the inclusion of VPC23019 were variable.
The VPC23019-induced increase in outflow facility indicates the presence of a basal S1P receptor activation level in the outflow pathway. W146 effects on the phosphorylation status of MLC indicate that the S1P1 and S1P3 receptors may have opposing roles in regulating cell contractility. The inability of the antagonists tested to block S1P effects may suggest involvement of a separate S1P receptor subtype.
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