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G. M. Sumida, A. T. Read, K. M. Perkumas, W. D. Stamer, C. R. Ethier; S1P Receptor-Mediated Effects on Outflow Facility of Human Eyes in Organ Culture. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3927.
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The lipid mediator sphingosine 1-phosphate (S1P) decreases outflow facility in perfused porcine eyes and dramatically increases giant vacuole density with no obvious changes in the juxtacanalicular (JCT) region. These observations, along with known effects of S1P on junctional assembly between vascular endothelial cells, motivated us to determine the impact of S1P treatment on outflow facility in human eyes, where a complete Schlemm’s canal (SC) exists.
RT-PCR was used to determine the expression profile of the S1P1-5 receptor subtypes in 4 strains of cultured human SC endothelial cells (mature monolayers). S1P receptor expression was confirmed at the protein level by western blot analysis of total cell lysates. Paired ostensibly normal post mortem human eyes were perfused for 60-90 min at 8 mmHg constant pressure (equivalent to 15 mmHg in vivo) using standard techniques to measure a baseline facility. Anterior chamber contents were exchanged and eyes were further perfused for ~3 hours with 5.0 µM S1P (experimental) or vehicle (control).
In three of four human SC cell strains, S1P1-3 receptor subtypes were readily detectable by RT-PCR, whereas only S1P1 was detected in the fourth. Expression of S1P1-3 mRNA in SC cells was similar to human control cells (trabecular meshwork, microvascular endothelial, and umbilical vein endothelial) with S1P1 receptor being higher than either S1P2 or S1P3 receptors . S1P1-3 receptor expression was confirmed in SC cells by western blot. Densitometry analyses of blots showed that SC cells contained comparable levels of S1P1 receptor but ~2-fold greater amount of S1P3 receptor over all control cells. In perfusion studies, baseline outflow facilities were in the normal range (mean = 0.24 µl/min/mmHg; n = 8 pairs), decreasing gradually for 60-90 minutes after S1P administration. The net facility decrease due to S1P was 37 ± 22% (mean ± std. dev; p = 0.003).
S1P decreases outflow facility in human eyes. The facility-altering effects of S1P were previously ascribed to effects on trabecular meshwork cells, but the finding that S1P receptors are expressed on SC inner wall cells raises the possibility that S1P maybe acting directly on inner wall of SC.
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