Purpose: Fluid flow across various endothelia results in a variety of intracellular and extracellular adaptations. In the living eye, aqueous humor flows across the surface of endothelial cells on trabecular meshwork (TM) beams and in the juxtacanalicular tissue and through or between a continuous monolayer of endothelial cells that line Schlemm's canal (SC). This study was undertaken to test the hypothesis that fluid flow induces biochemical changes in the endothelial cells of the outflow pathway that may modify outflow resistance.
Methods: Trabecular meshwork and SC cells isolated from the outflow pathway of human cadaveric eyes were seeded onto porous filters, placed in Ussing-type chambers, and subjected to fluid flow driven by a pressure head of 15 mm Hg on their apical surface. Cell lysates were prepared and analyzed for adenosine 3',5'-cyclic monophosphate (cAMP) accumulation. Barrier function of cell monolayers was examined using transendothelial electrical resistance measurements.
Results: Three different SC cell strains in 14 independent experiments responded with at least a threefold increase in cAMP that was both time and pressure dependent. Conversely, flow-treated TM cells failed to respond in six independent experiments in which five different TM cell strains were used. Electrical resistance across cell monolayers positively correlated with cAMP accumulation and was calcium sensitive.
Conclusions: cAMP signaling is affected by pressure differentials across SC cell monolayers and provides evidence for the participation of SC cells in the regulation of aqueous outflow.