Modulation of aqueous humor outflow facility by the rho kinase-specific inhibitor Y-27632

PURPOSE. The goal of this study was to investigate the role of Rho kinase i n the modulation of aqueous humor outflow facility. Rho kinase, a critical downstream effector of Rho GTPase is recognized to control the formation of actin stress fibers, focal adhesions, and cellular contraction. METHODS. Expression of Rho GTPase, Rho kinase, and other downstream targets of Rho GTPase were determined in human trabecular meshwork (HTM) and Schle mm's canal (SC) primary cell cultures by Western blot analysis. The Rho kin ase-specific inhibitor (Y-27632)-induced changes in actin stress fibers, fo cal adhesions, and protein phosphotyrosine status were evaluated by stainin g with rhodamine-phalloidin, anti-paxillin, and anti-phosphotyrosine antibo dies. respectively. Myosin light-chain phosphorylation was determined by We stern blot analysis. Y-27632-induced changes in SC cell monolayer permeabil ity were quantitated using a colorimetric assay to evaluate horseradish per oxidase diffusion through SC cell monolayers grown in transwell chambers. A queous humor outflow facility was measured using enucleated porcine eyes an d a constant-pressure perfusion system. RESULTS. Treatment of HTM and SC cells with Y-27632 (10 muM) led to signifi cant but reversible changes in cell shape and decreases in actin stress fib ers, focal adhesions, and protein phosphotyrosine staining. SC cell monolay er permeability increased (by 80%) in response to Y-27632 (10 muM) treatmen t, whereas myosin light-chain phosphorylation was decreased in both HTM and SC cells. Aqueous humor outflow facility increased (40%- 80%) in enucleate d porcine eyes perfused with Y-27632 (10-100 muM), and this effect was asso ciated with widening of the extracellular spaces, particularly the opticall y empty area of the juxtacanalicular tissue (JCT). The integrity of inner w all of aqueous plexi, however, was observed to be intact. CONCLUSIONS. Based on the Rho kinase inhibitor-induced changes in myosin li ght-chain phosphorylation and actomyosin organization, it is reasonable to conclude that cellular relaxation and loss of cell-substratum adhesions in HTM and SC cells could result in either increased paracellular fluid flow a cross Schlemm's canal or altered flow pathway through the JCT, thereby lowe ring resistance to outflow. This study also suggests Rho kinase as a potent ial therapeutic target for the development of drugs to modulate intraocular pressure in glaucoma patients.