PURPOSE. There is a correlation between cell volume changes and changes in the rate of aqueous humor outflow; agents that decrease trabecular meshwork (TM) cell volume increase the rate of aqueous humor outflow. This study investigated the effects of the nitric oxide (NO)-independent activators of soluble guanylate cyclase (sGC), YC-1, and BAY-58-2667 on TM cell volume and the signal transduction pathways and ion channel involved. METHODS. Cell volume was measured with the use of calcein AM

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... rescent dye, detected by confocal microscopy. Inhibitors and activators of sGC, 3Ј,5Ј-cyclic guanosine monophosphate (cGMP), protein kinase G (PKG), and the BK Ca channel were used to characterize their involvement in the YC-1-and BAY-58-2667-induced regulation of TM cell volume. cGMP was assayed by an enzyme immunoassay. RESULTS. YC-1 (10 nM-200 M) and BAY-58-2667 (10 nM-100 M) each elicited a biphasic effect on TM cell volume. YC-1 (1 M) increased TM cell volume, but higher concentrations decreased TM cell volume. Similarly, BAY-58-2667 (100 nM) increased TM cell volume, but higher concentrations decreased cell volume. The YC-1-induced cell volume decrease was mimicked by 8-Br-cGMP and abolished by the sGC inhibitor ODQ, the PKG inhibitor (RP)-8-Br-PET-cGMP-S, and the BK Ca channel inhibitor IBTX. The BAY-58-2667-induced cell volume decrease was mimicked by 8-Br-cGMP and was abolished by the PKG inhibitor and the BK Ca channel inhibitor. Unlike the YC-1 response, ODQ potentiated the BAY-58-2667induced decreases in cell volume. CONCLUSIONS. These data suggest that the NO-independent decrease in TM cell volume is mediated by the sGC/cGMP/PKG pathway and involves K ϩ efflux. (Invest Ophthalmol Vis Sci.