Interaction between hydrogen sulfide, nitric oxide, and carbon monoxide pathways in the bovine isolated retina

Purpose: Nitric oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S) are physiologically relevant gaseous neurotransmitters that are endogenously produced in mammalian tissues. In the present study, we investigated the possibility that NO and CO can regulate the endogenous levels of H2S in bovine isolated neural retina. Methods: Isolated bovine neural retina were homogenized and tissue homogenates were treated with a NO synthase inhibitor, NO donor, heme oxygenase-1 inhibitor, and/donor. H2S concentrations in bovine retinal homogenates were measured using a well-established colorimetric assay. Results: L-NAME (300 nM-500 mu M) caused a concentration-dependent decrease in basal endogenous levels of H2S by 86.2%. On the other hand, SNP (10-300 mu M) elicited a concentration-related increase in H2S levels from 18.3 nM/mg of protein to 65.7 nM/mg of protein. ZnPP-IX (300 nM-10 mu M) caused a concentration-dependent increase in the endogenous production of H2S whereas hemin (300 nM-20 mu M) attenuated the basal levels of H2S. Conclusion: We conclude that changes in the biosynthesis and availability of both NO and CO can interfere with the pathway/s involved in the production of H2S in the retina. The demonstrated ability of NO, CO and H2S to interact in the mammalian retina affirms a physiological/pharmacological role for these gaseous mediators in the eye.