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 (H 2 S) 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 H 2 S 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. H 2 S concentrations in bovine retinal homogenates were measured using a well-established colorimetric assay. Results: L-NAME (300 nM–500 μM) caused a concentration-dependent decrease in basal endogenous levels of H 2 S by 86.2%. On the other hand, SNP (10–300 μM) elicited a concentration-related increase in H 2 S levels from 18.3 nM/mg of protein to 65.7 nM/mg of protein. ZnPP-IX (300 nM–10 μM) caused a concentration-dependent increase in the endogenous production of H 2 S whereas hemin (300 nM–20 μM) attenuated the basal levels of H 2 S. 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 H 2 S in the retina. The demonstrated ability of NO, CO and H 2 S to interact in the mammalian retina affirms a physiological/pharmacological role for these gaseous mediators in the eye.