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.