Abstract
PurposeNitric 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.MethodsIsolated 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.ResultsL-NAME (300 nM–500 µM) caused a concentration-dependent decrease in basal endogenous levels of H2S by 86.2%. On the other hand, SNP (10–300 µM) 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 µM) caused a concentration-dependent increase in the endogenous production of H2S whereas hemin (300 nM–20 µM) attenuated the basal levels of H2S.ConclusionWe 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.
Highlights
The presence of enzymes responsible for the biosynthesis of hydrogen sulfide (H2S) from the amino acid, L-cysteine in mammalian tissues has stimulated a surge of interest in its potential physiological significance in biological processes [1,2]
We investigated the possibility that Nitric oxide (NO) and carbon monoxide (CO) can regulate the endogenous levels of Hydrogen sulfide (H2S) in bovine isolated neural retina
The basal production of H2S is dependent upon the activity of two pyridoxal-5′phosphate dependent-enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), whilst NO is synthesized from L-arginine by NO synthase and CO is endogenously produced from heme by heme oxygenase [10,11,12,13,14,15]
Summary
The presence of enzymes responsible for the biosynthesis of hydrogen sulfide (H2S) from the amino acid, L-cysteine in mammalian tissues has stimulated a surge of interest in its potential physiological significance in biological processes [1,2]. The three gaseous molecules are present in specific concentrations in disease states such as Alzheimer’s when their endogenous production is known to be compromised [6,7,8] These gases possess similar features and modes of action, H2S has been reported to exhibit a number of distinct characteristics from both NO and CO [7]. Under physiological conditions, CO/heme oxygenase and H2S/CSE pathways have been demonstrated to inhibit each other in aortic smooth muscle cells [29] It remains to be determined whether NO and CO can interact with the pathway leading to H2S biosynthesis in the retina. Parts of the work described in this paper have been communicated in an abstract form [30]
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