Interactions of the gaseous neuromodulators nitric oxide, carbon monoxide, and hydrogen sulfide in the salamander retina.J Neurosci Res. 2009 Aug 01; 87(10):2356-64.JN
The three gaseous neuromodulators nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S) are endogenously produced in vertebrate retinas. The NO/cyclic guanosine monophosphate (cGMP) and CO/cGMP pathways have been previously shown to interact synergistically in the turtle retina to increase cGMP levels. In this study, we examined H2S as a modulator of cGMP-like immunoreactivity (-LI) and its interactions with the NO/CO/cGMP signaling pathways in the tiger salamander retina. Stimulation with NO donor or CO significantly increased cGMP-LI from basal levels in bipolar and amacrine cells and in stratified arborizations in the inner plexiform layer. Stimulation with a combination of NO donor and CO significantly increased cGMP-LI above that seen with either stimulation alone. Nitric oxide synthase inhibitors reduced CO-induced cGMP-LI, suggesting that CO-induced cGMP-LI is not produced from direct activation of soluble guanylate cyclase. Exogenous H2S alone, from the donor NaHS, did not significantly modify cGMP-LI in dosages ranging from 2 to 1,200 microM NaHS, but there was a significant decrease in NO-induced cGMP-LI in the presence of 200 muM NaHS. This reduction of NO-induced cGMP-LI was not significantly affected by the addition of CuCl2, suggesting that the decrease was not a result of H2S and NO sequestering to form a novel nitrosothiol. NaHS did not have any significant effect on CO-induced cGMP-LI levels. Our results concur with previous studies showing synergistic interactions between NO and CO/cGMP retinal signaling pathways. We now show that H2S inhibits NO-induced cGMP-LI but not CO-induced cGMP-LI. In conclusion, all three gaseous neuromodulators have interactive roles in modulating retinal cGMP signaling.