Hydrogen sulfide (H2S) has recently been recognized as a signaling molecule as well as a cytoprotectant. Cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE) are well-known as H2S-producing enzymes. We recently demonstrated that 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase (CAT) produces H2S in the brain and in vascular endothelium. However, the cellular distribution and regulation of these enzymes are not well understood. Here we show that 3MST and CAT are localized to retinal neurons and that the production of H2S is regulated by Ca2+; H2S, in turn, regulates Ca2+ influx into photoreceptor cells by activating vacuolar typeH(+)-ATPase (V-ATPase). We also show that H2S protects retinal neurons from light-induced degeneration. The excessive levels of light exposure deteriorated photoreceptor cells and increased the number of TUNEL- and 8-hydroxy-2'-deoxyguanosine (8-OHdG)-positive cells. Degeneration was greatly suppressed in the retina of mice administered with NaHS, a donor of H2S. The present study provides a new insight into the regulation of H2S production and the modulation of the retinal transmission by H2S. It also shows a cytoprotective effect of H2S on retinal neurons and provides a basis for the therapeutic target for retinal degeneration.