PATEL, S.B.; WOHLEGEMUTH, S.E.; JULIAN, D.; University of Florida, Gainesville: Mitochondrial injury induced by sulfide exposure in coelomyocytes from a sulfide-adapted marine invertebrate.
Exposure of animal cells to hydrogen sulfide (H2S) causes rapid cell death, but the mechanisms of toxicity are not completely known. Since H2S and cyanide both inhibit cytochrome c oxidase, the final electron acceptor of mitochondrial oxidative phosphorylation, it might be assumed that both toxins would have similar effects on mitochondrial membrane potential. In this study, we used coelomocytes from the intertidal polychaete Glycera dibranchiata to test whether exposure to H2S and cyanide each cause mitochondrial depolarization. Coelomocytes were isolated and loaded with the dye tetramethylrhodamine methyl ester (TMRM), which diffuses into healthy, polarized mitochondria where it forms a multimer that fluoresces at 585 nm when excited at 488 nm. The coelomocytes were then exposed to 0.1, 0.2, 0.3, 0.5, 0.75, 1.2 and 1.9 mM H2S or 10, 100 and 100 mM NaCN for up to 60 min (n = 4 at each concentration). H2S exposure caused significant mitochondrial depolarization even at 0.1 mM (P = .039), with maximal depolarization at 1.2 mM and an EC50 of 0.70 mM. This depolarization was not reversible, even after 12 h recovery. In contrast, NaCN did not cause a decrease in mitochondrial membrane potential, even at 100 mM, and in fact produced slightly increased fluorescence (P = .083). The mitochondrial decoupler CCCP (20 mM) produced depolarization with a magnitude and time-course nearly identical to that of H2S (n = 4). These results indicate that at least some mechanisms of H2S cytotoxicity differ from those of cyanide, and suggest that inhibition of cytochrome c oxidase is not the only, or perhaps even the most important, lethal mechanism of H2S exposure.
