Tissue-dependent variation of hydrogen sulfide homeostasis in anoxic freshwater turtles.

Hydrogen sulfide (H2S) controls numerous physiological responses. To understand its proposed role in metabolic suppression, we measured free H2S and bound sulfane sulfur (BSS) in tissues of the freshwater turtle Trachemys scripta elegans, a species undergoing strong metabolic suppression when cold and anoxic. In warm normoxic turtles, free H2S was higher in red blood cells (RBCs) and kidney (∼9-10 µmol l-1) than in brain, liver and lung (∼1-2 µmol l-1). These values overall aligned with the tissue H2S-generating enzymatic activity. BSS levels were similar in all tissues (∼0.5 µmol l-1) but ∼100-fold higher in RBCs, which have a high thiol content, suggesting that RBCs function as a circulating H2S reservoir. Cold acclimation caused significant changes in free and bound H2S in liver, brain and RBCs, but anoxia had no further effect, except in the brain. These results show tissue-dependent sulfide signaling with a potential role in brain metabolic suppression during anoxia in turtles.