Hydrogen sulfide (H₂S), which is produced by astrocytes in the central nervous system, inhibits the mitochondrial electron transport chain (ETC). We have previously shown that H₂S releases Ca²⁺ from the endoplasmic reticulum (ER) in spinal cord astrocytes. Here, we examined the relationship between H₂S-induced metabolic changes and Ca²⁺ response.
Intracellular Ca²⁺ concentration ([Ca²⁺]_i) in cultured rat spinal cord astrocytes was measured using Fura 2-AM. Na₂S was used as a H₂S donor. The extracellular lactate and intracellular ATP were measured by enzymatic reaction using lactate dehydrogenase and luciferase, respectively.
Na₂S (150 µM) increased [Ca²⁺]_i, which was inhibited by rotenone, an ETC inhibitor, and FCCP, an uncoupler of oxidative phosphorylation. Na₂S also increased extracellular lactate, and decreased intracellular ATP content when glycolysis was inhibited by iodoacetic acid. The increase in both Ca²⁺ and extracellular lactate by Na₂S were inhibited by emetine, an inhibitor of translocon complex, which mediates Ca²⁺ leak from the ER.
In conclusion, inhibition of the mitochondrial ETC by H₂S induces Ca²⁺ release from the ER and lactate production in spinal cord astrocytes. H₂S may facilitate the supply of lactate from astrocytes to neurons as an energy substrate.