Hydrogen sulphide regulates calcium homeostasis in microglial cells

Hydrogen sulphide (H2S), which is produced endogenously from L-cysteine in mammalian tissues, has been suggested to function as a neuromodulator in the brain. However, the role of H2S in microglial cells is unclear. In this study, the effect of exogenous and endogenous H2S on intracellular calcium homeostasis was investigated in primary cultured microglial cells. Sodium hydrosulphide (NaHS), a H2S donor, caused a concentration-dependent (0.1-0.5 mM) increase in intracellular calcium concentration ([Ca2+]i). This effect was significantly attenuated in the presence of a calcium-free extracellular solution, Gd3+ (100 microM), a nonselective Ca2+ channel blocker, or thapsigargin (2 microM), an inhibitor of the sarcoplasmic/endoplasmic reticulum Ca2+ -ATPase. These observations suggest that the increase in [Ca2+]i in response to H2S involves both calcium influx across the plasma membrane and calcium release from intracellular stores. The H2S-induced calcium elevation is partly attenuated by H-89, a selective cAMP-dependent protein kinase (PKA) inhibitor, but not by U73122, a phospholipase C (PLC) inhibitor, and chelerythrine, a selective protein kinase C (PKC) inhibitor, suggesting the involvement of cAMP/PKA, but not PLC/PKC/phosphoinositol-3,4,5-inositol (IP3) pathway. Using RT-PCR, only cystathionine gamma-lyase (CSE), a H2S producing enzyme, was detected in primary cultures of microglia. Lowering endogenous H2S level with, D,L-propargylglycine and beta-cyano-L-alanine, two CSE inhibitors, significantly decreased [Ca2+]i, suggesting that endogenous H2S may have a positive tonic influence on [Ca2+]i homeostasis. These findings support the possibility that H2S may serve as a neuromodulator to facilitate signaling between neurons and microglial cells.