Hydrogen sulphide regulates calcium homeostasis in microglial cells

Hydrogen sulphide (H 2 S), 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 H 2 S in microglial cells is unclear. In this study, the effect of exogenous and endogenous H 2 S on intracellular calcium homeostasis was investigated in primary cultured microglial cells. Sodium hydrosulphide (NaHS), a H 2 S donor, caused a concentration‐dependent (0.1–0.5 mM) increase in intracellular calcium concentration ([Ca 2+ ] i ). This effect was significantly attenuated in the presence of a calcium‐free extracellular solution, Gd 3+ (100 μM), a nonselective Ca 2+ channel blocker, or thapsigargin (2 μM), an inhibitor of the sarcoplasmic/endoplasmic reticulum Ca 2+ ‐ATPase. These observations suggest that the increase in [Ca 2+ ] i in response to H 2 S involves both calcium influx across the plasma membrane and calcium release from intracellular stores. The H 2 S‐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 (IP 3 ) pathway. Using RT‐PCR, only cystathionine γ‐lyase (CSE), a H 2 S producing enzyme, was detected in primary cultures of microglia. Lowering endogenous H 2 S level with, D , L ‐propargylglycine and β‐cyano‐ L ‐alanine, two CSE inhibitors, significantly decreased [Ca 2+ ] i , suggesting that endogenous H 2 S may have a positive tonic influence on [Ca 2+ ] i homeostasis. These findings support the possibility that H 2 S may serve as a neuromodulator to facilitate signaling between neurons and microglial cells. © 2006 Wiley‐Liss, Inc.