Hydrogen sulfide promotes calcium uptake in larval zebrafish

Hydrogen sulfide (H2S) can act as a signalling molecule for various ion channels and/or transporters, however, little is known about its potential involvement in Ca2+ balance. Using developing zebrafish (Danio rerio) as an in vivo model system, the present study demonstrated that acute exposure to H2S donors increased Ca2+ influx at 4 days post fertilization (dpf) while chronic (3-day) exposure caused a rise in whole-body Ca2+ levels. The mRNA expression of Ca2+-transport related genes was unaffected by H2S exposure, suggesting that post-transcriptional modifications were responsible for the altered rates of Ca2+ uptake. Indeed, treatment of fish with the protein kinase A (PKA) inhibitor H-89 abolished the H2S-mediated stimulation of Ca2+ influx, suggesting that H2S increased Ca2+ influx by activating cAMP-PKA pathways. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) are two key enzymes in the endogenous synthesis of H2S. Using an antisense morpholino knockdown approach, we demonstrated that Ca2+ influx was reduced in CBSb- but not in CSE-deficient fish. Interestingly, the reduction in Ca2+ influx in CBSb-deficient fish was observed only in fish that were acclimated to low Ca2+ water (i.e., 25 µM Ca2+; control: 250 µM Ca2+). Similarly, mRNA expression of cbsb but not cse was increased in fish acclimated to low Ca2+ water. Results from whole-mount immunohistochemistry further revealed that CBSb was expressed in Na+/K+-ATPase-rich cells (NaR cells), which are implicated in Ca2+ uptake in zebrafish larvae. Collectively, the present study suggests a novel role for H2S in promoting Ca2+ influx, particularly in a low Ca2+ environment.