Hydrogen sulfide inhibits Na+ uptake in larval zebrafish, Danio rerio

The present study investigated the role of hydrogen sulfide (H2S) in regulating Na+ uptake in larval zebrafish, Danio rerio. Waterborne treatment of larvae at 4 days post-fertilization (dpf) with Na2S or GYY-4137 (chemicals known to generate H2S) significantly reduced Na+ uptake. Exposure of larvae to water enriched with NaCl (1 mM NaCl) caused a pronounced reduction in Na+ uptake which was prevented by pharmacological inhibition of cystathionine beta-synthase (CBS) or cystathionine gamma-lyase (CSE), two key enzymes involved in the endogenous synthesis of H2S. Furthermore, translational gene knockdown of CSE and CBSb significantly increased the basal rate of Na+ uptake. Waterborne treatment with Na2S significantly decreased whole-body acid excretion and reduced Na+ uptake in larval zebrafish preexposed to acidic (pH 4.0) water (a condition shown to promote Na+ uptake via Na+-H+-exchanger 3b, NHE3b). However, Na2S did not affect Na+ uptake in larvae depleted of NHE3b-containing ionocytes (HR cells) after knockdown of transcription factor glial cell missing 2 (gcm2) in which Na+ uptake occurs predominantly via Na+-Cl- co-transporter (NCC)-containing cells. These observations suggest that Na+ uptake via NHE3b, but not NCC, is regulated by H2S. Whole-mount immunohistochemistry demonstrated that ionocytes expressing NHE3b also express CSE. These data suggests a physiologically relevant role of H2S as a mechanism to lower Na+ uptake in zebrafish larvae, probably through its inhibitory action on NHE3b.