Assessing the role of the acid-sensing ion channel asic4b in sodium uptake by larval zebrafish

Zimmer, A.M., Dymowska, A.K., Kumai, Y., Goss, G.G., Perry, S.F., Kwong, R.W.M.
Comparative biochemistry and physiology. Part A, Molecular & integrative physiology   226: 1-10 (Journal)
Registered Authors
Goss, Greg, Perry, Steve F.
ASIC4b, Danio rerio, H(+)-ATPase rich cells, Ion regulation, Ionocytes, Sodium uptake
MeSH Terms
  • Acid Sensing Ion Channels/drug effects
  • Acid Sensing Ion Channels/metabolism
  • Acid Sensing Ion Channels/physiology*
  • Animals
  • Female
  • Indoles/pharmacology
  • Ion Transport
  • Larva/metabolism*
  • Male
  • Morpholinos/pharmacology
  • Sodium/metabolism*
  • Zebrafish/growth & development*
  • Zebrafish Proteins/metabolism
  • Zebrafish Proteins/physiology*
29913320 Full text @ Comp. Biochem. Physiol. A Mol. Integr. Physiol.
Na+ uptake in larval zebrafish (Danio rerio) is coordinated by three mechanisms: Na+/H+-exchanger 3b (NHE3b) expressed in H+-ATPase-rich (HR) cells, an unidentified Na+ channel coupled to electrogenic H+-ATPase expressed in HR cells, and Na+-Cl--cotransporter (NCC) expressed in NCC cells. Recently, acid-sensing ion channels (ASICs) were proposed to be the putative Na+ channel involved in H+-ATPase-mediated Na+ uptake in adult zebrafish and rainbow trout. In the present study, we hypothesized that ASICs also play this role in Na+ uptake in larval zebrafish. In support of this hypothesis, immunohistochemical analyses revealed that ASIC4b was expressed in HR cells on the yolk sac skin at 4 days post-fertilization (dpf). However, neither treatment with the ASIC-specific blocker 4,6-diamidino-2-phenylindole (DAPI) nor morpholino knockdown of ASIC4b reduced Na+ uptake in circumneutral conditions at 4 dpf. However, because ASIC4b knockdown led to significant increases in the mRNA expression of nhe3b and ncc and a significant increase in HR cell density, it is possible that Na+ influx was sustained by increased participation of non-ASIC4b pathways. Moreover, when fish were reared in acidic water (pH = 4), ASIC4b knockdown led to a stimulation of Na+ uptake at 3 and 4 dpf, results which also were inconsistent with an essential role for ASIC-mediated Na+ uptake, even under conditions known to constrain Na+ uptake via NHE3b. Thus, while ASIC4b clearly is expressed in HR cells, the current functional experiments cannot confirm its involvement in Na+ uptake in larval zebrafish.
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