title: Rhcg1 and NHE3b are involved in ammonium-dependent sodium uptake by zebrafish larvae acclimated to low-sodium water.
abstract: To investigate whether Na(+) uptake by zebrafish is dependent on NH4(+) excretion, a scanning ion-selective electrode technique was applied to measure Na(+) and NH4(+) gradients at the yolk-sac surface of zebrafish larvae. Low-Na(+) acclimation induced an inward Na(+) gradient (uptake), and a combination of low Na(+) and high NH4(+) induced a larger inward Na(+) gradient. When measuring the ionic gradients, raising the external NH4(+) level (5 mM) blocked NH4(+) excretion and Na(+) uptake; in contrast, raising the external Na(+) level (10 mM) simultaneously enhanced Na(+) uptake and NH4(+) excretion. The addition of MOPS buffer (5 mM), which is known to block NH4(+) excretion, also suppressed Na(+) uptake. These results showed that Na(+) uptake and NH4(+) excretion by larval skin are associated when ambient Na(+) level is low. Knockdown of Rhcg1 translation with morpholino-oligonucleotides decreased both NH4(+) excretion and Na(+) uptake by the skin and Na(+) content of whole larvae. Knockdown of nhe3b translation or inhibitor (5-ethylisopropyl amiloride) treatment also decreased both the NH4(+) excretion and Na(+) uptake. This study provides loss-of-function evidence for the involvement of Rhcg1 and NHE3b in the ammonium-dependent Na(+) uptake mechanism in zebrafish larvae subjected to low-Na(+) water.
authors: Department of Life Science, National Taiwan Normal University, Taipei, Taiwan.
authors: Tin-Han
authors: TH
authors: Shih
authors: Jiun-Lin
authors: JL
authors: Horng
authors: Sian-Tai
authors: ST
authors: Liu
authors: Pung-Pung
authors: PP
authors: Hwang
authors: Li-Yih
authors: LY
authors: Lin
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000136:Acid-Base Equilibrium / Q000502:physiology; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D017736:Ion-Selective Electrodes; D023421:Models, Animal; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D054712:Salinity; D012964:Sodium / Q000378:metabolism*; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D014882:Water-Electrolyte Balance / Q000502:physiology; D015017:Yolk Sac / Q000378:metabolism; D015027:Zebrafish / Q000378:metabolism*; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; D000644:Quaternary Ammonium Compounds; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D029961:Zebrafish Proteins; C524419:rhcgb protein, zebrafish; D012964:Sodium