Na+/H+ and Na+/NH4 + exchange activities of zebrafish NHE3b expressed in Xenopus oocytes

Yusuke Ito, Akira Kato, Taku Hirata, Shigehisa Hirose, Michael F Romero

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

Zebrafish Na+H+ exchanger 3b (zNHE3b) is highly expressed in the apical membrane of ionocytes where Na+ is absorbed from ion-poor fresh water against a concentration gradient. Much in vivo data indicated that zNHE3b is involved in Na+ absorption but not leakage. However, zNHE3b-mediated Na+ absorption has not been thermodynamically explained, and zNHE3b activity has not been measured. To address this issue, we overexpressed zNHE3b in Xenopus oocytes and characterized its activity by electrophysiology. Exposure of zNHE3b oocytes to Na+-free media resulted in significant decrease in intracellular pH (pHi) and intracellular Na+ activity (aNai). aNai increased significantly when the cytoplasm was acidified by media containing CO2-HCO3- or butyrate. Activity of zNHE3b was inhibited by amiloride or 5-ethylisopropyl amiloride (EIPA). Although the activity was accompanied by a large hyperpolarization of ~50 mV, voltage-clamp experiments showed that Na+/H+ exchange activity of zNHE3b is electroneutral. Exposure of zNHE3b oocytes to medium containing NH3/NH4 + resulted in significant decreases in pHi and aNai and significant increase in intracellular NH4 + activity, indicating that zNHE3b mediates the Na+/NH4 + exchange. In low-Na+ (0.5 mM) media, zNHE3b oocytes maintained aNai of 1.3 mM, and Na+-influx was observed when pHi was decreased by media containing CO2-HCO3- or butyrate. These results provide thermodynamic evidence that zNHE3b mediates Na+ absorption from ion-poor fresh water by its Na+/H+ and Na+/NH4 + exchange activities.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume306
Issue number5
DOIs
StatePublished - Mar 1 2014

Fingerprint

Sodium-Hydrogen Antiporter
Zebrafish
Xenopus
Oocytes
Butyrates
Fresh Water
Ions
Amiloride
Electrophysiology
Thermodynamics
Cytoplasm

Keywords

  • Ammonium
  • Intracellular pH
  • NHE3
  • Xenopus oocyte electrophysiology
  • Zebrafish

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)
  • Medicine(all)

Cite this

Na+/H+ and Na+/NH4 + exchange activities of zebrafish NHE3b expressed in Xenopus oocytes. / Ito, Yusuke; Kato, Akira; Hirata, Taku; Hirose, Shigehisa; Romero, Michael F.

In: American Journal of Physiology - Regulatory Integrative and Comparative Physiology, Vol. 306, No. 5, 01.03.2014.

Research output: Contribution to journalArticle

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