Euryhaline pufferfish NBCe1 differs from nonmarine species NBCe1 physiology

Min Hwang Chang, Consuelo Plata, Yukihiro Kurita, Akira Kato, Shigehisa Hirose, Michael F. Romero

Research output: Contribution to journalArticle

19 Scopus citations

Abstract

Marine fish drink seawater and eliminate excess salt by active salt transport across gill and gut epithelia. Euryhaline pufferfish (Takifugu obscurus, mefugu) forms a CaCO 3 precipitate on the luminal gut surface after transitioning to seawater. NBCe1 (Slc4a4) at the basolateral membrane of intestinal epithelial cell plays a major role in transepithelial intestinal HCO 3 - secretion and is critical for mefugu acclimation to seawater. We assayed fugu-NBCe1 (fNBCe1) activity in the Xenopus oocyte expression system. Similar to NBCe1 found in other species, fNBCe1 is an electrogenic Na +/HCO 3 - cotransporter and sensitive to the stilbene inhibitor DIDS. However, our experiments revealed several unique and distinguishable fNBCe1 transport characteristics not found in mammalian or other teleost NBCe1-orthologs: electrogenic Li +/nHCO 3 - cotransport; HCO 3 - independent, DIDS-insensitive transport; and increased basal intracellular Na +accumulation. fNBCe1 is a voltage-dependent Na +/nHCO 3 - cotransporter that rectifies, independently from the extracellular Na + or HCO 3 - concentration, around -60 mV. Na + removal (0Na + prepulse) is necessary to produce the true HCO 3 --elicited current. HCO 3 -addition results in huge outward currents with quick current decay. Kinetic analysis of HCO 3 - currents reveals that fNBCe1 has a much higher transport capacity (higher maximum current) and lower affinity (higher Km) than human kidney NBCe1 (hkNBCe1) does in the physiological range (membrane potential = -80 mV; [HCO 3 -] = 10 mM). In this state, fNBCe1 is in favor of operating as transepithelial HCO 3 - secretion, opposite of hkNBCe1, from blood to the luminal side. Thus, fugu-NBCe1 represents the first ortholog-based tool to study amino acid substitutions in NBCe1 and how those change ion and voltage dependence.

Original languageEnglish (US)
Pages (from-to)C1083-C1095
JournalAmerican Journal of Physiology - Cell Physiology
Volume302
Issue number8
DOIs
StatePublished - Apr 15 2012

Keywords

  • Acid-base
  • Bicarbonate secretion
  • Electrophysiology
  • Euryhaline teleost
  • Intracellular ph
  • Mefugu
  • Membrane current
  • Sodium-bicarbonate cotransporter
  • Xenopus oocyte

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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