Euryhaline pufferfish NBCe1 differs from nonmarine species NBCe1 physiology

• Published in: American Journal of Physiology: Cell Physiology Vol. 302; no. 8; pp. C1083 - C1095
• Main Authors: Chang, Min-Hwang, Plata, Consuelo, Kurita, Yukihiro, Kato, Akira, Hirose, Shigehisa, Romero, Michael F
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 15.04.2012
• Subjects: 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid - pharmacology; Amino Acid Substitution - drug effects; Animals; Bicarbonates - metabolism; Biological Transport - drug effects; Epithelial Cells - drug effects; Epithelial Cells - metabolism; Epithelial Cells - physiology; Female; Fish; Gene expression; Humans; Kidneys; Kinetics; Lithium - metabolism; Marine; Membrane Potentials - drug effects; Membrane Transporters, Ion Channels and Pumps; Nonnative species; Salt; Sodium - metabolism; Sodium-Bicarbonate Symporters - genetics; Sodium-Bicarbonate Symporters - metabolism; Takifugu - genetics; Takifugu - metabolism; Takifugu - physiology; Takifugu obscurus; Teleostei; Xenopus; Xenopus laevis
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.00233.2011

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 K(m)) 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.