Euryhaline pufferfish NBCe1 differs from nonmarine species NBCe1 physiology

Area of Science:

• Physiology
• Molecular Biology
• Comparative Biochemistry

Background:

• Marine fish adapt to saltwater by actively transporting salt across gill and gut epithelia.
• Euryhaline pufferfish (Takifugu obscurus) form CaCO(3) precipitates in the gut after seawater transition.
• NBCe1 (Slc4a4) is vital for intestinal bicarbonate secretion and pufferfish seawater acclimation.

Purpose of the Study:

• To characterize the function and transport properties of fugu-NBCe1 (fNBCe1) in a Xenopus oocyte expression system.
• To compare fNBCe1 activity with mammalian and other teleost NBCe1 orthologs.
• To investigate the role of fNBCe1 in transepithelial bicarbonate secretion and ion transport.

Main Methods:

• Xenopus oocyte expression system to assay fugu-NBCe1 activity.
• Electrophysiological recordings to measure ion currents and transport kinetics.
• Kinetic analysis of bicarbonate currents under varying ionic and voltage conditions.

Main Results:

• fNBCe1 functions as an electrogenic Na(+)/HCO(3)(-) cotransporter, sensitive to DIDS, similar to other NBCe1s.
• Unique characteristics observed: electrogenic Li(+)/nHCO(3)(-) cotransport, HCO(3)(-) independent/DIDS-insensitive transport, and increased basal intracellular Na(+) accumulation.
• fNBCe1 exhibits voltage-dependent rectification around -60 mV and favors bicarbonate secretion from blood to lumen, unlike human kidney NBCe1.

Conclusions:

• fugu-NBCe1 possesses distinct transport properties compared to mammalian and other teleost orthologs.
• The transporter's characteristics suggest a role in promoting transepithelial bicarbonate secretion in pufferfish.
• fugu-NBCe1 serves as a valuable tool for studying structure-function relationships in the NBCe1 family.