Cloning, tissue distribution, genomic organization, and functional characterization of NBCS, a new member of the sodium bicarbonate cotransporter family

Previous functional studies have demonstrated that muscle intracellular pH regulation is mediated by sodium-coupled bicarbonate transport, Na+/H+ exch ange, and Cl-/bicarbonate exchange. We report the cloning, sequence analysi s, tissue distribution, genomic organization, and functional analysis of a new member of the sodium bicarbonate cotransporter (NBC) family, NBC3, from human skeletal muscle. mNBC3 encodes a 1214-residue polypeptide with 12 pu tative membrane-spanning domains. The similar to 7.8-kilobase transcript is expressed uniquely in skeletal muscle and heart. The NBCS gene (SLC4A7) sp ans similar to 80 kb and is composed of 25 coding exons and 24 introns that are flanked by typical splice donor and acceptor sequences. Expression of mNBC3 cRNA in Xenopus laevis oocytes demonstrated that the protein encodes a novel stilbene-insensitive 5-(N-ethyl-N-isopropyl)-amiloride-inhibitable sodium bicarbonate cotransporter.