Wang C Z, Yano H, Nagashima K, Seino S
Department of Molecular Medicine, Chiba University Graduate School of Medicine, 1-8-1 Inohana, Chuo-ku, Chiba 260-8670, Japan.
J Biol Chem. 2000 Nov 10;275(45):35486-90. doi: 10.1074/jbc.C000456200.
The Na(+)-driven Cl(-)/HCO(3)(-) exchanger is an important regulator of intracellular pH in various cells, but its molecular basis has not been determined. We show here the primary structure, tissue distribution, and functional characterization of Na(+)-driven chloride/bicarbonate exchanger (designated NCBE) cloned from the insulin-secreting cell line MIN6 cDNA library. The NCBE protein consists of 1088 amino acids having 74, 72, and 55% amino acid identity to the human skeletal muscle, rat smooth muscle, and human kidney sodium bicarbonate cotransporter, respectively. The protein has 10 putative membrane-spanning regions. NCBE mRNA is expressed at high levels in the brain and the mouse insulinoma cell line MIN6 and at low levels in the pituitary, testis, kidney, and ileum. Functional analyses of the NCBE protein expressed in Xenopus laevis oocytes and HEK293 cells demonstrate that it transports extracellular Na(+) and HCO(3)(-) into cells in exchange for intracellular Cl(-) and H(+), thus raising the intracellular pH. Thus, we conclude that NCBE is a Na(+)-driven Cl(-)/HCO(3)(-) exchanger that regulates intracellular pH in native cells.
钠离子驱动的氯离子/碳酸氢根离子交换体是多种细胞内细胞内pH值的重要调节因子，但其分子基础尚未确定。我们在此展示了从胰岛素分泌细胞系MIN6 cDNA文库中克隆出的钠离子驱动的氯离子/碳酸氢根离子交换体（命名为NCBE）的一级结构、组织分布及功能特性。NCBE蛋白由1088个氨基酸组成，与人骨骼肌、大鼠平滑肌及人肾脏碳酸氢钠协同转运体的氨基酸序列一致性分别为74%、72%和55%。该蛋白有10个推测的跨膜区域。NCBE mRNA在脑和小鼠胰岛素瘤细胞系MIN6中高表达，而在垂体、睾丸、肾脏和回肠中低表达。对非洲爪蟾卵母细胞和HEK293细胞中表达的NCBE蛋白进行的功能分析表明，它将细胞外的钠离子和碳酸氢根离子转运到细胞内，以交换细胞内的氯离子和氢离子，从而提高细胞内pH值。因此，我们得出结论，NCBE是一种钠离子驱动的氯离子/碳酸氢根离子交换体，可调节天然细胞内的pH值。
