Ishibashi K, Sasaki S, Marumo F
Second Department of Internal Medicine, Tokyo Medical and Dental University, Japan.
Biochem Biophys Res Commun. 1998 May 19;246(2):535-8. doi: 10.1006/bbrc.1998.8658.
Sodium bicarbonate cotransport is an electrogenic process and a principal regulator of pH. A recently cloned sodium bicarbonate cotransporter (NBC1) is predominantly expressed in kidney. The presence of several isoforms is suggested from functional studies. We have cloned a new member of this family from human retina, which was named hNBC2 (for human sodium bicarbonate cotransporter 2). The hNBC2 has 1018 amino acid residues with 10 hydrophobic transmembrane domains. A cluster of five N-glycosylation sites is present at the second extracellular loop. It has 53% amino acids identity with hNBC1 and 38% identity with anion exchanger 1. Thus, NBC2 is a new member of the anion exchanger superfamily. Northern blot of human tissues revealed its expression in many tissues such as testis, spleen, ovary, small intestine, colon, thymus, heart, and muscle (8.5 kb). The predominant expression at retina was documented with Northern blot of rat tissues. NBC2 may be a major regulator of extracellular pH of retina where light stimulation produces an extracellular alkalization and may contribute as a solute transporter to the prevention of retinal detachment.
碳酸氢钠协同转运是一种生电过程，也是pH值的主要调节因子。最近克隆出的一种碳酸氢钠协同转运蛋白（NBC1）主要在肾脏中表达。功能研究表明存在几种亚型。我们从人视网膜中克隆出了该家族的一个新成员，命名为hNBC2（人类碳酸氢钠协同转运蛋白2）。hNBC2有1018个氨基酸残基，具有10个疏水跨膜结构域。在第二个细胞外环上有一组5个N - 糖基化位点。它与hNBC1有53%的氨基酸同源性，与阴离子交换蛋白1有38%的同源性。因此，NBC2是阴离子交换蛋白超家族的一个新成员。人组织的Northern印迹分析显示其在许多组织中表达，如睾丸、脾脏、卵巢、小肠、结肠、胸腺、心脏和肌肉（8.5 kb）。大鼠组织的Northern印迹分析证实其在视网膜中主要表达。NBC2可能是视网膜细胞外pH值的主要调节因子，在视网膜中光刺激会导致细胞外碱化，并且作为溶质转运体可能有助于预防视网膜脱离。
