Li Z, Matsuoka S, Hryshko L V, Nicoll D A, Bersohn M M, Burke E P, Lifton R P, Philipson K D
Department of Physiology, UCLA School of Medicine 90024-1760.
J Biol Chem. 1994 Jul 1;269(26):17434-9.
The Na(+)-Ca2+ exchanger is an important regulator of cellular Ca2+ levels, and one isoform of this transporter, NCX1, has been cloned previously (Nicoll, D.A., Longoni, S., and Philipson, K.D. (1990) Science 250, 562-565). We now report the cloning of a second isoform (NCX2) of the Na(+)-Ca2+ exchanger which was present in a rat brain cDNA library. NCX2 is predicted to code for a protein of 921 amino acids. NCX1 and NCX2 are 61 and 65% identical at the nucleotide and amino acid levels, respectively, and are the products of different genes. The genes for NCX1 and NCX2 are located on human chromosomes 2 and 14, respectively. Hydropathy profiles of the two exchangers are very similar. Transcripts of NCX2 are detected in brain and skeletal muscle. NCX2 was expressed in Xenopus oocytes and Na(+)-Ca2+ exchange activity was analyzed electrophysiologically by the giant inside-out, excised patch technique. Outward currents were evoked by the application of Na+ with the exchanger operating in the reversed mode (extracellular Ca2+ exchanging for intracellular Na+). The affinity for Na+ (30 mM) and the current-voltage relationship of NCX2 are similar to those for NCX1. Like NCX1, NCX2 is secondarily regulated by intracellular Ca2+, but the affinity of NCX2 for regulatory Ca2+ (1.5 microM) upon initial application of Na+ is lower than that of NCX1 (0.3 microM). The existence of multiple Na(+)-Ca2+ exchanger isoforms may provide flexibility for regulation and expression.
钠钙交换体是细胞内钙离子水平的重要调节因子，该转运体的一种同工型NCX1此前已被克隆（尼科尔，D.A.，隆戈尼，S.，和菲利普森，K.D.（1990年）《科学》250，562 - 565）。我们现在报告在大鼠脑cDNA文库中克隆出钠钙交换体的第二种同工型（NCX2）。预计NCX2编码一种含921个氨基酸的蛋白质。NCX1和NCX2在核苷酸和氨基酸水平上分别有61%和65%的同一性，且是不同基因的产物。NCX1和NCX2的基因分别位于人类染色体2和14上。两种交换体的亲水性图谱非常相似。在脑和骨骼肌中检测到NCX2的转录本。NCX2在非洲爪蟾卵母细胞中表达，并通过巨大的内向外膜片钳技术对钠钙交换活性进行电生理分析。当交换体以反向模式运行（细胞外钙离子与细胞内钠离子交换）时，施加钠离子可诱发外向电流。NCX2对钠离子的亲和力（30 mM）和电流 - 电压关系与NCX1相似。与NCX1一样，NCX2也受到细胞内钙离子的继发性调节，但在最初施加钠离子时，NCX2对调节性钙离子（1.5 microM）的亲和力低于NCX1（0.3 microM）。多种钠钙交换体同工型的存在可能为调节和表达提供灵活性。
