Cloning of the NCX2 isoform of the plasma membrane Na(+)-Ca2+ exchanger

• Published in: The Journal of biological chemistry 1994-07, Vol.269 (26), p.17434-17439
• Main Authors: ZHAOPING LI, MATSUOKA, S, HRYSHKO, L. V, NICOLL, D. A, BERSOHN, M. M, BURKE, E. P, LIFTON, R. P, PHILIPSON, K. D
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Analytical, structural and metabolic biochemistry; Animals; Base Sequence; Binding and carrier proteins; Biological and medical sciences; Calcium - metabolism; Carrier Proteins - genetics; Carrier Proteins - metabolism; Chromosome Mapping; Chromosomes, Human, Pair 14; Chromosomes, Human, Pair 2; Cloning, Molecular; DNA, Complementary; Fundamental and applied biological sciences. Psychology; Humans; Membrane Potentials; Molecular Sequence Data; Proteins; Rats; Sequence Homology, Amino Acid; Sodium - metabolism; Sodium-Calcium Exchanger; Xenopus
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/s0021-9258(17)32458-4

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.