Cloning of the NCX2 isoform of the plasma membrane Na(+)-Ca2+ exchanger.
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.
Li
Z
Z
Department of Physiology, UCLA School of Medicine 90024-1760.
Matsuoka
S
S
Hryshko
L V
LV
Nicoll
D A
DA
Bersohn
M M
MM
Burke
E P
EP
Lifton
R P
RP
Philipson
K D
KD
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping; D002883:Chromosomes, Human, Pair 14; D002889:Chromosomes, Human, Pair 2; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006801:Humans; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism*; D019831:Sodium-Calcium Exchanger; D014981:Xenopus
D002352:Carrier Proteins; D018076:DNA, Complementary; D019831:Sodium-Calcium Exchanger; D012964:Sodium; D002118:Calcium