Physiological functions of the regulatory domains of the cardiac Na+/Ca2+ exchanger NCX1

• Published in: American Journal of Physiology: Cell Physiology 2000-08, Vol.279 (2), p.C393
• Main Authors: Pan, Yan, Iwamoto, Takahiro, Uehara, Akira, Nakamura, Tomoe Y, Imanaga, Issei, Shigekawa, Munekazu
• Format: Article
• Language: eng ; jpn
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.2000.279.2.c393

1  Department of Molecular Physiology, National Cardiovascular Center Research Institute, Suita, Osaka 565-8565; and 2  Department of Physiology, School of Medicine, Fukuoka University, Fukuoka 814-0180, Japan Physiological functions of the intracellular regulatory domains of the Na + /Ca 2+ exchanger NCX1 were studied by examining Ca 2+ handling in CCL39 cells expressing a low-affinity Ca 2+ regulatory site mutant (D447V/D498I), an exchanger inhibitory peptide (XIP) region mutant displaying no Na + inactivation (XIP-4YW), or a mutant lacking most of the central cytoplasmic loop ( 246-672). We found that D447V/D498I was unable to efficiently extrude Ca 2+ from the cytoplasm, particularly during a small rise in intracellular Ca 2+ concentration induced by the physiological agonist -thrombin or thapsigargin. The same mutant took up Ca 2+ much less efficiently than the wild-type NCX1 in Na + -free medium when transfectants were not loaded with Na + , although it appeared to take up Ca 2+ normally in transfectants preloaded with Na + . XIP-4YW and, to a lesser extent, 246-672, but not NCX1 and D447V/D498I, markedly accelerated the loss of viability of Na + -loaded transfectants. Furthermore, XIP-4YW was not activated by phorbol ester, whereas XIP-4YW and D447V/D498I were resistant to inhibition by ATP depletion. The results suggest that these regulatory domains play important roles in the physiological and pathological Ca 2+ handling by NCX1, as well as in the regulation of NCX1 by protein kinase C or ATP depletion. calcium flux; sodium loading; cell viability; cell death; protein kinase C