Ni2+ transport by the human Na+/Ca2+ exchanger expressed in Sf9 cells.
The mechanism of Ni2+ block of the Na+/Ca2+ exchanger was examined in Sf 9 cells expressing the human heart Na+/Ca2+ exchanger (NCX1-NACA1). As predicted from the reported actions of Ni2+, its application reduced extracellular Na+-dependent changes in intracellular Ca2+ concentration (measured by fluo 3 fluorescence changes). However, contrary to expectation, the reduced fluorescence was accompanied by measured 63Ni2+ entry. The 63Ni2+ entry was observed in Sf 9 cells expressing the Na+/Ca2+ exchanger but not in control cells. The established sequential transport mechanism of the Na+/Ca2+ exchanger could be compatible with these results if one of the two ion translocation steps is blocked by Ni2+ and the other permits Ni2+ translocation. We conclude that, because Ni2+ entry was inhibited by extracellular Ca2+ and enhanced by extracellular Na+, the Ca2+ translocation step moved Ni2+, whereas the Na+ translocation step was inhibited by Ni2+. A model is presented to discuss these findings.
D000814:Aniline Compounds; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology; D002132:Calcium Radioisotopes / Q000378:metabolism; D005456:Fluorescent Dyes; D015870:Gene Expression; D006801:Humans; D009532:Nickel / Q000378:metabolism* / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000235:genetics* / Q000378:metabolism*; D018411:Spodoptera / Q000378:metabolism*; D014162:Transfection; D014966:Xanthenes