Differential inhibition of Na+/Ca2+ exchanger isoforms by divalent cations and isothiourea derivative.
We compared the properties of three mammalian Na+/Ca2+ exchanger isoforms, NCX1, NCX2, and NCX3, by analyzing the effects of Ni2+ and other cations as well as the recently identified inhibitor isothiourea derivatives on intracellular Na+-dependent 45Ca2+ uptake into CCL-39 (Dede) fibroblasts stably expressing each isoform. All these NCX isoforms had similar affinities for the extracellular transport substrates Ca2+ and Na+. Ni2+ inhibited 45Ca2+ uptake by competing with Ca2+ for the external transport site, with 10-fold less affinity in NCX3 than in NCX1 or NCX2. Ni2+ and Co2+ were most efficient in such discrimination of NCX isoforms, although their inhibitory potencies were less than those of La3+ and Cd2+. The monovalent cation Li+ stimulated 45Ca2+ uptake rate by all NCX isoforms similarly with low affinity, although the extent of stimulation was somewhat smaller in NCX1. On the other hand, the isothiourea derivative KB-R7943 was threefold more inhibitory to NCX3 than to NCX1 or NCX2. Thus distinct differences in the kinetic and pharmacological properties were detected between NCX3 and the other two isoforms.
Department of Molecular Physiology, National Cardiovascular Center Research Institute, Suita, Osaka 565, Japan.
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Iwamoto
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Shigekawa
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology*; D002460:Cell Line; D006224:Cricetinae; D005347:Fibroblasts; D006801:Humans; D007668:Kidney; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology; D008168:Lung; D026901:Membrane Transport Proteins; D009532:Nickel / Q000494:pharmacology; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000235:genetics; D013329:Structure-Activity Relationship; D013890:Thiourea / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D002413:Cations, Divalent; D026901:Membrane Transport Proteins; D011994:Recombinant Proteins; C101832:SLC38A3 protein, human; C491102:Slc8a3 protein, rat; D019831:Sodium-Calcium Exchanger; C110374:sodium-calcium exchanger 1; D007811:Lanthanum; D009532:Nickel; D008094:Lithium; D013890:Thiourea; D002118:Calcium