Transport of magnesium by two isoforms of the Na+-Ca2+ exchanger expressed in CCL39 fibroblasts.
Cytoplasmic concentrations of Ca2+ ([Ca2+]i) and Mg2+ ([Mg2+]i) were measured with fluorescent indicators in CCL39 cells, a cell line established from Chinese hamster lung fibroblasts, transfected with complementary deoxyribonucleic acid (cDNA) of the Na+-Ca2+ exchanger isolated either from canine heart (NCX1) or from rat brain (NCX3). Raising extracellular [Mg2+] to 10 mM increased Mg2+ influx and the resultant change in [Mg2+]i (delta[Mg2+]i) was monitored with furaptra under Ca2+-free conditions. In control (vector-transfected) cells, delta[Mg2+]i at 45 min was similar with or without extracellular Na+ (130 mM or 0 mM) and when [Na+]i was raised by 1 mM ouabain treatment. delta[Mg2+]i in NCX1-transfected cells was attenuated significantly in the presence of 130 mM Na+, but became comparable to (or slightly larger than) that in control cells on either removal of extracellular Na+ or treatment with 1 mM ouabain. Cells expressing NCX3 showed an intermediate dependence of delta[Mg2+]i on Na+, probably reflecting a lower degree of expression of the exchanger protein. Extracellular Na+-dependent changes in [Ca2+]i (measured with fura-2 in the presence of extracellular Ca2+ and 10 microM ionomycin, a Ca2+ ionophore) were minimal in control cells, marked in the NCX1-transfected cells and intermediate in the NCX3-transfected cells. These results suggest that the Na+-Ca2+ exchanger (either NCX1 or NCX3) can transport Mg2+ and may play a role in the extrusion of magnesium from cells.
Tashiro
M
M
Department of Physiology, The Jikei University School of Medicine, Tokyo, Japan.
Konishi
M
M
Iwamoto
T
T
Shigekawa
M
M
Kurihara
S
S
D000818:Animals; D001692:Biological Transport; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006224:Cricetinae; D003412:Cricetulus; D004285:Dogs; D005347:Fibroblasts / Q000378:metabolism*; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives*; D015759:Ionomycin / Q000494:pharmacology; D008168:Lung; D008274:Magnesium / Q000008:administration & dosage / Q000378:metabolism*; D009206:Myocardium / Q000737:chemistry; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D012964:Sodium / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D005456:Fluorescent Dyes; D011994:Recombinant Proteins; D019831:Sodium-Calcium Exchanger; C058776:2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid; D015759:Ionomycin; D010042:Ouabain; D012964:Sodium; D008274:Magnesium; D002118:Calcium; D016257:Fura-2