Effect of glutamate and extracellular calcium on uptake of inorganic lead (Pb2+) in immortalized mouse hypothalamic GT1-7 neuronal cells.
We have previously shown that although glutamate alone has no effects on viability of mouse hypothalamic GT1-7 cells, it clearly enhances Pb2+-induced cytotoxicity. It is likely that Pb2+ must enter cells to exert most of its toxic effects. Pb2+ is known to substitute for Ca2+ in many cellular processes. Therefore, we studied the uptake mechanisms of Pb2+ into GT1-7 neuronal cells with a special focus on the role of extracellular calcium (Ca2+), voltage-sensitive calcium channels (VSCCs) and glutamate. Basal uptake of Pb2+ (1 microM or 10 microM), i.e. without any external stimulus, clearly increased in nominally Ca2+-free buffer and was partially abolished by 13 mM Ca2+ when compared to uptake in the presence of a physiological concentration of extracellular Ca2+ (1.3 mM). Depolarization by 25 mM K+, or antagonists of VSCCs, verapamil (10 microM) or flunarizine (10 microM) had no clear effect on basal Pb2+ uptake. Glutamate (1 mM) increased Pb2+ uptake, but only when cells were treated with 1 microM Pb2+ in the presence of 1.3 mM Ca2+. Our data suggest that Pb2+ competes for the same cellular uptake pathways with Ca2+, although not via VSCCs. In addition, enhancement of Pb2+-induced neurotoxicity by glutamate may be due to increased neuronal uptake of Pb2+.
Loikkanen
J
J
Department of Pharmacology and Toxicology, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland. jarkko.loikkanen@uku.fi
Naarala
J
J
Vähäkangas
K H
KH
Savolainen
K M
KM
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes; D018698:Glutamic Acid / Q000494:pharmacology*; D007031:Hypothalamus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007854:Lead / Q000493:pharmacokinetics* / Q000633:toxicity; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009942:Organometallic Compounds / Q000493:pharmacokinetics / Q000633:toxicity; D013050:Spectrometry, Fluorescence
D005456:Fluorescent Dyes; D009942:Organometallic Compounds; D007854:Lead; D018698:Glutamic Acid; C008261:lead acetate; D002118:Calcium