Regulation of the glutamate uptake by extracellular calcium.
To determine whether [Ca(2+)](e) modulates glutamate re-uptake, we studied the uptake mechanism into rat cerebrocortical synaptosomes. The removal of extracellular Ca(2+) caused a negative modulation in the uptake mechanism. The calculated K(50) value was 0.185 +/- 0.019 mM (n = 4). The Michaelis-Menten data analysis indicate that absence of Ca(2+) diminished the V(max) kinetic parameter by about 60% without changing significantly the K(m) suggesting a non-competitive mechanism. We also tested the involvement of intracellular Ca(2+) in this phenomenon by trapping BAPTA into the synaptosomal vesicles to control the Ca(2+) concentration. Our results suggest that intracellular Ca(2+) changes have a less predominant role on the glutamate uptake than do extracellular Ca(2+). These findings argue in favor of an important role of extracellular [Ca(2+)] in maintaining the L-glutamate re-uptake mechanism in the mammalian central nervous system.
Mafra
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RA
Departamento de Fisiologia e Biofísica, ICB, Universidade Federal de Minas Gerais, Av. Antônio Carlos 6627, 31270-901, Belo Horizonte MG, Brazil.
de Oliveira
L C
LC
Ferreira
C A G
CA
De Lima
M E
ME
Beirão
P S L
PS
Cruz
J S
JS
D000818:Animals; D002118:Calcium / Q000172:deficiency* / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D002614:Chelating Agents; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D010599:Pharmacokinetics; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014316:Tritium
D002614:Chelating Agents; D014316:Tritium; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D018698:Glutamic Acid; D004533:Egtazic Acid; D007770:L-Lactate Dehydrogenase; D002118:Calcium