L-glutamate increases internal free calcium levels in synaptoneurosomes from immature rat brain via quisqualate receptors.
Internal free calcium concentrations ([Ca2+]i) have been monitored in synaptoneurosomes from 8-d-old rat whole brain previously loaded with the calcium-sensitive fluorescent probe Fura 2. Under basal conditions, [Ca2+]i was around 200 nM, this concentration increasing only slowly during storage of the synaptoneurosomes at room temperature (40% increase 2 hr after loading). Opening of sodium channels with veratridine- (10 microM) or KCl- (30 mM) induced depolarization caused rapid increases in synaptoneurosomal [Ca2+]i. [Ca2+]i was also markedly increased by addition of the Ca2+ ionophore A23187 (10-100 nM). The effect of veratridine, but not of KCl was prevented by previous addition of TTX (1 microM). KCl-induced [Ca2+]i increase was dependent on external Ca2+ and was partially blocked by the dihydropyridine derivative PN 200-110 (IC50 0.15 microM, maximal inhibition 55% at 3 microM). L-Glutamate elicited a concentration-dependent fast increase in synaptoneurosomal [Ca2+]i in the 8-d-old (but not in the adult) rat brain (EC50 = 2 microM). The effect of glutamate was stereospecific, the EC50 of the D-isomer being 47 times higher than that of L-isomer. The magnitude of the L-glutamate response differed in several brain regions, being highest in the cerebral cortex and lowest in the cerebellum.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D066298:In Vitro Techniques; D017275:Isradipine; D008297:Male; D009994:Osmolar Concentration; D010069:Oxadiazoles / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D018091:Receptors, AMPA; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000502:physiology; D017981:Receptors, Neurotransmitter / Q000187:drug effects* / Q000502:physiology; D013237:Stereoisomerism; D013574:Synaptosomes / Q000187:drug effects* / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
D005971:Glutamates; D010069:Oxadiazoles; D018091:Receptors, AMPA; D017459:Receptors, Amino Acid; D011956:Receptors, Cell Surface; D017981:Receptors, Neurotransmitter; D000001:Calcimycin; D018698:Glutamic Acid; D013779:Tetrodotoxin; D004533:Egtazic Acid; D011189:Potassium Chloride; D014701:Veratridine; D002118:Calcium; D017275:Isradipine