Glutamate-induced increase in intracellular Ca2+ in cerebral cortex neurons is transient in immature cells but permanent in mature cells.
The free cytosolic Ca2+ concentration ([Ca2+]i) of cultured cerebral cortex neurons was determined using a fluorescent Ca2+ chelator (Fluo-3) after exposure of the neurons to glutamate. Mature neurons (8 days in culture) responded within 45 s to 100 microM glutamate by an increase in [Ca2+]i from 75 to 340 nM, an increase that during the following 6 min of exposure reached 400 nM. This increase in [Ca2+]i could not be reversed by removal of glutamate. In the absence of extracellular CaCl2, only part of the initial, rapid, glutamate-induced increase in [Ca2+]i was observed in these neurons. In contrast to these findings, neurons cultured for only 2 days (immature neurons) exhibited only a small (from 75 to 173 nM) increase in [Ca2+]i after exposure to 100 microM glutamate, and this rapid increase in [Ca2+]i tended to decline on prolonged exposure to glutamate. Moreover, after removal of glutamate, the increase in [Ca2+]i was fully reversible. Pharmacological characterization of the response to glutamate in mature neurons showed that the N-methyl-D-aspartate (NMDA) receptor antagonists phencyclidine and D-2-amino-5-phosphonovalerate phosphonovalerate blocked 75 and 90%, respectively, of the response, whereas the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione had little effect.
Wahl
P
P
Department of Biochemistry A, Panum Institute, University of Copenhagen, Denmark.
Schousboe
A
A
Honoŕe
T
T
Drejer
J
J
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000378:metabolism*; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007700:Kinetics; D051379:Mice; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors
D005971:Glutamates; D018698:Glutamic Acid; D002118:Calcium