A functionally active presynaptic high-affinity kainate receptor in the rat hippocampal CA3 subregion.
We studied the modulation of the intracellular free calcium concentrations ([Ca2+]i) by kainate/AMPA receptor activation in synaptosomes isolated from whole rat hippocampus, or from its CA1, CA3 or dentate gyrus subregions. The receptor was activated either by 100 microM S-alpha-amino-3-hydroxy-5-methyl-4-isoxazolopropionic acid (AMPA) (EC50 = 26.6 +/- 4.9 microM) or by 100 microM kainate (EC50 = 0.81 +/- 0.1 microM), but the effects of these agonists were not additive. The response to either AMPA or kainate was competitively inhibited by 10 microM 6-cyano-7-nitroquinoxaline-2,3-dioxine. Higher [Ca2+]i responses to 100 microM AMPA or to 100 microM kainate were observed in the CA3 subregion (43.2 +/- 2.5 nM or 42.8 +/- 2.3 nM, respectively) than in the whole hippocampus (22.4 +/- 1.1 nM or 22.4 +/- 1.6, respectively), in the CA1 subregion (26.4 +/- 1.1 nM or 26.6 +/- 2.6 nM, respectively) or in dentate gyrus (24.6 +/- 1.4 nM or 21.5 +/- 1.0 nM, respectively). These results indicate that the CA3 subregion of the hippocampus is enriched in a presynaptic high-affinity kainate receptor which modulates the [Ca2+]i in nerve terminals.
Malva
J O
JO
Department of Zoology, University of Coimbra, Portugal.
Ambrósio
A F
AF
Cunha
R A
RA
Ribeiro
J A
JA
Carvalho
A P
AP
Carvalho
C M
CM
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006624:Hippocampus / Q000502:physiology*; D007608:Kainic Acid / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors / Q000502:physiology*; D013574:Synaptosomes / Q000502:physiology*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D002118:Calcium; D007608:Kainic Acid; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid