Extracellular application of glutamate elicited cytoplasmic Ca2+ transients in freshly dissociated rat neurones of the dorsal cochlear nucleus (DCN) (identified as pyramidal cells) with half-maximal concentration of 513 μmol/l while saturating doses (5 mmol/l) of this neurotransmitter caused transients of 46.1 ± 3.0 nmol/l on an average. The genesis of these glutamate-evoked Ca2+ transients required extracellular Ca2+. When [Mg2+]o was 1 mmol/l, the NMDA receptor antagonist AP5 (100 μmol/l) had no effects while 100 μmol/l CNQX and 10 μ mol/l NBQX, inhibitors of the AMPA receptors, greatly decreased the glutamate-induced Ca2+ transients (a decrease of 92 and 57%, respectively). When facilitating the activation of the NMDA receptors (50 μmol/l glycine, 20 μmol/l [Mg2+]o) in the presence of 100 μmol/l CNQX, Ca2+ transients of 55.4 ± 13.1 nmol/l could be produced. Block of the voltage-gated Ca2+ channels (200 μmol/l Cd2+) decreased the Ca2+ transients to approx. 50%. The data indicate that under our control experimental circumstances the glutamate-induced Ca2+ transients of the isolated DCN neurones are produced mainly by Ca2+ entry through voltage-gated Ca2+ channels and AMPA receptors. However, when the activation of the NMDA receptors may take place, these receptors also contribute significantly to the genesis of the glutamate-evoked cytoplasmic [Ca2+] elevations.
|Number of pages||18|
|Journal||General physiology and biophysics|
|Publication status||Published - márc. 1 2004|
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