Glutamate-Induced Cytoplasmic Ca2+ Transients In Neurones Isolated From The Rat Dorsal Cochlear Nucleus

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 mumol/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+], was 1 mmol/l, the NMDA receptor antagonist AP5 (100 mumol/l) had no effects while 100 mumol/l CNQX and 10 mumol/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 mumol/l glycine, 20 mumol/l [Mg2+](o)) in the presence of 100 mumol/l CNQX, Ca2+ transients of 55.4 +/- 13.1 nmol/l could be produced. Block of the voltage-gated Ca2+ channels (200 mumol/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.