Differences in magnesium and calcium effects on N-methyl-D-aspartate- and 
quisqualate-induced decreases in extracellular sodium concentration in rat 
hippocampal slices

Köhr, Georg; Heinemann, Uwe

doi:10.1007/BF00247502

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Differences in magnesium and calcium effects on N-methyl-D-aspartate- and quisqualate-induced decreases in extracellular sodium concentration in rat hippocampal slices

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Köhr, Georg
Department of Molecular Neurobiology, Max Planck Institute for Medical Research, Max Planck Society;
Directly responsible to the Managing Director, Max Planck Institute for Medical Research, Max Planck Society;
Georg Köhr Group, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Köhr, G., & Heinemann, U. (1988). Differences in magnesium and calcium effects on N-methyl-D-aspartate- and quisqualate-induced decreases in extracellular sodium concentration in rat hippocampal slices. Experimental Brain Research, 71(2), 425-430. doi:10.1007/BF00247502.

Cite as: https://hdl.handle.net/21.11116/0000-0000-B86F-5

Abstract

Decreases in extracellular sodium concentration [( Na+]o) and associated slow negative field potentials (fp's) were monitored with double barreled sodium sensitive/reference microelectrodes in area CA1 of rat hippocampal slices during iontophoretic application of the glutamate receptor agonists N-methyl-D-aspartate (NMDA) and quisqualate (quis). The effects of lowering [Ca2+]o on these signals were compared to those of lowering [Mg2+]o. Both NMDA- and quis-induced decreases in [Na+]o of up to 60 mM and in the fp's of up to 8 mV. Decreasing [Mg2+]o enhanced NMDA-induced signals, whereas quis-induced signals were unaffected. Lowering [Ca2+]o also enhanced NMDA signals, although somewhat less than lowering [Mg2+]o. This effect was still present, even when voltage dependent Na+ currents were blocked by 10(-7) tetrodotoxin. Interestingly, quis-induced signals could be enhanced in a low Ca2+ medium as well, but only when high quis concentrations were used. The results suggest that, during the sorts of large decreases of [Ca2+]o observed during seizure activity, activation of NMDA receptors is facilitated.