Combined Effects of a Metabotropic Glutamate Receptor Agonist and an Ionotropic Glutamate Receptor Agonist on Cytosolic Ca2+ Concentrations in Cultured Hippocampal Cells

Changes in the cytosolic Ca2+ concentration ([Ca2+]i) of cultured hippocampal cells from rat embryos were investigated using a fluorescent Ca2+ indicator, fura-2. An ionotropic and a metabotropic glutamate receptor agonist were applied singly or simultaneously to the same cell and Δ[Ca2+]i (the maximum increase in [Ca2+]i) after each application was calculated. In cells that responded well to 30 μM N-methy1-D-aspartate (NMDA), Δ[Ca2+]i induced by simultaneous application of trans-1-amino-cyclopenty1-1, 3-dicarboxylic acid (trans-ACPD) and α-amino-3-hydroxy-5-methy1-4-isoxazoleprppionic acid (AMPA) was 101.2±40.3 nM, whereas the sum of Δ[Ca2+]i values induced by these agents alone was 87.6±32.2 nM (p=0.061, n=55). In 18% of these cells, yhe mean Δ[Ca2+]i evoked by the simultaneous application of AMPA and trans-ACPD was at least twice the mean sun of Δ[Ca2+]i values evoked by these agents alone. In cells which only responded to 30 μM NMDA with small Δ[Ca2+]I changes, Δ[Ca2+]I induced by simultaneous application of AMPA and trans-ACPD was significantly higher than the sum of Δ[Ca2+]I values induced by these agants alone, 130.1±35.2 and 41.2±24.0 nM, respectively (p＜0.001, n=17). These results suggest that activation of metabotropic glutamate receptors upregulates AMPA receptors in hippocampal cells.

trans-ACPD

AMPA

NMDA

fura-2

cytosolic calcium concentration