Increased perinuclear Ca++ activity evoked by metabotropic glutamate receptor activation in rat hippocampal neurones.

Journal of Physiology 1995, in press

Biosciences Imaging Group, Department of Physiology and Pharmacology, University of Southampton, Southampton SO9 3TU, UK.

SUMMARY:

1. The effect of metabotropic glutamate receptor activation on intracellular Ca++ activity (Ca++i) of rat hippocampal pyramidal neurones in vitro was examined using ratiometric confocal laser scanning microscopy with the Ca++-sensitive fluorescent probe indo-1 AM.

2. Metabotropic receptors were selectively activated with 1S, 3R-1- aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 100 uM) in the presence of D-2- amino 5-phosphonovaleric acid (D-APV), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and CdCl2. Most pyramidal neurones (77/84) responded with an elevation in Ca++ activity, maximal after 3-5 min. Fluorescence ratio responses were concentration- dependent (EC50 ÷ 10ĉM), and were blocked by prior application of the antagonist (RS)- 4-carboxy-3-hydroxyphenylglycine [300ĉM].

3. Responses to 1S,3R-ACPD [100 ĉM], also caused acidification of the neurones, from estimated control pH 7.2 to pH 6.6 (measured with the pH-sensitive dye SNAFL- calcein). The correction factor for indo-1 determination of Ca++ was estimated to be x1.4.

4. Elevations in Ca++i were greater within the perinuclear region (>1000nM), than in the cytoplasm (÷ 200nM). This region was devoid of staining by the endoplasmic reticulum staining dye 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)).

5. It is concluded that activation of metabotropic receptors in immature rat hippocampal pyramidal neurones leads to a large increase in perinuclear Ca++ which would be well positioned to interact with the genome.

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