Mechanisms of glutamate induced swelling in astroglial cells

Relative changes in volume were registered in single cells by using a microspectrofluorometric equipment and the fluorescent probe fura-2/AM, excited at its isosbestic point. At this wavelength the probe is ion-insensitive and the fluorescent signals emitted is dependent on variations in the concentration of the dye. Variations in cell volume thus lead to changes in fluorescence intensity as the probe concentration is changed in the lightened delimited zone selected for each cell. When changing the excitation wavelength Ca2+ transients can be recorded. Glutamate (Glu) induced swelling of type I astroglial cells in primary culture and a parallel intracellular Ca2+ increase was obtained. A Glu induced swelling was obtained even after blockade of the Glu ionotropic receptors with NBXQ, suggesting that activation of ionotropic receptors might not be necessary for swelling to occur. On the other hand, blockade of the Glu carrier, or of pertussis toxin sensitive G-proteins reduced the Glu induced swelling. Blockade of Ba2+ or TEA sensitive K+ channels completely blocked the Glu induced swelling as did also blockade with furosemide of the Na+/K+/Cl- co-transporter. Glu induced swelling occurred in parallel with intracellular Ca2+ transients but extracellular Ca2+ did not seem necessary for swelling to occur.