Delayed increase of cell volume of single pyramidal cells in live rat hippocampal slices upon kainate application

Cell volume is an important physiologic parameter but is not directly accessible by conventional microscopy in vivo or in slice preparations. After staining of rat hippocampal slices with 1,1'-dioctadecyl-3,3,3',3'-tetramethylinso-carbocyanineperchlor ate (DiI), living single CA1 pyramidal cells were visualized by confocal microscopy while others in the illuminated area were recorded intracellularly. Resting membrane potential and action potentials were not affected by staining with DiI (4 microM) and repeated laser illumination (up to 600 times). A time- and dose-dependent increase of cell volume succeeds membrane depolarization upon bath application of kainate (40 microM and 100 microM) with a delay of several minutes indicating active regulation of cell volume. We conclude that cell swelling as visualized by confocal microscopy is a relatively late event of kainate excitotoxicity.