Fig. 5.

a Current features of putative oligodendrocyte precursor cells in the mouse corpus callosum. a I Bright-field image of a corpus callosum slice showing the location of the cell. II Bright-field image at high magnification of the patched cell during recording. III Fluorescence image of the recorded cell dialyzed with Alexa Fluro 594 via the pipette solution. Bar 120 μm (I), 15 μm (II, III). IV Membrane currents from the cell shown were evoked by 50-ms voltage steps ranging from –210 mV to +80 mV from a holding potential of –70 mV (for the recording protocol, see inset in V). V Outwardly rectifying current to voltage curve was obtained from IV; current amplitudes at the beginning (black circles) and at the end (open circles) of the voltage pulse were plotted against the holding potential. b Putative oligodendrocyte progenitor cells in the corpus callosum lack glutamate transporter current expression. I As described in Fig. 4a, no current response to D-aspartate (D-Asp) application (0.5 mM, 30 s) was recorded in a putative oligodendrocyte progenitor cell (n=10 out of 10). II, left Two series of voltage steps from the recording shown in I taken (1) before and (2) during the D-aspartate application. Current voltage curve: no current was recorded after the D-aspartate application. c Functional expression of AMPA/kainate glutamate receptors in the putative oligodendrocyte precursor cells in the corpus callosum. I As described in Fig. 4a, kainate (KA, 0.5 mM, 30 s) was applied while membrane currents were recorded (n=7 out of 10). II Three series of voltage steps from the recording shown in I taken (1) at the peak of the kainate response, (2) after long-term blockage of the resting K⁺ conductance, and (3) with higher time resolution. III, left Current voltage curves of kainate-triggered responses were obtained by subtracting current amplitudes at the corresponding membrane potentials before and at the peak response during the kainate application (2-1). The reversal potential was at 0 mV. III, right The current voltage curves of long term blockage of the resting K+ conductance were obtained by subtracting current amplitudes at the corresponding membrane potentials before and about 12 min after the kainate application (3-1)