Is Ca2+-mediated activation of glial cells necessary for heterosynaptic depression?
To test whether Ca2+-mediated glial cell activation was necessary for the induction of heterosynaptic depression, we blocked glial Ca2+ responses by intracellular dialysis of the Ca2+ chelator BAPTA in glial cells with whole-cell recordings. BAPTA was dialyzed during recordings from a single glial cell via a patch pipette that also contained biocytin to visualize a syncytium of glial cells that was labeled after NMDA application (20 200 biocytin-labeled glial cells covering an area 300 µm in diameter) (Fig. 3A) (see also Latour et al., 2001). Intracellular labeling with Oregon-green BAPTA, a Ca2+ indicator of the BAPTA family (with a higher molecular weight than BAPTA alone), revealed a similar spread into the glial syncytium after NMDA application, thus indicating that dialyzed BAPTA had spread into the syncytium (Fig. 3B, green cells). Identification of glial cells was confirmed by electrophysiological criteria (low resting membrane potential and absence of action potential); they we
