Astrocytes release glutamate upon hyperexcitation in the normal brain, and in response to pathologic insults such as ischemia and trauma. In our experiments using cultured mouse astrocytes, both hypotonic and ischemic stimuli caused the release of glutamate, which occurred with little or no contribution of gap junction hemichannels, vesicle-mediated exocytosis, or reversed operation of the Na-dependent glutamate transporter. Cell swelling and chemical ischemia activated, in cell-attached membrane patches, anionic channels (maxi-anion channels) with a large unitary conductance (～ 400 pS) and inactivation kinetics at potentials more positive than +20 mV or more negative than -20 mV. These properties are different from those of volume-sensitive outwardly rectifying (VSOR) Cl^- channels, which were also expressed in these cells and exhibited an intermediate unitary conductance ( ～ 80 pS) and inactivation kinetics at large positive potentials of more than +40 mV. Both maxi-anion channels and VSOR Cl^- channels were permeable to glutamate with permeability ratios of glutamate to chloride of 0.21 ± 0.07 and 0.15 ± 0.01, respectively. However, the release of glutamate was significantly more sensitive to Gd³⁺, a blocker of maxi-anion channels, than to phloretin, a blocker of VSOR Cl^- channels. We conclude that these two channels jointly represent a major conductive pathway for the release of glutamate from swollen and ischemia-challenged astrocytes, with the contribution of maxi-anion channels being predominant. On the other hand, in our separate study, we demonstrated that maxi-anion channels but not VSOR chloride channels are involved in ATP release from astrocytes under the stress of OGD (oxygen-glucose deprivation). In our recent study using neuron-glia cocultures, we have shown that the involvement of VSOR, but not maxi, anion channels in bradykinin-induced glutamate-mediated signalling from astrocytes to neurons. Thus, both maxi-anion channels and VSOR Cl^- channels in astrocytes play important roles in the brain functions dependent on the situations.