Differential intracellular calcium responses to glutamate in type 1 and type 2 cultured brain astrocytes

Abstract

Fluorescence image analysis using the calcium indicator fluo-3 was used to examine changes in [Ca2+]i induced by glutamate in mixed glia populations cultured from neonatal rat brains. [Ca2+]i responses were correlated with glia type by performing immunohistochemistry using markers specific for type 1 and type 2 astrocytes on the same cells used in the imaging experiments. Glutamate (30-500 microM) induced two markedly different [Ca2+]i responses in the two astrocyte types: the response in type 1 astrocytes consisted of an initial fast transient followed by varying degrees of oscillations, whereas the predominant response in type 2 astrocytes was a slow rise in [Ca2+]i to a more or less sustained and nonoscillatory level. In some type 2 astrocytes, an initial spikelike transient similar to that in type 1 astrocytes was observed; the overall size of the spike, however, was smaller than in type 1 astrocytes. Two agonists for the ionotropic glutamate receptor, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and kainate, elicited a 6-cyano-7-dinitroquinoxaline-2,3-dione (CNQX)-sensitive, external Ca(2+)-dependent, sustained [Ca2+]i rise in type 2 but not type 1 astrocytes. The initial spike in type 2 astrocytes was less dependent on external Ca2+ and not blocked by CNQX. [Na+]i as measured by the Na(+)-fluorescence dye SBFI, was elevated by kainate in both astrocyte types, though the increase was larger in type 2 astrocytes. This increase was reduced by CNQX, suggesting this [Ca2+]i increase was mediated, at least in part, by ionotropic glutamate receptors. The results are discussed in terms of the relative distribution of two classes of glutamate receptors on these two astrocyte types: one, the ionotropic class, is linked directly to an ion channel, and the other, the metabotropic class, induces internal mobilization of Ca2+ via inositol phospholipid hydrolysis.

Serine racemase: Activation by glutamate neurotransmission via glutamate receptor interacting protein and mediation of neuronal migration

“…AMPA receptors have been demonstrated in astrocytes biochemically and functionally, and GRIP has been identified in glia (11,12). Our immunohistochemical staining of mouse brain and primary cultures of mixed glia confirms GRIP's localization to astrocytes, whose identity is verified by staining with GFAP (Fig.…”

Selective destruction of glioblastoma cells by interference with the activity or expression of ATF5

“…We have recently reported (Angelastro et al, 2003) that neural progenitor/stem cells in the developing brain express high levels of activating transcription factor 5 (ATF5; also referred to as ATFx), a member of the ATF/CREB family of bZip proteins (Jensen and Chiu, 1991;Nishizawa and Nagata, 1992;Pati et al, 1999;Hansen et al, 2002;Persengiev et al, 2002;Angelastro et al, 2003). Cells in the developing nervous system that expressed ATF5 included neural stem cells positive for CD133, a marker recently shown to be expressed by tumor-initiating cells in glioblastomas and other brain tumors (Singh et al, 2004).…”

On the Role of Voltage-Dependent Calcium Channels in Calcium Signaling of AstrocytesIn Situ

“…Numerous stimuli such as neurotransmitters, membrane depolarization, or mechanical stress elicit in astrocytes increases in the concentration of intracellular calcium ([C a 2ϩ ] i ) that are quite variable in terms of amplitude and spatiotemporal organization: [Ca 2ϩ ] i peaks and prolonged plateaus and oscillations (CornellBell et al, 1990;Glaum et al, 1990;Jensen and Chiu, 1991;Pasti et al, 1995), often followed by propagating [C a 2ϩ ] i waves (Cornell-Bell et al, 1990;Charles et al, 1991). This complexity reflects the expression of a variety of molecules that control Ca 2ϩ entry from the extracellular space as well as C a 2ϩ release from intracellular compartments (Berridge, 1993;Verkhratsky and Kettenmann, 1996).…”

“…The expression of C a 2ϩ channels in cultured astrocytes appears to depend either on the presence of neurons (Corvalan et al, 1990) or on treatments with agents that increased cAMP intracellular levels (MacVicar and Tse, 1988;Barres et al, 1989). Using classical Ca 2ϩ imaging techniques, [Ca 2ϩ ] i elevations attributed to Ca 2ϩ influx through Ca 2ϩ VOCs were observed in astrocytes on a depolarizing stimulus (Jensen and Chiu, 1991;MacVicar et al, 1991). Although the evidence for the expression of Ca 2ϩ VOCs in cultured astrocytes is beyond any doubt, results obtained in culture do not necessarily represent faithfully the behavior of astrocytes in vivo.…”