Exocytotic Release of Glutamate from Gliosomes

The experiments shown above point out that gliosomes represent a highly purified astrocyte-derived subcellular preparation that possess the machinery to actuate exocytotic gliotransmitter release. We tested this hypothesis by monitoring directly the release of glutamate from gliosomes evoked by stimuli that augment the cytosolic ( 2r concentration [C i , by means of different mechanisms, in in vitro release experiments. 

Functional experiments conducted in rat cerebral cortex showed that purified gliosomes are able to take up and release glutamate when exposed to stimuli able to induce increase of intracellular Ca2+, such as ionomycin. 

External Ca2+ entry, leading to the increase of [Ca2+] , has been reported to occur after electrical (MacVicar el al., 1991) or chemical (Jensen and Chiu, 1991) depolarization of cultured astrocytes, as well as after KC1 depolarization of astrocytes in situ utilizing acute brain slices (Porter and McCarthy, 1995). Accordingly, astrocytes express membrane ion channels, including voltage-sensitive Na+ and K+ channels as well as VSCCs, which may represent the molecular substrate of this aptitude (Barres et al., 1990 Verkhratsky and Steinhauser, 2000). 

Similar results have been obtained when the effect of GABA on the release of glutamate was studied in spinal cord gliosomes. In this experiment, purified gliosomes were labeled with [3H]- D-aspartate and exposed in superfusion to GABA. 

Glutamate Release from Gliosomes in a Mouse Model of Amyotrophic Lateral Sclerosis 

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