Cultured astrocytes express proteins involved in vesicular glutamate release

Abstract

Bradykinin induces receptor-mediated calcium-dependent release of glutamate from cultured astrocytes through a mechanism that is neither due to cell-swelling mechanism nor due to the reversal of the glutamate transporter. Astrocytes may thus release glutamate using a mechanism resembling the neuronal vesicular release of neurotransmitters. Synaptobrevin is a vesicular protein that together with plasma membrane proteins syntaxin and SNAP-25 participate in formation of the anchoring core complex required for initiation of exocytosis. Here, we demonstrate that synaptobrevin II is present in cultured astrocytes. Furthermore, we demonstrate that botulinus toxin type B and tetanus toxin cause a decrease in synaptobrevin II immunoreactivity and abolish bradykinin-induced release of glutamate from cultured astrocytes. While we were not able to demonstrate the presence of SNAP-25 or syntaxin immunoreactivity in cultured astrocytes, pretreatment with BoTx-A (which cleaves SNAP-25) and BoTx-C (which cleaves syntaxins) result in a decrease in the baseline release of glutamate and diminish the bradykinin-evoked release of glutamate from cultured astrocytes. These findings strongly support the notion that astrocytes may release neurotransmitters using a mechanism similar to the neuronal secretory process.