Expression of synaptobrevin II, cellubrevin and syntaxin but not SNAP-25 in cultured astrocytes

Astrocytes, a sub-type of glial cell in the central nervous system, can release the excitatory transmitters glutamate and aspartate in response to elevated levels of internal calcium. To investigate potential release mechanisms that may be present in these cells we have determined whether protein components of the neuronal secretory apparatus are expressed in astrocytes. Western blots, immunocytochemistry and RT PCR demonstrate that astrocytes express cellubrevin, synaptobrevin II and syntaxin, proteins known to form a macromolecular fusion complex. However, SNAP-25 which is another neuronal protein of the fusion complex, was not detected. Astrocyte cellubrevin and synaptobrevin II were also shown to be sensitive to the proteolytic activity of tetanus toxin. Together these data indicate that astrocytes express some proteins that are known to form a fusion complex indicating that regulated exocytosis might mediate calcium-regulated transmitter release from these cells.