Dual regulation of Ca 2+- dependent glutamate release from astrocytes: Vesicular glutamate transporters and cytosolic glutamate levels

摘要

Vesicular glutamate transporters (VGLUTs) are responsible for vesicular glutamate storage and exocytotic glutamate release in neurons and astrocytes. Here we selectively and efficiently over-expressed individual VGLUT proteins (VGLUT1, 2 or 3) in solitary astrocytes and studied their effects on mechanical stimulation-induced Ca ²⁺- dependent glutamate release. Neither VGLUT1 nor VGLUT2 over-expression changed the amount of glutamate release, while over-expression of VGLUT3 significantly enhanced Ca ²⁺- dependent glutamate release from astrocytes. None of the VGLUT over-expression affected mechanically-induced intracellular Ca²⁺ increase. Inhibition of glutamine synthetase activity by L-methionine sulfoximine in astrocytes, which leads to increased cytosolic glutamate concentration, greatly increased their mechanically-induced Ca ²⁺- dependent glutamate release, without affecting intracellular Ca²⁺ dynamics. Taken together these data indicate that both VGLUT3 and the cytosolic concentration of glutamate are key limiting factors in regulating the Ca ²⁺- dependent release of glutamate from astrocytes.