Dual regulation of Ca21-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 overexpressed 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 overexpression changed the amount of glutamate release, whereas overexpression of VGLUT3 significantly enhanced Ca~(2+)-dependent glutamate release from astrocytes. None of the VGLUT overexpression affected mechanically induced intracellular Ca~(2+) 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 Ca~(2+) 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.