Description:
<jats:p>Classical neurotransmitters, including monoamines, acetylcholine, glutamate, GABA, and glycine, are loaded into synaptic vesicles by means of specific transporters. Vesicular monoamine transporters are under negative regulation by α subunits of trimeric G-proteins, including Gα<jats:sub>o2</jats:sub>and Gα<jats:sub>q</jats:sub>. Furthermore, glutamate uptake, mediated by vesicular glutamate transporters (VGLUTs), is decreased by the nonhydrolysable GTP-analog guanylylimidodiphosphate. Using mutant mice lacking various Gα subunits, including Gα<jats:sub>o1</jats:sub>, Gα<jats:sub>o2</jats:sub>, Gα<jats:sub>q</jats:sub>, and Gα<jats:sub>11</jats:sub>, and a Gα<jats:sub>o2</jats:sub>-specific monoclonal antibody, we now show that VGLUTs are exclusively regulated by Gα<jats:sub>o2</jats:sub>. G-protein activation does not affect the electrochemical proton gradient serving as driving force for neurotransmitter uptake; rather, Gα<jats:sub>o2</jats:sub>exerts its action by specifically affecting the chloride dependence of VGLUTs. All VGLUTs show maximal activity at ∼5 m<jats:sc>m</jats:sc>chloride. Activated Gα<jats:sub>o2</jats:sub>shifts this maximum to lower chloride concentrations. In contrast, glutamate uptake by vesicles isolated from Gα<jats:sub>o2</jats:sub><jats:sup>-/-</jats:sup>mice have completely lost chloride activation. Thus, Gα<jats:sub>o2</jats:sub>acts on a putative regulatory chloride binding domain that appears to modulate transport activity of vesicular glutamate transporters.</jats:p>