The heterotrimeric G protein Go2 regulates catecholamine uptake by secretory vesicles

Secretory vesicles store neurotransmitters that are released by exocytosis, Their membrane contains transporters responsible for transmitter loading that are driven by an electrochemical proton gradient across the vesicle membrane, We have now examined whether uptake of noradrenaline is regulated by heterotrimeric G proteins, In streptolysin O-permeabilized PC 12 cells, GTP-analogues and AIF(4)(-) inhibited noradrenaline uptake, an effect that was sensitive to treatment with pertussis toxin, Inhibition of uptake was prevented by G alpha o-specific antibodies and mimicked by purified activated G alpha o(2). No effect was seen when G alpha o(2) in its inactive GDP-bound form or purified activated G alpha o(1), G alpha i(1) and G alpha i(2) were tested, Down-regulation of uptake remained unchanged when exocytosis was inhibited by the light chain of tetanus toxin, Vesicular acidification was not affected whereas binding of [3H]reserpine was reduced by GTP gamma S and G alpha o(2). These data suggest that the monoamine transporter rather than the vacuolar ATPase is affected, We conclude that catecholamine uptake is controlled by G alpha o(2), suggesting a novel function for heterotrimeric G proteins in the control of neurotransmitter storage.