THE HETEROTRIMERIC G-PROTEIN GO(2) REGULATES CATECHOLAMINE UPTAKE BY SECRETORY VESICLES

Secretory vesicles store neurotransmitters that are released by exocyt osis, 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 noradrena line is regulated by heterotrimeric G proteins, In streptolysin O-perm eabilized PC 12 cells, GTP-analogues and AIF(4)(-) inhibited noradrena line uptake, an effect that was sensitive to treatment with pertussis toxin, Inhibition of uptake was prevented by G alpha o-specific antibo dies and mimicked by purified activated G alpha o(2). No effect was se en when G alpha o(2) in its inactive GDP-bound form or purified activa ted G alpha o(1), G alpha i(1) and G alpha i(2) were tested, Down-regu lation of uptake remained unchanged when exocytosis was inhibited by t he light chain of tetanus toxin, Vesicular acidification was not affec ted whereas binding of [3H]reserpine was reduced by GTP gamma S and G alpha o(2). These data suggest that the monoamine transporter rather t han the vacuolar ATPase is affected, We conclude that catecholamine up take is controlled by G alpha o(2), suggesting a novel function for he terotrimeric G proteins in the control of neurotransmitter storage.