PHOSPHOCREATINE-DEPENDENT GLUTAMATE UPTAKE BY SYNAPTIC VESICLES - A COMPARISON WITH ATP-DEPENDENT GLUTAMATE UPTAKE

ATP-dependent uptake of glutamate into synaptic vesicles has been well documented. Stimulation of glutamate uptake into synaptic vesicles by other high-energy phosphates has not been described, In this paper, w e examine the stimulation of phosphocreatine (PCr)-induced glutamate u ptake and determine whether this stimulation is secondary to conversio n of PCr to ATP. We found the following, 1) PCr stimulates glutamate u ptake into synaptic vesicles in the absence of added ATP. 2) At a glut amate concentration of 50 mu M, no concentration of added ATP could pr oduce the degree of stimulation seen in the presence of PCr. 3) 0.5 mM iodoacetamide completely inhibits synaptic vesicle creatine kinase ac tivity but does not inhibit PCr-stimulated glutamate uptake, 4) PCr-de pendent glutamate uptake, unlike ATP-dependent uptake, is not magnesiu m- or chloride-dependent. 5) 0.5 mM N-ethylmaleimide, a selective H+-A TPase inhibitor, completely inhibits ATP-dependent glutamate uptake bu t only slightly inhibits PCr dependent glutamate uptake, 6) PCr-depend ent glutamate uptake is sensitive to valinomycin, a K+/H+ translocator , whereas the ATP-dependent uptake is not, Therefore, it appears that in addition to the well-known ATP-dependent glutamate uptake system, t here is a previously unreported PCr-dependent glutamate uptake system in synaptic vesicles, The total glutamate uptake by synaptic vesicles is likely the sum of both ATP- and PCr-dependent glutamate uptake.