The role of GTP-binding protein activity in fast central synaptic transmission

Guanosine 5'-triphosphate (GTP)-binding proteins (G proteins) are involved in exocytosis, endocytosis, and recycling of vesicles in yeast and mammalia n secretory cells. However, little is known about their contribution to fas t synaptic transmission. We Loaded guanine nucleotide analogs directly into a giant nerve terminal in rat brainstem slices. Inhibition of G-protein ac tivity had no effect on basal synaptic transmission, but augmented synaptic depression and significantly slowed recovery from depression. A nonhydroly zable GTP analog blocked recovery of transmission from activity-dependent d epression. Neither effect was accompanied by a change in presynaptic calciu m currents. Thus, G proteins contribute to fast synaptic transmission by re fitting synaptic vesicles depleted after massive exocytosis.