DISSOCIATION BETWEEN CA2-TRIGGERED SYNAPTIC VESICLE EXOCYTOSIS AND CLATHRIN-MEDIATED ENDOCYTOSIS AT A CENTRAL SYNAPSE()

We have tested whether action potential-evoked Ca2+ influx is required to initiate clathrin-mediated synaptic vesicle endocytosis in the lam prey reticulospinal synapse. Exo- and endocytosis were temporally sepa rated by a procedure involving tonic action potential stimulation and subsequent removal of extracellular Ca2+ (Ca-e(2+)). A low concentrati on of Ca2+ ([Ca2+](e) of 11 mu M) was found to be required for the ind uction of early stages of endocytosis. However, the entire endocytic p rocess, from the formation of clathrin-coated membrane invaginations t o the generation of synaptic vesicles, proceeded in the absence of act ion potential-mediated Ca2+ entry. Our results indicate that the membr ane of synaptic vesicles newly incorporated in the plasma membrane is a sufficient trigger of clathrin-mediated synaptic Vesicle endocytosis .