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Abstract

Complexins are small synaptic proteins which cooperate with the SNARE-complex during synaptic transmission. Different roles of complexins in the regulation of vesicle exocytosis have been proposed. Based on the results of genetic mutation or knock down/out studies, it is generally agreed that complexins are involved in vesicle priming and exocytosis during fast synchronous release and in clamping vesicles to prevent asynchronous release. However, depending on cell type, organism and experimental approach used, complexins appear to either facilitate or inhibit vesicle fusion. Here, we study the function of complexin I at the calyx of Held synapse. By taking advantage of the large size of the calyx terminal, allowing direct patch-clamp recordings, we investigate the consequences of the loss of function of complexin I. We demonstrate a developmentally aggravating phenotype of reduced EPSC amplitudes and enhanced asynchronous release. We provide evidence for a role of CPX I in recruiting Ca2+ channels to docked vesicles which may determine their release probability. The enhanced asynchronous release in complexin-deficient mice slowed-down the recovery of synchronous EPSCs after stimulus trains suggesting both, synchronous and asynchronous release events, were fed by a common pool of vesicles.