TY - JOUR TI - Calcium dependence of neurotransmitter release at a high fidelity synapse AU - Eshra, Abdelmoneim AU - Schmidt, Hartmut AU - Eilers, Jens AU - Hallermann, Stefan A2 - Westbrook, Gary L VL - 10 PY - 2021 DA - 2021/10/06 SP - e70408 C1 - eLife 2021;10:e70408 DO - 10.7554/eLife.70408 UR - https://doi.org/10.7554/eLife.70408 AB - The Ca2+-dependence of the priming, fusion, and replenishment of synaptic vesicles are fundamental parameters controlling neurotransmitter release and synaptic plasticity. Despite intense efforts, these important steps in the synaptic vesicles’ cycle remain poorly understood due to the technical challenge in disentangling vesicle priming, fusion, and replenishment. Here, we investigated the Ca2+-sensitivity of these steps at mossy fiber synapses in the rodent cerebellum, which are characterized by fast vesicle replenishment mediating high-frequency signaling. We found that the basal free Ca2+ concentration (<200 nM) critically controls action potential-evoked release, indicating a high-affinity Ca2+ sensor for vesicle priming. Ca2+ uncaging experiments revealed a surprisingly shallow and non-saturating relationship between release rate and intracellular Ca2+ concentration up to 50 μM. The rate of vesicle replenishment during sustained elevated intracellular Ca2+ concentration exhibited little Ca2+-dependence. Finally, quantitative mechanistic release schemes with five Ca2+ binding steps incorporating rapid vesicle replenishment via parallel or sequential vesicle pools could explain our data. We thus show that co-existing high- and low-affinity Ca2+ sensors mediate priming, fusion, and replenishment of synaptic vesicles at a high-fidelity synapse. KW - synapse KW - release KW - calcium KW - vesicle fusion KW - vesicle priming JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -