CaV1 and CaV2 calcium channels mediate the release of distinct pools of synaptic vesicles

Activation of voltage-gated calcium channels at synapses leads to local increases in calcium and the fusion of synaptic vesicles. However, presynaptic output will be determined by the density of calcium channels, the dynamic properties of the channel, the distance to docked vesicles, and the release probability at the docking site. We demonstrate that at C. elegans neuromuscular junctions two different classes of voltage-gated calcium channels, CaV2 and CaV1, mediate the release of distinct pools of synaptic vesicles. CaV2 channels are concentrated in densely packed clusters [~]300 nm in diameter with the active zone proteins Neurexin, -Liprin, SYDE, ELKS/CAST, RIM-BP, -Catulin, and MAGI1. CaV2 channels mediate the fusion of vesicles docked adjacent to the dense projection and are colocalized with the synaptic vesicle priming protein UNC-13L. By contrast, CaV1 channels are dispersed in the synaptic varicosity and are coupled to internal calcium stores via the ryanodine receptor. CaV1 and ryanodine receptor mediate the fusion of vesicles docked broadly in the synaptic varicosity and are colocalized with the vesicle priming protein UNC-13S. Distinct synaptic vesicle pools, released by different calcium channels, could be used to tune the speed, voltage-dependence, and quantal content of neurotransmitter release.