text: The reserve pool is not directly connected to the active zone.  The increase in presynaptic calcium concentration activates calcium–calmodulin-dependent protein kinase (CaMK).  CaMK phosphorylates a protein, synapsin, that mediates the clustering of the reserve pool vesicles and attachment to the cytoskeleton.  Phosphorylation of synapsin mobilizes vesicles in the reserve pool and allows them to migrate to the active zone and replenish the readily releasable pool.