Fig. 8.

A schematic view of the distribution of Ca²⁺ channels in the calyx of Held (not drawn to scale). Within a release site, three subtypes of channels, P/Q-, N-, and R-type channels are equally close to the docked vesicle. The local Ca²⁺ domains created by the opening of channels overlap within the release site. Some Ca²⁺ channels, labeled as “distant Ca²⁺ channel”, are located so far from this or other release sites that their Ca²⁺ domains do not contribute to release. A larger fraction of N- and R-type than P/Q-type channels are distant Ca²⁺ channels.