Multiple types of Calcium channels and their distribution in the presynaptic nerve terminal

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After exocytosis the synaptic vesicle (SV) membrane is recycled by endocytosis. Exocytosis requires external Ca and so does endocytosis, which is supplied through voltage-gated Ca channels in the presynaptic membrane. Multiple types of calcium channels in the presynaptic terminal are participating in these processes. Ca channels designated for exocytosis are highly localized at the release site. Other types of Ca channels are probably diffusely distributed and may contribute to endocytosis. Two types of endocytosis have been demonstrated in EM at the Drosophila neuromuscular junction, namely, active-zone endocytosis that occurs at the presynaptic active zone and non-active-zone endocytosis that operates at the area away from the active zone. Recently we found that two separate types of Ca channels support these two types of endocytosis. Non-active-zone endocytosis is blocked by low concentrations of La, while active-zone endocytosis is inhibited by a spider toxin, PLTXII. Yet another type of Ca channel encoded by the gene, cacophony, is specifically designated for exocytosis. This type of channel, cac-Ca channel, is highly localized at the presynaptic active zone. The distribution of other types of Ca channels is difficult to demonstrate, but physiological findings indicate that PLTXII-sensitive channels are located close to or within the active zone, while the La-sensitive channels reside away from it. Ca is ubiquitously used a messenger. Its temporal and spatial characteristics mold its specific role. [J Physiol Sci. 2006;56 Suppl:S19]