Chasing channels: Progress in calcium channel localization in the C. Elegans synapse

Calcium channels play a crucial role in neurotransmission by facilitating the flow of calcium ions necessary for synaptic vesicle fusion and neurotransmitter release. Different types of calcium channels participate in this process in the neurons of the nematode C. elegans. L- and N-type channels respond to high voltages, and L-type channels inactivate more slowly. Both are thought to contribute to synaptic transmission. Ryanodine receptors are implicated in calcium-induced calcium release and may contribute to vesicle fusion via the release of calcium ions from internal stores. We are interested in localizing these channels to further understanding of their coordination of this vital process. Aside from its intrinsic value, such knowledge may prove beneficial in the understanding the nature of channelopathies that have been shown to be related to a variety of neurological disorders. Here, we present our findings regarding the localization of these three different types of channels in relation to the dense projection, an important organizing center that demarcates the most active area of the synapse. We localize the channels directly using correlative super-resolution fluorescence electron microscopy. Functional channels are genetically tagged with photo-convertible proteins that can be precisely localized using photoactivateable localization microscopy (PALM). We image the same sections using scanning electron microscopy (SEM) to create a map of protein distribution at the synapse. We combine these imaging data with those from an optogenetic experimental approach to the same question. We hypothesize that N-type channels initiate vesicle release in closest proximity to the dense projection while L-type channels and ryanodine receptors do so at further distances.