Ca²⁺from One or Two Channels Controls Fusion of a Single Vesicle at the Frog Neuromuscular Junction

Are unreliable release mechanisms conserved from NMJ to CNS?

“…These findings are also consistent with previous studies at this synapse that have proposed that Ca 2+ flux through only one or two Ca 2+ channels can trigger transmitter release [23, 24]. Experiments combining high resolution Ca 2+ imaging [22] and MCell [25] computer modeling have provided evidence that each vesicle fusion event at this synapse is controlled predominately by a single Ca 2+ channel positioned nearby.…”

Resolution of fusion pore formation in a cell-attached patch

“…This has not been achieved previously in chromaffin cells, because existing methods for resolving transmitter release disrupt the Ca 2+ -dependence of vesicle exocytosis in the patch configuration (Albillos et al, 1997;Ales et al, 1999;Henkel et al, 2000). These data are in accord with the estimation that opening of one or two Ca 2+ channels promotes vesicle exocytosis at the neuromuscular junction (Shahrezaei et al, 2006). The discrepancy between secretory delay in neurons and neuroendocrine cells has been widely documented, and has been suggested to be due to differences in the localization of Ca 2+ channels and the release sites (Neher, 1998).…”

Calcium-channel number critically influences synaptic strength and plasticity at the active zone

“…How many open calcium channels are needed to trigger release has been debated for two decades: 1–125 channels have been proposed at different synapses 11,13,14,20,21,49 . This large discrepancy might be partly due to the use of indirect techniques such as imaging and modeling.…”