Nanodomain
A nanodomain is a nanometer-sized cluster of proteins found in a cell membrane. They are associated with the signal which occurs when a single calcium ion channel opens on a cell membrane, allowing an influx of calcium ions (Ca) which extend in a plume a few tens of nanometres from the channel pore. In a nanodomain, the coupling distance, that is, the distance between the calcium-binding proteins which sense the calcium, and the calcium channel, is very small, less than , which allows rapid signalling. The formation of a nanodomain signal is virtually instantaneous following the opening of  the calcium channel, as calcium ions move rapidly into the cell along a steep concentration gradient. The nanodomain signal collapses just as quickly when the calcium channel closes, as the ions rapidly diffuse away from the pore. Formation of a nanodomain signal requires the influx of only approximately 1000 calcium ions. Coupling distances greater than , mediated by a larger number of channels, are referred to as microdomains. nanodomain Properties. Nanodomain signals are thought to improve the temporal precision of fast exocytosis of vesicles due to two specific properties: Single channels are able to cause vesicular release, however, the cooperativity of  different calcium channels is synapse-specific. The release driven by a single calcium ion channel minimizes the total calcium ion influx, overlapping domains can provide greater reliability and temporal fidelity.