What is a Nanodomain?
In molecular biology, a nanodomain, in reference to calcium signaling, is where highly localized Ca2+ signals associated with a single (or very few at most) ion channel(s) that extend over a few tens of nm from the channel pore. Larger signalling distances from the pore (>100 nm) mediated by a larger number of channels, are referred to as microdomains. Nanodomains are related to, but not the same as coupling distance, which explicitly refers to the distance between the calcium-binding proteins (or "sensors") that are located within a few nanometers of an open calcium channel. The coupling distance is particularly important in the temporality of pre-synaptic signalling and if Ca2+ influx is seen in a nanodomain then one would also expect to see tighter coupling distances in order to expose the calcium sensor to high enough concentrations of Ca2+ to cause vesicular exocytosis of neurotransmitters to occur.
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Properties of Nanodomains
Nanodomains are thought to improve the temporal precision of fast exocytosis of vesicles due to two specific properties:
It is found that single channels are able to cause vesicular release, however the cooperativity of different calcium channels is synapse specific. The release driven by a single Ca2+ channel minimizes the total Ca2+ influx, overlapping domains can provide greater reliability and temporal fidelity.