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Googling for "voltage-independent" ion channels neurons doesn't give a good overview over the topic (and yields only approx. 50,000 hits, compared to 500,000 hits when searching for "voltage-dependent" ion channels neurons).

What I want to learn:

  1. How many voltage-independent ion channels are there in the brain (or in specific parts of the brain, e.g. cortex) compared to voltage-dependent ion channels? (Rough estimate, order of magnitude: a tenth, a percent, ...?)

  2. Which functional role do they play (compared to voltage-dependent channels which are mainly (?) concerned with the propagation of action potentials along the axon)?

Are there other (and possibly more concise) references than the one I found: ROLES OF THE ION CHANNEL NALCN IN NEURONAL EXCITABILITY CONTROL (which states, that NALCN is "widely expressed in the nervous system")?

(I guess voltage-independent channels could support the mechanisms of Rall's model which doesn't pressume voltage-dependent ion channels but only modifiable membrane resistances, possibly realized by voltage-independent ion channels, right?)

Addendum: I made a bad mistake not pointing out, that I meant ion channels that are neither voltage- nor ligand-gated but just influence the membrane resistance passively. (Ligand-gated ion channels are of course examples of voltage-independent ion channels, but not the ones I wanted to ask for.) Are the voltage-independent ion channels I wanted to ask for possibly just what is called leak channels?

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  • $\begingroup$ Yes those would be called leak channels; please don't change your question here though because that would be far to big a change. Note that like in my comment below, the prototypical leak channels (the two-pore-domain potassium channels) are not gated by voltage per se, but they still have some voltage sensitivity. $\endgroup$ – Bryan Krause Sep 18 '17 at 15:17
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Those would be referred to simply as 'ion channels'. Voltage-dependent channels should get special mention.

This link from the Blue Brain Project should prove useful:

http://channelpedia.epfl.ch/ionchannels/

  1. A query for 'voltage-dependent' gives me results from 58 channels. According to the original reference there should be at least 187 channels in this database (out of the estimated ~500 ion channels expressed in the brain). That should give you at least the order of magnitude.

    An additional resource can be: https://icg.neurotheory.ox.ac.uk/.

  2. 'Non-voltage gated' channels are used to depolarize and hyperpolarize the membrane. That is as much as specific the answer can be when talking about all of the ion channels. Their specific compartment localization makes a big difference, though. Those that are located in synapses have different functions compared to those that are non-synaptic, for example.

    No, voltage-dependent channels are not solely found in the axon. That is what makes dendrites active compartments as well. See this very good review and my answer to How does a neuron change as you learn?. In brief, voltage-gated channels facilitate the integration of inputs on the dendrites independently from the integration at the level of the soma. This is thought to extent the information processing capacity of the neuron.

PS: A lot of your questions suggest that you would be interested in the NEURON simulation environment, as previously suggested to you by @bryan-krause. Using this tool could save you some trouble of trying to re-invent the wheel, as you can start off by using a pre-existing model from ModelDB.

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  • $\begingroup$ Oops, I seem to have overseen something (what a shame): when did Bryan suggest NEURON to me? $\endgroup$ – Hans-Peter Stricker Sep 12 '17 at 15:50
  • $\begingroup$ Thanks anyway for your answer, I'll try to follow your advice(s). $\endgroup$ – Hans-Peter Stricker Sep 12 '17 at 15:51
  • $\begingroup$ First thing I stumbled upon at channelpedia: What does "distributed exponentially" mean? With respect to which variable (distance from soma?), and with positive or negative exponent? (I would guess negative, because channels decrease resistance, thus increase the time constant, thus decrease speed of propagation). $\endgroup$ – Hans-Peter Stricker Sep 12 '17 at 16:06
  • $\begingroup$ Marginal note: I said "mainly concerned", not "solely concerned". $\endgroup$ – Hans-Peter Stricker Sep 12 '17 at 16:09
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    $\begingroup$ Nice answer, I have two add-ons: 1) a lot of ion channels, regardless of gating, are made up of multiple subunits. In some cases they are not only heteromultimers, but each protein component can have multiple varieties that can each fit in with the other subunits. Because those subunits are somewhat exchangeable, the number of unique ion channels is quite high, although not all combinations are often observed for various reasons. 2) Lots of channels that are not thought of as voltage-gated still show some voltage dependancy. For example, IRK channels. $\endgroup$ – Bryan Krause Sep 12 '17 at 17:04

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