X-Message-Number: 26895 From: Date: Sun, 28 Aug 2005 08:13:43 EDT Subject: Uploading technology (1.vi.1) Channel diversity (2 tension gated). Uploading technology (1.vi.1) Channel diversity (2 tension gated). I'll try to see here how the very large channel number can be compressed to a manageable value in a uploading neuron. Very often, neurobiology find a large number of similar channels, the question then arise: Are they useful on an information ground?The first idea is that if they are here they are good for something. In fact, a gene can be duplicated and each copy start to evolve along its own path, if that gene code for a channel protein, after some time there will be a number of different channels. They'll persist if there is no selective pressure to discard them. In fact, they may be useful, assume for example that after some diverging evolution, a bacterial toxin cling to one channel receptor and not at an equivalent one. If there is sucha bacterial infection, it will block one channel species and let the other free. This could be a life or death question for the organism concerned. So, here is indeed a selective pressure for a large channel diversity. Even if that diversity has no information processing usefulness. The tension gated channels are one of the main component of the fast information processing. they open at the millisecond level and can close nearly as rapidly. If they are not ion selective, Na+ and K+ are the main ionic species to contemplate. Na+ is depolarising and K+ is hyperpolarising. Most interesting channels are ion selective, at least to some degree. So, here are four ionic channels famillies: Those using Na+, the K+, the Cl- and the Ca++. Ca++ and Na+ are depolarising, ie they tend to start an action potential, the other are hyperpolarising and silence the neuron. These could be defined by a two bits identification system, for example: 00 = Na+, 01 = Ca++, 10 = Cl- and 11 = K+. The next property is the opening threshold, it is near the - 65 mV equilibrium tension of the membrane for Na+, so that even a small depolarisation open them and produce a larger depolarisation. Ca++ ones ask for a larger depolarisation to open in most case, even if there are some channels with threshold in the -50 to -60 mV range. Tension generated depolarisation works often as a two stage system: First Na+ channels open and then the Ca++. Four tension threshold seems sufficient for each ion, but Ca++ may need up to five possibilities, so that this property would be coded on 3 bits and give 8 possibilities. A channel may remain open without time limit if the membrane tension allows it. Other close after some time, whateven the tension. We can define a 2 bits command to express that: 00 No closing. 01 Closing after a long time, tens of milliseconds. 10 Medium time closure. 11 fast closure. Some channels have a second closing system that forbid any new function for a given time. There could be one bit for that: 0 for non refractory closure, 1 for the refractory system present. It may not be useful for tension gated channels to take into accound a parameter such the channel conductivity or modulation by some extra parameters. It could be neverthless interesting to include that in the identification word, so that the format would be the same for chemicaly gated channels. Here, I have been one step beyond a simple factual description of the tension gated channels, The computer information format of the command word has been defined in broad lines. All the information processing elements of the neuron must be worked out this way. Yvan Bozzonetti. Content-Type: text/html; charset="US-ASCII" [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=26895