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Homework Help: Calculating number of ion channels in lipid bilayer

  1. Dec 18, 2009 #1
    1. The problem statement, all variables and given/known data

    Calculate number of channels present in a lipid bilayer

    q = 1.6^-19; D (diffusion constant) = 1.2E-9; C (Concentration); 4.36; k = 1.38E-23; T=298; d = 2.5E-9

    Therefore G1 = 1.27E-17

    Channel area = 7.07E-18

    measured conductance (from injecting Na+ concentration of 100mM) = 149.24uS

    2. Relevant equations

    G1 (conductance) = q^2DC/kTd

    Gm = g/[tex]\pi[/tex]r^2

    3. The attempt at a solution

    Conductance of a single channel = 1.27E-12 x 7.07E-18
    Number of channels = Gm/G1 ??

    Calculating the number of channels is what is getting to me. I have the area of the channel, and I have a measured conductance from injecting a concentration

  2. jcsd
  3. Dec 19, 2009 #2
    The conductances sum as you mention. I would think that N = Gm/G1 just as you suppose. Did you not get the right answer?
  4. Dec 19, 2009 #3
    Yep. Tried that and my answer came out a few order of magnitudes out...double and triple checked all my work and still..could be that the answer given is incorrect.
  5. Dec 19, 2009 #4
    Not sure and without access to my books/notes, may be unable to help here: in your modelling, do you assume that a leak conductance is present?
  6. Dec 20, 2009 #5
    Thanks denverdoc.

    I figured it out (I think). But yes, leak conductance was taken into account; I think the only way to go is to divide Gm/G1.

  7. Dec 20, 2009 #6
    Your welcome for what is is was worth--amazing how much one forgets--once upon a time,many moons ago, I was a post doc in an electrophysiology lab.:blushing:
  8. Jan 2, 2010 #7
    So I thought I figured this out - but I haven't!

    I have some values, as a test, and I can't seem to get it right.

    Can anybody please help!? I know it uses the equations above, but something is going wrong in the last step when I'm trying to calculate the number of channels and conductance...I know what the answers should be; number of channels is 3E6


    bilayer area = 1.1E-6m2
    bilayer thickness = 2.5E-9m
    channel radius = 1.5E-9m
    channel thickness = 2.5E-9
    diffusion constant = 1.2E-9
    dielectric constant = 2.3
    change in energy (i.e [tex]\Delta[/tex]U or sometimes [tex]\Delta[/tex]E)

    can anybody help please?
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