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Homework Help: Electrical processes through a membrane - active transport

  1. Feb 24, 2017 #1


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    1. The problem statement, all variables and given/known data

    I am given the configuration below of a membrane and it is said that Na+ ions are transported actively through transporters from the inside to the outside.
    The J_Na_a seen below is the active current density of the Na ions and it is constant.
    Vm is the potential difference on the membrane.
    M is a neutral macromolecule that cannot be transported (n_M mol of it).
    Both the sodium and chloride ions can be transported with the conductivities stated in the figure below.

    Using the quantities given (everything I've mentioned and in the figure), I need provide equations that satisfy:
    1. Electo-neutrality
    2. Osmotic balance
    3. Chloride ion equilibrium
    4. Sodium ion equilibrium

    Draw an equivalent circuit that describes this.

    Vm0 is the resting potential. Find the inner concentrations, the resting potential and the volume V as a function of the outer concentrations, n_M, the conductivites and the active current density.


    2. Relevant equations

    3. The attempt at a solution

    This is what I've done so far:

    1. For electro-neutrality I required outside and inside that the concentrations be equal

    2. For osmotic balance, equal concentrations

    3. For each ion equilibrium, the potential across the membrane equal to the Nernst potential of each of the ions

    However I am quite unsure of 3. The fact that there's this macromolecule is bothering me and making me think that taking the Nernst potential of each ions equal to the Vm is wrong.

    Can anybody tell me if this is right please?

    Thanks in advance.
  2. jcsd
  3. Mar 1, 2017 #2
    Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
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