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Two concentrations of calcium ions inside and outside the membrane

  1. Jan 7, 2010 #1
    This isn't homework - just working through questions in my text. The question gives two concentrations of calcium ions inside and outside the membrane and asks to find the Nernst potential - ok no problem there.

    Then it asks if the calcium ions are in equilibrium if the resting potential is 70mV. If they were in equilibrium, then

    E = (RT/zF)(ln([outisde]/[inside])

    But then, at calcium equilibrium, the ratio would be 1... ln(1) = 0 and there would be no potential... am I correct?

    Thanks,

    Mark
     
  2. jcsd
  3. Jan 7, 2010 #2

    Andy Resnick

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    Re: Biophysics

    I can't exactly figure out what you mean, but I wonder if you are mixing up a couple of ideas. At equilibrium, there is not equal concentrations; there is no current flow. The difference in concentration is balanced by the resting potential (which is the E in your equation). Don't forget calcium has 2 charges.
     
  4. Jan 7, 2010 #3
    Re: Biophysics

    I still can't see how to figure out if the calcium is in equilibrium, I would only be able to get the ratio of the two concentrations... no?

    mark
     
  5. Jan 8, 2010 #4

    Andy Resnick

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    Re: Biophysics

    I suppose that's true, the concentration *gradient* is what drives motion, not the absolute value of concentration. But again, I think I am not really understanding your original question. It almost seems as if you are treating the Nernst and resting potential to be the same (and I don't think they are).
     
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