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Concentration gradient force Vs. electrical gradient force

  1. Aug 2, 2017 #1
    Hi Everyone,

    I was just learning about action potential generation via electrochemical gradients. I was just wondering, does anyone know whether a +1 unit of concentration gradient is stronger/weaker than a +1 unit of electrical gradient?

    For example: If side-A of a split chamber had a net charge of +1, while side-B had a balanced net charge of 0. But side-B had one extra K+ ion than side-A. If the membrane was only permeable to K+ ions, the concentration gradient of side B would cause a force on the K+ ions (on side-B) to go to side-A, but the electrical gradient on side-A would cause a force on K+ ions (on side-A) to go to side-B. Which force is stronger?

    What term would I have to google to learn more about the forces generated by each gradient and each marginal unit of increase/decrease of concentration/charge? - This is all very interesting to me! :)

    Nate
     
  2. jcsd
  3. Aug 2, 2017 #2

    jim mcnamara

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    Staff: Mentor

    Actually this is a pretty good first question.

    I think you mean osmotic pressure for a concentration gradient. And there is a practical limit to the number of ionized K+ can diffuse through a membrane. The actual differences in either of these is only important over small distances across a membrane, limited by how fast Potassium or other ions can diffuse through water. There is also something called active transport - molecules move into or out of a cell against osmotic pressure through special structures in the membrane itself. Let's stop there for now.

    Osmosis is your first choice here - video:
    https://www.khanacademy.org/science/biology/membranes-and-transport/diffusion-and-osmosis/v/osmosis

    The action potential in neurotransmission (how nerves "talk"to one another):
    https://en.wikipedia.org/wiki/Neurotransmission This has nice graphics. Note the calcium channels.


    Now come and ask if you get confused.
     
  4. Aug 2, 2017 #3
    What is the origin of this 'practical limit' to the number of ionized K+ that can diffuse though a membrane? - isn't any limit of an ion's travel from one side to the other side of the membrane just determined by the electrochemical gradient (the combined forces derived from the concentration/electrical gradients)?

    If we were to exclude active transport, and just think about passive transport.. how can i determine the likelihood of whether an efflux of an influx of K+ will occur with my original question of one extra +1 net charge on side-A and one extra K+ on side-B?

    My original question arose from the following picture - an example of showing the two forces in action:

    figure_04_05a_labeled.jpg
     
  5. Aug 2, 2017 #4

    jim mcnamara

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    Staff: Mentor

    Your picture shows an equilibrium state and gives you the results in terms of electric potential.
    http://antranik.org/movement-of-substances-across-cell-membranes/

    Look for the words maximal flux in the second graphic - that is what I refer to for maximum limits. Think of it as traffic flow during rush hour, no more room for more cars (or ions) on the road sometimes.
     
  6. Aug 2, 2017 #5
    Thankyou! This was all very helpful!
     
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