Physiology: Effect on Membrane Potential

[bjgawp]

Hello all.

I just had a few conceptual problems if someone wouldn't mind explaining to me.

When looking at a simple cell membrane, potassium ions tend to move out of the cell along their concentration gradient until its electrical gradient is strong enough to counterbalance it, thus producing its equilibrium potential.

Typically, the equilibrium membrane potential is about -60 mV while that of potassium is -90 mV.

Now, if we increased the concentration of potassium outside, this would cause both the equilibrium membrane and potassium potential to become less in magnitude, right? However, I'm not quite sure how to exactly formulate in words what exactly is going on.

Is it because the presence of the extra external potassium ions compensate for the negative charge inside the cell? Also, I would presume that the concentration gradient outward becomes considerably less and thus the rate of ions flowing out would be as well but I'm not entirely sure how that directly affects membrane potential.

Any help would be appreciated, thanks!

 

[Veovis]

Membrane eq. potential is relatively close to the K+ eq. potential. If the K+ eq. potential decreases in magnitude, then the membrane eq. potential follows it.
However, as we could think, the membrane potential is caused by the charge distribution among the inner and outer sides of the cell, and therefore one shloud expect that the adding of K+ outside implies an increse in magnitude of the membrane potential.
I'm also lost, and even with the equations at hand, I'm unable to explain the phenomenom in words