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

 

[quicknote]

I can explain the effect of potassium concentration on membrane potential in the following way:

Increasing the concentration of potassium ions outside the cell will indeed cause the equilibrium membrane potential to become less negative in magnitude. This is because the presence of more potassium ions outside the cell will create a higher concentration gradient, driving more potassium ions out of the cell. This will result in a decrease in the overall negative charge inside the cell, thus decreasing the magnitude of the membrane potential.

In addition, the increased concentration of potassium ions outside the cell will also directly affect the rate of ions flowing out. As you mentioned, the concentration gradient outward becomes less, meaning there is less of a difference in concentration between the inside and outside of the cell. This will result in a slower rate of ions flowing out of the cell.

Overall, the increase in potassium concentration outside the cell will lead to a decrease in the magnitude of the membrane potential due to both the compensating effect of the extra external potassium ions and the decrease in concentration gradient driving ions out of the cell. I hope this helps to clarify the concept.