Why a decrease in serum potassium causes the resting membrane potential to become more negative? ?

Question

Why a decrease in serum potassium causes the resting membrane potential to become more negative? ?

Answer 1

Hmm, this is a little tough to answer without diagrams, but I'll give it a bash.

Consider a whole bunch of potassium ions (K+) on the inside of the cell.  Some will tend to run down their concentration gradient and end up outside the cell, right?

This process will continue for a bit, but after a short while the other potassium ions OUTSIDE the cell start opposing this tendency.  This is because the potassium ions outside the cell (like those inside) are positively charged, and so repel any other positively charged K+ ions from moving out the cell.

Thus, eventually the CHEMICAL gradient (tending to move potassium ions out of the cell) is balanced by ELECTROSTATIC repulsion (tending to keep the ions within the cell).

If you now suddenly drop the serum potassium (i.e. the K+ outside the cell), the chemical gradient becomes steeper, and the electrostatic repulsion lessens (fewer K+ ions).  Therefore, more K+ ions will leave the inside of the cell and move to the outside.

Therefore the inside of the cell will become more negative relative to the outside, since more positively charged ions have left it than did so before.  This is another way of saying that the resting membrane potential will become more negative.

Hope that all made sense!  Another way of looking at it would be to simply plug the figures into the Nernst equation and see what you get out.  You can find a website for this here: http://www.medicalcomputing.net/action_p...