Last Entry B4 Common Test

What your teacher do in his free time sometimes:
think of possible misconceptions or highly contestable areas of discussions with himself. dun you ever read something or realise something out of the blue that just doesn't fit right in your schema of knowledge but yet cannot pinpoint the source until you start a discussion with yourself? or with someone for that matter. or felt that impulse for a thorough check as you flipped thru pages n pages of books or webpages?

Anyway, here is something which I try to reconcile after spending quite a large part of my day talking to my alter-ego.

Question:
How is the resting membrane potential (RMP) restored after hyperpolarization?

Well, after an extensive search, this issue is actually not very well-documentated but reference has often been made to a role of Na+/K+ pump in restoring the RMP. Most would not even discuss it (with particular reference to ion movements) and simply refer to a restoration of RMP with the efflux of K+ ions.

Sub-Question: If Na+/K+ pump is involved, wouldn't the membrane potential be even more hyperpolarized? - note the pump will exchange 3 Na+ (out) for 2 K+ (in), thus there is a net outward ionic current.
So here is my thought which I believed is correct and reasonably so after consulting several books, reading in-betw lines and based on prior knowledge of the field.

After hyperpolarization has occured, the two voltage-gated channels (Na+/K+) are closed so we are only going to take a look at the leak channels of Na+ and K+.

Because now the membrane is now more -ve inside, there is a greater attraction for the Na+ as the ion - greater Na+ influx. Concurrently there is a greater attraction for the K+ in the cells as well so there is less K+ efflux. The interplay between the two ions movements will eventually bring the membrane potential to RMP.

How does Na+/K+ pump come to play?

Because the pump will naturally cause nett -ve charge in the cell, it helps to facilitate the ions movements.

THUS, it would be more accurate to say that the Na+/K+ pump HELPS to restore the RMP.

(The above is OFS)


You may ask: Do we need to know about leak channels?

Yup yup yup. But only in the context of how RMP is established.
And you should know that Na+/K+ pump is critical in maintaining the Na+ and K+ ionic gradient across the membrane but not with the formation of AP.



A penny for your thoughts?