The closing of e.g. a Na-gate

[Function]

Hello everyone

 

First of all, Merry Christmas.

 

Closing a Na-gate causes hyperpolarization.

 

Why won't Goldman's formula tell us this?

 

Goldman tells us that you get hyperpolarization if the ratio

 

[math]\frac{p_K[K^+]_i+p_{Na}[Na^+]_i}{p_K[K^+]_e+p_{Na}[Na^+]_e}[/math]

 

is getting bigger and bigger.

 

Closing the sodium channels only has an effect on the permeability of sodium, so either the internal concentration of sodium must raise, or either the external concentration must lower.

 

(Consider pK, [K+]i and [K+]e constant. So the potential would now only rely on pNa, [Na]i and [Na]e.)

 

However, closing a sodium channel causes the external sodium concentration to raise, and the internal concentration to lower... Which is quite contradictory to which is written above.

 

I could, however, count in terms of those permeabilities: closing sodium channels lowers the permeability for Na, so, relatively seen, raises the permeability for K... So the membrane potential would go more to the Em(K), causing a hyperpolarization...

 

But why won't Goldman work?

 

Thanks.

 

Other problem, more in the form of a question:

 

What will closure of K-channels provoke?

 

a) hyperpolarization

b) depolarization

 

I've got, once again, 2 hypotheses:

• Intuitively, internal K-concentration raises, external lowers, so, according to Goldman, hyperpolarization.
• Relative permeability pK/pNa lowers, so the potential must go more towards Em(Na), which results in a depolarization.

I'm desperate. Which one is correct? And, more important, why is the other one incorrect, or less correct?

 

F.

Edited December 25, 2014 by Function