LEC 50 Ion Channels & Epithelial Transport

Question 1

What is the Nernst equation?

Answer 1

E = (60/z) log([Xout]/[Xin])

or

these are the same equation; top is just simplified

Question 2

What does the Nernst equation solve for?

Answer 2

the membrane potential (V) of an ion possessing a charge of z when the ion is in electrochemical equilibrium

Question 3

How do we use the calculated membrane potential?

How do we interpret it?

Answer 3

• Subtracting calculated volatge (Ei) from the actual membrane voltage (Vm) tells us the direction of the net force acting on an ion
• A result greater than zero means the actual membrane potential is too electrically positive for the ion to be at equilibrium

Question 4

What direction is the net K+ movement if:

Vm = Ek

Answer 4

No net movement

Question 5

What direction is the net K+ movement if:

Vm - Ek > 0

Answer 5

There is outward movement

Cell is too positive and repels the K+

Question 6

What direction is the net K+ movement if:

Vm - EK < 0

Answer 6

there is inward K+ movement

Cell is more negative and attracts the K+

Question 7

What is the equation for electrical current through ion channels?

Answer 7

I(k)=g(k) (Vm-Ek)

Ik= electrical current
g(k)= conductance
(Vm-Ek) = difference between membrane potential (Vm) and Nernst potential (Ek)