Lecture 4 - The Resting Membrane Potential

Question 1

What is the resting membrane potential?

Answer 1

The voltage difference between the inside and the outside of the cell

Question 2

What is the m gate? and what is it like during rest?

Answer 2

The m gate is the activation gate, and it is closed during rest

Question 3

What is the h gate? and what is it like during rest?

Answer 3

The h gate is the inactivation gate and it is usually open during rest

Question 4

What is meant by flux?

Answer 4

Movement, occurring due to the difference in concentration across the membrane

Question 5

What is meant by diffusion?

Answer 5

Principle of moving from regions of high to low concentrations

Question 6

Why can Equilibrium potential occur?

Answer 6

Due to the permeability of the membrane

Question 7

Explain the experiment to find equilibrium potential:

Answer 7

Beaker with partition separating two sides, with two different ion concentrations either side, measure electrical differences using voltmeter, no potential difference will be detected between them, this is because of the impermeable membrane barrier between the solutions, so there is no flux, no movement of electrical charge, so no potential difference
Now we change the partition to a permeable membrane, so we now have a route for the high concentration to move to the low, a mechanism for diffusion to occur, e.g. add a potassium channel, so K+ will move down its concentration gradient by diffusion, so a positive charge will build up in the other chamber, thus an electrical charge builds up, opposing the movement down the concentration
Continues to build up until the electrical difference exactly balances the concentration difference, and equilibrium is reached – ions continue to move, but the same number leave as enter, so it is balanced, so electrical difference (charge) exactly balance the chemical difference (concentration)

Question 8

What equation can be used to calculate Equilibrium potential?

Answer 8

The Nernst Equation

Question 9

What is the Nernst Equation?

Answer 9

Elon = RT/zF ln[ion]1/[ion]2
R = Gas constant
T = Absolute temperature (K)
z = Valence of ion
F = Faraday constant

However can remove the constant as they are always going to be the same, and we can remove the natural log to leave:
Elon = 61/z log [Ion]outside/[Ion]inside

Question 10

What is valency?

Answer 10

The measure of the combining capacity of atoms or molecules

The electrons present in the outermost shell/orbit of an atom are called valence electrons

Question 11

What is the Goldman-Hodgkin-Katz Equation?

Answer 11

E = 61/z log P[K+]outisde + P[Na+]outside…
———————————————-
P[K+]inside + P[Na+]inside…
This equation considers other ions

Question 12

What is the RMP of a ventricular cell? And how does this effects movement of ions?

Answer 12

Around -80mV
This is less negative than the Eq pot for K+ (-90mV) so K+ tends to move out the cell as the electrical potential isn’t sufficiently negative to match the outward concentration gradient
Also, at -80mV, sodium will tend to move into the cell, driven by both a concentration and an electrical gradient
If all Na+ comes into the cell and K+ leaves, then RMP would eventually disappear
Action of NA+/K+ ATPase prevents this

Question 13

Features of Sodium-Potassium Pump:

Answer 13

An active transport - requires ATP
3 Na+ out and 2 K+ in
The pump moves ions against their electrochemical gradient, by forming complexes with them and then changing their conformation to deliver the ion to the other side of the membrane

Question 14

What are normal potassium levels?

Answer 14

3.5 - 5.3 mmol/l

Question 15

What is too much K+ called?

Answer 15

HYPERkalaemia

Question 16

What is too little K+ called?

Answer 16

HYPOkalaemia

Question 17

What happens if we get altered potassium levels?

Answer 17

We get disruption of the resting membrane potential, leading to dysfunctional cells, leading to a dysfunctional body