Membrane Potentials

Question 1

Define membrane potentials.

Answer 1

Difference between electrical charge inside the cell compared to outside

Question 2

Is membrane potential quantifiable?

Answer 2

YES
- If there are more positively charged ions outside the cell compared to inside, there is an electrical difference since outside is more positive
- This can be measured using a voltmeter in mV

Question 3

What allows membrane potential to be managed in cells?

Answer 3

Ions don’t move freely through bilayer.

Question 4

What would occur to membrane potential if a channel protein is inserted into membrane?

Answer 4

• Ions will move down concentration gradient
• EXAMPLE: Movement of positively charged ions out of cell cause inside of cell to become more progressively negative

Question 5

What can happen if membrane potential rises?

Answer 5

Intracellular changes e.g release of chemicals

Question 6

Give examples of electrically active cells.

Answer 6

• Neurons
• Muscle cells - contraction occurs upon a change in membrane potential
• Pancreatic cells - alter electrical activity to regulate blood glucose

Question 7

Ion distribution between intracellular and extracellular space is uneven. What does this allow?

Answer 7

Concentration gradients

Question 8

Why does potassium favour outward movement?

Answer 8

Intracellular [K+] > Extracellular [K+]
- Moves down concentration gradient

Question 9

Why does sodium favour inward movement?

Answer 9

Intracellular [Na+] < Extracellular [Na+]
- Moves down concentration gradient

Question 10

What charge do proteins have? Are they permeable to the membrane?

Answer 10

• Negative
• No

Question 11

Describe maintenance of resting membrane potential in neurons.

Answer 11

• Mediated by potassium ions out of cell to maintain negative potential
• Permeability is 1
• Relative permeability of sodium is 0.04 and chloride is 0.45

Question 12

Describe the Gibbs-Donnan effect.

Answer 12

• Positively charged ions move down a concentration gradient until two sides are of equal concentrations i.e chemical potential
• Negatively charged ions will attract positively charged ions in opposite direction to concentration gradient i.e electrical potential
• Ions become unevenly distributed

Question 13

When is the Nernst equation used?

Answer 13

• Find equilibrium potential
• Opposing forces from the Gibbs Donnan effect are equal so no net movement of ion across membrane

Question 14

Outline the Nernst equation.

Answer 14

𝐸_𝑥=(𝑅 𝑇)/(z 𝐹) x ln(𝑋_𝑜𝑢𝑡/𝑋_𝑖𝑛)

Question 15

What is the resting membrane potential of a neuron at rest?

Answer 15

-70 mV

Question 16

If a cell is only permeable to potassium, what would resting membrane potential be expected to be?

Answer 16

• Expected to be close to equilibrium potential of potassium

Question 17

When would the Goldman-Hodgin-Katz equation be used?

Answer 17

• Cell is permeable to various ions
• Uses relative permeabilities and concentrations of ions to find a cell’s resting membrane potential

Question 18

What has the largest effect on resting membrane potential?

Answer 18

POTASSIUM - due to its high permeability

Question 19

Resting membrane potential of a cell is measured to be -75 mV. What contributes to it/

Answer 19

• -70 mV from ‘leak’ channels - allowing specific ions to move down concentration gradient
• -5 mV from sodium potassium ATPase

Question 20

How does the sodium potassium ATPase work?

Answer 20

• Uses ATP since ions moved against concentration gradient
• 3 sodium ions moved out of cell in exchange for 2 potassium ions into cell
• Inside becomes slightly more negative than outside

Question 21

Resting membrane potential is close to equilibrium potential of potassium in neurons. What can be inferred from this?

Answer 21

• Potentials are close - potassium plays role in determining RMP
• RMP slightly more positive than Ek so other ions are involved

Question 22

In cardiomyocytes, RMP is closer to Ek (iin relation to the neurons)?

Answer 22

• RMP determination is more influenced by potassium ions in cardiomyocytes, compared to neurons