3 - Action Potentials I

Question 1

What affects sensitivity of membrane bound ion channels?

Answer 1

Physical shape and chemical properties

Question 2

Gated membrane-bound channels may open/close depending on…

Answer 2

• mempot

- binding of a ligand to channel

Question 3

Aquaporins are specialised channels that allow what to cross membrane?

Answer 3

Water

Question 4

T/F at equilibrium, there’s absolutely no ion flow at all

Answer 4

False - no net flow but ion movement still occurs

Question 5

Ions move towards…

Answer 5

Opposite charges depending on electrical field across membrane and open channels

Question 6

Nernst equation predicts…

Answer 6

Mempot at equilibrium if membrane is only permeable to a single ion

Question 7

What do you need to know for Nernst?

Answer 7

1. Ionic concentrations (inside and outside cell)

2. Ionic charge (eg: +1 for Na+)

Question 8

Equilibrium potential is independent of what?

Answer 8

Permeability and ionic conduction

Question 9

What will mempot move towards if membrane only permeable to one ion?

Answer 9

That ion’s equilibrium potential

Question 10

What equation do we use if membrane permeable to multiple ions?

Answer 10

GHK

Question 11

What do you need to know for GHK?

Answer 11

1. Internal and external concentration of each ion

2. Membrane permeability for each ion

Question 12

At rest, what is the membrane’s permeability?

Answer 12

Weakly permeable to Na+ and quite permeable to K+

Question 13

What is Resting Membrane Potential?

Answer 13

-65mV -> inside cell negative relative to outside

Question 14

Does the Na/K-ATPase pump transport passively?

Answer 14

No - actively

Question 15

What ion does the Na/K-ATPase pump push out of cell?

Answer 15

Pushes Na+ out and K+ in

Question 16

How many ions does Na/K-ATPase pump transport?

Answer 16

For every 3 Na+ pumped out of cell, 2 K+ are pumped in

Question 17

All K channels have how many subunits?

Answer 17

4 subunits with pore loops that regulate permeability

Question 18

What are the 4 types of potassium channels?

Answer 18

1. Two pore domain potassium channels (K2p)
2. Voltage gated potassium channels
3. Calcium-activated potassium channels
4. Inward-rectifying potassium channels

Question 19

K2p channels

Answer 19

• contain 2 pore loop domains which are usually open, contributing to ongoing K+ leak
• helps set RMP

Question 20

Kv channels

Answer 20

• start opening when mempot >RMP

Question 21

When do Nav channels open?

Answer 21

When membrane depolarises

Question 22

At -65mV, are Nav channels open or closed?

Answer 22

Closed

Question 23

At -40mV, are Nav channels open or closed?

Answer 23

Open for about 1ms, allowing Na influx

Question 24

When do Nav channels inactivate?

Answer 24

When pore blocked by globular portion of protein

Question 25

When do Nav channels reactivate (but still remain closed)?

Answer 25

When mempot reaches -65mV

Question 26

What does textrodotoxin do?

Answer 26

Blocks one class of Nav channel so depolarisation can’t occur

You remain conscious but lose ability to generate APs in peripheral nerves

Question 27

Describe how selectivity and gating occur in Na+ and K+ channels

Answer 27

Pore loops act as a physical filter (due to their close proximity)
Charged domains on amino acid residues act as a chemical filter