Lecture 1 (Intro & ion channels)

Question 1

What does movement of ions through ion channel produce?

Answer 1

Current

Question 2

What are the 3 ways of classifying Ion channels and explain them? (3)

Answer 2

-Selectivity (What is the main ion that moves through pore?)

-Gating (What is needed to open channel? e.g voltage/ligand-dependant)

-Regulation (What regulates the channel? e.g ATP, G-proteins, Ca2+. etc)

Question 3

What are molecular ion channel families?

Answer 3

Ion channels with similar amino acid structure but have a slightly different genetic code, so expressed differently in sequence

Question 4

Describe the difference inn structure between Kv and Kir in potassium ion channels in their structural family? (3)

Answer 4

Kv made of 4 subunits, 1 voltage sensor and 1 pore

Kir made of 2 subunits, no voltage sensor and 1 pore

Question 5

What technique measures ion channel function?

Answer 5

The patch clamp technique

Question 6

Describe the patch clamp technique? (4)

Answer 6

-You take glass pipette filled with salt solutions; glass pipette is measured with call back to reference electrode

-Glass pipette touches surface of membrane and you suck on glass pipette

-Membrane of cell seals to pipette

-Allows us to measure current through pipette

Question 7

What are the two types of patch clamp technique? (2)

Answer 7

-Single channel

-Whole cell

Question 8

Describe the different between the two types of the patch clamp technique? (2)

Answer 8

Single Channel - Membrane of cell seals to pipette

Whole Cell - Suction applied after first step, rips part of membrane so can measure whole membrane potetial (all different ion channels in cell)

Question 9

What do these stand for? (5)
I -
N -
Po -
Vm -
Ei -

Answer 9

N = Number of channels
Po = open probability
g = single channel conductance
Vm = membrane potential
Ei = Nernst (equilibrium) potential ion i

Question 10

What is open probability (Po)?

Answer 10

Open probability – how often channels are open (0 = open all the time, 1 = open all the time, 0.5 = open half the time)

Question 11

What is single channel conductance (g)?

Answer 11

g – how many ions move through the pore per unit time

Question 12

What is the equation for total current carried by population channels in cell membrane (I)?

Answer 12

I = N.Po.g.(Vm-Ei)

N = Number of channels
Po = open probability
g = single channel conductance
Vm = membrane potential
Ei = Nernst (equilibrium) potential ion i

Question 13

What is the Nernst potential (Ei)?

Answer 13

Membrane potential with no net flow of ions

Question 14

When does Membrane potential (Vm) move towards Nernst potential (Ei)?

Answer 14

When you open ion channels?

Question 15

What is the equation for the Nernst potential (Ei)? (1)
And what is the difference when at Body/Room temp? (2)

Answer 15

Eion= RT / zF X Ln [ion]out / [ion]in

Room Temp - RT / zF = 58.2 / z
Body Temp - 61.5 / z
(z usually ignored)

Question 16

How can blockers be used with patch clamp technique?

Answer 16

A blocker (e.g Ba2+ which blocks K+) inhibits K+ ion channels that mediate current so current changes (more positive) showing that K+ ion channels were present

Question 17

What could a small current mean in regulation of channels? (2)

Answer 17

-Less channels

-Reduction in probability

Question 18

Describe how FHEIG (inherited diseases) is caused by potassium ion channels mutation? (5)

Symptoms:
Bi-temporal narrowing, hypertrichosis (hair), thin upper lip, bushy/long eyebrows

Delayed development of intellectual ability and motor skills
Seizures/EEG anomalies

Answer 18

-Mutants have larger currents

-So more K+ loss

-Increases extracellular K+ and accumulates in interstitial spaces

-Depolarises Nernst potential for potassium (lowers) (e.g if Nernst potential is -89mv becomes -70mv)

-More likely to fire action potentials when not needed