Recording ion channels Flashcards Preview

E: Quantitative Pharmacology > Recording ion channels > Flashcards

Flashcards in Recording ion channels Deck (64):
1

Distribution of ions in the cell?

Sodium, calcium and chloride are higher outside the cell.

Potassium is higher inside

2

What ion gives rise to the resting potential of the cell?

What is the resting potential of the cell?

Potassium

-70mV

3

What pH are cells normally at?

pH 7.4

4

What ion is actively pumped out by active transport?

Chloride

5

How to calculate pH?

Depends on the Hions.

10-1 pH1 

 

6

What is the pH inside the cell?

Very similar to the outside

pH 7.4

7

How 2 types of energy barrier does the membrane present to stop ion crossing?

  1. Schematic of a postive charged cation solvated by polar water moelcules.
  2. Lipid bilayer.

Means it takes a lot of energy to actively bring something into the cell

8

Ion channels?

The primary route for ions to cross the membrane.

Others are activated by specific stimuli eg. voltage.

 

9

What ion channels are open at rest?

Potassium

10

Microelectrodes?

Intracellular recording

Different to patch clamp

High electro-resistance (not too high about 3mmol)

Records the intracellular voltage

11

Name the 3 types of electrophysiological recordings?

  1. Extracellular recording
  2. Intracellular recording
  3. Whole-cell patch recording

 

12

What are the 3 factors responsible for the uneven distribution of ions?

  1. Selective permeability of the membrane.
  2. Large organic anions within the cytoplasm.
  3. Ion pumps

 

13

For steady state?

Must be no net movement of ions into or out of the cell.

Osmotic balance

Electrically neutral between intra and extracellular

14

What is the ion concentration outside and inside the cell

Outside:

Na:150.

K: 5.5.

 Chorine:125.

Ca: 2

 

Inside:

Na: 15.

K: 150

Cl: 9

Ca: 0.001

AS30

 

15

Since potassium channels are open at rest. 

Why doesnt potassium passively diffuse?

Well if potassium left the cell.

The cell would become negative

Negative charge attracts cation (like potassium)

Therefore brings back potassium ions back into the cell

16

Equilbrium potential

The voltage in which there is no net movement of ions

17

The work required to keep the equilibrium?

As potassium is diffused outwards through the membrane

Increase in negative charge

Work is required to overcome this pull and prevent flow of potassium

18

The work to keep the equilbrium equation?

AS31

19

Work equation required to oppose the electrical froce tending to pull potassium back into the cell?

AS31

20

What is the gas constant value?

8.3J/K

21

What is the faraday's constant?

96485C/m

22

The work done to overcome the electrical difference for potassium must equal?

The work done to overcome the chemical difference

23

Nernst equation?

use?

AS32

We=Wc

Used to determine the potential difference

24

What does the graph for extracellular potassium vs membrane potential?

Should be linear

Isnt

Something else is taking effect

25

Resting potential?

-70mV

More depolarised than the potassium equilibrium potential (-85mV)

Caused by a slight permeability to sodium.

Inward leak causes the more depolarised value.

 

26

What is the dynamic range of voltage the cells can work between?

34 -> -85mV

34mV: The potential difference for sodium

-85mV: the potential difference for potassium

27

What needs to be present for this inward leak of sodium ions?

A pump reguired to prevent depletion of intracellular potassium and build up of sodium

28

Na-K ATPase

Sodium and potassium are transported

2K in: 3 Na out.

AS33

29

The action potential:

The different parts to it

AP goes beyound 0mV: overshoos.

as34

30

what is the overshoot phase?

When the cell depolarises beyond the 0mV mark

31

What is the undershoot phase?

When the cell becomes so hyperpolarised it goes beyond the -70mV.

Goes to -85mV become returning back to -70mv

32

Action potential initiation?

positive feedbakc cycle occurs

Involving sodium channels.

Gives rise to all sodium channels becoming opened.

all or non event: either all the sodium channels opened or none.

AS35

33

Threshold?

Enough sodium channels are open

All or nothing response

Positive feedback no longer needed

34

What signals cause depolarisation?

Chemical signals

Electric signals

35

Name the 2 gates of sodium?

M gate (activation gate)

H gate (inactivate gate- in the inside of the cell)

36

What is the name of that gate for potassium

N gate

37

Gating at work to cause AP?

AS36

38

The undershoot phase?

Vm goes below the resting membrane potential.

Sodium channels are inactivated

Potassium channels are still open

Known as the afterhyperpolarisation

39

The Refractory Period can be split into 2 periods?

 

  1. Absolute refractory period:
    1. Sodium channels are still inactivated
    2. Never produce an AP.
  2. Relative refractory period:
    1. Some sodium channels can open
    2. Can produce an AP with a stronger depolarisation.

40

Absolute refractory period and AP?

Is the interval during which a second AP can never be initiated- no matter how large the stimulus.

 

41

Relative Refractory period?

Interval immediately following absolute (AS37)

An initiation of a second AP is inhibited but not impossible

42

Voltage gated sodium channels?

Made up of?

6TMs make up a subunit

4 subunits make up the channel.

S4 domain is positivity charged. 

 

AS38

43

How is the voltage gated sodium channel opened?

S4 domain is positively charged.

Attracted towards the inside of the cell when it is negatively charged- keeping it closed.

When the cell becomes depolarised the S4 moves up and opening the channel.

AS38

44

What happens when the voltage gated sodium channels are opened?

Sodium enters the cells.

Cause it to depolarise

45

Mechanism for sodium channel inactivation

4 subunit domains

Intracellular loop between 3 and 4 that is attracted into the inner mouth of the channel at depolarised potentials. 

Ball and chain model of inactivation

AS39

46

Voltage clamp?

Adds a wire into the inside of the cell and inject crent

Ability to control the membrane potential

47

Name the 3 patch clamp recordings:

How do you get to each one?

AS40

48

TTX?

Tetrodotoxin

Neurotoxin

Inhibits the firing of AP in nerves by binding to voltage-gated sodium channels.

49

TEA?

Tetraethylamnonium

Block voltage-dependent potassium channels.

Prolongs the AP.

50

Distribution of ion channels in neurones

eg. neuromuscular junction

Sodium channels are clustered within the nodes of Ranvier.

Potassium channels are distributed between the nodes.

AS41

51

Name the 4 types of calcium channels?

L type

T type

N type

P/Q type 

52

Distrubtion of the different types of calcium channels?

AS42

53

L-type calcium channels?

Long-lasting activation

Responsible for skeletal, smooth and cardiac tissue.

54

T-type calcium channels?

Transcient (Short) activation

Distrubed in the nodes of ranvier

55

N type or P/Q type calcium channel?

Alpha1 subunit forms the pore

Important for the uptake of calcium in the presynaptic cleft.

56

Excitatory ligands?

Glutamate (ions: sodium and calcium)

Important excitatory in brain

57

Inhibitory ligands?

GABAA

Ions: chlorine and HCO3-

Important in brain

58

How is glutamate and GABA synthesised?

AS43

59

Totography of the GABAA receptors?

Members of the cysteine-loop receptor family.

4TM domains. 5 subunits make the receptor

TM2: contributes to ion selectivity.

 

AS44

60

Totography of the glutamate receptor?

4 subunits per channel

Poor loop structure that participates in ion selectivity.

AS45

61

EPSP?

Excitatory postsynpatic potential

Stimulate production of AP if threshold is meet.

62

IPSP?

Inhibitory postsynpatic potential

 

63

Balance between EPSP and IPSP?

Balance between them

More EPSP needed to cause AP.

AS46

64

Name the 5 domains that make up the GABAA receptor?

2x alpha1

2x beta2

1x gamma2