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Cellular And Molecular > Lecture 2- Voltage Gated Na+ Channel > Flashcards

Lecture 2- Voltage Gated Na+ Channel Flashcards

1
Q

What are 2 electrodes inserted into?

A

Squid giant axon

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2
Q

What are the 2 types of electrodes?

A
  1. Recording voltage difference across membrane

2. Intracellularly injecting current

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3
Q

What are electrodes connected to?

A

Feedback circuit

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4
Q

What does feedback circuit do?

A

Compare the measured voltage across the membrane with voltage desired by the experimenter

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5
Q

What happens if 2 values differ?

A

Current is injected into axon to compensate for the difference

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6
Q

What is continuous feedback cycle?

A

Voltage is measured and current injected effectively clamps the membrane at a voltage

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7
Q

What happens in a voltage clamp?

A

The membrane potential is maintained constant or held at a command potential

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8
Q

What is the purpose of making axons bigger?

A

Conduct impulses more quickly

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9
Q

What does amplifier receive?

A

Input from inside/outside of axons

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10
Q

What does amplifier detect?

A

Changes in potential across membrane

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11
Q

What does Na+ channels confer?

A

Excitability

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12
Q

What depends on sodium channel ?

A

Nerve cells
Muscle cells
Heart cells

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13
Q

What is present at internode?

A

Transmembrane current

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14
Q

What current is present at node?

A

Inward current

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15
Q

What allows activation of the next node?

A

Current that flows in a circuit

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16
Q

What are necessary to propagate impulse?

A

Local circuit

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17
Q

What do Na+ channels exhibit?

A

Voltage- dependent activation

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18
Q

Clamp steps

A

Start from a negative baseline

Step more positive

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19
Q

What does voltage clamp allow?

A

Separation of membrane ionic and capacitance currents

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20
Q

What is the whole cell patch clamp arrangement?

A

Studying the properties of small patch of membrane

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21
Q

What is the process of whole cell patch clamp arrangement?

A

A glass pipette with a very small opening is used to make tight contact with a very small area of neuronal membrane
2. small suction happens to back of pippete
3. Seal between pipette and membrane become so tight - no ions can flow between pipette and membrane
4. All ions gang flow when single ion channel open flow into pipette
5.

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22
Q

How is the electrical current measured?

A

Electronic amplifier connected to the pippete

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23
Q

What is depolarising pre-pulse?

A

Electrical stimulus that causes potential difference measured across membrane to become more positive or less negative

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24
Q

What happens when DPP is short?

A

Threshold will decrease

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25
Q

What happens when DPP is at a negative value?

A

All the Na+ channels are available

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26
Q

What happens when DPP is depolarised?

A

All the Na+ channels are inactivated

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27
Q

What does depolarisation activate?

A

Available sodium channels

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28
Q

What can be plotted?

A

Availability of sodium channels

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29
Q

What is conductance ?

A

How easily current can flow across the membrane

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30
Q

Na+ channels have a similar structure comprising?

A

Alpha subunit and beta subunits

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31
Q

Alpha subunit

A

260 Kda

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32
Q

Beta subunit

A

33-36 Kda

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33
Q

What does alpha subunit have ?

A

4 repeat domains each containing 6 membrane spanning segments (s1-s6)

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34
Q

What is S4 segment?

A

Positively charged
Act as voltage gate changing shape when activated
Opening and closing the channel (voltage sensor)

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35
Q

How is inactivation brought?

A

IFM motif on the linker between domain 3-4

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36
Q

What is IFM motif?

A

Hydrophobic
When the channel is opened it can be blocked by IFM loop
Giving rise to inactivation

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37
Q

Where are P loops located?

A

Domain 5 and 6

Response for ion selectivity

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38
Q

What are Beta subunits responsible for?

A

Neuronal excitability

Cellular adhesion

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39
Q

What does potassium channels have with sodium channel?

A

Structural homology

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40
Q

What do potassium channels form?

A

Homo and Hetero multimers

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41
Q

What is the crystal structure for Na+ channel?

A

Arcobacter butzleri

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42
Q

When do local anaesthetics target sodium channel?

A

when they are in conformational state

Inactivated

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43
Q

What do local anaesthetics do?

A

Put sodium gabbros into sleep state preventing them from working

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44
Q

What happens at a negative potential?

A

All the channels are available

45
Q

What happens at a positive potential?

A

All the sodium channels can be put into the inactivated state

46
Q

What happens in the or sender of LA?

A

The sodium availability curve shifts left

Less sodium channels available to be activated

47
Q

What does beta1-subunit accelerate?

A

Sodium current inactivation in Xenopus oocytes

Cell lines that do not express beta-subunits

48
Q

What do Beta subunits have?

A

Large IG loops

49
Q

What do Beta subunits interact with?

A

Intercellular and extracellular proteins
Controlling sodium channel localisation
Control of channel density

50
Q

Where are sodium channels concentrated?

A

At nodes and initial segments

The very beginning of the axon

51
Q

What does Beta subunit change?

A

Rate of inactivation

52
Q

What does Beta Increase?

A

Rate of inactivation

53
Q

What are Na+ channels?

A

Targets for toxins and drugs

54
Q

Neurotoxin binding site 1

A

TTX
STX
Micro-conotoxin

55
Q

Neurotoxin binding site 2

A

Veratridine

Batrachotoxin

56
Q

Neurotoxin binding site 3

A

Alpha-scorpion toxin

Sea anemone toxin

57
Q

Neurotoxin binding site 4

A

Beta-scorpion toxin (outside)

58
Q

What is tetrodotoxin?

A

Guaninium group
Mimics sodium paralytic poison found in puffed fish (Californian)
Salamander and a South American fro
May be made by symbiotic bacteria

59
Q

What are the steps that lead to action potential?

A

Recording of AP in sensory neuron
Due to stimulus, gradual activation of sodium channel
depolarisation
Action potential

60
Q

Action potential is around …

A

25mm long

61
Q

If there are nodes at 1mm interval, over how many will by involved simultaneously in propagating a single impulse?

A

20

62
Q

In the frogs node of Ranvier what channels give rise to an outward current?

A

Sodium channel

Kinetically fast potassium channel

63
Q

What does mammalian node of Ranvier do not have?

A

Fast potassium channels

64
Q

What does biological membrane provide?

A

Large capacities

Taken to be 1mFcm-2

65
Q

What does intermodal membrane provide?

A

Capacity about 1000 times more than a node of Ranvier

66
Q

In parallel, what is the total capacity?

A

100 + 100 + 100 + 100 = 400pf

67
Q

In series, what is the total capacity?

A

1/(1/100 + 1/100 + 1/100 + 1/100)

68
Q

How does the node repolarize?

A

Myelin has a low capacitance

Barrett and Barrett resistance make myelin a poor insulator because here are current pathways across it

69
Q

Axolemma

A

Large capacitance

70
Q

What happens when DAP occurs?

A

Current flow across the node

71
Q

What happens when sodium channel activate?

A

They charge the internode generating DAP

72
Q

Current flows in a circuit

A

Includes a part that goes through and underneath the myelin

73
Q

Myelin sheath is what?

A

Leaky

74
Q

What does myelin provide?

A

Low capacity sheath

75
Q

What has a high capacity?

A

Single intermodal axon membrane

76
Q

If myelin was a good insulator, why wouldn’t the axon work?

A

It would not have a resting potential

The action potential at the node couldn’t repolarise

77
Q

Gigohm resistance

A

> 1 x10^9

78
Q

Across a whole myelin sheath (over 100 stacked lamellae)

A

Close to 50 megaohms

79
Q

How are axons ensheathed?

A

Sequentially by single Schwann cells

80
Q

What does Schwann cells produce?

A

Basement membrane that included laminin

81
Q

What is laminin?

A

A matrix protein that is essential for normal nerve development, function and regeneration

82
Q

In the CNS, what do oligodendrocytes do?

A

Wrap axons with myelin

Each oligodendrocyte can interact with more than one axon

83
Q

What is present underneath the myelin?

A

Juxta paranode

Consist of fast potassium channels

84
Q

At the internodal axon

A

Bigger diameter than at the node

85
Q

Why does the internodal axon have a bigger diameter than at the node?

A

Neurofilaments that are phosphorylated in the internode

Make internodal axons thicker/fatter at the node

86
Q

Alpha subunits

A

Tethered in position in the node

87
Q

Beta subunits

A

Interact with other cell-adhesion molecules

88
Q

What do Glial CAMS recruit?

A

Axons CAMs at point of contact

89
Q

What is expressed by Schwann cells that interact with neurofatin 106?

A

Gliomedin

90
Q

What is present at the end of myelin (NF-155) that binds and contacts with Casper?

A

Paranodal loop

91
Q

What are Axonal CAMs?

A

Attachment sites for cyto-skeletal proteins

92
Q

What channel is the most important for conducting impulses down the axon?

A

Sodium channel 6, Nav 1.6
Present at the node of Ranvier
Allows conduction of impulses over long distances

93
Q

What is the major sodium channel found in the brain and is found near the initial segment?

A

Sodium channel 2
Nav 1.2
Involved in initiating AP close to the cell body before it’s propagated away

94
Q

TTX-s

A

Sodium channel sensitive to/ blocked by TTC at nanomolar concentration

95
Q

TTX-r

A

resistant to TTx

Famously resistant is cardiac sodium channel 5

96
Q

What is the sensitivity to TTX determined by?

A

Amino acid sequence in the P loop

97
Q

What does TTx Contain?

A

Guanidinium which is believed to mimic sodium

Positively charged

98
Q

What is TTX made by?

A

symbiotic bacteria

99
Q

NTBS1

A

Interacts with the pore loop for TTX and saxitoxin
STX (marine toxin, super anaesthetic) - found in algae in a red tide
Algae fed on by shellfish become concentrate with STX
Toxic to eat

100
Q

NTBS2

A

Batrachotoxin
Frogs produce this and on feathers in the rubbish bird
Open sodium channels at rest

101
Q

NTBS3

A

Alpha scorpion toxin

Prevent sodium channel inactivation

102
Q

NTBS4

A

Beta scorpion toxin

Activated the sodium channel at rest

103
Q

What does mutation in beta subunit cause?

A

Major effects on how the channels work in the brain

104
Q

Whole cell patch clamp arrangement

A

Signal amplifier used
Single wire passes current and measures potential
Respond to command voltage and passes current into neuron
Can measure potential across membrane
Sits inside blunt microelectrode
Can make a seal - slight patch of membrane broken by suction
Solution inside cytoplasm = solution inside electrode
Feedback amplifier

105
Q

B1

A

SCN1B
Both CNS and PNS
Epileptic phenotype
Dravet syndrome model

106
Q

B2

A

SCN2B
Both CNS and PNS
Reduced excitability and optic nerve function

107
Q

B3

A

SCN3B
Known PNS
KI shows important cardiac effects

108
Q

B4

A

SCN4B
Both CNS and PNS
Persistent Na* current in purkinje neurons

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