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

Lecture 2- Voltage Gated Na+ Channel Flashcards

(108 cards)

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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
What happens when DPP is at a negative value?
All the Na+ channels are available
26
What happens when DPP is depolarised?
All the Na+ channels are inactivated
27
What does depolarisation activate?
Available sodium channels
28
What can be plotted?
Availability of sodium channels
29
What is conductance ?
How easily current can flow across the membrane
30
Na+ channels have a similar structure comprising?
Alpha subunit and beta subunits
31
Alpha subunit
260 Kda
32
Beta subunit
33-36 Kda
33
What does alpha subunit have ?
4 repeat domains each containing 6 membrane spanning segments (s1-s6)
34
What is S4 segment?
Positively charged Act as voltage gate changing shape when activated Opening and closing the channel (voltage sensor)
35
How is inactivation brought?
IFM motif on the linker between domain 3-4
36
What is IFM motif?
Hydrophobic When the channel is opened it can be blocked by IFM loop Giving rise to inactivation
37
Where are P loops located?
Domain 5 and 6 | Response for ion selectivity
38
What are Beta subunits responsible for?
Neuronal excitability | Cellular adhesion
39
What does potassium channels have with sodium channel?
Structural homology
40
What do potassium channels form?
Homo and Hetero multimers
41
What is the crystal structure for Na+ channel?
Arcobacter butzleri
42
When do local anaesthetics target sodium channel?
when they are in conformational state | Inactivated
43
What do local anaesthetics do?
Put sodium gabbros into sleep state preventing them from working
44
What happens at a negative potential?
All the channels are available
45
What happens at a positive potential?
All the sodium channels can be put into the inactivated state
46
What happens in the or sender of LA?
The sodium availability curve shifts left | Less sodium channels available to be activated
47
What does beta1-subunit accelerate?
Sodium current inactivation in Xenopus oocytes | Cell lines that do not express beta-subunits
48
What do Beta subunits have?
Large IG loops
49
What do Beta subunits interact with?
Intercellular and extracellular proteins Controlling sodium channel localisation Control of channel density
50
Where are sodium channels concentrated?
At nodes and initial segments | The very beginning of the axon
51
What does Beta subunit change?
Rate of inactivation
52
What does Beta Increase?
Rate of inactivation
53
What are Na+ channels?
Targets for toxins and drugs
54
Neurotoxin binding site 1
TTX STX Micro-conotoxin
55
Neurotoxin binding site 2
Veratridine | Batrachotoxin
56
Neurotoxin binding site 3
Alpha-scorpion toxin | Sea anemone toxin
57
Neurotoxin binding site 4
Beta-scorpion toxin (outside)
58
What is tetrodotoxin?
Guaninium group Mimics sodium paralytic poison found in puffed fish (Californian) Salamander and a South American fro May be made by symbiotic bacteria
59
What are the steps that lead to action potential?
Recording of AP in sensory neuron Due to stimulus, gradual activation of sodium channel depolarisation Action potential
60
Action potential is around ...
25mm long
61
If there are nodes at 1mm interval, over how many will by involved simultaneously in propagating a single impulse?
20
62
In the frogs node of Ranvier what channels give rise to an outward current?
Sodium channel | Kinetically fast potassium channel
63
What does mammalian node of Ranvier do not have?
Fast potassium channels
64
What does biological membrane provide?
Large capacities | Taken to be 1mFcm-2
65
What does intermodal membrane provide?
Capacity about 1000 times more than a node of Ranvier
66
In parallel, what is the total capacity?
100 + 100 + 100 + 100 = 400pf
67
In series, what is the total capacity?
1/(1/100 + 1/100 + 1/100 + 1/100)
68
How does the node repolarize?
Myelin has a low capacitance | Barrett and Barrett resistance make myelin a poor insulator because here are current pathways across it
69
Axolemma
Large capacitance
70
What happens when DAP occurs?
Current flow across the node
71
What happens when sodium channel activate?
They charge the internode generating DAP
72
Current flows in a circuit
Includes a part that goes through and underneath the myelin
73
Myelin sheath is what?
Leaky
74
What does myelin provide?
Low capacity sheath
75
What has a high capacity?
Single intermodal axon membrane
76
If myelin was a good insulator, why wouldn’t the axon work?
It would not have a resting potential | The action potential at the node couldn’t repolarise
77
Gigohm resistance
>1 x10^9
78
Across a whole myelin sheath (over 100 stacked lamellae)
Close to 50 megaohms
79
How are axons ensheathed?
Sequentially by single Schwann cells
80
What does Schwann cells produce?
Basement membrane that included laminin
81
What is laminin?
A matrix protein that is essential for normal nerve development, function and regeneration
82
In the CNS, what do oligodendrocytes do?
Wrap axons with myelin | Each oligodendrocyte can interact with more than one axon
83
What is present underneath the myelin?
Juxta paranode | Consist of fast potassium channels
84
At the internodal axon
Bigger diameter than at the node
85
Why does the internodal axon have a bigger diameter than at the node?
Neurofilaments that are phosphorylated in the internode | Make internodal axons thicker/fatter at the node
86
Alpha subunits
Tethered in position in the node
87
Beta subunits
Interact with other cell-adhesion molecules
88
What do Glial CAMS recruit?
Axons CAMs at point of contact
89
What is expressed by Schwann cells that interact with neurofatin 106?
Gliomedin
90
What is present at the end of myelin (NF-155) that binds and contacts with Casper?
Paranodal loop
91
What are Axonal CAMs?
Attachment sites for cyto-skeletal proteins
92
What channel is the most important for conducting impulses down the axon?
Sodium channel 6, Nav 1.6 Present at the node of Ranvier Allows conduction of impulses over long distances
93
What is the major sodium channel found in the brain and is found near the initial segment?
Sodium channel 2 Nav 1.2 Involved in initiating AP close to the cell body before it’s propagated away
94
TTX-s
Sodium channel sensitive to/ blocked by TTC at nanomolar concentration
95
TTX-r
resistant to TTx | Famously resistant is cardiac sodium channel 5
96
What is the sensitivity to TTX determined by?
Amino acid sequence in the P loop
97
What does TTx Contain?
Guanidinium which is believed to mimic sodium | Positively charged
98
What is TTX made by?
symbiotic bacteria
99
NTBS1
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
NTBS2
Batrachotoxin Frogs produce this and on feathers in the rubbish bird Open sodium channels at rest
101
NTBS3
Alpha scorpion toxin | Prevent sodium channel inactivation
102
NTBS4
Beta scorpion toxin | Activated the sodium channel at rest
103
What does mutation in beta subunit cause?
Major effects on how the channels work in the brain
104
Whole cell patch clamp arrangement
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
B1
SCN1B Both CNS and PNS Epileptic phenotype Dravet syndrome model
106
B2
SCN2B Both CNS and PNS Reduced excitability and optic nerve function
107
B3
SCN3B Known PNS KI shows important cardiac effects
108
B4
SCN4B Both CNS and PNS Persistent Na* current in purkinje neurons

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