2. Ion channels

Question 1

Subcomponents of GABA?

Answer 1

5

Question 2

Subcomponents of acid-sensitive channels?

Answer 2

3

Question 3

Subcomponents of Mechano-sensitive channels?

Answer 3

6

Question 4

Explain setup of an AMPA receptor

Answer 4

Consists of 4 subunits. Has 2 dimmers (1st is the red and green, the 2nd is the blue and yellow).

Question 5

Mutations in the channels can lead to:

Answer 5

• reduced protein expression (if mutation is a the proteins)
• folding problems, leading to no correct assembly/topology; reduced transport; unstable protein
• no correct anchoring to scaffold
• altered ligand binding
• altered gating
• loss/gain of funciton

Question 6

Channelopathies can be caused by

Answer 6

Exocytosis, Channel mutations and Autoimmune disorders

Question 7

Channel types related to channelopathies

Answer 7

ligand gated or voltage gated

Question 8

Excitotoxicity can be caused by

Answer 8

ischemic stroke or trauma

Question 9

Penumbra

Answer 9

synaptic diffusion of neuronal damage –> the the primary damage causes secondary damage through excitotoxicity

Question 10

How does ishemic stroke cause Excitotoxicity

Answer 10

Ischemia –> no oxygen to microcondria –> decreased ATP –> Na/K Pump stops working –> ionic gradient changes –> cause the sodium/calcium exchanger (brings 3 Na+ into the cell and 1 Ca++ out) to slow down, as more Na is already in the cell. Other problem with ATP going down is that the plasma membrane associated calcium ATPase pump stops sending Ca++ out of the cell.
Subconclusion: we have too much CA2+ in the cell

Ca2+ causes the vesicles to fuse to the membrane and cause exocytosis. Glutamate is now sent into the synapse, but because we have a lot CA2+, we have a lot of glutamate sent out.
Glutamate receptors (NADA & AMPA) fire, so you get the movement of Na+ in (more than K+ goes in) --> leads to graded potential --> leads to voltage gated Na+ channels to open --> leads to a big depolarization. An NMDA receptor was blocked by Mg2+ because the cell was negatively polarized before. Now NMDA is un-blocked and will lead Ca2+ into the neuron --> Ca2+ in the ion goes up --> will lead to an activation of calpain --> calpain deactivates the NA/Ca2+ exchange pump --> leads to the positive feedback loop the Ca2+ will become higher and higher --> can lead to necrosis or apoptosis (voluntary death) --> will lead to the neuron sending out all it's NT's and we now have a loop (glutamate transporters reverse what they normally do and now sends out all the glutamate into the synapse)

Question 11

How does the resting potential membrane form?

Answer 11

The membrane is more permeable to K than Na, meaning that more K is leaving the cell than Na is coming in, which leads to a lower internal change inside the cell. When we reach the resting potential, the positive ions will not want to move out of the cell as much, because they like the negative enviournment inside the cell. Because of the change in membrane potential, the membrane will be more permeable to Na now. At some point, the movement of K out and Na in will be the same (electrical equilibrium). In order to obtain a chemical equilibrium, the NA/K pump is what what reverses the movement of the ions, so it helps the chemical balance and not the electrical one.

Question 12

Edema

Answer 12

Cell swelling (cause by unbalance of concentrations of ions)

Question 13

Reactive oxygen species or oxygen radical

Answer 13

A type of unstable molecule that contains oxygen and that easily reacts with other molecules in a cell. A build up of reactive oxygen species in cells may cause damage to DNA, RNA, and proteins, and may cause cell death. Reactive oxygen species are free radicals. Also called oxygen radical.

Question 14

phosphatidylserine

Answer 14

Phosphatidylserine is a fatty substance called a phospholipid. It covers and protects the cells in your brain and carries messages between them

Question 15

Opsonins

Answer 15

Opsonins are extracellular proteins that, when bound to substances or cells, induce phagocytes to phagocytose the substances or cells with the opsonins bound

Question 16

Caspase-3

Answer 16

Caspase-3 is a caspase protein who’s sequential activation of caspases plays a central role in the execution-phase of cell apoptosis

Question 17

What does the binding of annexin V to toxine treated neurones imply?

Answer 17

a translocation of phosphatidylserin towards to outer neuronal, which is a marker for early apoptosis

Question 18

Glutamate is important in which disorders?

Answer 18

Epilepsy, ischemia, Parkinson, Huntingtons, ALS, Schizophrenia

Question 19

Glutamates role in Epilepsy

Answer 19

Glutamatergic synapses are hyperactive

Question 20

Glutamates role in Ischemia

Answer 20

Too much glutamate - we need a blocker of glutamate receptors (NMDA subtype) prevent neuronal cell damage

Question 21

Glutamates role in preventing issues in Morbus Parkinson

Answer 21

cell death in substantia nigra is prevented by NMDA receptor antagonists

Question 22

Glutamates role in Morbus Huntington

Answer 22

quinolinic acid, an endogenous glutamatergic agonist, is involved in cell death in the striatum

Question 23

Glutamates role in ALS

Answer 23

misregulation of glutamate metabolism, loss of cortical neurons important for voluntary muscle movement;

Question 24

Glutamates role in Schizophrenia and possible treatment

Answer 24

NMDA receptor blocker as PCP (anaesthetics) are able to induce psychosis; hypofunction of NMDA receptors postulated, Gly and D-cycloserine administration improve positive symptoms

Question 25

Medications against excitotoxicity in Alzheimer‘s disease

Answer 25

memantine, a NMDA-R channel blocker that interacts rapidly in a voltage dependent manner -> less Ca2+ influx

Question 26

Medications against excitotoxicity in ALS

Answer 26

riluzole (Rilutek®) prevents/slows release of Glutsmate vesicles -> prolongs life a few months “neuroprotection”; no repair of damage

Question 27

Medications against excitotoxicity in Schizophrenia

Answer 27

glycine transporters are used as a blocking target (when you block glycine transporter, we have more glycine available, which can increase the activity of the hypoactive NMDA receptor)

Question 28

Cys-loop receptors

Answer 28

The Cys-loop ligand-gated ion channel superfamily is composed of nicotinic acetylcholine, GABAA, GABAA-ρ, glycine, 5-HT₃, and zinc-activated receptors

Question 29

Apnea

Answer 29

describing slowed or stopped breathing

Question 30

Autosomal dominant gene

Answer 30

Autosomal dominance is a pattern of inheritance characteristic of some genetic diseases. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the disease-associated mutation is enough to cause the disease.
One way to get Hyperekplexia/stiff baby syndrome

Question 31

Choline acetyltransferase/ chAT

Answer 31

Choline acetyltransferase (commonly abbreviated as ChAT, but sometimes CAT) is a transferase enzyme responsible for the synthesis of the neurotransmitter acetylcholine

6% of all cases of Congenital myasthenia is caused by mutations in this transporter. To treat, use inhibitor of AChE or 3.4 DAP

Question 32

Acetylcholinesterase/AChE

Answer 32

Acetylcholinesterase (HGNC symbol ACHE; EC 3.1.1.7), also known as AChE or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme that catalyzes the breakdown of acetylcholine and of some other choline esters that function as neurotransmitters

Question 33

RAPSN gene

Answer 33

The RAPSN gene provides instructions for making a protein called rapsyn that attaches (binds) to the different parts (subunits) of a protein found in the muscle cell membrane called acetylcholine receptor (AChR). This binding helps keep the receptor subunits together and anchors the AChR protein in the muscle cell membrane

15% of all cases of Congenital myasthenia is caused by mutations in this gene

Question 34

antigenic epitope

Answer 34

the part of the antigen that is recognized by the antibodies

Question 35

glycine receptor setup

Answer 35

Has 5 subunits with 4 transmembrainic domains. The 2nd domain form the pore.

Question 36

Hyperekplexia/ stiff baby syndrome

Answer 36

A syndrome where the baby is startled by unexpected stimuli (could also be adults). Leads to stiffness in babies and possibly fatal apnea. Clonazepam is the only treatment. Can be caused by autosomal dominant or recessive (with incomplete penetrance) mutations

Question 37

What is glycines neurotransmitter function in the spinal cord?

Answer 37

the DRG sends out glutamate and activate motor neurons that sends out ACH
process is very controlled - in the lower motor neuron, a collateral axon forms synapses with Renshaw cells, activating them by the action of the excitatory ACH, when the Renshaw cell is active, it releases glycine to the membrane of the motor neuron. So it’s a feedback control inhibition, which controls the firing of the motor neuron. When the glycine receptor is not working, the motor neurons will fire randomly and muscle will over contract and become stiff

Question 38

What happens if the glycine transporter 2 is mutated

Answer 38

glycine transporter 2 can be affected by mutation - important for re-transport of glycine (if mutation is here, there is not enough glycine to send out) - we might have a spill over to excitatory synapses, so we would have even more active (AMPA receptors can also respond to glycine)

Question 39

Findings on the dominant startle disease

Answer 39

Overall we see disturbed channel properties.
For P250 mutations: less activation of glycine receptors, receptors close after short duration of time
mutation in the ion channel pore, which affects ethanol. Ethanol can increase the potentiation in controls. For the mutated form we don’t have the potentiation for ethanol.

Question 40

Findings on the Recessive Startle disease

Answer 40

Overall we see disturbed biogenesis
H mutations has a decrease to 14 and 44% at the surface expressed proteins
Our mutated isoform seems to be seems to co-localize 100% in the ER
The R252H seems to be the worst mutation, as we see a much lower protein weight

Question 41

Most common mutation leading to Congenital myasthenia?

Answer 41

Mutations at the ACh receptor (55%)

Question 42

Slow vs fast-channel syndrome for Congenital myasthenia

Answer 42

Related to mutated ACh receptors
slow-binding: At binding we have ACh that takes a long time to un-bind. We have overactive receptors, but they close fast.
Fast channel syndrome: there is a decreased affinity for the agonist, so they don’t take ACH as much as they should, leading to an under-active receptor

Question 43

How to deal with overactive AChE in Congenital myasthenia

Answer 43

when you inhibt the AChE, more ACH will be in the synaptic cleft, but the inhibitors also have an effect on the production of AChE in itself.
2 forms of AChE: AChE-S & AChE-R
AChE-S is usually present at the membrane is slowed down in production, the cell deals with producing more AChE-R, which can stay in they synapse, but leads to an increased degradation of ACH. We therefore need to combine the inhibitor with a olligo(?) which inhibits AChE-R as well, so we have increased ACH and muscle strength

Question 44

How does autoantibodies enter the brain?

Answer 44

They do so when the BBB is leaky

Question 45

Ways AChR stops working in Myasthenia

Gravis

Answer 45

1st complement gets activated when AAB binds to the receptor –> C1 protein gets activated, leading to the formation of membrane attack complexes (MACs)

2nd: antigenic modulation –> signal for the cells to internalize and degrade them
3rd: antibodies can block the function of the receptor

this is the mechanisms behind MG - not all IgG will be able to do each of these, so this is why there are different backgrounds
See slide 31

Question 46

Anti-NMDA receptor encephalitis

Answer 46

cause: presence of a neural antigen in a teratoma or other tumor (trigger unknown)
tumor cells express NMDA receptors –> immune response –> antibodies against NMDA receptors –> abnormal expression of NMDA receptors lead to a disrupted immune tolerance and the BBB becomes leaky, so these antibodies can attack the brain, leading to encephalitis.

2nd mechanism: T-cells enter the brain and generate B-cells and lead to the generation of cells that secrete the autoantibodies

Question 47

Criteria for autoimmune disease

Answer 47

1) antibody is present in almost all cases
2) the antibody reacts with an antigen that is important for the pathophysiology
3) features of the disease can be transferred to experimental animals by injecting the antibodies
4) an experimental form of the disease can be reproduced by immunizing animals with the antigen
5) therapeutic reduction of antibody levels ameliorates the symptoms

Question 48

PERM

Answer 48

Progressive encephalomyelitis with rigidity and myoclonus (PERM) is part of the variant type of the Stiff Person Syndrome (SPS) and is a rare neurological disease.

Question 49

Hyperkalemic periodic paralysis can be caused by mutations in what channel?

Answer 49

NaV1.4

Question 50

NaV1.4

Answer 50

voltage gated sodium channel with a voltage sensor, who’s biggest subunit is alpha

Question 51

Hyperkalemic periodic paralysis

Answer 51

Hyperkalemic periodic paralysis is a condition that causes episodes of extreme muscle weakness or paralysis, usually beginning in infancy or early childhood. Most often, these episodes involve a temporary inability to move muscles in the arms and legs. Episodes tend to increase in frequency until mid-adulthood, after which they occur less frequently in many people with the condition. Factors that can trigger attacks include rest after exercise, potassium-rich foods such as bananas and potatoes, stress, fatigue, alcohol, pregnancy, exposure to hot or cold temperatures, certain medications, and periods without food (fasting). Muscle strength usually returns to normal between attacks, although many affected people continue to experience mild stiffness (myotonia), particularly in muscles of the face and hands.

Question 52

HyperPP mutations in NaV1.4

Answer 52

leads to the voltage sensor not working. The mutation causes the channels to

1) have slow inactivation. The mutated channel closes much slower than normal –> at the muscle level we have extra firing, which is what we see in myotonia (stiffness).
2) the receptor stays slightly open, which leads to a periodic paralysis due to hyper-activation of the muscles

Question 53

Why you should not eat K+ rich food if you have periodic perallysis

Answer 53

K+ rich food causes increase in extracellular K+ levels, which leads to a depolarization –> opens voltage gated Na+ channels –> more depolarization –> AP’s in the muscles leading to myotonia –> increase in depolarization due to mutated Na+ –> long lasting activation leads to muscle paralysis

Question 54

Why is periodic paralysis also known as ‘impressive disorder’

Answer 54

A race horse showed these symptoms and was a useful animal model, as he had the autosomal dominant mutation

Question 55

mytonia induced in Paramyotonia congenita is often seen by what

Answer 55

muscle cooling, so don’t go swimming in spring

Question 56

Long QT syndrome

Answer 56

an arrhythmia heart disorder, caused by mutation-induced loss of potassium channel function or gain of sodium channel function. This causes the repolarization of the T to occur later, leading to a prolonged Q-T interval.
We might also observe a Torsade Tachykardie, which is a sustained period of enhanced pulse (beat) 100 beats/min (seen in C, slide 45), rapid contraction results in reduced ventricular refilling., cardiac output is less and the blood flow to the brain decreases which may cause the loss of consciousness

at the receptor level, we see the same as in hyperkalemic periodic paralysis - when a sodium channel is affected and having a deleted component, you might have a fast inactivation or an incomplete inactivation - has impact on muscle, which we can see on the EKG