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Cellular Week 4 > Disorders of Membrane Excitation > Flashcards

Disorders of Membrane Excitation Flashcards

1
Q

electrical signals play key roles in control functions when what is needed..?(2)

A

speed and propagation

e.g. cardiac and muscle contraction, insulin secretion, signaling in the brain, spinal cord, peripheral motor neurons

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2
Q

electrical functions are affected in acquired and hereditary diseases which involve ion channel proteins… lots of them

A

…

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3
Q

what is an example of disorders of resting K channels?

A

Type II diabetes of infancy

resting k+ channel in pancreatic beta cell - helps release insulin… does make insulin just can’t release it

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4
Q

Type II Diabetes of Infancy is really rare!! It is 1-5% of diabetes in young people

Due to Katp channel defect

Often misdiagnosed

Most are spontaneous mutation - spermatogenesis problem

A

…

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5
Q

What is the pancreas?

A

Endocrine organ that is nestled between the liver and the intestine!

Regulates blood glucose etc

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6
Q

Type II diabetes of infancy have a mutation in what gene?

what does it prevent?

A

the gene encoding the SUR subunit of the Katp channel

it prevents the channel from closing in response to elevated ATP

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7
Q

what do children of type II diabetes of infancy not respond to?

what type of drug do they respond to?

A

insulin!

sulfonylurea drugs - drug targets the SUR subunit and causes the channel to CLOSE!

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8
Q

What is the Katp (resting K+ channel) channel a sensor of?

What does it control?

What binds to it to close it?

A

glucose sensor

controls insulin secretion in beta cells

ATP closes the pore (ligand gated - binds from the inside)

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9
Q

Give the mechanism of insulin secretion:

A

Glucose enters beta cells via Glut2 transporters

metabolism of glucose increases the ATP/ADP ratio

ATP binds to the KATP channel, causing it to close

K channel closing depolarizes the membrane

Depolarization opens voltage-dependent Ca2+ channels, Ca2+ influx follows

Increased intracellular Ca2+ leads to fusion of secretory vesicles, insulin release

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10
Q

For a NORMAL functioning B cell the Katp channel is what at rest?

A

open at rest!

it is allowing K+efflux, maintaining a negative RMP

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11
Q

K+ channel closing in pancreatic beta cel depolarizes the membrane and triggers….

A

repetitive action potentials!!!

there is a slow depolarization followed by bursting APs!!!

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12
Q

at low glucose…

A

Katp open, Ca2+ closed, low ATP

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13
Q

at high glucose…

A

Katp close, Ca2+ open, high ATP

insulin secreted

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14
Q

Ca2+ channels require a greater depolarization threshold than Na+

How can Ca2+ fire in bursts?

A

They do not have the property of fast/slow inactivation

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15
Q

Beta cells in the pancreas use slow changes in RMP to trigger insulin secretion

A

…

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16
Q

RMP depolarizes when the PNa/PK ratio is..

A

higher!

17
Q

Katp acts as a sensor for plasma glucose and as a switch to turn insulin secretion on/off

A

…

18
Q

in absence of glucose, beta cells have a stable RMP near..

A

-60mV

19
Q

neonatal diabetes = type II diabetes of infancy

A

…

20
Q

Give the structure of the Katp channel

A

8 subunit protein:

4 pore forming subunits (Kir6.2) - binds ATP!

4 reg subunits (SUR1)
- regulates channel activity - target of sulfonylurea drugs (hint the name)

21
Q

What is SUR?

A

unique ATP-binding cassette protein that functions as an ion channel regulator

22
Q

In neonatal diabetes, the channel loses its gating by ATP, stays OPEN! - no insulin secretion

A

…

23
Q

Kir6.2 (KCNJ11) mutations

A

Most common is R201H (Arg to His)

Decreases ability of ATP to bind

24
Q

SUR1 (ABCC8) mutations

A

Increase ability of Mg2+ ADP to bind, which inhibits channel gating by ATP binding

25
Q

What is the most common mutation resulting in neonatal diabetes?

A

substitution for Arg to His at aa 201 in the Kir6.2 subunit

This decreases the ability of ATP to bind and the channel remains open…. idk if this is important….

26
Q

What are some Katp drugs?

A

Diazoxide and Sulfonylureas bind to the SUR subunit; close the channel

Sulfyonylureas also alleviate symptoms due to mutated Katp channels in extrapancreatic tissues

27
Q

What is an example of disorders of action potential generation?

A

myotonia congenita

28
Q

what is myotonia congenita (MC)?

A

disease of action potential generation in skeletal muscle from an abnormal CI channel

pts have difficulty relaxing their skeletal muscles

syndrome of abnormal membrane excitability

experience additional contraptions of their muscles following a voluntary (Willed) effort

the extra contractions occur because the muscle membrane is firing extra action potentials in response to input from the motor nerve

29
Q

Skeletal muscle normally has a high permeability to what ion…

A

chloride

30
Q

Skeletal muscle has two channels to help depolarize it…. they are?

A

voltage gated potassium channel and a chloride channel

31
Q

What does the EMG show in MC pts?

A

dive bomber response

EMG records AP activity in skeletal muscle

32
Q

Muscle fibers from unaffected individuals fire a single action potential and then become refractory.

A

…

33
Q

muscle fibers from individuals with MC fire action potentials repetitively in a high-frequency pattern which continues for some time

This extra contraction can produce stiffness which hinders movement. Myotonic individuals have difficulty relaxing the voluntary muscles in a normal manner

***see pp that has for normal and then MC action potentials!

A

…

34
Q

What is slower in myotonia?

A

repolarization!

if slower, the Na+ have time to reset, then they retire because the membrane is still above threshold

35
Q

skeletal muscle depolarization:

recall that Cl- moves into the cell and K+ moves out; both make the inner membrane surface negative

A

….

36
Q

Skeletal muscles have a large safety factor in the number of Na channels, and it is possible to trigger a second action potential if only a few percent have reset to the closed state. In MC, the extra action potentials continue to excite the muscles to contract, preventing the patient from relaxing the voluntary muscles in a normal manner.

A

…

37
Q

What is the structure of the Cl- channel?

Mutation in MC?

A

12 membrane spanning helices - assemble to form a central pore

mutation in MC results from a gly changing to a glutamate at aa 230 (or opposite)

38
Q

disorders of AP propagation?

A

multiple schlerosis - a demyelinating disorder

Cellular Week 4 (11 decks)

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