Electrophysiology

Question 1

True or false: different cells have different Vm, but all below 0 mV

Answer 1

True

Question 2

What are the differneces in the methods microelctrode and flourescent dyes to measure Vm?

Answer 2

Microelectrodes: selective
Flourescent dyes: regional differences

Question 3

How does a Vm arise?

Answer 3

When a membrane is semipermeable and there is a concentration difference of ions on each side

Question 4

When does the passive ion transport stop?

Answer 4

At Nernst/equilibrium potential, which is when the driving force (aka the electrochemical gradient) is 0

Question 5

Describe what happen when the electrochemical gradient 1) isn’t 0, 2) is constant, and 3) = 0

Answer 5

1) X is transported in the direction determined by tthe electrochemical gradient, the direction of the negative deltaG
2) steady state condition
3) no net flux, and X is per definition at equilibrium

Question 6

What is the Nernst potential (Ex)?

Answer 6

Ex is the Vm at which the electrochemical gradient = 0

Question 7

Describe the Nernst equation.

Answer 7

Ex = RT/zxF * ln ([x]o/[x]i)

Question 8

What is the Vm?

Answer 8

The difference between the electrical potentials in the cytoplasm and the extracellular space

Question 9

Which ions contribute to the Vm?

Answer 9

Only permeable, mainly K+

Question 10

What is the difference between the Nernst equation and the Goldman-Hodgkin-Katz equation?

Answer 10

Nernst: describes the theoretical Ex for one ion
GHK: describes the Vm for a real cell

Question 11

What ion is mainly responsible for the Nernst slope?

Answer 11

Na+

Question 12

Whatis the most important role of the Na+/K+ ATPase?

Answer 12

To create the K+ gradient, which drives the efflux of K+ through K+ channels –> creating the negative Vm

Question 13

What can the patch-clamp method be used to measure?

Answer 13

Whole cell voltage or singel channel voltage

Question 14

Describe the topology of the Kv channel.

Answer 14

Tetramer
Each subunit: 6 TMD
Pore domain: TM5-6
Sensor domain: TM4

Question 15

Describe the topology of the Nav and Cav channels.

Answer 15

Same as Kv, but as a monomers (pseudotetramers): 4x6 TMD

Question 16

Describe the relationship between the alpha and beta subunits of the Kv channel.

Answer 16

The Kv channels are homotetramers of pore-forming alpha subunits, and interact with four intracellular beta subunits. The intracellular N- and C-terminals of the alpha-subunits and the beta-subunits comprise a large intracellular domain, that regulates channel activity

Question 17

Which was the first Kv channel to be cloned, and how did it get its name?

Answer 17

The shaker Kv family, because a loss-of-function mutation lead to shaking Drosophila phenotypes

Question 18

Describe the alpha-beta subunit composition of Nav channels

Answer 18

Alpha: pseudotetramers - 4x6 TMD
Beta: single pass TM proteins, and enclose the alpha-subunits

Question 19

What is the Nav channels regulated by?

Answer 19

[Ca2+]o

Question 20

Describe the subunit composition of Cav channels.

Answer 20

Alpha1: pseudotetramers - 4x6 TMD
Alpha2: extracellular, connected to sigma by sulfur bridges
Sigma and delta: single pass TM proteins, enclosing the alpha1 subunit
Beta: intracellular subunit

Question 21

Describe the generic action potential of non-cardiac cells.

Answer 21

Initiation stimulus reach threshold –> Nav channels open –> Na+ influx –> Vm depolarize: rise to app. +40 mV –> Nav inactivate + Kv channels open –> K+ efflux –> Vm repolarize, but goes lower than resting Vm (undershoot/hyperpolarize) –> Kv close, Nav close (not inactivated anymore) –> Vm repolarize to resting Vm

Question 22

How can the action potential be dissectedinto their different components?

Answer 22

By using pharmacological inhibitors

Question 23

How quick is an AP in a 1) motor neuron, 2) skeletal muscle cell, and 3) cardiac ventricle cell

Answer 23

1) 2 msec, 2) 5 msec, and 3) 200 msec

Question 24

Describe the cardiac ventricle action potential.

Answer 24

(L-type) Cav channels contribute to the characteristic long cardiac AP (plateau forming AP)
Not only Kv type K+ channels contribute to cardiac AP

Question 25

Why does the AP differ in different regions of the heart?

Answer 25

Because of different current composition

Question 26

What does the Q-T interval reflect?

Answer 26

The time until complete ventricular repolarization.

Question 27

What are prolonged Q-T intervals associated with?

Answer 27

Potentially life-threatening ventricular arrhythmias

Question 28

How is the AP propagated in neurons?

Answer 28

Along the axon: Nav and Kv channels sense depolarization in the axon initial segment (AIS) and translate this into APs –> travlels to the presynaptic nerve terminals and activate Cav channels –> increase [Ca2+]i –> NT release

Question 29

What are channelopathies, and what can cause is?

Answer 29

Diseases originated from channel dysfunctions, can be caused from misfolding, digested channels etc.

Question 30

In which channels can gain of function mutations lead to cardiac arrhythmias? Explain the effect of these mutations on the action potential and why this causes arrhythmias.

Answer 30

LQT syndrome: caused by gain-of-function mutations in NaV channels. This mutation are prolonging the Q-T (depolarizing) phase in the cardiac rhythm

Question 31

In which channels can loss of function mutations lead to cardiac arrhythmias?

Answer 31

LQT syndrome: caused by loss-of-function mutations in Kv channels.

Question 32

What can drugs with inhibitory effects on Kv lead to?

Answer 32

Drug induced LQT

Question 33

Explain the role of Nav channels in pain perception, and give examples of the consequences of their dysregulation.

Answer 33

The NaV1,7 channel play a role in pain perception, by facilitating the action potential along the dendrite of the neuron sensing pain, as well as along the axon and in the synapse.
NaV loss-of-function mutations leads to lack of sensitivity pain syndrome.
Gain of function mutations –> hyper sensitivity

Question 34

What is Timothy syndrome, and what is it caused by?

Answer 34

Caused by gain-of-function mutations in Cav1.2 (L-type Ca2+ channel)
Can lead to autism, and problems with a lot of bodily functions