Electrophysiology Flashcards
True or false: different cells have different Vm, but all below 0 mV
True
What are the differneces in the methods microelctrode and flourescent dyes to measure Vm?
Microelectrodes: selective
Flourescent dyes: regional differences
How does a Vm arise?
When a membrane is semipermeable and there is a concentration difference of ions on each side
When does the passive ion transport stop?
At Nernst/equilibrium potential, which is when the driving force (aka the electrochemical gradient) is 0
Describe what happen when the electrochemical gradient 1) isn’t 0, 2) is constant, and 3) = 0
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
What is the Nernst potential (Ex)?
Ex is the Vm at which the electrochemical gradient = 0
Describe the Nernst equation.
Ex = RT/zxF * ln ([x]o/[x]i)
What is the Vm?
The difference between the electrical potentials in the cytoplasm and the extracellular space
Which ions contribute to the Vm?
Only permeable, mainly K+
What is the difference between the Nernst equation and the Goldman-Hodgkin-Katz equation?
Nernst: describes the theoretical Ex for one ion
GHK: describes the Vm for a real cell
What ion is mainly responsible for the Nernst slope?
Na+
Whatis the most important role of the Na+/K+ ATPase?
To create the K+ gradient, which drives the efflux of K+ through K+ channels –> creating the negative Vm
What can the patch-clamp method be used to measure?
Whole cell voltage or singel channel voltage
Describe the topology of the Kv channel.
Tetramer
Each subunit: 6 TMD
Pore domain: TM5-6
Sensor domain: TM4
Describe the topology of the Nav and Cav channels.
Same as Kv, but as a monomers (pseudotetramers): 4x6 TMD
Describe the relationship between the alpha and beta subunits of the Kv channel.
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
Which was the first Kv channel to be cloned, and how did it get its name?
The shaker Kv family, because a loss-of-function mutation lead to shaking Drosophila phenotypes
Describe the alpha-beta subunit composition of Nav channels
Alpha: pseudotetramers - 4x6 TMD
Beta: single pass TM proteins, and enclose the alpha-subunits
What is the Nav channels regulated by?
[Ca2+]o
Describe the subunit composition of Cav channels.
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
Describe the generic action potential of non-cardiac cells.
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
How can the action potential be dissectedinto their different components?
By using pharmacological inhibitors
How quick is an AP in a 1) motor neuron, 2) skeletal muscle cell, and 3) cardiac ventricle cell
1) 2 msec, 2) 5 msec, and 3) 200 msec
Describe the cardiac ventricle action potential.
(L-type) Cav channels contribute to the characteristic long cardiac AP (plateau forming AP)
Not only Kv type K+ channels contribute to cardiac AP
Why does the AP differ in different regions of the heart?
Because of different current composition
What does the Q-T interval reflect?
The time until complete ventricular repolarization.
What are prolonged Q-T intervals associated with?
Potentially life-threatening ventricular arrhythmias
How is the AP propagated in neurons?
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
What are channelopathies, and what can cause is?
Diseases originated from channel dysfunctions, can be caused from misfolding, digested channels etc.
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.
LQT syndrome: caused by gain-of-function mutations in NaV channels. This mutation are prolonging the Q-T (depolarizing) phase in the cardiac rhythm
In which channels can loss of function mutations lead to cardiac arrhythmias?
LQT syndrome: caused by loss-of-function mutations in Kv channels.
What can drugs with inhibitory effects on Kv lead to?
Drug induced LQT
Explain the role of Nav channels in pain perception, and give examples of the consequences of their dysregulation.
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
What is Timothy syndrome, and what is it caused by?
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
