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
