SEClamp for cable model

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BVGH
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Joined: Fri Nov 03, 2017 4:12 pm

SEClamp for cable model

Post by BVGH » Sun Nov 05, 2017 6:31 pm

Hi,

I am not sure if it is a weird question or not. Does it make sense to apply the voltage clamp, using "SEClamp", to the first compartment and measure the current response of the last compartment (ic, capacitor current) instead of the current of SEClamp in the first compartment? By doing this, I want to get the I-V curve for voltage clamping.

Thanks.

ted
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Re: SEClamp for cable model

Post by ted » Sun Nov 05, 2017 10:02 pm

Usually voltage clamp is used to measure currents carried by ion channels. For measurements to be most useful, (1) the channels must close to the location of the clamp, where membrane potential is under best control, and (2) the recorded currents should be as free of capacitive current as possible. These requirements are best met in cells that are anatomically compact (and therefore electrotonically compact). If a cell has sufficient spatial extent that it must be represented by multiple compartments in order to get good spatial accuracy, then the clamp current is of questionable use as a means for studying the properties of the ion channels. Also, it is not useful to record membrane capacitive current, because the experimental question is not "how does membrane capacitive current depend on membrane potential and time"--the question is "how does a particular ionic current depend on membrane potential and time."

BVGH
Posts: 2
Joined: Fri Nov 03, 2017 4:12 pm

Re: SEClamp for cable model

Post by BVGH » Tue Nov 07, 2017 5:24 pm

Thank you, Ted.

One more question. For modeling in NEURON, If we have both voltage-clamp and current-clamp results from bouton, so that the clamping was done in bouton and the channels responsible for the action potential are located at 30um from bouton, is it better to use voltage-clamp results or current-clamp results? No channel was blocked but we know the types of ion channels in this neuron.

One more thing. Does it make sense to calculate Cm, Rm, and Ra for this model by using the sum of all areas (area_bouton+area_unmylinated part) or we have to only consider the area of bouton (where we applied voltage clamp in the experiment)?

ted
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Re: SEClamp for cable model

Post by ted » Wed Nov 08, 2017 10:23 am

A side-comment: if we were having this discussion at a table with a pad of paper and some pencils, the following questions would be resolved very quickly.
is it better to use voltage-clamp results or current-clamp results?
I can't answer the question because it lacks context. Is it better to use them for what? Why were the measurements made, how were they performed (where was the electrode attached to the cell, what was measured), and what results were calculated from those measurements?
Does it make sense to calculate Cm, Rm, and Ra for this model by using the sum of all areas (area_bouton+area_unmylinated part) or we have to only consider the area of bouton (where we applied voltage clamp in the experiment)?
This question also lacks context. What does the model represent?

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