Excitatory Postsynaptic Current Measurement

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BigPharmBoy
BigPharmBoy's picture
Excitatory Postsynaptic Current Measurement

Hi Everyone,

What an incredible forum!  Thanks to the admins for forming it.

I am very new to electrophysiology and patch clamping and struggling to understand some of the fundamentals.  My question pertains to excitatory postsynaptic currents (EPSCs).

1.)  What is the command voltage used for measuing EPSCs during voltage clamping?  Is it the resting membrane potential?

2.) During voltage clamping, an influx of cations into the cell will raise the membrane potential and will thus require an influx of negative charge from the current electrode to offset the rise in membrane potential.  How does this occur?  Does the current electrode supply electrons to the cell?

3.) On a similar note, an influx of anions will lower the membrane potential and will require an influx of  positive charge from the current electrode to offset the fall in membrane potential.  How does this occur?  Does the current electrode remove electrons from the cell?

I trully appreciate all the help that anyone gives me.

Thanks again for this most awesome website/forums.

azylbetal
azylbetal's picture
Hi Pharmer,

Hi Pharmer,

Regarding your questions:

1. The clamping voltage you would use to record EPSCs depends on your experimental needs. The further you are from the EPSCs reversal potential (usually around 0 for excitatory synapses), the higher the EPSCs amplitude you would get, does making them easier to detect when analyzing your data. Usually a value between -60mV and -70mV would be good.

2+3. The micropipette indeed supplies negative or positive current to counter-balance changes in membrane potential. These currents are carried by a mixture of ions in the solution (electrolytes). Electrons are not the charge carriers of currents in aqueous solutions (as they are in metal wires for example).

Hope it helps...

BigPharmBoy
BigPharmBoy's picture
Thanks a bunch Azylbetal. 

Thanks a bunch Azylbetal.  That definitely helps. 

In part 1 of your response you essentially clarified why the investigators in the journal article that I read used a holding potential of -80mV. 

Thanks again and much luck in your research.