An electrophysiology quesiton

Christian Wilms usenet at out-of-phase.de
Tue Feb 10 06:40:26 EST 2004


Xiaoshen Li <xli6 at gmu.edu> wrote:

> I am always confused EPSC and EPSP. In voltage clamp condition, 
> are we measuring EPSCs?

Yes, under voltage clamp you measure you are measuring EPSCs. It tends
to be confusing at first, but after a while one gets acustomed to it.
When you voltage clamp a cell that means you are injecting a current in
order to keep the cell at a constant voltage. What you measure is that
injected current.

When you current clamp a cell you are injecting a constant current into
that cell and what you measure is the resulting voltage of the cell (the
cell potential). The name current clamp is a bit misleading, as it
implies that you are keeping the current through the cell membrane
constant, which you are not.

The connection between postsynaptic currents (PSC) and postsynaptic
potentials (PSP) isn't as trivial as it might seem at first. Ohm's law
is only one of the factors, that play a role here. More important is
that the membrane functions as a capacitance _and_ a resistor. Because
of this capacitance PSP are always longer than the PSC which causes
them.

Hoping that I did add too much to your confusion, Chris 



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