[Neuroscience] Re: Different reversal potential or just poor space-clamp?

jonesmat via neur-sci%40net.bio.net (by jonesmat from physiology.wisc.edu)
Tue Jun 15 15:56:41 EST 2010

On Jun 5, 12:25 am, Bill <connelly.b... from gmail.com> wrote:
> Hi,
> So I'm using whole-cell voltage clamp to record from a cell that has
> two classes of inhibitory inputs. One to the soma, and one (largely)
> to the dendrites, which I can activate independently. I/V plots show
> me that the apparent reversal potential of the dendritic input is 10mV
> lower than the somatic input. This could be due to the fact that a)
> there is active Cl- homeostatis in the dendrites, which means that the
> reversal potential truly is lower there, or b) I have poor space
> clamp, and hence I have to drive the somatic voltage below the actual
> reversal potential to get the potential at the dendrite to the
> reversal potential. (or I suppose both). There is plenty of evidence
> that I don't have proper voltage clamp of the dendritic events (slower
> rise and decay time).
> Is there any way to figure out whether this effect is solely due to
> cable filtering of my command voltage?

Hi Bill,

There is a way to estimate the electrotonic attenuation between your
headstage and the synapse, though it's a little involved. It relies on
giving voltage jumps at a series of times leading up to, and
following, stimulation of the synapse.

The method is thoroughly described here, with real data and
simulations to test its accuracy:

Estimating the time course of the excitatory synaptic conductance in
neocortical pyramidal cells using a novel voltage jump method.
Häusser M, Roth A.
J Neurosci. 1997 Oct 15;17(20):7606-25.



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