[Neuroscience] Re: Nystatin for perforated patches

Christian Wilms usenet02 at out-of-phase.de
Fri Jul 8 04:21:57 EST 2005

SJM Guzman <jose.guzman at medizin-uni-leipzig.de> wrote:


> I am electrophysiologist working in neural plasticity of the cortex, in
> the Pharmacology department of the Leipzig University.
So you're with Prof. Illes? I'm at the Carl-Ludwig-Institut for
Physiology :-)

> [...] but I am not familiar with the term "Bridge-mode". Would you be so
> nice to briefly describe this to me?
Okay ... I'm afraid there are more qualified participants in this group
to explain this, but I'll give it a go.

"Bridge Mode" is actually current-clamp with a compensation for the
voltage drop over the series resitance. Traditionally an actual
bridge-circuit was used for this compensation, nowadays the only
"bridge" involved is in the name.

The beauty of the whole thing is the simplicity during experimenting: 
you patch the cell, switch to current-clamp and apply a test pulse. Now
you normally see an instantaneous voltage jump at the onset and at the
end of the test pulse. These are artifacts caused by the series
resistance. Now you proceed to adjust the bridge until these jumps
disappear. While your doing so, the voltage you are measuring will
change. This is to be expected, as you are now measuring the membrane
voltage without the voltage drop over the series resistance.

Chances are, if you are using the Axoclamp 2A, that you are already
patching in current-clamp mode and possibly already using bridge
compensation, just calling it different ...

The "Axon Guide" has a lot of information on this. If you don't have a
printed version of it in your lab, you can download the pdf from Axon
Inc.'s website. Otherwise I could mail you the file.

Regards, Christian

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