increase in electrode resistance

Matt Jones jonesmat at physiology.wisc.edu
Wed Mar 24 15:45:57 EST 2004


ethomas at ulg.ac.be (Elizabeth Thomas) wrote in message news:<1987c6fa.0403240256.c32ceee at posting.google.com>...
> I am currently doing sharp electrode current clamp recordings on
> thalamic slices.  I have an intermittent problem (but it occurs with
> high frequency) with the recordings that has been bothering me.  When
> I start out with the electrodes in the bath, I can start at very
> reasonable resistances like 90-120 Mohms.  But once I penetrate a
> neuron and stablize it with hyperpolarizing currents - the resistance
> climbs up very high to more than 300 MOhms.  At this point it is no
> longer possible for me to continue the experiment.
> 
> This problem only occurs after I have penetrated a neuron.  The
> resistance is stable even when I leave the electrode in the bath for a
> long time.  I also have the impression that the problem is very
> reduced during lunch hour.
> 
> Has anyone had this problem before?  Any suggestions?
> 
> Sincerely
> 
> Elizabeth


Hi, 

I assume that you're measuring electrode resistance by the
"instantaneous" deflection of Vm during the bridge balance procedure,
and that you are specifically asking about the electrode "series"
resistance, not the total input resistance of the recording (which
would naturally get bigger in the cell as compared to the bath).

My guess would be that the nucleus or endoplasmic reticulum is
partially obstructing the pipette tip. This happens a lot in whole
cell recording, and I assume it might happen in sharp electrode
recording too. In whole cell recording, I try to minimize it by
withdrawing the pipette by about 1 micron immediately after breaking
into the cell, to reduce how much the pipette might be pushing against
the internal membranes of the cell.

You could try doing that to see if it helps any.

Can't see how lunch time would affect this though...

Cheers,

Matt



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