increase in electrode resistance

r norman rsn_ at _comcast.net
Wed Mar 24 17:51:41 EST 2004


On 24 Mar 2004 12:45:57 -0800, jonesmat at physiology.wisc.edu (Matt
Jones) wrote:

>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

Does the resistance stay high even after withdrawing from the cell?  I
always thought it was "crud" in the electrode tip -- never thinking to
call it by a more elegant term -- endoplasmic resistance or nucleus.
With sylgard (silicone polymer) bottomed preparation dishes I could
sometimes fix my "crudded up"electrodes by jabbing the electrode into
the soft silicone.  Of course that also often broke the tip, but it
was worth trying since as you say the electrode was shot anyway.

As to lunchtime -- are you sure you are not enjoying a martini (or
maybe a couple of beers) with your repast?  That will loosen you up
enough so you don't really care about electrode resistance anymore!





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