Electrode drift

Ken Scholz kps2 at kimbark.uchicago.edu
Mon Sep 18 09:11:15 EST 1995


>>  Anyone can give me some suggestions on how to get rid of electrode drift?
>> I'm doing whole-cell patch on isolated cells, using a Narashige 3-D hydraulic
>> (oil) manipulator. It's not big drift, about 5 micron or so, but is enough to
>> have effects on my recording.

Although the drift could very well be in your oil-based manipulator, don't
rule out your course mechanical manipulator as a source of drift.  I 
had a problem very similar to your and tried everythin until I discovered
it was the mechanical manipulator that was causing the problem.

Aside from that, be sure to use the hydraulic manipulator as little as 
possible. Get as close to the cell as you can with the mechanical manip.

I also found that hanging a big headstage oout at the end of a pole suspended
from the manipulator was a major source of trouble.  I don't know the
specifics of your set-up but try to support the headstage over the center
of gravity of the manip. itself.  Better yet, take the headstage off of the
manipulator entirely and use a sshort unshielded connecting wire.  I found this
to work great and cause no increase in noise, even in single channel recording.

Make sure there is nothing applying tension to any part of the manipulator.

If leads wires are stiff, hydraulic lines bowed with tension, etc.. all of 
these can be sources of drift that you can't see with the naked eye but can
cause trouble every time you reposition the electrode over a cell.

As a first step in diagnosing this typ of problem, I would recommend for
anyone to remove everything from the set-up except the manip. and electrode
holder.  Remove the headstage, lead wires and be sure to relax any tension
in the hydraulic lines.  If you still have the drift then look into which
manip. is causing it.  

Most of all, remember that you are a scientist.  USe the same rational
well-thought out approach to diagnosing your manip. problems that you
would use to examine what second messenger is activating your channel!
I've seen lots of people throw away perfectly good $3000 manipulators
because they became too irrational to figureout what the REAL problem was!

Good Luck
-- 
Ken Scholz                    Department of Pharm. and Physiology
kps2 at midway.uchicago.edu      Univ. of Chicago



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