Intracellular Blocker of GABAa Receptor

Matt Jones jonesmat at ohsu.edu
Fri Jun 19 12:33:35 EST 1998


In article <6m4nsg$j4h4 at amy.umin.ac.jp> Yasunori Hayashi,
hayashi at cshl.org writes:
>I am looking for anybody who has experience with intracellular blocker of
>GABAa receptor.  I tried DNDS as reported in J. Neurophysiol. (1996) 75:
>2167-2173.  The original paper uses 0.5 mM in intracellular pipet and saw a
>good inhibition.  However, I tried upto 10 mM (x 20) in whole cell
>configuration but could only partially block the response.  Does anybody has
>experience with DNDS or other blockers?  Any positive and negative feedback
>will be welcomed.
>
>Thanks.
>
>
>Yasunori Hayashi
>Cold Spring Harbor Laboratory
>POB100 Cold Spring Harbor 11724 N.Y. U.S.A.
>Tel : 516-367-8485/Fax : 516-367-8372
>

It's funny that you say that, because I have had zero success blocking
GABA-A receptors intracellularly. I have tried DIDS, picrotoxin and
niflumic acid at much higher concentrations than have been reported to
work in the literature on either the inside or the outside. I also met a
woman from David Copenhagen's lab at the Neuroscience meeting two years
ago who had a very similar experience. In fact, she had compiled a
"survey" of people who had similar findings, which included about five
people and ten drugs!  One possibility, I suppose, is that my access
resistance is too high to allow the drug in. But I find that very hard to
believe,  because I monitor it and discard experiments where it gets > 15
MOhm (average is about 7 MOhm). These experiments were done on IPSCs in
cultured hippocampal neurons, by the way, so another possibility is that
the drug never gets out to the synapses. I find that pretty hard to
believe, too, because I can get other drugs, even peptides, out to the
synapses. So I really don't know what to think about reports (in vivo, no
less) where the authors show such dramatic block of IPSCs by channel
blockers filled into the pipette. One potential artifact in such
experiments is that it is rarely feasible to achieve "washout", so one
has trouble deciding whether an effect is really a reversible drug
effect, or rather just nonstationarity of the response. A lot of control
data would be required to convince me of the former. Anyway, I'd be
interested in anyone else's experiences with this method.

Cheers,

Matt Jones
The Vollum Institute
Portland, OR



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