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[QUESTION] How determine or define single channel conductances ?

Matt Jones jonesmat at ohsu.edu
Tue Apr 13 15:43:58 EST 1999


In article <7eujme$5kk$1 at news2.kornet.net> sos, tsnam at yumc.yonsei.ac.kr
writes:
>Hello, everyone !
>
>As you know, ion channel conductance is dependent on the concentration of
>the ions that is transported through the channel (so called "normal"
>rectification). For example, when we increase the ion concentration, the
>channel conductance measured by single channel current will also be
>increased, even in the condition of same electrochemical potential gradient.
>However, in some paper, the value of the ion channel conductances is
>described without specifying the detailed ion concentration. In that
>ase( namely, not mentioned about ion concentration or measured condition
>such as symmetrical ? etc...), I wonder if there are any general rules(?) or
>conditions(?) for defining(or describing) single channel conductances ?
>
>Thank you in advance !!!
>Good luck
>


If a paper really doesn't give any information about the ion
concentrations used when the channel conductance was determined, you have
two options: 1) Ignore the paper completely, and disregard everything
that it says, because this is an incredibly sloppy way of reporting data;
or 2) assume that they used some relatively "standard" set of solutions,
designed to mimic the endogenous physiological environment. For example,
if someone reports that a ligand-gated channel has a 30 pS conductance,
you might be charitable and assume that this was measured in
approximately 120 mM NaCl outside and 120 mM KCl inside. But this is
dangerous in my opinion, because more often than not, people studying
single channels are using special solutions to maximize their signal to
noise ratio, or to isolate their channel of interest from other channels
in the same membrane.

Matt Jones



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