[QUESTION] How determine or define single channel conductances ?

sos tsnam at yumc.yonsei.ac.kr
Fri Apr 16 03:48:38 EST 1999


Thank you for your kind answer !
May I ask some further questions ?

In almost all experimental report, authors usually specify the condition in
which conductance was determined.
However, as you know, often in "general textbook"(or some review articles),
authors usually describe channel conductance without specifying the measured
condition.
Let me give you one example.
In the famous textbook "From neuron to brain(third edition, 118p)", authors
describe the K channel type, and they distinguish the Ca activated K
channel(Kca) by single channel conductance, they say ...  the conductance of
small conductance Kca is 10pS .. and that of large conductance Kca is 200pS
....
In such case, they mentioned about the intracellular Ca concentration, but
mentioned nothing about the concentration of the transported ions or ...
something like that.
Then how should we figure out the meaning of the conductance value ?
I think symmetric(inside & outside) K concentration may be used. (even
though that experimental setting is not physiological condition,.. since
actually K concentration is not symmetric in physiological condition)
If symmetric concentration was used, how much concentration ???
So, what I'd like to know is, in many cases like that, how should we guess
the measured condition, .. or figure out the meaning of the value of single
channel conductance.

One more question ,... You say 120mM KCl, 120mM NaCl... then symmetric
Chloride concentration..OK ... but osmolality is 240mOsm/kgH2O ? ...
physiological osmolality is 300mOsm/kgH2O , isn't it ? ... then, is there
any reason for you to say 120mM ? ... I guess... 150mM would be more
reasonable ?????  I'm not sure for that...

Thank you in advance !!!
Good luck !


Matt Jones ÀÌ(°¡) <7f0aae$3bm$1 at fremont.ohsu.edu> ¸Þ½ÃÁö¿¡¼­
ÀÛ¼ºÇÏ¿´½À´Ï´Ù...
>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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