question about activated channels

David Capelle dcapelle at gmx.de
Tue Jun 10 08:07:56 EST 2003


hi,

i have got a question about so called activated membrane channels.
having read in "from neuron to brain" that membrane channels can be
activated by extracellular application of ACh I was wondering what
exactly this means. i suppose it refers to the fact that activated
channels are constantly switching between an open and a closed state
whereas unactivated channels are most likely to be closed at any time.
however in the mentioned book it is stated (in box 1 in chapter 2)
that if all channels were activated there would not be any noise in
the overall membrane current to be expected.
therefore it is argued the formula relating variance, mean current and
the current  through an individual channel ought to be

c=Var/I(1-p) rather than c=Var/I; where c is the individual current, I
the mean current and p the fraction of activated channels.
i would appreciate if anyone could explain this to me as it does not
make sense at the moment (possibly becos i am not getting the meaning
of "activated"). besides i fear the book which is supposedly so
brilliantly elucidating just does not suit the level of medical
undegraduates like me .........

thanks a heap in advance,
david



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