IUBio

question about activated channels

KP_PC k.p.collins at worldnet.att.net
Tue Jun 10 18:29:01 EST 2003


"David Capelle" <dcapelle at gmx.de> wrote in message
news:754d51cf.0306100507.42c984d5 at posting.google.com...
| 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

The view I'll discuss is not [yet] accepted
by others, so do not 'quote' it as if it is.

It requires a =lot= of discussion, but in my
view, the "noise" to which the Author refers
probably occurs as a function of detector-
response characteristics, rather than any-
thing in the Biology.

It's a problem through all of Science where
'detector' probes are employed.

The detectors have their response character-
istics, and experimenters attribute their
data as 'capturing everything' that's going
on within the experimental set-up.

But this's =never= the case.

In the view I hold, although an ion gate
can be "open" or "closed", it can also be
"in-between" - that is, the gates' func-
tionality is not 'instantaneous', but the
detectors' responses give the illusion
that they are 'instantaneous'.

The difference is important because it's
important to see the overall Continuity,
which is in the "in-between" stuff.

Which leads me to 'lean' toward the
formulation that the book 'denies'.

ken [K. P. Collins]





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