Richard Norman wrote:
> Austin So (Hae Jin) wrote in message <38175D80.96AC5698 at netinfo.ubc.ca>...
> >Since no one but that guy ken collins replied...
>> Actually Ken Collin's reply, for once, was on topic and actually relevant!
Good for you. Hopefully when people some back from Neuroscience, they
can point
out how wrong all of us are...
> >"leak" currents are due to things like transporters (in either direction,
> and
> >may or may not involve ATP) which generally co-transport ions through the
> >membrane.
>> Since leak currents are responsible for electrotonic potentials,
? Maybe it's just been too long since I've looked at this stuff, but
could you
explain in what way they are responsible?
> they are
> directly proportional to the driving force.
Are you saying that if you make a I-V plot of leak current you will see
a
straight line?
> That is usually not the case
> with transporters, especially the active ones involving ATP. Those usually
> show saturation kinetics.
That doesn't matter...the magnitude of the leak is pretty small from
what I
remember, and they exhibit gradual kinetics. It ain't something with the
kinetics or magnitude of an AP or EPSP.
> The pumps, in particular, are controlled by other
> factors and do not readily respond to changes in potential.
Of course they are and they just go on functioning in their merry way
although
driving force also determines their "kinetics".
> And, besides,
> the leaks continue in the absence of metabolic energy.
You seem to have the belief that there is a specific channel that gives
rise to
the "leak"...but by definition these leak currents are undefined.
Like I said...things like transporters *contribute*...they are not the
source.
> >And yes...ion channels do not "leak".
>> No, in the closed position they do not. But at resting potential some may
> remain open and therefore be responsible for the "resting" or "leak"
> permeability.
Okay...semantics...ion channels when they are closed do not leak.
Membrane
potential changes the probability of a given channel population being in
this closed,
non-conducting state. So at any given membrane potential a subpopulation
will be
open and will give rise to a current of particular magnitude. You can
call this
"leaky" if you like...
> >Any good neurophysiology text should give you good information about them.
>> The specific reason I ask is that no good neurophysiology text gives the
> information
> I requested. Of course, they all describe the leak and they all describe in
> detail
> the molecular structure of the gated channels. And some have long lists of
> varieties of gated channels. But NO text I checked indentifies specifically
> what
> ion channel is reponsible for the resting leak.
Go figure...you are looking for a specific channel...current does not
equate to the existence of a channel...
When you are talking about "resting potential" (i.e. not clamped), you
are
talking about a state of equilibrium between things that go in and
things that
go out (and by things I mean inorganic or organic ions). Therefore you
invoke
the whole range of channels, transporters, etc. to maintain this
equilibrium and therefore the resting potential...
Maybe there will be a followup from someone else next week about this...
--
---
Austin P. So (Hae Jin)
I.I.S.G.P.
Biotechnology Laboratory
University of British Columbia
E-mail: haejin at netinfo.ubc.cahttp://www.interchange.ubc.ca/haejin/index.html (under construction)
