[Neuroscience] Re: number of ion channels in a neuron, type and probability of open/closed

pennsylvaniajake from gmail.com via neur-sci%40net.bio.net (by pennsylvaniajake from gmail.com)
Sun Oct 10 17:09:55 EST 2010


On Oct 9, 1:57 pm, r norman <r_s_nor... from comcast.net> wrote:
> On Sat, 9 Oct 2010 10:11:29 -0700 (PDT), "pennsylvaniaj... from gmail.com"
>
>
>
> <pennsylvaniaj... from gmail.com> wrote:
> >On Oct 7, 5:07 pm, Bill <connelly.b... from gmail.com> wrote:
> >> Wow, that is a lot more of a complicated question than I suspect you
> >> know.
>
> >> The best answer I can give you is to look up the Hodgkin and Huxley
> >> equations. Theres are arbitrary functions that phenomenologically
> >> explain the excitable behaviour of neurons. They do not work on a
> >> single ion channel level, but model the total conductance of ions that
> >> pass across a neurons membrane.
>
> >> We could do a pretty rough back of an envelope calculation though.
> >> Lets say a "typical" neuron has a resting input conductance of 10
> >> nS... a twin pore K channel that mediates a lot the resiting membrane
> >> conductance has a single channel conductance of about 30 pS and I
> >> think, quite a high open probability at rest, of about 0.5... while
> >> Ih, another important leak channel is about 500 fS and an open
> >> probability of about 0.2 at resting membrane potentials... lets just
> >> say the conductance is half and half of these two... so 50,000 Ih
> >> channels and 350 Twin Pore channels... this is just at the perisomatic
> >> region...
>
> >> That's my attempt anyway. I've probably made some fundamental flaw in
> >> my logic, which I'm sure someone will correct.
>
> >> I think Greg Stuart has a paper where he estimates the density of Ih
> >> expression in channels per um^2 from the soma out to the dendrite
>
> >> On Oct 5, 7:15 am, "pennsylvaniaj... from gmail.com"
>
> >> <pennsylvaniaj... from gmail.com> wrote:
> >> > How many ion channels are in a typical neuron?  And of these, how many
> >> > are K, Cl, Na and so on?
> >> > Also, is there an equation that give the probability of how many are
> >> > open and closed based on time?
>
> >I appreciate you trying to answer my question.  I know it is a hard
> >one.  I have seen so many equations including the H & H and K
> >equations.  But I have never run across in 25 years any one taking
> >about the summation of all of the channels and types in a single
> >neuron.
>
> >Due to my education, engineer and mathematician, with the engineer
> >coming out in me, too wonder if any one has ever looked at "the total
> >picture" vs just one ion channel or 3 at the most (K,Na,Cl).
> >Thanks once again.
>
> In general, single channel dynamics is the key to understanding the
> membrane mechanisms underlying nerve activity.  This is the
> "microscopic" level.  The "macroscopic" level of summed channel
> activity is really what determines cell-level activity.  Patch clamp
> studies clearly show that both synaptic currents and voltage clamp
> currents from whole cells are most definitely the result of summed ion
> channel events.  But it really isn't useful to consider single channel
> activity in most levels of neurobiology just as it really isn't useful
> to consider single molecules reacting in most levels of biochemistry.
> Reaction rates result from the summation of large numbers of
> elementary actions:  nerve potentials are the same.
>
> Here is one web site (out of many) that discusses the relation between
> single channel events and summed membrane currents
>  http://nerve.bsd.uchicago.edu/med98b.htm

You are describing exactly what I have been thinking about, but have
no idea how to get informtion about.  I would appreciate any other web
sites that would be of help.  Has any one ever considered an equation
that took this matter into consideration?

Thanks


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