The mitochondrion as a flip-flop memory element in neurons

Andrew Gyles syzygium at alphalink.com.au
Tue Dec 12 19:33:56 EST 2000


In article <J3rZ5.16970$Uj7.546529 at typhoon.mw.mediaone.net>,
  "Richard Norman" <rsnorman at mediaone.net> wrote:
> "Andrew Gyles" <acgyles at my-deja.com> wrote in message
> news:913oq4$6on$1 at nnrp1.deja.com...
> >
> >
> > (Related articles at: http://www.geocities.com/acgyles)
> >
> > The mitochondrion as a flip-flop memory element in neurons
> >
> > I suggested in an earlier article that if certain mitochondria in
> > neurons worked with all of their ATPsynthase/ATPase enzymes
rotating in
> > phase or [to allow for geometric effects at the bends of cristae] in
> > phase plus or minus 120 degrees, they would produce 'minor floods'
of
> > protons when working as ATPsynthase, which could trigger nerve
impulses.
> >
> > Protons are positively charged. The arrival of positive charges at
the
> > negatively charged inner surface of a neuron membrane that is ready
> > to 'fire' will trigger a nerve impulse. The triggering positive
charge
> > need only be very small; the main strength of a nerve impulse is
> > contributed by the subsequent increase in permeability of the
membrane
> > to sodium ions, and the inrush of that ion into the neuron.
>
> <snip a lot of stuff>
>
> I have not noticed in electron micrographs any particular
concentration
> of mitochondria right under the cell membrane especially at the site
> of spike initiation.  Have you tried calculating the actual number of
> protons that would be required to depolarize a neuron by even a few
> mv for a reasonable time (at least a significant fraction of a time
> constant)
> over a substantial distance (at least a significant fraction of a
space
> constant) and allowing for diffusion in the bulk intracellular medium?
> Then have you tried calculating the effect on the intracellular pH?
>
> I would guess that you will kill all the proteins in the vicinity
with all
> those protons.  These are not inert charge carriers like K+ or Na+.
> They are exceptionally active!
>
>

Thank you for your comments. I have not calculated how many protons
would be required to trigger a nerve impulse. But I suggest that a
mitochondrion would be capable of pumping out many protons in
each 'minor flood' or 'wave'. There might be millions of identical
ATPase enzymes rotating in phase in a single mitochondrion.

Would it be true to say that the smaller the diameter of the part of
the nerve concerned the fewer the protons required to trigger an
impulse?

Is it possible that protons would have a more powerful triggering
effect (in relation to their number) than other positive ions? And that
fewer of them would be required because of this?

I am aware that the proton is the active part of acids (I assume that
in the cell it is in the form of the hydronium ion), and I am concerned
about its potentially destructive effects. However, all mitochondria
produce protons when their ATPsynthase/ATPase enzymes are working 'in
reverse'as ATPase. The protons are pumped to the outside of the inner
membrane of the mitochondrion; the outer membrane is permeable to ions,
I understand. So I assume that the bulk intracellular medium is
sufficiently well buffered to prevent a big fall in pH. It is also
possible that most of the protons are 'tethered' to the inner membrane
by the attraction of negative ions in the matrix of the mitochondrion.

(There is a sodium ATPsynthase/ATPase in a bacterium, which pumps out
sodium ions when it is running 'in reverse' as an ATPase. It is thought
to be very similar in its rotary mode of operation to the proton
ATPsynthase/ATPase in eukaryotes.)


I suggested that the mitochondrion might have one side close to the
inside of the membrane of the neuron. That would reduce diffusion into
the bulk intracellular medium. If no mitochondria are observed close to
the membrane of neurons in places where an impulse could be triggered
my hypothesis would seem unlikely to be correct. Have you seen any in
the dendrites?

Andrew Gyles

http://www.geocities.com/acgyles


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