Could a cell membrane provide an electromagnetic shield ?

r norman rsn_ at _comcast.net
Wed Feb 11 08:49:33 EST 2004


On Wed, 11 Feb 2004 08:18:58 GMT, "k p  Collins"
<kpaulc@[----------]earthlink.net> wrote:

>Hi Dr. Norman,
>
>"r norman" <rsn_ at _comcast.net> wrote in message
>news:077j20drks8gq72pv9f52dj088phro99m2 at 4ax.com...
>> [...]
>
>>Incidentally, the membrane capacitance is
>> pretty close to 1 microfarad/square
>>centimeter or 0.01 farad/m2.
>
>I =only= want to try to convey a 'new'
>position with respect to such 'membrane
>capacitance', and I'm not expecting you
>to reply. [It's too-hot, just now. I under-
>stand.]
>
>In my view, what you refer to as a
>"membrane capacitance" is not a  
>"capacitance", but a result of active
>ionic pumping that maintains the
>resting potential.
>
>In "capacitance", the "capacity"
>fills-up and the result is a =passive=
>storage, not anything that is actively
>maintained.
>
>I'm not saying it well enough. What
>I'm getting at is that the 3-D energy-
>dynamics that maintain the resting
>potential are the wellsprings of
>information-content. That is, they
>are not uniform, as is a capacitor's
>passive response, but, through stuff
>like gate-location and ionic response
>selectivity, exist as they do as activa-
>tion-dependent =results= of prior
>neural experience.

Ken, I do understand that you have a world-view that includes
something about 3-D energy-dynamics.  Unfortunately, that view
deviates from what everyone else in the world considers the state of
affairs.  I have studiously avoided getting into long discussions with
you about your ideas and simply don't bother reading them.  I must say
here that, when you are not into your energy-dynamics thing, you do
have some intelligent ideas to contribute.  However, your alternative
non-traditional theories  dominate almost all of your posts.

I will abide by classical electricity and magnetism that has served
humankind so successfully for about 150 years (quantum mechanics and
more recent theories aren't necessary for phenomena at the level we
are describing).

The membrane is composed of a lipid bilayer through which electrical
charge cannnot pass.  That is: ions cannot move across the lipid
bilayer.  That is: the lipid bilayer is a dielectric that separates
charge.  You can get a kind of current to flow across it --
displacement current -- which obeys the law I = C dV/dT.  An
electrical component that obeys this law is called a capacitor.

The membrane also contains ion channels through which charged
particles can move, carrying current.  The rate of current is, to a
good degree, directly proportional to the "forces" acting on the
charge.  Since there are both diffusional "forces" and true electrical
forces, the ionic current for substance x obeys the law 
          Ix = gx (V - Ex)
where gx is a constant called conductance and Ex is the Nernst or
equilibrium potential for substane x,  Ex = RT/F ln [X]/[X].  An
electrical component in which current is proportional to voltage is
called a resistor.  The extra term in the ionic current equation can
be represented by a voltage source.

There is an enormous body of experimental work dating back some 50
years now confirming the validity of this "ionic theory".  In fact, no
one even calls this the "ionic theory" any more, it is simply the way
membranes work.

And the ion pumps do NOT really maintain the resting potential and, of
course, have absolutely nothing to do with capacitance, apparent or
real.  The ion pumps maintain the concentration gradients across the
membrane.  The potential is caused by the differential selective
permeability of the membrane and the ion concentration gradients. One
proof is to kill the pump.  Except for a small term caused by the
electrogenic action of the pump (net charge transport across the
membrane), the potential remains until the ion movements eventually
alter the concentrations.  Another demonstration is the success of the
Goldman constant-field equation in describing electrical potential in
virtually all experimentally tested situations.  This equation
includes only concetrations and permeabilities.

 Approximately 85%-90% of the 60+ students in my intro neurobiology
class know all of this.  It was the subject for the most recent exam.
You should sit in on my lectures!





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