IUBio

Myelin capacitance measurement

Administrador del Nodo Postmaster at neubio.sld.ar
Fri May 17 18:19:22 EST 1996


Hello all!

            We have plenty of brains with homologous
myelinized and demyelinized areas (even a lot of tho-
se brains still in use!), but the global measurement
of  capacitance per tissue volume seems me too uncer-
tain to assess absolute values per axon length.  So
I would like proposing to heuristically putting memo-
ry-issues aside and searching for capacitance values
of myelin in gray matter.  How could we measure them?

             Just as almost everybody else, I believe
that myelin-sheath capacitance is low.  An undeniable
merit of Gordon Gray is making us to realize that the
measurements grounding our belief are not a daily ma-
tter. I find useless discussing it theoretically whi-
le at least some measurement reports are not indicated,
so as to ascertain what was really measured, and then
criticizing the design. So I would like to pray everybo-
dy for directing us to published measurements, hopefu-
lly commenting them in the net.
 
               ---------------

               Now due to the good will of Gordon Gray
I have seven copies of his paper though I am unable of
decoding them, and a paper copy of Figure 3 (sent by
surface). So I cannot completely understand his expla-
nations of today, with which he attempts to cope with
R. Norman's indication of a crucial difference with the
conventional lore.  In particular I would like to ask
Gordon (to grasp his views) for the following:

1) What is that which Gordon calls nodal "edges"?
   Can "in parallel with the nodal edges" means "in
   series on other accounts"?  (I cannot draw the cir-
   cuit on Gordon's depiction; see below a mention
   on the morphology of those "edges"). So,

2) What is the circuitry assumed by Gordon to keep
   the high capacitance of myelin as a sheet, when it 
   infolds?  How does such a circuit differ from a
   single rectangular sheet of deflated cell?

3) Up to my knowledge, each infolded layer is made by
     four constituents:

     a) interstitial extracellular fluid 40 A thick;
     b) membrane bilayer;
     c) reducing cytoplasm about 200 A thick;
     d) membrane bylayer

(Please correct me if my thickness values are old).

Is Gordon considering any transmembrane difference 
among both electrolytes to account for such anomalous
scale effect as he proposes? I.e., making oxidizing
the interstitial fluid?  In such a case, with which
pH values can such anomalous scale effect be done?
And, in such a case: 

4) "The ends of the lamellar turns", Gordon writes,
   "are connected in parallel". By what?  Am I mistaken
   in suppossing that those ends overlap yet remain loo-
   se in extracellular fluid? Or is this last electroly-
   te what is taken as making the connexion, among the
   double tiles made by the deflated cell at the nodal
   end of every turn? (= Norman's "very high resistance
   thin layer of electrolyte" as connector).   

5) How does Gordon understand the role of the cytoplasm
   in the non-deflated part of the myelin cell regarding
   the capacitance of the sheet(s) to which it is connec-
   ted?  As a source or as a sink? Ionic charge carriers
   cannot circulate fast enough to make myelin a kind of
   Leiden flasks (bottles, reservoirs: I know not the pre-
   cise word) making Eniac-like memories.  So, what role
   could the cytoplasm in the non-deflated part of the
   myelin cell play?

All these questions are not meant to replace the most di-
rect measurement of capacitance values.  Nor are them ob-
jections but sincere wonderings.  It might be that former
measurements could have been done regarding sectors of the
morphology irrelevant for the possibility of the effect
that Gordon tries to point to us. So I dare to press the
issue in this way; I find it valuable.

                Cheers,
                Mariela
NB: Please Gordon dispose of that horrendous zipping program!
Cheers again, M.
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       Prof. Mariela Szirko,
       <postmaster at neubio.sld.ar> 
                            
       Centro de Investig. Neurobiologicas, Ministry of Health 
& Welfare, Argentine Republic; and 
       Lab. of Electroneurobiological Res., Neuropsychiatric
Hospital "Dr. Jose Tiburcio Borda", Municipality of Buenos Aires,
       Office:  Phone/Fax (54 1) 306 -7314
                e-mail <postmaster at neubio.gov.ar>
       Standard disclaimer: Las opiniones de este mensaje son
personales y no comprometen las dependencias a cargo de la firmante
  Reply to THIS message,  ONLY to: <postmaster at neubio.sld.ar> 
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