Thermodynamic problems (Pentcho Valev)

RUMYM at BGEARN.ACAD.BG RUMYM at BGEARN.ACAD.BG
Wed Oct 22 05:42:32 EST 1997


In reply to Lukasz Salwinski

Lukasz, below is the only concrete answer you have given, and it is wrong.


I asked:
>5. What if the initial KCl concentration in the left-hand compartment is <
>10 mM whereas that in the right-hand compartment is zero? Please try to  <
>describe how the charge density, the field and the potential change      <
>from the membrane to the right, up to infinity. (The potential in the    <
>right-hand compartment cannot be measured since the phase is non-conductive,
>but calculations based on thermodynamics show that the potential goes to <
>infinity with distance. Would you agree?)                                <

Lukasz Salwinski answered:
nope. can be measured, do not go to infinity. hint: some of K ions cross the<
membrane and generate transmembrane potential. value depends on the ratio of<
the compartments                                                            <

Yes it can be measured. This was an "insinuation" of mine - so far everybody
has refered to unmeasurability in order to beg the question.
   However you are wrong that the potential depends on the ratio of the
compartments. The only thermodynamic requirement is that the
electrochemical potential

     MU(elchm) = MUo + RTln(C_K+) + F(Phi)                 /1/

where C_K+ is the concentration of K+, F is the Faraday and Phi is the
electrical potential, be uniform throughout the system. As C_K+ goes
to zero with distance to the right, it follows unequivocally from /1/ that
Phi goes to infinity. This has been recognized by a number of scientists;
I have even found it published somewhere, but cannot remember the reference
(if I find it, I will inform you immediately).

Best regards,
Pentcho



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