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A criticism of the paper, that I published in this journal,
1
which pointed out the contradiction between measured and theoretical hair reversal
potential has validity and is addressed in this note. This paper, “Falsification of
the ionic channel theory of hair cell transduction “applies the Nernst equation to
hair cell measurements which deal with the movement of ions through the putative ‘transduction
ion channel’. The Nernst equation applied to these measurements yielded a reversal
potential that did not match the measured reversal potential.
The criticism is that there is not only sodium on both sides of the cell membrane
but there is also 140 mM of potassium inside the cell (Ki)while there is no potassium
outside the cell (Ko). To take into account the presence more than one type of ion
simultaneously traversing a ion channel the Nernst equation is not adequate. An expanded
version of the Nernst equation the Goldman equation must be used.
In the measurement by Corey and Hudspeth,
3
described above, the only ion available for transduction outside the cilia is 124 mM
Na+. However inside the cell there is not only 12 mM Na+ but also 140 mM K+. In order
to take into account the effect of both sodium and potassium ions passing in opposite
directions through this proposed nonspecific ion channel we use an extension of the
Nernst equation adapted for multiple ions which is the Goldman equation. A discussion
of the Goldman equation can be found in Hill.
2
The Goldman equation gives us an expression for the reversal potential of a nonspecific
ion channel.
E
r
e
v
=
R
T
Z
F
I
n
P
N
a
N
a
o
+
P
k
K
o
P
N
a
N
a
i
+
p
k
K
i
With only one permeable ion, E
rev
becomes the Nernst potential for that ion. With several permeable ions, E
rev
is a weighted mean of all the Nernst potentials.2
To solve this equation for zero reversal potential it is necessary to set the argument
of the natural log function on the right side of the Goldman equation equal to 1.
P
N
a
N
a
o
+
P
k
K
o
P
N
a
N
a
i
+
p
k
K
i
=
1
From Cory and Hudspeth
1
we get an estimate of the relative ion permeability of P
Na
= .9 and P
k
= 1
The ion concentrations: Nao = 129 mM; N
ai
= 12 mM; and k
i
= 140mM are known. The value of K
0
may therefore be solved for.
The resulting value for the concentration of potassium outside the cell which is necessary
to obtain a zero reversal potential is K
0
= 33 mM. But in this experiment there is no potassium in the external medium. This
result reaffirms the “falsification of the ionic theory of hair cell transduction”
that is developed in reference.1 Before embracing new satisfyingly simple theories,
we would do well to keep in mind the observation made by Italio Calvino in 1943: “When
a man cannot give clear form to his thinking, he expresses it in fables.”reference
4

- Record: found
- Abstract: found
- Article: not found

Oliver Holton, A. J. Hudspeth (1986)

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- Abstract: found
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Michelangelo Rossetto (2013)

Taylor & Francis

1942-0889

This is an Open Access article distributed under the terms of the Creative Commons Attribution-Non-Commercial License http://creativecommons.org/licenses/by-nc/3.0/, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. The moral rights of the named author(s) have been asserted.

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