Biology Reference
In-Depth Information
3.
IMPLICATIONS OF THE HODGKIN-HUXLEY MODEL AND
THEIR METHODOLOGY
3.1. One basic mechanism with many types of molecular realizations?
An examination of the form of the key equations, especially the batch summa-
rized beginning with [26] above and then numbers [30-31] might suggest that H
and H's accomplishment is not that different than, say, James Clerk Maxwell's
articulation of the electromagnetic theory of light and Maxwell's derivation of
the wave equation for an electromagnetic disturbance. (That disturbance impor-
tantly had the transverse wave features and the same velocity as light, which
led Maxwell to postulate that light was an electromagnetic wave.) But the H
and H equations are not universal equations as were Maxwell's - the H and
H equations were empirically generated from curve fittings to the squid action
potential changes read using the voltage clamp technique. Hodgkin and Huxley
remarked on the limitations of their model a number of times during the course
of their 1952 article, limitations that are well summarized by Bogen (2005) and
Craver (2006).
Toward the very end of the 1952 paper, H and H wrote
Applicability to other tissues. The similarity of the effects of changing the con-
centrations of sodium and potassium on the resting and action potentials of many
excitable tissues (Hodgkin, 1951) suggest that the
basic mechanism
of conduction
may be the
same
as implied by our equations, but the
great differences
in the
shape of action potentials show that even if equations of the same form as ours are
applicable in other cases, some at least of the parameters must have
very different
values.
(p. 542) (my emphases)
In addition, toward the end of his Nobel lecture, Hodgkin returned to this issue
and the related theme of a specific or 'definite' model of the membrane when
he wrote
To begin with we hoped that the analysis might lead to a definite molecular model
of the membrane. However, it gradually became clear that different mechanisms
could lead to similar equations and that no real progress at the molecular level could
be made until much more was known about the chemistry and fine structure of the
membrane. On the other hand, the equations that we developed proved surprisingly
powerful and it was possible to predict much of the electrical behaviour of the
giant axon with fair accuracy. Examples of some of the properties of the axon
which are fitted by the equations are: the form, duration and amplitude of the
action potential; the conduction velocity; impedance changes; ionic movements;
and subthreshold phenomena including oscillatory behaviour.
(1962, p. 42)
