[Prev][Next][Index][Thread]
Re: WSN: Dielectric Constant for weak electrolyte (fwd)
Sender: varghese@poincare.wbme.jhu.edu (Tony Varghese)
Subject: Re: WSN: Dielectric Constant for weak electrolyte
Bruce Bush Merck Research Laboratories writes:
> This is a very interesting problem. Though I have no expertise in the
> area, I wonder whether aqueous dielectric constant(s) have much effect on
> membrane currents? Perhaps it is good enough to assume infinite (or very
> large) static dielectric constant, and some fast (or infinite) diffusion rate
> for each ion species within the aqueous media -- i.e. assume instantaneous
> equilibration of electrolyte at constant potential throughout the cell?
This is a reasonable suggestion. It has been used since Julius Bernstein
suggested that the theories of Nernst and Planck are applicable to the
biological membrane phenomena (circa 1902). I use the resulting approximation
everyday in my models of electrical activity in nerve and heart cells.
However, there are a number of phenomena that cannot be explained by this
approximation: 1. Calcium waves: Experimenters have observed waves of calcium
propagating at about 100 um/sec in muscle, nerve, oocytes and other cells.
2. Nonlinear current-dv/dt relations: experimenters have seen nonlinear
relationships between fast currents and the rate of change of potential;
the simplified Nernst-Planck analysis predicts a linear one.
3. Discrepancies in stimulus-activation relations obtained in experiments
vs. computations based on the simplified Nernst-Planck analysis.
While these observations do not point directly at the investigation I have
suggested, I do believe that a more accurate model (the Nernst-Planck-Poisson
equations) may help us get a better idea of what is happening at the
membrane and the space around it.
Thanks,
Tony Varghese