Tuesday, August 30, 2005

Chapter 2 (2) : HH Conductance Model

The previous post summarized, in somewhat qualitative terms, the HH model of the action potential. Since then, I've written up a supplement to Hille's description of their quantitative model. It is available online as HH_Conduct.pdf. It goes into a little more detail than Hille about their model. For instance, it motivates and describes the equation they actually used to fit their gk data, thus explicitly connecting their speculative lower-level model (in terms of charged 'gating particles') to observed macroscopic conductances. The first paragraph follows.

Hodgkin and Huxley (HH) were able to reliably measure the voltage- and time-dependent changes in sodium and potassium conductance (gna and gk) during the action potential (Figure 2.11 [Hille]). The story that emerged from such experiments is now part of the core knowledge of all neurophysiologists. After a suprathreshold voltage step, gna quickly rises and falls while gk slowly increases to a steady state (Figure 2.11 [Hille]). In a cell that is not voltage-clamped, this increase in gna causes Vm to rapidly approach Ena. However, the subsequent gk increase, and gna decrease, causes Vm to quickly fall back down to the resting potential near Ek. HH quantified these conductance changes in a model with explanatory and predictive power that only continues to grow. In what follows, I will describe in more detail their model of gk and gna.

Each time I revisit the HH corpus, I am impressed by their profound creativity, technical skills (both quantitative and experimental), and luck.


Elias said...

Hi, the link to the pdf file is broken. I was wondering if you still have it somewhere?


Eric Thomson said...

Hi Elias I will try to find it.