Firing behaviour in stochastic nerve membrane models with different pore densities.

A stochastic nerve membrane model with a two-state pore system was investigated by computer simulation in the uniform (space-clamped) case. The model was based upon the Hodgkin-Huxley equations for the giant axon in squid, but where both the maximal membrane conductances and the rate constants were changed systematically. This was done in order to simulate nerve membranes of small axons, where both of these parameters are smaller than in squid. It was found that the effects upon the firing behaviour due to a finite number of pores were not greatly affected by changes in these parameters. When the specific injected current was calculated relative to the maximal membrane conductances, the threshold for firing was increased somewhat, and the frequency-current relationship became slightly more linear when the maximal conductances (or pore density) were decreased, or the rate constants increased. In the discussion it is shown how the results obtained could be applied qualitatively to the firing behaviour of nerve cells, and that firing in small nerve cells should be significantly influenced by the stochastic effects of a finite number of pores. Gating currents were also discussed, and their effects were found to be insignificant in small nerve cells.