[Relationship between ionic membrane currents and stationary rates of stable and unstable spike propagation].

Pulse propagation in a model of excitable fibre is analyzed. Fibre membrane is described by a nonlinear system of 2 differential equations with small parameter (reduced system of the Hodgkin--Huxley type [1]). Both fast and slow ionic currents of excitable membrane are incorporated into the model. Explicit expressions for fast (stable pulse) and low (unstable pulse) velocities are obtained by using perturbation method. The growth of fast ionic current was shown to result in increase in fast and decrease of slow velocities while the growth of slow ionic current results in increase in slow velocity, fast velocity being almost constant.