A Spatially-Ordered Pacemaker Observed in Squid Giant Axons

It was both theoretically and experimentally demonstrated that a spatially-ordered pacemaker generating action potentials at a constant rhythm was formed at a restricted region on the squid giant axon in the state of self-sustained oscillation of the action potentials. The dynamics of the Hodgkin-Huxley equations with one-dimensional diffusion were analysed to study the spatially-ordered pacemaker under the following conditions; (1) the rate constants of sodium activation and inactivation, and potassium activation changed with the effective calcium concentration in the external medium, according to Frankenhaeuser and Hodgkin (J. Physiol. 137 (1957) 218), and (2) the membrane potentials at both ends of the axon were fixed to be zero. These experiments and calculation show that the repetitive firing state is spatially well organized and integrated, and that it could be called as the dissipative structure of Glansdorff and Prigogine macroscopically