A kinetic model for the sodium conductance system in squid axon.

We describe a kinetic reaction sequence for the sodium conductance system in the squid axon. It closely matches the original Hodgkin and Huxley model for voltage clamp experiments but it generates an action potential without a bump on the falling phase. When calcium ions are included in the reaction, this model faithfully reproduces the experimental observations of Frankenhaeuser and Hodgkin on the effects of altered calcium in the medium. The fit to experiment is much better than when a voltage shift in rate constants is assumed. The gating currents recently observed by Armstrong and Bezanilla are not compatible with the Hodgkin and Huxley model but can be reprocuced in considerable detail by the kinetic model. Thus it appears that the kinetic model differs from that of Hodgkin and Huxley perhaps in an important and fundamental way that makes it more realistic.