Solutions of the Hodgkin‐huxley Equations for Squid Axon Treated With Tetraethylammonium and in Potassium‐rich Media

SUMMARY Solutions to the Hodgkin‐Huxley (H‐H) equations have been obtained using the fast digital computer SILLIAC. In these theoretical calculations the parameters were adjusted to correspond to the experimental conditions prevailing in a series of experiments reported by Tasaki and his collaborators, namely, (a) normal axon in potassium‐enriched sea water, or (b) tetraethylammonium (TEA) treated axon in normal sea water. Under conditions (a) the theoretical solutions demonstrated a response to hyperpolarising currents, the threshold of which was dependent on the value of the outside potassium concentration. The resulting theoretical waveforms and resistance variations were similar to those observed experimentally. The effect of TEA was simulated by reducing by a factor, k, the rate of change with time of those terms in the Hodgkin‐Huxley equations governing the potassium permeability. It was found that for k < 22·5, the action potentials were prolonged but were not modified significantly in shape. For k > 22·5, however, a plateau reminiscent of some cardiac waveforms appeared after the initial spike. The effect of hyper‐ and depolarising currents, of abolition pulses, and of the response to successive stimuli, was investigated. The theoretical results were found to correspond closely with the experimental observations. It is concluded that the prolonged action potential under TEA and some features of the hyperpolarising response in potassium‐rich sea water can be satisfactorily accounted for within the existing framework of the Hodgkin‐Huxley equations.