Quantitative description of sodium and potassium currents and computed action potentials in Myxicola giant axons.

All analysis of the sodium and potassium conductances of Myxicola giant axons was made in terms of the Hodgkin-Huxley m, n, and h variables. The potassium conductance is proportional to n(2). In the presence of conditioning hyperpolarization, the delayed current translates to the right along the time axis. When this effect was about saturated, the potassium conductance was proportional to n(3). The sodium conductance was described by assuming it proportional to m(3)h. There is a range of potentials for which tau(h) and h(infinity) values fitted to the decay of the sodium conductance may be compared to those determined from the effects of conditioning pulses. tau(h) values determined by the two methods do not agree. A comparison of h(infinity) values determined by the two methods indicated that the inactivation of the sodium current is not governed by the Hodgkin-Huxley h variable. Computer simulations show that action potentials, threshold, and subthreshold behavior could be accounted for without reference to data on the effects of initial conditions. However, recovery phenomena (refractoriness, repetitive discharges) could be accounted for only by reference to such data. It was concluded that the sodium conductance is not governed by the product of two independent first order variables.