Accommodation in Myelinated Nerve Fibres of Xenopus Laevis as Computed on the Basis of Voltage Clamp Data

Abstract

The equation system earlier derived from the voltage clamp analysis on myelinated nerve fibres from Xeonpus laevis was programmed for a digital computer. The response of the nerve model to linearly rising currents was computed for a number of quantitative modifications of the nerve model. The agreement between the computations and the earlier experimental results was qualitatively satisfactory. The quantitative agreement was not perfect but the discrepancies were not greater than what is expected from the known errors in the voltage clamp technique. The computations indicated that changes of any of the constants of the nerve model have effects on the rate of accommodation. The greatest effects were obtained by changing the inactivation of the sodium permeability. It was concluded, on the basis of the results obtained in the present and in the earlier investigation, that the slow excitability changes of the nerve fibres are well predicted by the equation system describing the ionic currents. Further, it was concluded that the normal variation in accommodation among myelinated nerve fibres from Xenopus laevis is accounted for mainly by variations in the rate constants ah although this may not be the only variable of importance. A variation in the turning on of the potassium permeability might also be significant.