Differences in action potentials and accommodation of sensory and motor myelinated nerve fibres as computed on the basis of voltage clamp data

Abstract

1. Voltage clamp experiments were performed on sensory and motor nerve fibres of the frog using a digital computer for automatic experiment control and data recording. 2. Rates of rise and maximum amplitudes of potassium currents were determined in both sensory and motor fibres, so that comparative values of n infinity and tau-n could be obtained. 3. The results indicate that the n infinity-V curve for sensory fibres is displaced from the curve for motor fibres in a depolarising direction. The potassium kinetics are similar in both for voltage steps up to about - 20 m V, beyond which tau-n becomes progressively smaller for sensory than for motor fibres. 4. These comparative values of n affinity and tau-n have been used to calculate alpha-n and beta-n values for a model "motor" action potential by considering the Frankenhaeuser-Huxley computed action potential to be "sensory". This modification of the potassium system, together with some alteration to the sodium inactivation system produces a satisfactory model "motor" action potential. 5. The model sensory and motor action potentials behave quite similarly to their experimentally recorded counterparts with respect to action potential shape and relative duration, repetitive firing, accomodation and the simulated action of T.E.A.