Action Potential Generation in Denervated Rat Skeletal Muscle

It was concluded that denervation produces a genuine reduction in the rate of rise of the action potential in muscle fibre.

Abstract

Abstract R edfern , P. and S. T hesleff , Action potential generation in denervated rat skeletal muscle. I. Quantitative aspects . Acta physiol. scand. 1971. 81 . 557–564. Action potential generation was studied at various periods up to one week after denervation in individual muscle fibres of the extensor digitorum longus muscles of the adult rat. To allow a comparison of action potential generation at various stages of denervation, it was necessary to establish adequate conditions for spike generation. It was found that when fibres were locally polarized to a level of ‐90 to ‐100 mV, and the external calcium concentrations was increased to 4 mM, the peak rate of rise and the overshoot of the action potential were maximal. Between 30 and 40 hrs following section of the motor nerve, the mean maximal rate of rise of action potentials, recorded under the aforementioned conditions, was reduced by about one third, and remained at about this reduced level during the subsequent days. Two days after denervation the resting membrane potential was reduced from a mean of 82 mV in innervated muscle to a mean of 68 mV, and remained at about this level for the remaining 5 days studied. The electrical time constant and the input resistance of the muscle fibres gradually increased during the 7 days following denervation, the time constant by about 70 % and the input resistance by about 50 %. With anodal polarization in denervated muscle no significant correlation was found between the resting membrane potential and the maximal peak rate of rise of the spike. It was concluded that denervation produces a genuine reduction in the rate of rise of the action potential in muscle fibre.