[Effect of blockade of axonal transport on endplate currents of muscle fibers in the frog]

Abstract

The evoked and spontaneous end-plate currents (EPC) were measured in normal voltage-clamped frog sartorius muscle fibres and after colchicine blockade of axoplasmic transport in the corresponding nerve. Colchicine application decreased the growth rate and increased the decay time constant of EPC without changes in the average amplitude of EPC and miniature EPC, quantum content of EPC and frequency of miniature EPC. The increase in EPC time constant was combined with an increase in the sensitivity of the time constant to holding potential, but there were no changes in the amplitude of EPC as a function of holding potential in the reversal potential of EPC. It is suggested that the increase in the EPC decay time constant was due to the appearance of a new population of receptor--ion channel complexes with opening time similar to that described for extrajunctional receptors after denervation. The neurotrophic control of chemosensitive muscle fibre membrane depended on the axoplasmic flow.