Dependence of acetylcholine receptor channel conversion on muscle activity at denervated neonatal rat endplates

During the development of the motor endplate, the apparent mean open time of the junctional acetylcholine (AChR) channels decreases during the first 3 weeks of postnatal life from about 4 to about 1 ms. This decrease is prevented by early denervation of the muscle, suggesting a neural control of subsynaptic AChR channel properties. To further examine the nature of this neural influence, neonatal rat soleus muscles were now denervated at an early stage of endplate development and the muscles were kept active by chronic stimulations in vivo for 4 days. The gating properties of AChR channels at the denervated endplates and at control endplates of similar age were then examined by analysis of acetylcholine-induced endplate current fluctuations and of the time course of miniature endplate currents, respectively. The results indicate, that stimulation restores the maturation of 'adult' AChR channel properties even in the absence of the nerve, suggesting an important role of muscle activity in synapse development.