Properties of junctional acetylcholine receptors that appear rapidly after denervation

It was previously found that the number of junctional acetylcholine receptors of rat diaphragm, as measured with [125I]alphabungarotoxin binding, suddenly increased 2 days after denervation in vivo or in vitro. Organ culture was used here to characterize further this unusual class of junctional receptors. The 'new' acetylcholine receptors were physiologically functional and were functionally located only in the junctional region. The rate of degradation of new receptors was slower than that of extrajunctional receptors and similar (in the first 24 h) to that of typical junctional receptors. In addition, the appearance of new junctional receptors was inhibited by cycloheximide and actinomycin D given at critical periods, implicating a protein synthetic step. Finally, nerve stimulation in the presence of a post-synaptic blocker (pancuronium) advanced the time of appearance of new junctional receptors. This last finding coupled with our previous report of nerve stump length effects on junctional acetylcholine receptors reinforces the suggestion that under certain conditions the level of junctional receptors can be regulated by the motor neuron.