The effect of chronic neostigmine treatment on channel properties at the rat skeletal neuromuscular junction.

We have studied the effects of chronic neostigmine treatment on single channel properties at the rat skeletal neuromuscular junction. Rats received 0.86 mg kg-1 neostigmine (s.c.) daily for 9-11 days. Microelectrode recordings were then made from the extensor digitorum longus muscle. The amplitude of miniature endplate potentials was significantly reduced in muscles from neostigmine-treated rats as compared with controls. Acetylcholine (2-5 microM) applied in the bath produced a depolarization and associated channel opening frequency (from voltage noise analysis) which were significantly reduced in neostigmine-treated muscles with respect to controls. The depolarization resulting from the opening of a single channel (from voltage noise analysis) and single channel open time and conductance (from current noise analysis) were not significantly changed by chronic neostigmine treatment. It is concluded that chronic neostigmine treatment causes an adaptive reduction in the number of functional acetylcholine receptors at the endplate without otherwise affecting single channel properties themselves.