Control of ACh sensitivity by muscle activity in the rat.

1. Rat soleus and extensor digitorum longus (EDL) muscles were examined following complete blockade of sciatic nerve impulses with anaesthetics or diphtheria toxin for periods up to 14 days.2. Muscles showed atrophy equivalent to that seen after similar periods of denervation.3. Nerve blockade appeared to have little or no effect on neuromuscular transmission when tested by stimulation beyond the block. Normal spontaneous miniature end-plate potentials were present.4. Nerve impulse blockade caused the entire muscle membrane to become sensitive to iontophoretically applied acetylcholine.5. The increase in sensitivity in soleus could be prevented by chronic nerve stimulation distal to the region of block.6. Tenotomy, of 5-12 days duration, which produced atrophy, had no effect on the sensitivity of soleus to acetylcholine.7. Chronic direct stimulation of denervated soleus or EDL muscles could prevent the usual denervation supersensitivity, or cause it to decline towards normal once it had appeared. However, the sensitivity of the end-plate region remained normal.