Localization of the acetylcholine receptors in denervated muscles of rats

ACh contractures of denervated lumbricalis muscles of rats were washed in Tris-methanesulfonate solutions and in sucrose solutions. The peak tension was diminished by about 80% following a 30 min exposure to solutions containing 400-600 mM glycerol when Tris solutions were used in the testing period, and by about 50% when sucrose solutions were used. The amplitude of the membrane potential changes provoked by ACh was decreased by about 36% following the glycerol treatment. The treatment had no effect on the ACh-induced 45Ca uptake of muscles. Electron microscopy of the glycerol-treated muscles showed widespread vacuolization apparently originating from swelling and disruption of the T system. It was concluded that ACh receptors which arise in the muscle membrane following nerve section are distributed in the external surface membrane and in the membranes of the T system.