Effects of atropine and neostigmine on receptor interaction at the neuromuscular junction.

Rats treated chronically with atropine or atropine and neostigmine showed marked alterations in the responsiveness of receptors at the neuromuscular junction. Receptors in the phrenic nerve-hemidiaphragm interacting with d-tubocurarine were unaffected by atropine but exhibited a supersensitivity after neostigmine administration. Succinylcholine-sensitive sites developed a subsensitivity with both atropine and neostigmine treatment. Acetylcholine-induced contractures in the denervated hemidiaphragm showed a hypersensitivity after both drug administrations, but responses to carbamylcholine were unaffected. It is suggested that there exists a heterogeneous population of receptors at the mammalian neuromuscular junction who can be identified by their responses to the effects of chronic drug application.