Acetylcholine sensitivity in myotubes of nerve-muscle co-culture cultured with anti-muscle antibodies, α-bungarotoxin and d-tubocurarine

The effects of alpha-bungarotoxin (alpha-BuTX), D-tubocurarine (D-TC) and antibodies against muscle extract on acetylcholine (ACh) sensitivity were investigated in developing mouse myotubes in a nerve-muscle co-culture. Antibodies clearly suppressed the ACh potential amplitude in adult mouse diaphragm muscle, but antibodies in muscle pre-treated with D-TC (1 microgram/ml) weakly suppressed it. The addition of D-TC to muscle extract dose-dependently inhibited the formation of the immunoprecipitation lines. The exposure of developing myotubes to antibodies for 10 days in culture suppressed both resting potential and ACh potential, whereas co-existence of alpha-BuTX (1 microgram/ml) or D-TC (0.1 mg/ml) with antibodies suppressed ACh potential but did not affect resting potential compared with antibodies alone. The ACh potentials in myotubes cultured with alpha-BuTX and D-TC alone were also suppressed. The appearance (day 8 in culture) of this suppressive effect by alpha-BuTX was faster than that (day 11 in culture) of D-TC. These different effects depending on the time in culture may account for the conformational change of developing ACh receptors to alpha-BuTX and D-TC.