Direct effects of neostigmine on aneural myotube cultures

Long term (24--96 h) treatment of a mouse-derived myogenic cell line (G8) with meostigmine or physostigmine markedly reduces binding of alpha-bungarotoxin (alpha-BuTx) to these cells. Protein synthesis in these cultures is markedly reduced and cell morphology degenerates. Myotubes maintain slightly hyperpolarised resting membrane potentials, and are able to respond to iontophoretic acetylcholine (ACh) application with overshooting action potentials. Prolonged exposure to neostigmine also inhibits protein synthesis in a fibroblastic cell line (B82). The results suggest that degenerative changes at the neuromuscular junction associated with chronic neostigmine treatment in vivo are due to a direct action of the anticholinesterase on the muscle, rather than to altered intracleft ACh levels [2] or to presynaptic effects of the anticholinesterase [15].