A physiological study of chick myotubes grown in tissue culture.

1. A study has been made of some passive and active membrane properties of myotubes of different ages obtained in culture from explants of chick embryo thigh muscle.2. After 3 days in vitro the mean values for the myotube resting membrane potential and input resistance were - 63.8 mV and 1.30 MOmega respectively. By 13 days these values had fallen to - 51.0 mV and 0.80 MOmega.3. Current/voltage relations were measured in the presence of tetrodotoxin. The relations were linear for membrane potentials between - 120 and - 35 mV. Further depolarization usually resulted in a delayed increase in conductance which inactivated with time.4. All myotubes tested using anodal break excitation were capable of generating action potentials. Action potentials were blocked by tetrodotoxin, saxitoxin and procaine.5. All myotubes were sensitive to iontophoretically applied ACh. The potential change produced by ACh reversed polarity at a membrane potential between 0 and + 10 mV. The depolarization produced by ACh was unaffected by anticholinesterases.6. The ACh response was blocked by cobra neurotoxin, D-tubocurarine and atropine.7. The electrical properties of the myotubes appear to resemble those of normal adult twitch-type skeletal muscle fibres.8. The pharmacological properties of the myotube cholinergic receptor have been compared with those of the neuromuscular junction and the denervated muscle fibre membrane.