A lesion of the transverse tubules of skeletal muscle.

1. A method is described by which a selective lesion can be made in vitro in the transverse tubules of frog skeletal muscle.2. The method consists of exposing the muscle for 1 hr or more to a buffered salt solution made hypertonic by the inclusion of 400 mM glycerol and then returning the muscle to an isotonic salt solution. The lesion is induced during the washout of the glycerol.3. Electron micrographs reveal that the lesion consists of a rearrangement of the T-system membranes in such a way that the continuity of the tubules is lost. The membranes appear to coalesce into large vesicles scattered irregularly throughout the sarcoplasm.4. The glycerol treatment results in a depression of the resting potential of up to 30 mV. The treated fibres are depolarized by high concentrations of K as are normal muscle fibres.5. T-tubule lesioned fibres are unable to respond mechanically either to electrical stimulation or to elevated K but they do contract in the presence of caffeine and relax when the caffeine is removed.6. Problems concerning the variability of the procedure are presented and certain considerations concerning the mechanism of the effect are discussed.