Tetanus toxin: fine structure localization of binding sites in striated muscle.

When striated muscle from mice poisoned with purified tetanus neurotoxin was incubated with tetanus antitoxin labeled with horseradish peroxidase and stained for peroxidase activity, an electron-opaque reaction product was found in the transverse and terminal sacs of the longitudinal elements of the sarcotubular system. Demonstration of toxin in this location suggests that it acts by interfering with contraction coupling or mechanisms of contraction-relaxation.