Aconitine-induced repetitive firing in frog skeletal muscle and the effect on cable properties

Abstract

The repetitive firing in curarized frog sartorius muscle caused by aconitine was found to be associated with a dose-dependent membrane depolarization and a decrease in membrane resistance (R m). Shortly after aconitine treatment, when repetitive discharges began to occur spontaneously in a few fibers (the pre-burst state), the muscle fibers were hypersensitive to mechanical and electrical stimulation. After a repetitive discharge (the post-burst state), the membrane potential fell to the 40–50 mV range. Cable measurements demonstrated that R m decreased by 27% in the pre-burst state and by 47% in the post-burst state. Substitution of choline for sodium in the post-burst state restored the membrane potential to normal and raised the R m toward the control level. It is proposed that aconitine's production of repetitive discharges in skeletal muscle is partly the result of maintaining the sodium conductance g Na at a higher-than-normal level once excitation has been initiated.