Effects of series of tetani on dystrophic and normal muscles of mouse

Abstract

Isolated gastrocnemius muscles of dystrophic and normal mice were stimulated tetanically at 150 C. The dystrophic muscles showed much less variability of tension output and much greater resistance to fatigue than normal muscles. Between repeated series of 10 tetani the dystrophic muscles were capable of complete recovery: whereas the normal muscles continued decline. Curare, 6 x 10-5 [image] and adrenaline [epinephrine], 10-4 [image], applied together, increased the tetanus tension. The half-relaxation time was longer and its coefficient of variation was greater in the dystrophic muscles than in the normal muscles. However, after a series of 10 tetani the half-relaxation time of the dystrophic muscle became shorter and its coefficient of variation smaller, whereas in a normal muscle it became longer and its coefficient of variation greater. The decreased tension output, the longer relaxation period and the increased coefficients of variation after prolonged stimulation are considered to be signs of fatigue in the normal muscle. Their absence or delayed appearance expresses the increased threshold to fatigue in a dystrophic muscle.