The mechanical properties of polyneuronally innervated, myotomal muscle fibres isolated from a teleost fish (Myoxocephalus scorpius).

Single or small bundles of fibres were isolated from the abdominal myotomes of the sculpin Myoxocephalus scorpius, a teleost with a polyneuronal pattern of fast muscle innervation. Fibres responded to a supra-threshold stimulus with an all-or-none twitch. Tetanic fusion frequency at 3 degrees C was 40-60 Hz, and the twitch tetanus ratio 0.70. Maximum isometric tension was 281 kN m-2. Similar isometric contractile properties were obtained from the focally innervated fast muscle fibres of another teleost, the eel, Anguilla anguilla. The response of sculpin fibres to stretch during tetanus was similar to that reported for frog twitch fibres. A 5% stretch of 25-50 ms duration increased force to 1.4 Po which decayed to a steady level 5-10% above that of a control tetanus. The force-velocity relationship was also studied. Maximum contraction velocity was 4.75 Ls-1. Force-velocity data were not adequately described by a simple hyperbola. Alternative methods of curve fitting have been explored and discussed.