Influence of pH and temperature on force development and shortening velocity in skinned muscle fibres from fish.

Three species of fish were studied: Atlantic cod (Gadus morhua), sculpin (Myoxocephalus scorpius) (from the North Sea, temperature 2 to 12°C) andNotothenia neglecta (from Antarctica, temperature -2 to +2°C). Single fast muscle fibres were isolated from anterior myotomes and skinned with detergent in order to directly determine the effects of pH and temperature on force production and shortening velocity.In all species maximum force production (Po) was independent of pH over the range 7.3-8.0. Decreasing the pH from 7.3 to 6.6 reduced maximum force by 28% in fibres fromG. morhua andN. neglecta but had no effect on fibres fromM. scorpius. The depression in maximum force with acidosis was accompanied by a proportional decrease in stiffness and an increase in the rate of force recovery after stretch.Unloaded contraction velocity of cod fibres (Vmax) showed a pH optimum at around pH 7.6 decreasing by 31% at pH 6.6. Vmax of fibres from the other species was independent of pH over the range 6.6-8.0.The effects of pH on Po and Vmax were similar at 0 and 10°C. Thus for maximally activated fibres both force and contraction velocity are independent of temperature induced changes in pH. In some species acidosis depresses contractility and is likely to be a contributory factor to muscle fatigue.