Twitch characteristics and energy metabolites of mature muscle fibres of Xenopus laevis in culture.

Mature, high-oxidative, skeletal muscle fibres of Xenopus laevis were kept in culture in L-(Leibovitz's)-15 medium supplemented with creatine and antibiotics and some other additions. Single fibres were mounted at a fixed sarcomere length in a flow-through culture chamber which accommodates stimulus electrodes and a force transducer. Twitch characteristics were determined daily. Depending on culture conditions, fibres remained excitable electrically for up to two weeks at 20 degrees C when foetal calf serum and/or phosphate were added to the culture medium. During the second week, fibres lost phosphocreatine and ATP, but relatively small changes (if any) in total creatine, glycogen and protein contents, fibre volume and dry weight occurred. Succinate dehydrogenase activity decreased after 9 days-when ATP was reduced already. Fibres which were inexcitable electrically contracted normally when exposed to caffeine, indicating that excitation-contraction coupling failed and that the contractile apparatus was still functional.