RECOVERY AFTER CONTRACTION OF WHITE MUSCLE-FIBERS FROM THE DOGFISH SCYLIORHINUS-CANICULA

Recovery after contraction of white muscle fibres of dogfish was inves tigated using P-31-NMR and measurements of heat production. The muscle fibres were stimulated to perform either a single isometric tetanus o r a series of brief isometric tetani; the NMR measurements showed that approximately half of the phosphocreatine (PCr) was used. The period of activity was followed by a recovery period without stimulation. Bot h NMR and heat measurements agreed in showing that recovery was very s low, requiring at least 60 min for PCr resynthesis and for the product ion of recovery heat. The NMR results showed that changes in intracell ular pH and in the concentrations of PCr and intracellular phosphate ( P-i) had very similar time courses. Intracellular pH moved in the alka line direction during the period of activity and then returned monoton ically during recovery. The non-phosphate buffer power was 13.0+/-3.1 mmol l(-1) intracellular water per pH unit (N=4, mean +/- S.E.M.). The results are consistent with the view that oxidative processes resynth esize PCr during recovery, which is slow because of the low mitochondr ial content of these muscle fibres.