Heat production and oxygen consumption during metabolic recovery of white muscle fibres from the dogfish Scyliorhinus canicula

Oxygen consumption and heat production were measured during contraction and recovery of isolated, white muscle fibres from dogfish (Scyliorhinus canicula) at 19 degrees C. The contraction period consisted of 20 isometric twitches at 3 Hz; this was followed by a recovery period of 2 h without stimulation. We tested the hypothesis that recovery is wholly oxidative (not glycolytic) in these fibres. The following features support this hypothesis. (i) The ratio of total heat produced to oxygen consumed, 451+/-34 kJ mol(-)(1) (mean +/- s.e.m., N=29), was close to that expected for either the oxidation of carbohydrate, 473 kJ mol(-)(1), or the oxidation of fat, 439 kJ mol(-)(1). Even assuming the maximum value (95 % confidence limit) of the observed heat production, glycolysis could account for resynthesis of at most 18 % of the ATP used during the contractions. (ii) When the difference in rates of diffusion of oxygen and heat within the muscle are taken into account, the time courses of oxygen consumption and heat production match each other well during the entire recovery period. The efficiency of recovery (=energy used for ATP synthesis/energy available for ATP synthesis) was estimated from the results. This value, 84.0+/-20.1 % (mean +/- s.e.m., N=29), is relatively high and represents the first such measurement in functioning muscle.