Heat production and fluorescence changes of toad sartorius muscle during aerobic recovery after a short tetanus.

1. The time course of the aerobic recovery following a 0.5 sec tetanus at 20 degrees C of the sartorius muscle of the toad Bufo bufo, equilibrated in bicarbonate-CO(2) Ringer solution, has been followed by recording simultaneously the heat production and the fluorescence excited by ultra-violet light at 366 nm.2. The fluorescence light emitted in these conditions in the region of 450 nm monitors the state of oxidation-reduction of the nicotinamideadenine dinucleotides (NAD(+)-NADH). After a short tetanus, the cycle evoked consists of an initial increase of the fluorescence (reduction of NAD(+)) followed by a long lasting phase of decreased light emission. This includes an early period of oxidation of NADH succeeded by a slow reduction of the NAD(+) formed in excess over the resting state. After iodoacetate, the initial reduction is suppressed.3. The time course of both fluorescence and heat production may be analysed into a rapid and a slow component by a double exponential model.4. The time courses of the aerobic recovery heat and of the fluorescence changes are similar after five minutes, but differ in their fast components. IAA significantly increases the rate constants of the fast terms of both monitors.5. The slow component is mainly related to aerobic processes while the fast one is due to both oxidative and glycolytic reactions occurring simultaneously.