1 Neurologische Universit/itsklinik, Josef-Schneider-Strasse 11, W-8700 Wtirzburg, Federal Republic of Germany. 2 Fakult/it ftir Biologie, Universitfit Konstanz, ...
Pflfigers Arch (1991) 418 : 572- 574
EuP/iiii h Journal of Physiology
003167689100117B
9 Springer-Verlag1991
Enzyme activities of fatty acid oxidation and the respiratory chain in chronically stimulated fast-twitch muscle of the rabbit Heinz Reichmann 1, Rudolf Wasl 1, Jean-Aim~ Simoneau 2, and Dirk Pette 2 1 Neurologische Universit/itsklinik, Josef-Schneider-Strasse 11, W-8700 Wtirzburg, Federal Republic of Germany 2 Fakult/it ftir Biologie, Universitfit Konstanz, Postfach 5560, W-7750 Konstanz, Federal Republic of Germany Received December 5, 1990/Accepted February 26, 1991
Abstract. Fast-twitch tibialis anterior muscle of the rabbit was subjected to chronic low-frequency (10 Hz, 10 h/day) stimulation for different time periods up to 28 days. Total cellular activities of carnitine: palmitoyl-CoA transferase, crotonase, 3-hydroxyacyl-CoA dehydrogenase, 3-ketoacyl-CoA thiolase, citrate synthase, N A D H : cytochrome c oxidoreductase, succinate: cytochrome c oxidoreductase, and cytochrome c oxidase were measured in contralateral and stimulated muscles at various times. With the exception of crotonase, which increased only 1.6-fold after 28 days of stimulation, the other enzymes increased in parallel displaying 3-fold elevated absolute activities. These results, by supporting and extending our previous findings, indicate that the expression of the enzymes of the main metabolic systems of aerobic substrate oxidation, i.e. the citric acid cycle, the fatty acid oxidation and the respiratory chain, is regulated in a coordinate manner. Key words: Fatty acid oxidation - Chronic low-frequency stimulation - Rabbit fast-twitch muscle - Respiratory chain
Introduction The energy metabolism of skeletal muscle responds to sustained-endurance exercise by elevating its aerobic oxidative capacity (Holloszy 1975). This adaptive response is reflected by increases in the activities of mitochondrial enzymes. Using chronic low-frequency stimulation as a standardised model of persistently increased contractile activity, we have previously demonstrated severalfold increases in enzyme activities of terminal substrate oxidation (Pette et al. 1973). As shown for the enzymes of the citric acid cycle, these increases are accompanied by Offprint requests to: D. Pette
similar elevations in mitochondrial volume density (Reichmann et al. 1985). In view of similar changes of other mitochondrial enzymes (Pette et al. 1973; Reichmann et al. 1985; Henriksson et al. 1986; Simoneau and Pette 1988; H o o d et al. 1989), e.g. 3-hydroxyacylCoA dehydrogenase, an enzyme of fatty acid oxidation, or cytochrome c oxidase, the terminal compound of the respiratory chain, the question arises whether or not they follow similar time courses and are of similar magnitude. Parallel elevations might indicate a coordinate control of the enzymes of terminal substrate oxidation. The present study was undertaken in order to examine this possibility for the enzymes of fatty acid oxidation and the compounds of the respiratory chain. Rabbit fast-twitch tibialis anterior muscle was subjected to chronic lowfrequency stimulation for different periods up to 4 weeks and total cellular enzyme activities were measured over this time. Crotonase, 3-hydroxyacyl-CoA dehydrogenase and 3-ketoacyl-CoA thiolase were chosen as representative enzymes of/~-oxidation of fatty acids. Carnitine: palmitoyl-CoA transferase activity served as a marker of mitochondrial fatty acid transport. N A D H : c y t o c h r o m e c oxidoreductase, succinate:cytochrome c oxidoreductase and cytochrome c oxidase represented complexes I, II and IV of the respiratory chain, respectively. In order to compare the results with our previous work, measurements of citrate synthase, as reference enzyme of the citric acid cycle, and of two glycolytic enzymes (lactate dehydrogenase, phosphofructokinase) were also included.
Materials and methods Animals' and stimulation. Experiments were carried out on adult
White New Zealand rabbits. Electrode implantation and chronic stimulation (10Hz, 10h/day) were performed as previously described (Simoneau and Pette 1988). At different times (4, 7, 14, 28 days), an animal was killed and the tibialis anterior muscles of stimulated and contralateral legs were excised and passed through a small meat grinder. Because this muscle displays a heterogeneousfiber-type distribution, the minced muscle was thoroughly mixed before aliquots were taken for analyses.
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