Acta Biochimica et Biophysica 11. (1976)
1976 / 4. szám - Kerner, J.-Sándor, A.-Alkonyi, I.: The Effect of Denervation on Carnitine Metabolism in Rat Skeletal Muscle
240 Kerner et ah: Effect of Denervation on Carnitine Metabolism present. Histochemical and electron microscopic studies of muscles from the same patient show lipid droplets mainly in slow-twitch-oxidative fibres (type I). Since the dystrophic and denervated muscles have some common features (McCaman, 1960, 1962) we have taken the denervated muscle as a model. To correlate metabolic changes with a given fibre type we have investigated carnitine metabolism in two types of muscle, the “red” soleus (type I) consisting almost exclusively of slow-twitch-oxidative fibres (Booth, Kelso, 1973) and the “white” EDL (type 11) composed in equal parts of fast-twitch-oxidative-glycolytic and fast-twitchglycolytic fibres (Sciaffino, Pierobon Bormioli, 1973) according to the nomenclature recently introduced by Peter et al. (1972). Materials and methods Following pentobarbital anesthesia, adult male rats (230 to 260 g) were denervated unilaterally by removal of a 1-cm segment of the right sciatic nerve at midthigh level. At various times after denervation the rats were killed by decapitation and both the EDL and soleus were removed and freed from adhering fat and tendon. CPT was measured in crude muscle extracts by the hydroxamic acid method as described by Crabtree and Newsholme (1972). CAT activity was assayed by the combined optical test according to Marquis and Fritz (1965). The activities of both enzymes were expressed either as U/g muscle wet tissue or as U/mg noncollagen protein (NCP), as indicated in the appropriate legends. One unit of enzyme catalyzes the formation of 1 /unole NADH2 or palmitylhydroxamate per minute at 25°C. The noncollagen protein was measured by the biuret method after digestion of the tissue (Lilienthal et al., 1950). Total tissue carnitine was determined as free carnitine by Ellman’s reagent (5,5’-dithiobis-nitrobenzoic acid) after alkaline hydrolysis of the samples (Pearson et al., 1970). The concentration was expressed as nmole/g wet tissue or nmole/mg NCP (see the appropriate legends). The control muscle from the left leg and the denervated one from the right leg of the same animal were compared. P values "were determined by the Student’s test. L-acetylcarnitine and L-palmitylcarnitine were synthetized as described by Ziegler et al. (1967), and acetyl-CoA was prepared by Stadtman’s (1957) procedure. Results and discussion As shown in Table 1 none of the parameters studied showed any change in the muscles of the innervated side at any point of time. The greater activity of both CPT and CAT in the soleus as compared to the EDL reflects a higher capacity of the former for fat combustion (Pande, Blanchaer, 1971). The concentration of muscle carnitine was found to be significantly higher in the EDL than in the soleus (Table 1). This finding seems to confirm the acetyl buffering role of carnitine in the EDL muscle. Acta Biochimica et Biophysica Academiae Scientiarum Hungaricae 11, 1976