Acyl-coenzyme A binding protein expression is fibre-type specific in rat skeletal muscle but not affected by moderate endurance training

The metabolic active form of free fatty acids, long-chain acyl-coenzyme A (lc-acyl-CoA), binds to its 10-kDa binding protein with high affinity. In the present study, we investigated the content of lc-acyl-CoA binding protein (ACBP) in different skeletal muscle fibre types. Soleus had the highest expression of ACBP (0.33±0.02 μg mg protein^-1) and the content was as high as in heart muscle. The content in mixed gastrocnemius (0.27±0.02 gg mg protein^-1), extensor digitorum longus (0.21±0.01 gg mg protein^-1) and white gastrocnemius (0.16±0.01 μg mg protein^-1) were lower than in soleus and differed from each other (P<0.05). The ACBP content correlated positively with the fraction of myosin heavy chain I in the skeletal muscles (Spearman rank correlation rho=0.90; P<0.0001), and negatively with the myosin heavy chain IIB fraction (rho=-0.92; P<0.0001). The content of ACBP also correlated with 3-hydroxy-ac-yl-CoA dehydrogenase (HAD) and citrate synthase (CS). Five weeks of endurance training increased HAD and CS activities in soleus and mixed gastrocnemius but did not affect the ACBP content. These findings demonstrate that ACBP expression is fibre-type specific in skeletal muscles and correlates with β-oxidative potential. Training-induced increase in oxidative capacity was not paralleled by an increase in ACBP content.