Accumulation of acyl-CoA is hypothesized to be involved in development of insulin resistance. Acyl-CoA binds to acyl-CoA binding protein (ACBP) with high affinity, and therefore knowledge about ACBP concentration is important for interpreting acyl-CoA data. In the present study, we used a sandwich enzyme-linked immunosorbent assay to quantify ACBP concentration in different muscle fiber types. Furthermore, ACBP concentration was compared in muscles from lean and obese Zucker rats. Expression of ACBP was highest in the slow-twitch oxidative soleus muscle and lowest in the fast-twitch glycolytic white gastrocnemius (0.46 ± 0.02 and 0.16 ± 0.005 μg/mg protein, respectively). Expression of ACBP was soleus > red gastrocnemius > extensor digitorum longus > white gastrocnemius. Similar fiber type differences were found for carnitine palmitoyl transferase (CPT)-1, and a correlation was observed between ACBP and CPT-1. Muscles from obese Zucker rats had twice the triglyceride content, had approximately twice the long-chain acyl CoA content, and were severely insulin resistant. ACBP concentration was ∼30% higher in all muscles from obese rats. Activities of CPT-1 and 3-hydroxy-acyl-CoA dehydrogenase were increased in muscles from obese rats, whereas citrate synthase activity was similar. In conclusion, ACBP expression is fiber type-specific with the highest concentration in oxidative muscles and the lowest in glycolytic muscles. The 90% increase in the concentration of acyl-CoA in obese Zucker muscle compared with only a 30% increase in the concentration of ACBP supports the hypothesis that an increased concentration of free acyl-CoA is involved in the development of insulin resistance.
Address correspondence and reprint requests to Jorgen Jensen, Department of Physiology, National Institute of Occupational Health, P.O. Box 8149 Dep., NL-0033, Oslo, Norway. E-mail:.
Received for publication 19 April 2001 and accepted in revised form 29 October 2001.
ACBP, acyl-CoA binding protein; CPT, carnitine palmitoyltransferase; EDL, extensor digitorum longus; ELISA, enzyme-linked immunosorbent assay; FABP, fatty acid binding protein; FABPc, cytosolic FABP; FAT, fatty acid translocase; FFA, free fatty acid; HAD, 3-hydroxy-acyl-CoA dehydrogenase; IRS, insulin receptor substrate; PI, phosphatidylinositol; PNPP, p-nitrophenyl phosphate; TBS, Tris-buffered saline.