title: OCTN2 is associated with carnitine transport capacity of rat skeletal muscles.
abstract: OBJECTIVE
  Carnitine plays an essential role in fat oxidation in skeletal muscles; therefore carnitine influx could be crucial for muscle metabolism. OCTN2, a sodium-dependent solute carrier, is assumed to transport carnitine into various organs. However, OCTN2 protein expression and the functional importance of carnitine transport for muscle metabolism have not been studied. We tested the hypothesis that OCTN2 is expressed at higher levels in oxidative muscles than in other muscles, and that the carnitine uptake capacity of skeletal muscles depends on the amount of OCTN2.
  
  
  METHODS
  Rat hindlimb muscles (soleus, plantaris, and the surface and deep portions of gastrocnemius) were used for Western blotting to detect OCTN2. Tissue carnitine uptake was examined by an integration plot analysis using l-[(3)H]carnitine as a tracer. Tissue carnitine content was determined by enzymatic cycling methods. The percentage of type I fibres was determined by histochemical analysis.
  
  
  RESULTS
  OCTN2 was detected in all skeletal muscles although the amount was lower than that in the kidney. OCTN2 expression was significantly higher in soleus than in the other skeletal muscles. The amount of OCTN2 was positively correlated with the percentage of type I fibres in hindlimb muscles. The integration plot analysis revealed a positive correlation between the uptake clearance of l-[(3)H]carnitine and the amount of OCTN2 in skeletal muscles. However, the carnitine content in soleus was lower than that in other skeletal muscles.
  
  
  CONCLUSIONS
  OCTN2 is functionally expressed in skeletal muscles and is involved in the import of carnitine for fatty acid oxidation, especially in highly oxidative muscles.
authors.affiliation: Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa-city, Ishikawa, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Furuichi
authors.forename: T
authors.initials: T
authors.lastname: Sugiura
authors.forename: Y
authors.initials: Y
authors.lastname: Kato
authors.forename: Y
authors.initials: Y
authors.lastname: Shimada
authors.forename: Kazumi
authors.initials: K
authors.lastname: Masuda
mesh_terms: D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002331:Carnitine / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D006614:Hindlimb; D008297:Male; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D027701:Organic Cation Transport Proteins / Q000378:metabolism*; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D000074058:Solute Carrier Family 22 Member 5; D014316:Tritium
chemical_list: D005227:Fatty Acids; D027701:Organic Cation Transport Proteins; C115441:Slc22a5 protein, rat; D000074058:Solute Carrier Family 22 Member 5; D014316:Tritium; D002331:Carnitine