title: Evidence for organic cation transporter-mediated metformin transport and 5'-adenosine monophosphate-activated protein kinase activation in rat skeletal muscles.
abstract: OBJECTIVE
  5'-Adenosine monophosphate-activated protein kinase (AMPK) is a key molecule of metabolic enhancement in skeletal muscle. We investigated whether metformin (MET) acts directly on skeletal muscle, is transported into skeletal muscle via organic cation transporters (OCTs), and activates AMPK.
  
  
  METHODS
  Isolated rat epitrochlearis and soleus muscles were incubated in vitro either in the absence or in the presence of MET. The activation status of AMPK, the intracellular energy status, and glucose and MET transport activity were then evaluated. The effect of cimetidine, which is an OCT inhibitor, on AMPK activation was also examined.
  
  
  RESULTS
  MET (10 mmol/L, ≥60 min) increased the phosphorylation of Thr¹⁷² at the catalytic α subunit of AMPK in both muscles. AMPK activity assays showed that both AMPKα1 and AMPKα2 activity increased significantly. The AMPK activation was associated with energy deprivation, which was estimated from the ATP, phosphocreatine (PCr), and glycogen content, and with increased rates of 3-O-methyl-D-glucose (3MG) transport. MET did not change the basal phosphorylation status of insulin receptor signaling molecules. MET was transported into the cytoplasm in a time-dependent manner, and cimetidine suppressed MET-induced AMPK phosphorylation and 3MG transport.
  
  
  CONCLUSIONS
  These results suggest that MET is acutely transported into skeletal muscle by OCTs, and stimulates AMPKα1 and α2 activity in both fast- and slow-twitch muscle types, at least in part by reducing the energy state.
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Rieko
authors.initials: R
authors.lastname: Oshima
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Eriko
authors.initials: E
authors.lastname: Kurogi
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Yohei
authors.initials: Y
authors.lastname: Ogino
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Serizawa
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsuda
authors.affiliation: Key Laboratory of Puer Tea Science, Ministry of Education, Yunnan Agricultural University, Kunming 650201, Yunnan Province, China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Ma
authors.affiliation: Department of Physiology, Graduate School of Health Sciences, Toyohashi SOZO University, Toyohashi, 440-0016, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Egawa
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, 606-8501, Japan. Electronic address: tatsuya@kuhp.kyoto-u.ac.jp.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hayashi
mesh_terms: D019325:3-O-Methylglucose / Q000378:metabolism; D055372:AMP-Activated Protein Kinases / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002927:Cimetidine / Q000494:pharmacology; D004734:Energy Metabolism; D004789:Enzyme Activation / Q000187:drug effects; D007004:Hypoglycemic Agents / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D049990:Membrane Transport Modulators / Q000494:pharmacology; D008687:Metformin / Q000378:metabolism*; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D027701:Organic Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011897:Random Allocation; D017208:Rats, Wistar
chemical_list: D007004:Hypoglycemic Agents; D049990:Membrane Transport Modulators; D027701:Organic Cation Transport Proteins; D019325:3-O-Methylglucose; D002927:Cimetidine; D008687:Metformin; C543928:Prkaa2 protein, rat; D055372:AMP-Activated Protein Kinases; C568305:Prkaa1 protein, rat
keywords: 5′-adenosine monophosphate-activated protein kinase; Glucose transport; Metformin; Organic cation transporter; Skeletal muscle