Leucine modulates contraction- and insulin-stimulated glucose transport and upstream signaling events in rat skeletal muscle.
Leucine has profound effects on glucose metabolism in muscle; however, the effects of leucine on glucose transport in muscle have not been well documented. We investigated the effects of leucine on contraction- and insulin-stimulated glucose transport in isolated rat epitrochlearis muscle in vitro. In the absence of insulin, tetanic contraction increased 3-O-methyl-D-glucose (3-MG) transport and Thr(172) phosphorylation of the catalytic alpha-subunit of 5'-AMP-activated protein kinase (AMPK), a signaling intermediary leading to insulin-independent glucose transport. Leucine (2 mM, 30 min) significantly enhanced contraction-stimulated 3-MG transport and AMPK phosphorylation, accompanied by increased phosphorylation of p70 S6 kinase (p70S6K) Thr(389). The stimulatory effects of leucine on 3-MG transport and AMPK phosphorylation were canceled by STO-609 blockade of Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK) or rapamycin blockade of p70S6K. On the other hand, leucine blunted insulin-stimulated 3-MG transport and reduced insulin-stimulated Akt Thr(473) phosphorylation. Leucine increased insulin-stimulated p70S6K Thr(389) phosphorylation and enhanced the inhibitory phosphorylation of the insulin receptor substrate 1 (IRS1) Ser(636/639). Furthermore, the effects of leucine on insulin-stimulated 3-MG transport and IRS phosphorylation were abolished by rapamycin. These results indicate that leucine activates contraction-stimulated glucose transport and inhibits insulin-stimulated glucose transport in skeletal muscle by activating mammalian target of rapamycin (mTOR)/p70S6K signaling. Enhanced increases in contraction-stimulated AMPK Thr(172) phosphorylation and insulin-stimulated IRS1 Ser(636/639) phosphorylation might be responsible for these opposing effects of leucine, respectively.
Iwanaka
Nobumasa
N
Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto Univ., Yoshida-nihonmatsu-cho, Sakyo-ku, Kyoto 606-8501, Japan.
Egawa
Tatsuro
T
Satoubu
Nozomi
N
Karaike
Kouhei
K
Ma
Xiao
X
Masuda
Shinya
S
Hayashi
Tatsuya
T
D019325:3-O-Methylglucose / Q000378:metabolism; D000091162:AMP-Activated Protein Kinase Kinases; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects; D005947:Glucose / Q000378:metabolism* / Q000502:physiology*; D006003:Glycogen / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007930:Leucine / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D051058:Oncogene Protein v-akt / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*
D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010725:Phosphocreatine; D019325:3-O-Methylglucose; D000255:Adenosine Triphosphate; D006003:Glycogen; D011494:Protein Kinases; D051058:Oncogene Protein v-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D000091162:AMP-Activated Protein Kinase Kinases; D007930:Leucine; D005947:Glucose