Objective To investigate the influence of phenylalanine(Phe) on glucose uptake in mouse myoblast cell line C2C12 and to explore its relationship with mTOR-p70S6K pathway．Methods C2C12 cells were cultured to promote formation of multinucleated myotubes in vitro.The cells were deprived and incubated with Phe at different concentrations （1.25, 2.5, 5, 10, 20 mmol/L）．Krebs-Ringer buffer (KRB) was used as control．The 2-NBDG was used to measure glucose uptake of C2C12．The expression of mTOR， p70S6K， IRS-1， and Akt protein were evaluated by Western blot．Results Compared with KBP treatment， glucose uptake of the cells incubated with 5mmol/L leucine (Leu) was decreased by 30% (P=0.001)，while a 40% increase was detected in the cells incubated with 5 mmol/L Phe (PP=0.815)． Leu stimulated but Phe over 1.25 mmol/L inhibited phosphorylation of IRS-1 at Ser636/639，although the difference was not significant (P=0.381)．Neither Leu nor Phe affected the expression of phospho-Akt (Ser473) significantly．Conclusion Phenylalanine inhibits phosphorylation of IRS-1 at Ser636/639 possibly through inhibiting the activation of p70S6K．The effect of Phe on mTOR-p70S6K pathway is Akt-independent．
