Fig. 4

Effect of amino acids on insulin secretion from MIN6 cells. Subconfluent cells were preincubated in Hepes–Krebs buffer containing 3 mM glucose without or with amino acids for 1 h and incubated in the same medium containing 3 mM or 25 mM glucose for another 1 h. In addition to the medium without amino acids (0EAA in a and 0AA in b), amino acid-supplemented media were used; (a) 0AA supplemented with essential amino acids at half, equal or twice the concentration of minimum essential medium (MEM) (1/2EAA, 1EAA, or 2EAA, respectively), (b) 0AA supplemented with Val, Leu, Ile, or three BCAAs twice the concentration of MEM. Insulin concentration in the medium was normalized by protein content of the cell lysates. Values are expressed as means ± S.E.M. (n = 6 in each group). Results of the statistical analysis are given above the graphs (*P < 0.05, **P < 0.01 vs. 0EAA of the same glucose concentration or 0AA)