Effects of zinc supplementation on the gene expression levels of metallothioneins. INS-1E cells were exposed to the indicated concentrations of ZnCl2 for 24 h in the presence of 11 mM glucose. The gene expression levels of MT-1A (A) and MT-3 (B) were normalized for β-actin, HSP, and Cltc. Data are shown as the mean ± SEM (n = 4–6). *P < 0.05.