We have investigated the effects of prolonged exposure (24 h) to the amino acid L-glutamine, on gene and protein expression using clonal BRIN-BD11 beta-cells. Expression profiling of BRIN-BD11 cells was performed using oligonucleotide microarray analysis. Culture for 24 h with 10 mM L-glutamine compared with 1 mM resulted in substantial changes in gene expression with 148 genes upregulated more than 1.8-fold, and 18 downregulated more than 1.8-fold, including many genes involved in cellular signaling, metabolism, gene regulation, and the insulin-secretory response. Subsequent functional experiments confirmed that L-glutamine increased the activity of the Ca2+ regulated phosphatase calcineurin and the transcription factor Pdx1. Additionally, we demonstrated that beta-cell-derived L-glutamate was released into the extracellular medium at high rates. As calcineurin is a regulator of the glutamate N-methyl-D-aspartate (NMDA) receptor activity, we investigated the action of NMDA on nutrient-induced insulin secretion, and demonstrated suppressed insulin release. These observations indicate important long-term effects Of L-glutamine in regulating beta-cell gene expression, signaling, and secretory function.