Fig. 3. Time-dependent effect of high concentration of glucose on exe-4-induced cAMP formation in INS-1 cells. (A) Effect of glucose concentration on exe-4-mediated CRE-luc activity. INS-1 cells expressing the CRE-luc reporter gene were pretreated with 25 mM glucose for indicated times and then exposed with exe-4 for 6 h. HNMPA was pretreated for 2 h before exe-4 treatment. Luciferase activity by exe-4 was measured. (B) Effect of glucose concentration on exe-4-mediated CRE-luc activity in HEK293T cells. HEK293T cells harboring the CRE-luc reporter gene were pretreated with 25 mM glucose for 2, 8 or 20 h before exe-4-induced CRE-luc activity was measured. (C) Effect of glucose concentration on exe-4-mediated cAMP accumulation. INS-1 cells were pretreated with 25 mM glucose at different times with or without HNMPA. Exe-4-induced cAMP formation was measured. (D) Temporal changes in insulin secretion in a high glucose condition. INS-1 cells were stimulated with a high concentration of glucose (25 mM) for 2, 8, or 20 h. Secreted insulin in the medium was detected by ELISA (* P < 0.05).