Fig. 5. The activity of GSK3β is prerequisite for the initial insulin secretion upon elevated glucose in pancreatic islets and in pancreatic β-cells. GSIS is shown as insulin secretion rate in isolated murine pancreatic islets (A) and β-cells (INS-1) (D). Lines and points represent insulin secretion rate under control conditions (Ctrl; black) and after pretreatment with 2.5 µM of the GSK3β inhibitor CHIR99021 for 24h (CHIR99021; blue). Prior to experiments, freshly isolated pancreatic islets were kept on HBSS buffer containing 3 mM glucose for 30 min. Islets were challenged by 16 mM glucose in HBSS buffer and samples were collected at the given time points. Cumulative insulin secretion at the indicated time points from isolated pancreatic islets (B) and pancreatic β-cells (INS-1; E) calculated as increased concentration (ng/ml) either under control conditions (black) or after pre-treatment for 24 h with 2.5 µM CHIR99021 (blue). Total insulin content of isolated murine pancreatic islets (C) and pancreatic β-cells (INS-1; F) pre-treated with 2.5 µM CHIR99021 for 24 h. *p<0.05 versus control using the unpaired Student's t-test (pancreatic islets: n=3; INS-1 cells: n=5).