Figure 6.

ATF3 deficiency reduces total insulin secreted by the primary islets upon glucose challenge but does not affect calcium influx or oscillation. A, Primary islets from WT (black bars) and ATF3 KO (white bars) mice were analyzed for their intracellular insulin content using ELISA (left panel) or glucose-induced insulin secretion by measuring insulin in the supernatant (right panel). Shown are representatives of three independent experiments. For each experiment, 15 islets were pooled for assay, and five to 10 pools of islets per genotype were analyzed to generate the data. B, Primary islets were allowed to recover for 24 h in 5.5 mm glucose before fura-2 loading and analyzed by Ca²⁺ imaging for glucose-stimulated (from 2.5 mm to 25 mm glucose) change in intracellular Ca²⁺ concentration. Islets (n = 100) were analyzed for each group, and the experiments were repeated three times. Shown are traces of extracellular Ca²⁺ influx from 20 islets. Arrows indicate the expected Ca²⁺ sequestration by ER before influx. C, Fura-2 340/380 ratios from islets in panel B were combined to obtain the average preglucose minimum and postglucose maximum. Shown are representative of three experiments (n =100 islets). D, A representative trace of glucose-stimulated Ca²⁺ influx and oscillations from islets in panel B was shown. Arrows are as indicated in panel B. E and F, Period (panel E) and amplitude (panel F) of glucose-stimulated calcium oscillation from panel D were quantified (n = 100 islets). Presented are means ± sem. *, P < 0.05; **, P < 0.01 KO vs. WT.