Figure 6.

FlowGSIS with single islets versus three to four pooled islets for a) control GSIS and b) GSIS with dosage of exendin-4. A switch from low (2.8 × 10⁻³ M) to high (16.7 × 10⁻³ M) glucose concentrations induced highly dynamic insulin secretion in a bi-phasic manner with a dip at the beginning, a prominent first phase, which was followed by a sustained, pulsatile second phase. GSIS with single islets showed higher insulin secretion rates compared to pooled islets under both conditions. Exendin-4 stimulated insulin secretion in the first and second phases for both single islets and pooled islets, compared to the vehicle control. Samples were taken every 5 min between 60–95 min and 165–210 min, every 30 s for the high-resolution sampling (single islet), and every 2 min for the low-resolution sampling (pooled islets) during the high-glucose phase (95–165 min). Data for the “single islet low-resolution” condition were calculated from the “single islet high-resolution” data by averaging four sampling points to show effects of high (30 s) versus low (2 min) resolution sampling and to compare with the “pooled-islet low-resolution” condition. Islets from two different donors were used for the GSIS in the vehicle control (a) and islets from a single donor were used for the GSIS with exendin-4 (b).