Figure 9. Increases in FRET signals between SNARE probes by individual exocytosis of insulin vesicles.

(a) Fluorescence images of a pancreatic islet immersed in an Alexa594 solution, where arrowheads indicate an individual exocytotic event (scale bar, 1 μm). The islet was transfected with mtq-SNAP25 and Ven-VAMP2 using a lentivirus, and stimulated with a high-glucose (16 mM) solution. (b) Increases in Alexa594 fluorescence by exocytosis of a single insulin vesicle. (c–e) Increases in the binding fraction of mtq-SNAP25 and Ven-VAMP2 during individual exocytotic events. (f) Average time course of the binding fraction from 61 exocytotic events that were aligned to the onset of the Alexa594 signal (b). (g) A1 images before (f1 and f2) and after exocytosis (f3) (scale bar, 1 μm). (h,i) Schematic illustration of the formation of SNARE complexes and exocytosis in β cells (h) and presynaptic bouton (i).