Granule mobility, fusion frequency and stimulated insulin secretion are differentially affected by insulinotropic stimuli

Background and aims: The view that insulin granules constitute functionally distinct pools which are sequentially recruited to release insulin has been put into question by new imaging techniques. Here, we characterized the number and mobility of submembrane granules in response to insulinotropic stimuli. Methods: Insulin secretion, cytosolic Ca2+ concentration ([Ca2+]i) and granule mobility in the submembrane space were measured in perifused MIN6 pseudo-islets or single MIN6 cells. Granules were labeled by insulin-EGFP and imaged by TIRF microscopy. The temperature was set at 37 °C, 32 °C or 22 °C. Results: At…