Spatiotemporal Analysis of Glucagon Secretory Granule Dynamics

The secretion of insulin and glucagon by pancreatic β and α cells, respectively, is critical for glucose homeostasis. While the insulin granule dynamics are well-characterized, the intracellular behavior of glucagon secretory granules (GSG) remains poorly understood. Here, we analyze the mobility of GSGs in αTC1-9 cells and insulin secretory granules (ISG) in INS-1E cells using spatiotemporal correlation spectroscopy and single-particle tracking (SPT), with a focus on the role of the cytoskeleton in regulating their transport. Under basal conditions, SPT classification reveals that GSGs predominantly exhibit diffusive motion (57.6% ± 10%), with smaller fractions categorized as almost immobile (35.8% ± 10.6%) or drifted (6.6% ± 3%), closely resembling ISG dynamics. By disrupting microtubules, we confirmed their role as active tracks for directed granule transport in both cell types. Upon exposure to their respective secretory stimuli-high glucose for β cells and low glucose for α cells-both granule populations underwent a comparable shift toward increased diffusive and drifted motions. Treatment with the actin depolymerizing agent Latrunculin-B reproduced this stimulatory effect in INS-1E cells but not in αTC1-9 cells, suggesting that despite their overall similarity in granule behavior under physiological conditions, α and β cells may rely on partially distinct mechanisms to engage the cytoskeletal network.