Dynamic difference between GLUT4 storage vesicles and secretory vesicles revealed by evanescent-field imaging and single particle tracking
以消散场成像和单微粒跟踪技术揭示GLUT4囊泡和分泌囊泡的不同动态过程

Glucose transporter 4 (GLUT4) plays a crucial role in maintaining whole-body glucose homeostasis. It has been revealed that GLUT4 storage vesicles (GSV) and secretory vesicles in neuroendocrine cells contain similar proteins. Many studies have demonstrated that the intracellular transport of secretory vesicles is precisely mediated by these proteins. However, it is still unclear whether GSVs share similar dynamic features with secretory vesicles during intracellular trafficking. In this paper, GSV in 3T3-L1 fibroblasts and secretory large dense core vesicles (LDCVs) in neuroendocrine PC12 cells were taken as models for comparing GSV and LDCV mobility. Evanescent-field microscopy and Gaussian-fit-based single particle tracking were used to follow the three-dimensional trajectories of single GSVs and LDCVs. By fitting appropriate equations to particular mean squared displacement of single vesicles, three different motion modes were revealed for both GSVs and LDCVs. Quantitative analysis showed that the number of GSVs undergoing random diffusion and directed diffusion was much more than LDCVs. Furthermore, it was compared that three-dimensional diffusion coefficients for GSVs and LDCVs. The median diffusion coefficient of GSVs is 7.2×10-4 μm2/s and LDCVs 1.94×10-4 μm2/s. Although similar proteins have been found for both GSVs and secretory vesicles, our results reveal a significant difference between GSVs and LDCVs in their mobility, suggesting there are different molecular mechanism underlying the intracellular transport of GSVs.