Relationship Between Morphological Change And Exocytosis In MIN6 Cell Line

To investigate the cellular change during the dynamic activation of the cell for the secretory response, morphological details were observed in the pancreatic B-cell line—MIN6. The video-enhanced contrast differential interference contrast (VEC-DIC) microscopy was used to observe cell shapes before and after application of the stimuli. The confocal scanning microscope was used to observe the relationship between the newly formed structure and the cell membrane. The total internal reflection fluorescence microscopy was used to observe the exocy-totic responses of insulin-containing granules labeled with the green fluorescence protein, and to confirm the relationship between the exocytosis and the morphological changes. Upon application of secretagogues, vacuoles or invaginations appeared in variable sizes and shapes. They appeared on the cell membrane especially at the area facing the neighboring cells. The vacuoles could be suppressed totally when EGTA, a calcium chelator. A botulinum neurotoxin blocked the exocytosis completely but not the vacuole formation. Cytochalasin D, an actin filament modifier, did not affect the formation of vacuoles but prolonged its time course. These findings indicate that the vacuoles are formed by elevation of intracellular [ Ca + ] after stimulation, and thus they are coupled with the exocytosis. However, the formation of vacuoles was independent of exocytosis in terms of its underlying mechanism. A physiological significance of the vacuole formation would be to enhance the secretion from morphological aspects.