Quantitative visualization of synchronized insulin secretion from 3D-cultured cells

•An imaging method for protein secretion from 3D-cultured cells was established.•The fused protein of insulin to GLase, Insulin-GLase, was used as a reporter.•Synchronous insulin secretion was visualized in rat islets and spheroidal beta cells.•A rat beta cell line stably expressing Insulin-GLase, named iGL, was established.•Effect of an antidiabetic drug on insulin secretion was visualized in iGL cells.

Quantitative visualization of synchronized insulin secretion was performed in an isolated rat pancreatic islet and a spheroid of rat pancreatic beta cell line using a method of video-rate bioluminescence imaging. Video-rate images of insulin secretion from 3D-cultured cells were obtained by expressing the fusion protein of insulin and Gaussia luciferase (Insulin-GLase). A subclonal rat INS-1E cell line stably expressing Insulin-GLase, named iGL, was established and a cluster of iGL cells showed oscillatory insulin secretion that was completely synchronized in response to high glucose. Furthermore, we demonstrated the effect of an antidiabetic drug, glibenclamide, on synchronized insulin secretion from 2D- and 3D-cultured iGL cells. The amount of secreted Insulin-GLase from iGL cells was also determined by a luminometer. Thus, our bioluminescence imaging method could generally be used for investigating protein secretion from living 3D-cultured cells. In addition, iGL cell line would be valuable for evaluating antidiabetic drugs.