Constitutive and basal secretion from the endocrine cell line, AtT-20

In normal AtT-20 cells, ACTH is condensed and packaged into secretory granules, which have electron-dense cores when observed in electron micrographs. To see if dense core secretory granules were present or absent in the HYA.15.6 variant cells, sections of epon-embedded cells were examined in the electron microscope. Electron micrographs of 25 random fields of ACTH-negative HYA.15.6 or ACTHpositive HYA.15.10 cells were taken and the numbers of dense core granules counted. Photos of ACTH-positive cells (HYA.15.10) contained 681 morphologically identifiable dense core vesicles. In contrast, photos of the ACTHnegative cells (HYA.15.6), contained only one dense structure that could have been a dense core vesicle.