Electron dense plaques (calcium binding sites) in the plasma membrane of the endocrine cells in rodent pancreatic islets and parathyroid glands.

Small electron dense plaques (EDP) were found in the plasma membrane of pancreatic islet A-, B- and D-cells and parathyroid chief cells of mice and gerbils. The identification of the EDP was facilitated by the use of special fixation techniques. The EDP may represent sites of calcium binding in the cell membranes.