Secretory Granule Formation and Release in Rabbit Pancreatic A-Cells

A-cells of the islets of Langerhans from normal rabbits as well as rabbits treated with insulin, cortisone, or tolbutamide or subjected to a semistarvation diet were studied by light and electron microscopy. Consistent morphological differences between A-cells of normal and experimentally treated rabbits were not found. Individual A-cells varied considerably in degree of granulation and cytoplasmic electron density, however it was not possible to distinguish between A1- and A2-cells. Evidence is presented demonstrating that A-cell granules are formed in the Golgi complex, migrate to the cell membrane, and are extruded intact to the capillary border of the cell between the plasma membrane and basement membrane. The A-cell granules then appear to undergo dissolution and resorption. Based on the morphologic findings no relationship of glucagon secretion to insulin release could be established.