Immunocytochemical characterization of secretory granule maturation in pancreatic A-cells.
Antigenic sites related to glucagon and glucagon precursors were characterized by ultrastructural immunocytochemistry in secretory compartments of the pancreatic A-cell, namely Golgi cisternae, condensing granules in Golgi cisternae, coated immature secretory granules, and noncoated mature secretory granules. The C-terminal glucagon immunoreactivity was low in all these compartments except in the noncoated mature secretory granules. By contrast, N-terminal glucagon and glicentin immunoreactivities were high at the condensing granule stage and, respectively, increased (N-terminal) or decreased (glicentin) until the mature secretory granule stage. These data suggest that: 1) glucagon precursors and glucagon coexist at different concentrations in secretory compartments of the A-cell; 2) the condensing granules in Golgi cisternae and immature granules consist predominantly of glucagon precursors; and 3) the removal of the peptide masking the C-terminal of the glucagon molecule occurs between the coated and the mature granule stages.
D000818:Animals; D006224:Cricetinae; D003594:Cytoplasmic Granules / Q000502:physiology* / Q000648:ultrastructure; D005934:Glucagon / Q000032:analysis*; D007106:Immune Sera; D007118:Immunoassay; D007515:Islets of Langerhans / Q000502:physiology* / Q000648:ultrastructure; D008647:Mesocricetus; D008854:Microscopy, Electron
D007106:Immune Sera; D005934:Glucagon