Endocrinology, Vol 114, 481-485, Copyright © 1984 by Endocrine Society

ARTICLES

Immunocytochemical characterization of secretory granule maturation in pancreatic A-cells

M Ravazzola, A Perrelet, RH Unger and L Orci

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.

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