Chromogranin A in the pancreatic islet

Chromogranin A (CGA) is the major soluble protein within secretory
vesicles of chromaffin cells. A polyclonal antiserum was raised
against bovine CGA and characterized in two-dimensional
immunoblots. Cellular and subcellular distribution of CGA in bovine
pancreatic islet was investigated by immunocytochemistry. At the
light microscopic level, CGA-like immunoreactivity was found in the
same cells that react with antibodies against insulin, glucagon,
and somatostatin. A minority of cells containing pancreatic
polypeptide also showed faint immunostaining. At the
ultrastructural level (protein A-gold technique), CGA-like
immunoreactivity was confined exclusively to the secretory
vesicles. Whereas the hormones were localized mainly in the central
part of the secretory vesicles, CGA was present predominantly in
the periphery. These findings indicate that a CGA-like protein is a
regular constituent of the matrix of secretory vesicles in
pancreatic endocrine cells.