Ultrastructural localization of synaptophysin to the secretory granules of normal glucagon and insulin cells in human islets of Langerhans.

Immunogold labeling of the pancreatic islets in humans by means of monoclonal antibodies to synaptophysin resulted in a distinct localization of gold particles to the secretory granules of glucagon-immunoreactive cells. The same type of immunoreactivity was noted with antiserum to chromogranin A. Glucagon immunoreactivity was concentrated in the dense central core of the secretory granules. Some immunoreactivity for synaptophysin was also found in the secretory granules of the insulin-producing cells, although it was weaker in this location.