Novel secretory granule morphology in physically fixed pancreatic islets

Area of Science:

• Cell Biology
• Endocrinology
• Immunocytochemistry

Background:

• Pancreatic beta cells store insulin in secretory granules.
• Traditional fixation methods can obscure ultrastructure and antigenicity.
• Understanding insulin storage and release is crucial for diabetes research.

Purpose of the Study:

• To investigate the ultrastructure and insulin localization within rat beta cell secretory granules using advanced immunocytochemistry.
• To explore the potential for distinct insulin compartments within granules.

Main Methods:

• Application of Protein A-gold immunocytochemistry to physically fixed rat beta cells.
• High-resolution electron microscopy and stereo imaging of secretory granules.
• Assessment of insulin-like immunoreactivity on granule components.

Main Results:

• Physical fixation preserved fine ultrastructure and revealed filamentous material in the granule halo.
• Filaments exhibited insulin-like immunoreactivity, distinct from the dense core.
• Immunoreactivity was localized to filaments and the dense core surface.

Conclusions:

• A filamentous halo pool of insulin exists separately from the dense core aggregate within beta cell granules.
• Insulin release may involve multiple compartments, potentially altering models of exocytosis.
• Physical fixation and Protein A-gold offer superior resolution for studying granular contents.