Figure 6.

In β-cells of mouse pancreatic islets, lysosomes are morphologically distinct from secretory granules. (A) A typical lysosome (L) juxtaposed next to a mature secretory granule (star). The section was triple immunolabeled for C-peptide (5-nm gold), insulin (10-nm gold) and cathepsin B (15-nm gold). (B) Tubular lysosomes (L) immunopositive for cathepsin B (10-nm gold). (C) A crinophagic vacuole (L) juxtaposed next to a mature secretory granule (star). Triple immunolabeling was as in A. Consistent with previous reports (Orci et al., 1984b ; Halban et al., 1987), C-peptide labeling is absent from lysosomes, although insulin labeling may be present. Bars, 200 nm.