Abstract
Utilizing formaldehyde- or glutaraldehyde-fixed tissue and Gomori's lead method it was found by optical microscopy that rabbit pancreatic islet cell acid phosphatase activity is present in discrete, mostly perinuclear foci and that this distribution differs from that of the aldehyde fuchsin-positive secretory granules which are densely packed at the capillary pole of the cell. Electron microscopically lead reaction product was noted in dense bodies, as well as in structures thought to be Golgi vacuoles and vesicles, it was also present in the innermost of the Golgi cisternae, and at the periphery of adjacent single membrane-limited bodies whose origin can be traced from the proximal cisternae. These latter bodies in routinely prepared, osmium-fixed material show finely granular content, which is in contrast to the electron-dense, central body seen in secretory granules that appear to originate from endoplasmic reticulum. B-cell cytoplasm contained additional numerous, single membrane-limited vacuoles with pale content. These are thought also to represent secretion vacuoles but with insulin secretory product in a different physical or chemical state. The lack of acid phosphatase activity in B-cell secretion vacuoles, the dissimilarities in fine structure between the content of secretory elements and that of the Golgi-derived granular body, together with previous evidence that alteration in B-cell functional state does not result in altered number or distribution of acid phosphatase active elements in B-cell cytoplasm, indicate a lack of relationship between acid phosphatase and secretory granule formation or release in pancreatic B-cells. It is also hypothesized that the secretory vacuole with central dense granule may be a storage form while the pale vacuole is the one which liberates its content to the intercellular space.