Cytochemical staining methods for β-nicotinamide adenine dinucleotide phosphatase (β-NADPase) and trimetaphosphatase (TMPase) were applied to B cells of rat pancreas. β-NADPase was localized in one or two intermediary Golgi saccules, lysosomes, multigranular bodies, and in a variable percentage of secretory granules. It was also found in elongated tubules comparable to those previously reported in the acinar cell of pancreas. TMPase reaction product was not detected in Golgi saccules, but was present in lysosomes, multigranular bodies, some secretory granules, and elongated tubules. These observations have shown that β-NADPase and TMPase activities are present in B cells of pancreas; that these enzymes are present in “multigranular bodies” and lysosomes supporting previous evidence that these structures may be involved in the degradation of insulin; and that elongaged tubules similar to those described in the exocrine cell and muscle cells are also present in an endocri
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