Patterns of calcium localization in pancreatic endocrine cells.
Subcellular calcium localization in the dndocrine cells of rat pancreas was studied by the pyroantimonate precipitation technique. Calcium-containing electron-dense deposits in the endocrine cells were mostly found within secretory granules and along the plasma membrane, but their pattern of distribution in A-, B- and D-cells displayed qualitative and quantitative differences. In B-cells, numerous secretory granules contained deposits located in the halo surrounding the granule core. In A-cells, only few granules contained precipitates in their halo, whereas in D-cells, deposits were situated in the dense core of the secretory granules. Deposits along the plasma membrane occurred generally on the outer leaflet of the plasma membrane of B- and D-cells and on the inner leaflet of that of A-cells. In islets incubated at a high glucose concentration or in the presence of the calcium ionophore A23187, the number of beta granules containing precipitates was significantly increased. By contrast, only few deposits were observed in B-cells incubated in calcium-deprived medium enriched with EGTA. These findings indicate that: the pattern of calcium localization varies in different islet cell types; in B-cells the secretory granules represent one of the major stores of intracellular calcium; and that this store undergoes changes in conditions which alter insulin release.
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000032:analysis*; D002467:Cell Nucleus / Q000032:analysis; D003594:Cytoplasmic Granules / Q000032:analysis; D004533:Egtazic Acid / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D006056:Golgi Apparatus / Q000032:analysis; D006651:Histocytochemistry; D007515:Islets of Langerhans / Q000032:analysis* / Q000187:drug effects / Q000648:ultrastructure; D008928:Mitochondria / Q000032:analysis; D051381:Rats
D000001:Calcimycin; D004533:Egtazic Acid; D005947:Glucose; D002118:Calcium