title: Cytochemical localisation of calcium binding sites in adrenal chromaffin cells and their relation to secretion.
abstract: The ultrastructural localisation of calcium in the chromaffin cells of the adrenal medulla was investigated using the pyroantimonate technique. The electron-dense precipitate resulting from processing in the presence of pyroantimonate was removed by treatment of sections with 2 mM EGTA suggesting that the pyroantimonate technique was localising calcium since this chelator shows a 1000:1 preference for Ca2+ over Mg2+. Using dissociated cells from the bovine adrenal medulla, calcium was localised in control cells and in cells stimulated with 1 mM carbamylcholine for 1, 10 and 30 min. Stimulation resulted in an increase in plasma membrane-associated calcium within 1 min. Much of this calcium was localised at sites of granule-plasma membrane interaction and was also seen at sites of coated-vesicle formation at longer periods of stimulation. Membrane-bounded vacuoles, appearing in cells stimulated for 10 or 30 min, also showed associated electron-dense precipitate. The results obtained are consistent with a role for the calcium ion as a mediator in exocytosis at the stage of granule-plasma membrane fusion.
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000502:physiology; D002417:Cattle; D002838:Chromaffin System / Q000378:metabolism*; D005089:Exocytosis
chemical_list: D002147:Calmodulin; D002118:Calcium