Calcium ultracytochemistry in pancreatic B-cells.

Ultracytochemical studies in B-cells using the pyroantimonate technique in combination with x-ray microanalysis demonstrated calcium deposits in association with structures of functional importance. In a series of experiments precipitate distribution has been shown to depend on the functional state of the B-cell. Increased calcium precipitation during stimulation of insulin secretion occurred at the cell membranes, in the ground plasma and the halos of the secretory granules. If these data bear functional relevance and are not only concomitant effects of the activated secretory apparatus on pyroantimonate precipitation, they may point to a direct involvement of calcium in some early steps of exocytosis and in granule transport mechanisms.