Ultrastructural localization of zinc and calcium within the granules of rat Paneth cells.

Zinc (up to 300 mmol/kg dry weight) and calcium (up to 350 mmol/kg dry weight) were demonstrated in the granules of Paneth cells from the ileum of adult rats by quantitative electron probe X-ray microanalysis of freeze-dried frozen sections. In resin-embedded samples zinc was also localized by histochemical techniques, the validity of which were subsequently evaluated by X-ray microanalysis. The concentration of zinc was highest in granules towards the apex of the cell. Large differences were found between the zinc levels of granules from rats receiving different batches of the same stock laboratory diet. These differences were eliminated by both oral and intraperitoneal administration of supplementary zinc.