Ultrastructural and histochemical observations on intracellular and luminal microcalculi in the feline sublingual salivary gland.

As the genesis of salivary calculi in man has not been established, the fortuitous observation of microcalculi in sublingual glands of cats prompted this study. Microcalculi were seen occasionally within acinar cells and lumina and macrophages, and rarely interstitially. Microcalculi were stained with the periodic-acid/Schiff technique, and acid-phosphatase activity was associated with intracellular microcalculi. Intracellular microcalculi were seen ultrastructurally in acinar cells in membrane-bound vacuoles that also contained debris and sometimes what appeared to be secretory material. X-ray microanalysis showed the microcalculi to consist of crystals containing calcium and phosphorus. The observations suggest that the microcalculi form within autophagosomes in acinar cells by a precipitation of calcium and phosphorus present in degenerate material, and that the microcalculi eventually enter lumina, where they may be discharged in the saliva or retained and enlarge.