Effects of variations in calcium concentration on parathyroid morphology in vitro.

Morphologic examinations, including the use of the potassium pyroantimonate-technique and x-ray analysis for ultrastructural localization of cations, were carried out on parathyroid glands from Mongolian gerbils cultured for 2 to 6 days. At a high calcium concentration most (suppressed) chief cells were characterized by a moderate or high cytoplasmic density, inconspicuous endoplasmic reticulum and Golgi complex, numerous often enlarged mitochondria, and the occasional occurrence of accumulations of secretory granules, storage granules, and lysosomal bodies, whereas other (atrophic) cells were smaller and still more dense. At a low concentration of calcium some (stimulated) chief cells were characterized by a low cytoplasmic density, normal or structurally altered mitochondria, and smooth surface vacuoles occasionally connected with mitochondria, whereas the main features of other (active) chief cells were a moderate or low cytoplasmic density and a prominent endoplasmic reticulum and Golgi complex. Calcium-containing precipitates were found both inter- and intracellularly; the latter were mainly localized to nuclei, mitochondria, and rough surfaced vacuoles, and in stimulated cells also to the smooth surfaced vacuoles and the cytosol. Degenerative changes were seen, mainly in the suppressed cells; massive calcium loading in mitochondria seemed to precede degeneration and necrosis of whole cells. The findings indicate that clear differences exist between the different chief cell variants both as to the distribution of calcium-containing precipitates and to the structural appearance, and that these differences are influenced by the ambient calcium concentration. Suppressed cells occasionally seem to accumulate hormone which later may undergo lysosomal digestion. Calcium might be accumulated intracellularly, mainly in mitochondria of suppressed cells.