Basic calcium phosphate (BCP) crystals stimulate mitosis of cultured fibroblasts and synoviocytes in vitro. Although intimate crystal-cell contact is required for mitogenesis, and lysosomotropic agents such as chloroquine and ammonium chloride block the mitogenic effect of crystals, the requirement of endocytosis has not been demonstrated. Synthetic BCP crystals, uniformly trace-labeled with45Ca, were added to cultured, quiescent confluent human foreskin fibroblasts in the presence or absence of ammonium chloride. After 4 or 24 hours, cultures were pulsed with3H thymidine. The cells were, then released with EDTA and trypsin, and fractionated on preformed Percoll density gradients. Fractions were analyzed for incorporation of45Ca and [3H]thymidine and cell number. The cells containing45Ca crystals also were heavily labeled with thymidine. Ammonium chloride decreased the amount of crystals endocytosed, and inhibited mitogenesis. These data suggets, that mitogenosis induced by BCP crystals is preceded by endocytosis and dissolution in the acidic environment of phagolysosomes.
- Basic calcium phosphate crystals
ASJC Scopus subject areas
- Orthopedics and Sports Medicine
- Endocrinology, Diabetes and Metabolism