text: Induction of apoptosis in skeletal tissues: phosphate-mediated chick chondrocyte apoptosis is calcium dependent.
  In an earlier study, we have shown that Pi induced apoptosis of terminally differentiated hypertrophic chondrocytes. To ascertain whether Ca2+ modulates Pi-induced cell death, we asked the following two questions: First, can we prevent Pi-induced apoptosis by removing Ca2+ from the culture medium; alternatively, can we potentiate cell death by increasing the Ca2+ concentration? Second, can we inhibit chondrocyte apoptosis by blocking Pi transport? We also explored the mechanism of apoptosis by evaluating mitochondrial activity and reactive oxygen species (ROS) generation in cells treated with the ion pair. We noted that EDTA and EGTA blocked Pi-induced apoptosis in a dose-dependent manner. While high levels of Ca2+ alone had little effect on chondrocyte viability, the cation enhanced Pi-dependent cell death and greatly increased Pi uptake. When Pi transport was blocked, there was complete inhibition of cell killing. The process of cell death was characterized by mitochondrial hyperpolarization; two hours following apoptogen treatment, there was a significant decrease in the mitochondrial membrane potential. Coincident with the changes in mitochondrial function, there was an increase in intracellular Ca2+ that was maintained throughout the experimental period. A raised Ca2+ signal was observed in blebs at the cell membrane. Finally, we noted that, 75 minutes after treatment with the ion pair, there was a six-fold elevation in ROS levels. This increase declined to baseline values after three hours. Based on these observations, we suggest that, at the cartilage mineralization front, an elevation in local environmental Ca2+ and Pi concentrations modulates oxidative metabolism, and triggers apoptosis of terminally differentiated chondrocytes.
  
entities: ['skeletal tissues']
entities: Tissue
entities: PMID-14565598_T1
entities: ['chondrocyte']
entities: Cell
entities: PMID-14565598_T2
entities: ['chondrocytes']
entities: Cell
entities: PMID-14565598_T3
entities: ['cell']
entities: Cell
entities: PMID-14565598_T4
entities: ['cell']
entities: Cell
entities: PMID-14565598_T5
entities: ['chondrocyte']
entities: Cell
entities: PMID-14565598_T6
entities: ['mitochondrial']
entities: Cellular_component
entities: PMID-14565598_T7
entities: ['cells']
entities: Cell
entities: PMID-14565598_T8
entities: ['chondrocyte']
entities: Cell
entities: PMID-14565598_T9
entities: ['cell']
entities: Cell
entities: PMID-14565598_T10
entities: ['cell']
entities: Cell
entities: PMID-14565598_T11
entities: ['cell']
entities: Cell
entities: PMID-14565598_T12
entities: ['mitochondrial']
entities: Cellular_component
entities: PMID-14565598_T13
entities: ['mitochondrial membrane']
entities: Cellular_component
entities: PMID-14565598_T14
entities: ['mitochondrial']
entities: Cellular_component
entities: PMID-14565598_T15
entities: ['cell membrane']
entities: Cellular_component
entities: PMID-14565598_T16
entities: ['chondrocytes']
entities: Cell
entities: PMID-14565598_T17
entities: ['intracellular']
entities: Immaterial_anatomical_entity
entities: PMID-14565598_T18
entities: ['cartilage']
entities: Tissue
entities: PMID-14565598_T19