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Effects of inositol trisphosphate on calcium mobilization in bone cells
R Falsafi1, D N Tatakis, S Hagel-Bradway
1Department of Oral Biology, School of Dental Medicine, State University of New York, Buffalo 14214.
Abstract:
The effect of inositol 1,4,5 trisphosphate (IP3) on calcium mobilization was studied in human osteosarcoma lines, Saos-2 and G292, as well as isolated rat osteoblastic and osteoclastic cells. Cells were permeabilized with saponin and calcium mobilization was studied with the fluorescent dye, fura-2 in a recording spectrofluorometer. IP3 (10 microM) increased calcium release in all cell types studied. The effect was dependent on ATP and occurred in the presence of mitochondrial inhibitors. The effect was not seen with inositol 1-phosphate (IP) or inositol 1,4-diphosphate (IP2). Inositol 1,3,4,5 tetrakisphosphate (IP4) appeared to elicit a decrease in the calcium released. Depletion of the intracellular pool with the calcium ionophore, ionomycin, as well as incubation with the inhibitor of intracellular calcium mobilization, TMB-8, obliterated the IP3 effect. The results are consistent with the hypothesis that increases in IP3 can cause a rapid elevation of bone cell cytosolic calcium.
Insights
Inositol 1,4,5 trisphosphate (IP3) significantly increases calcium release in bone cells, a process vital for bone cell function. This calcium mobilization is ATP-dependent and specific to IP3, not other inositol phosphates.
Area of Science:
- Biochemistry
- Cell Biology
- Bone Physiology
Background:
- Inositol phosphates play crucial roles in cellular signaling pathways.
- Calcium ions are critical regulators of various cellular processes, including bone cell activity.
Purpose of the Study:
- To investigate the effect of inositol 1,4,5 trisphosphate (IP3) on calcium mobilization in human osteosarcoma and rat bone cells.
- To determine the dependence of IP3-induced calcium release on ATP and its specificity compared to other inositol phosphates.
Main Methods:
- Human osteosarcoma cell lines (Saos-2, G292) and isolated rat osteoblastic/osteoclastic cells were used.
- Cells were permeabilized, and calcium mobilization was measured using the fluorescent dye fura-2.
- Experiments involved varying concentrations of IP3, ATP, and inhibitors like TMB-8 and ionomycin.
Main Results:
- Inositol 1,4,5 trisphosphate (IP3) at 10 microM increased calcium release in all tested bone cell types.
- The calcium release was dependent on ATP and occurred even with mitochondrial inhibitors present.
- Inositol 1-phosphate (IP), inositol 1,4-diphosphate (IP2), and inositol 1,3,4,5 tetrakisphosphate (IP4) did not elicit the same calcium release effect.
- Depleting intracellular calcium pools or using the inhibitor TMB-8 abolished the IP3-induced calcium release.
Conclusions:
- IP3 is a potent stimulator of calcium release in human and rat bone cells.
- The findings support the hypothesis that elevated IP3 levels can rapidly increase cytosolic calcium in bone cells.
- This calcium signaling pathway mediated by IP3 likely plays a significant role in regulating bone cell function.