Journal
JOURNAL OF BONE AND MINERAL RESEARCH
Volume 17, Issue 10, Pages 1801-1813Publisher
AMER SOC BONE & MINERAL RES
DOI: 10.1359/jbmr.2002.17.10.1801
Keywords
dentinogenesis; phosphoprotein; collagen; cell culture; sodium-phosphate cotransporter
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Funding
- NIDCR NIH HHS [DE11442] Funding Source: Medline
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It has been suggested that odontoblasts are instrumental in translocating Ca2+ and inorganic phosphate (P-i) ions during the mineralization of dentin. The aim of this study was to characterize cellular P-i and Ca2+ uptake in the novel rat odontoblast-like cell line mineralizing rat pulpal cell line (MRPC) 1 during mineralization to see if changes in the ion transport activity would occur as the cultures develop and begin forming a mineralized matrix. MRPC-1 cells were cultured in chemically defined medium containing ascorbate and Pi, and cultures were specifically analyzed for cellular P-i and Ca2+ uptake activities and expression of type II high-capacity Na+-P-i cotransporters. The odontoblast-like phenotype of the cell line was ascertained by monitoring the expression of collagen type I and dentin phosphopoprotein (DPP). Mineralized nodule formation started at day 9 after confluency and then rapidly increased. Ca2+ uptake by the cells showed a maximum during the end of the proliferative phase (days 5-7). P-i uptake declined to a basal level during proliferation and then was up-regulated simultaneously with the onset of mineralization to a level fourfold of the basal uptake, suggesting an initiating and regulatory role for cellular Pi uptake in mineral formation. This up-regulation coincided with a conspicuously increased glycosylation of NaPi-2a, indicating an activation of this Na+-P-i cotransporter. The study showed that MRPC-1 cells express an odontoblast-like phenotype already at the onset of culture, but that to mineralize the collagenous extracellular matrix (ECM) that formed, a further differentiation involving their ion transporters is necessary.
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