S-phase independence of parathyroid hormone-induced calcium signalling in primary osteoblast-like cells.
Cell cycle-dependence of parathyroid hormone (PTH)-induced signal transduction was studied at the single cell level in fetal rat osteoblast-like cells (ROB) in primary culture. Responsiveness to 10(-7) M rPTH1-34 was measured as changes in the intracellular calcium concentration ([Ca2+]i) of cells loaded with Fura-2 using a video imaging setup. Cells in S-phase were identified by staining for incorporated 5-bromo-2'-deoxyuridine (BrdU). ROB were cultured on glass coverslips which had alphanumerically marked gratings so that cells could be located. Directly after measurement of the PTH-induced [Ca2+]i response of the individual cells, cells were fixed and stained for incorporated BrdU. Phase-contrast images taken with the video imaging setup were compared with phase-contrast micrographs and fluoro-micrographs taken after staining for BrdU incorporation. We found that 43% of the cells responding to PTH with a rise in [Ca2+]i had also incorporated BrdU. This percentage was not different from the percentage BrdU positive cells in the whole culture, showing that calcium responsiveness was randomly distributed between ROB in S-phase and those not in S-phase. We therefore conclude that PTH does not induce calcium responses preferentially during the S-phase of the cell cycle in ROB in primary culture.
Wiltink
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Department of Physiology and Physiological Physics, Leiden University, The Netherlands.
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D000818:Animals; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D004261:DNA Replication / Q000187:drug effects; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D051381:Rats; D016196:S Phase; D015398:Signal Transduction; D012886:Skull / Q000166:cytology / Q000196:embryology; D019379:Teriparatide
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D019379:Teriparatide; D002118:Calcium