Intracellular calcium responses to basic calcium phosphate crystals in fibroblasts

Paul B. Halverson, Andrew Greene, Herman S. Cheung

Research output: Contribution to journalArticlepeer-review

36 Scopus citations


Objective: To examine the intracellular calcium response to basic calcium phosphate (BCP) crystals in fibroblasts. Design: In this study, intracellular calcium [Ca2+](i) levels in fibroblasts were determined using the photoactive dye, fura-2. Interruption of these responses was accomplished by either removal of Ca2+ from the extracellular medium or addition of ammonium chloride that inhibits intracellular dissolution of BCP crystals by alkalinizing phagolysosomes. The effects of such interruptions on BCP induction expression of proto-oncogenes were demonstrated by the Northern blot analysis. Results: Addition of media containing BCP crystals yielded an immediate 10-fold rise of [Ca2+](i) over the baseline level in human fibroblasts. This peak was derived mostly from extracellular calcium and was not seen when BCP crystals in calcium-free media were added to fibroblasts. The [Ca2+](i) concentration returned to the baseline level within 8 min. A second rise of [Ca2+](i) started at 60 min and continued to increase up to at least 3 h. This peak was derived from intracellular dissolution of phagocytosed crystals and almost completely inhibited by 10 mM ammonium chloride. Conclusion: The initial transient [Ca2+](i) increase probably serves as a second messenger leading to activation of early cellular responses such as c-fos expression which is important in BCP crystal-induced mitogenesis. The second, slower and more sustained rise of [Ca2+](i) probably initiates other cellular processes needed for fibroblast mitogenesis.

Original languageEnglish (US)
Pages (from-to)324-329
Number of pages6
JournalOsteoarthritis and Cartilage
Issue number5
StatePublished - Sep 1998


  • Basic calcium phosphate crystals
  • Calcium
  • Fibroblasts
  • Fura-2

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine


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