title: Intracellular calcium responses to basic calcium phosphate crystals in fibroblasts.
abstract: OBJECTIVE
  To examine the intracellular calcium response to basic calcium phosphate (BCP) crystals in fibroblasts.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors: Division of Rheumatology, Medical College of Wisconsin, Milwaukee 53226, USA.
authors: P B
authors: PB
authors: Halverson
authors: A
authors: A
authors: Greene
authors: H S
authors: HS
authors: Cheung
mesh_terms: D015152:Blotting, Northern; D002118:Calcium / Q000378:metabolism*; D002130:Calcium Phosphates / Q000494:pharmacology*; D003460:Crystallization; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D010587:Phagocytosis
chemical_list: D002130:Calcium Phosphates; D002118:Calcium