title: Biphasic calcium response of platelet-derived growth factor stimulated glioblastoma cells is a function of cell confluence.
abstract: BACKGROUND
  Previous reports have linked the spiking or two-phased character of calcium transients evoked by platelet-derived growth factor (PDGF) to the position of cells in the cell cycle without regard to cell-cell contact and communication. Because cell confluence can regulate growth factor receptor expression and dephosphorylation, we investigated the effect of cell culture confluence and cell cycle on calcium responses of PDGF-BB-stimulated A172 glioblastoma cells.
  
  
  METHODS
  Digital imaging cytometry was used to correlate the peak and duration of calcium response with bromodeoxyuridine positivity and DNA content and with culture confluence on a cell-by-cell basis.
  
  
  RESULTS
  In serum-starved cultures, complete two-phase calcium signals and shorter, lower spikes occurred independent of cell cycle phase. However, the confluence of cell culture seemed essential for inducing a complete response because cells in sparse cultures exhibited mostly short spikes with lower peaks or no transients at all.
  
  
  CONCLUSIONS
  Because cell confluence, by virtue of cell-cell contacts, is assumed to be an important regulator of proliferation, one is tempted to speculate that in transformed cells the ability to produce stronger growth signals upon reaching confluence and facing contact inhibition could provide a proliferative advantage.
authors.affiliation: Department of Biophysics and Cell Biology, Research Center for Molecular Medicine, University of Debrecen, Debrecen, Hungary. vereb@dote.hu
authors.forename: György
authors.initials: G
authors.lastname: Vereb
authors.forename: Burt G
authors.initials: BG
authors.lastname: Feuerstein
authors.forename: William C
authors.initials: WC
authors.lastname: Hyun
authors.forename: Mack J
authors.initials: MJ
authors.lastname: Fulwyler
authors.forename: Margit
authors.initials: M
authors.lastname: Balázs
authors.forename: János
authors.initials: J
authors.lastname: Szöllosi
mesh_terms: D000077214:Becaplermin; D001973:Bromodeoxyuridine; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002448:Cell Adhesion; D002453:Cell Cycle / Q000187:drug effects; D002478:Cells, Cultured; D004247:DNA / Q000235:genetics / Q000378:metabolism; D005909:Glioblastoma / Q000378:metabolism* / Q000473:pathology*; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D020574:Proto-Oncogene Proteins c-sis; D013050:Spectrometry, Fluorescence
chemical_list: D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D000077214:Becaplermin; D004247:DNA; D001973:Bromodeoxyuridine; D002118:Calcium