Temporal switching and cell-to-cell variability in Ca2+ release activity in mammalian cells

Mol Syst Biol. 2009;5:247. doi: 10.1038/msb.2009.6. Epub 2009 Mar 17.


Genetically identical cells in a uniform external environment can exhibit different phenotypes, which are often masked by conventional measurements that average over cell populations. Although most studies on this topic have used microorganisms, differentiated mammalian cells have rarely been explored. Here, we report that only approximately 40% of clonal human embryonic kidney 293 cells respond with an intracellular Ca(2+) increase when ryanodine receptor Ca(2+) release channels in the endoplasmic reticulum are maximally activated by caffeine. On the other hand, the expression levels of ryanodine receptor showed a unimodal distribution. We showed that the difference in the caffeine sensitivity depends on a critical balance between Ca(2+) release and Ca(2+) uptake activities, which is amplified by the regenerative nature of the Ca(2+) release mechanism. Furthermore, individual cells switched between the caffeine-sensitive and caffeine-insensitive states with an average transition time of approximately 65 h, suggestive of temporal fluctuation in endogenous protein expression levels associated with caffeine response. These results suggest the significance of regenerative mechanisms that amplify protein expression noise and induce cell-to-cell phenotypic variation in mammalian cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Cell Cycle / drug effects
  • Cell Line
  • Cell Shape / drug effects
  • Fluorescent Antibody Technique
  • Humans
  • Immunohistochemistry
  • Intracellular Space / drug effects
  • Intracellular Space / metabolism
  • Models, Biological
  • Phenotype
  • Receptors, Purinergic / metabolism
  • Reproducibility of Results
  • Ryanodine Receptor Calcium Release Channel / metabolism
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / metabolism
  • Time Factors


  • Receptors, Purinergic
  • Ryanodine Receptor Calcium Release Channel
  • Caffeine
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases
  • Calcium