title: Effect of thapsigargin and caffeine on Ca2+ homeostasis in HeLa cells: implications for histamine-induced Ca2+ oscillations.
abstract: Several studies have already established that the stimulation of H1 receptors by exogenous histamine induces intracellular Ca2+ oscillations in HeLa cells. The molecular mechanism underlying this oscillatory process remains, however, unclear. A series of fura-2 experiments was undertaken in which the nature of the Ca2+ pools involved in the histamine-induced Ca2+ oscillations was investigated using the tumour promoter agent thapsigargin (TG) and the Ca(2+)-induced Ca(2+)-release promoter, caffeine. The results obtained indicate first that TG causes a gradual increase in cytosolic Ca2+ without inducing internal Ca2+ oscillations, and second that TG and histamine share common internal Ca2+ storage sites. The latter conclusion was derived from experiments performed in the absence of external Ca2+, where the addition of TG before histamine resulted in a total inhibition of the Ca2+ response linked to H1 receptor stimulation, whereas the addition of histamine before TG decreased by more than 90% the TG-induced Ca2+ release. Finally; TG was found to inhibit irreversibly histamine-induced Ca2+ oscillations when added to the bathing medium during the oscillatory process. The effect of caffeine at concentrations ranging from 1 mM to 10 mM on intracellular Ca2+ homeostasis was also investigated. The results obtained show that caffeine does not affect systematically the internal Ca2+ concentration in resting and TG-stimulated HeLa cells, but increases the Ca2+ sequestration ability of inositol-trisphosphate (InsP3)-related Ca2+ stores.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D006367:HeLa Cells / Q000378:metabolism*; D006632:Histamine / Q000494:pharmacology*; D006636:Histamine Release / Q000187:drug effects; D006706:Homeostasis; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D009991:Oscillometry; D013729:Terpenes / Q000494:pharmacology*; D019284:Thapsigargin
chemical_list: D013729:Terpenes; D002110:Caffeine; D019284:Thapsigargin; D006632:Histamine; D015544:Inositol 1,4,5-Trisphosphate; D002118:Calcium