Characterization of histamine-induced increases in intracellular free Ca2+concentrations in Chang liver cells

The effect of histamine on intracellular free Ca2+ levels ([Ca2+](i)) in Ch ang liver cells were investigated by using fura-2 as a Ca2+ dye. Histamine (0.2-50 muM) increased [Ca2+](i) in a concentration-dependent manner with a n EC50 value of 0.8 muM. The [Ca2+](i) response comprised an initial rise, a slow decay, and a sustained phase. Extracellular Ca2+ removal inhibited 5 0% of the maximum [Ca2+](i) signal and abolished the sustained phase. After pretreatment with 5 muM histamine in Ca2+-free medium for 4 min, addition of 3 mM Ca2+ induced a [Ca2+](i) increase with a magnitude 7-fold greater t han control. In Ca2+-free medium, after treatment with 1 muM thapsigargin ( an endoplasmic reticulum Ca2+ PUMP inhibitor), 5 muM histamine failed to in crease [Ca2+](i)j. Histamine (5 muM)-induced intracellular Ca2+ release was abolished by inhibiting phospholipase C with 2 muM 1-(6-((17b-3-methoxyest ra-1,3, 5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; U73122), and b y 5 muM pyrilamine but was unaltered by 50 muM cimetidine. Collectively, th e present study shows that histamine caused significant [Ca2+](i) increases in Chang liver cells by stimulating H1 histamine receptors. The [Ca2+](i) increase was triggered by Ca2+ release from thapsigargin-sensitive endoplas mic reticulum stores in an inositol 1,4,5-trisphosphate-sensitive fashion, and was accompanied by Ca2+ entry from extracellular space.