CHARACTERIZATION OF HISTAMINE-INDUCED INCREASES IN INTRACELLULAR FREE Ca²⁺ CONCENTRATIONS IN CHANG LIVER CELLS

Abstract

The effect of histamine on intracellular free Ca²⁺ levels ([Ca²⁺]_i) in Chang liver cells were investigated by using fura-2 as a Ca²⁺ dye. Histamine (0.2–50 μM) increased [Ca²⁺]_i in a concentration-dependent manner with an EC₅₀ value of 0.8 μM. The [Ca²⁺]_i response comprised an initial rise, a slow decay, and a sustained phase. Extracellular Ca²⁺ removal inhibited 50% of the maximum [Ca²⁺]_i signal and abolished the sustained phase. After pretreatment with 5 μM histamine in Ca²⁺-free medium for 4 min, addition of 3 mM Ca²⁺ induced a [Ca²⁺]_i increase with a magnitude 7-fold greater than control. In Ca²⁺-free medium, after treatment with 1 μM thapsigargin (an endoplasmic reticulum Ca²⁺ pump inhibitor), 5 μM histamine failed to increase [Ca²⁺]_i. Histamine (5 μM)-induced intracellular Ca²⁺ release was abolished by inhibiting phospholipase C with 2 μM 1-(6-((17b-3-methoxyestra-1,3,5-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; U73122), and by 5 μM pyrilamine but was unaltered by 50 μM cimetidine. Collectively, the 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 endoplasmic reticulum stores in an inositol 1,4,5-trisphosphate-sensitive fashion, and was accompanied by Ca²⁺ entry from extracellular space.