Mechanisms of histamine-induced intracellular Ca² release and extracellular Ca² entry in MG63 human osteosarcoma cells

The effect of histamine on intracellular free Ca² levels ([Ca²]_i) in MG63 human osteosarcoma cells was explored using fura-2 as a Ca² dye. Histamine increased [Ca²⁺]_i in a concentration-dependent fashion with an EC₅₀ value of 0.5 μM. Extracellular Ca² removal inhibited the [Ca²]_i signals. Histamine failed to increase [Ca²]_i in Ca² -free medium after cells were pretreated with thapsigargin (an endoplasmic reticulum Ca² pump inhibitor). Addition of Ca² induced concentration-dependent [Ca² ]_i increases after preincubation with histamine in Ca² -free medium. Histamine-induced intracellular Ca² release was abolished by inhibiting phospholipase C with 1-(6-((17β-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl) -1H-pyrrole-2,5-dione (U73122). The [Ca²]_i increase induced by histamine in Ca² medium was abolished by cimetidine, but was not altered by pyrilamine, nifedipine, verapamil, and La³. Together, this study shows that histamine increased in [Ca²]_i in osteosarcoma cells by stimulating H2 histamine receptors. The Ca² signal was caused by Ca² release from the endoplasmic reticulum in a phospholipase C-dependent manner. The Ca² release was accompanied by Ca² influx.