Mechanism of bradykinin-induced Ca2+ mobilization in MG63 human osteosarcoma cells

Background: The effect of bradykinin on intracellular free Ca2+ levels ([Ca2+](i)) in MG63 human osteosarcoma cells was explored using fura-2 as a Ca2+ dye. Methods/Results: Bradykinin (0.1 nM-1 muM) increased [Ca2+](i) in a concentration-dependent manner with an EC50 value of 0.5 nM. The [Ca2+](i) signal comprised an initial peak and a fast decay which returned to baseline in 2 min. Extracellular Ca2+ removal inhibited the peak [Ca2+](i) signals by 35 +/- 3%. Bradykinin (1 nM) failed to increase [Ca2+](i) in the absence of extracellular Ca2+ after cells were pretreated with thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor; 1 muM). Bradykinin (1 nM)-induced intracellular Ca2+ release was nearly abolished by inhibiting phospholipase C with 2 muM 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122). The [Ca2+](i) increase induced by 1 nM bradykinin in Ca2+-free medium was abolished by 1 nM HOE 140 (a 132 bradykinin receptor antagonist) but was not altered by 100 nM Des-Arg-HOE 140 (a B1 bradykinin receptor antagonist). Pretreatment with 1 pM pertussis toxin for 6 h in Ca2+ medium inhibited 30 +/- 3% of 1 nM bradykinin-induced peak [Ca2+](i) increase. Conclusions: Together, this study shows that bradykinin induced [Ca2+](i) increases in a concentration-dependent manner, by stimulating B2 bradykinin receptors leading to mobilization of Ca2+ from the thapsigargin-sensitive stores in a manner dependent on inositol-1,4,5-trisphosphate, and also by inducing extracellular Ca2+ influx. The bradykinin response was partly coupled to a pertussis toxin-sensitive G protein pathway. Copyright (C) 2002 S, Karger AG, Basel.