H2O2 directly activates inositol 1,4,5-trisphosphate receptors in endothelial cells.
The mechanisms of H2O2-induced Ca2+ release from intracellular stores were investigated in human umbilical vein endothelial cells. It was found that U73122, the selective inhibitor of phospholipase C, could not inhibit the H2O2-induced cytosolic Ca2+ mobilization. No elevation of inositol 1,4,5-trisphosphate (IP3) was detected in cells exposed to H2O2. By loading mag-Fura-2, a Ca2+ indicator, into intracellular store, the H2O2-induced Ca2+ release from intracellular calcium store was directly observed in the permeabilized cells in a dose-dependent manner. This release can be completely blocked by heparin, a well-known antagonist of IP3 receptor, indicating a direct activation of IP3 receptor on endoplasmic reticulum (ER) membrane by H2O2. It was also found that H2O2 could still induce a relatively small Ca2+ release from internal stores after the Ca2+-ATPase on ER membrane and the Ca2+ uptake to mitochondria were simultaneously inhibited by thapsigargin and carbonyl cyanide p-trifluoromethoxyphenyl hydrazone. The later observation suggests that a thapsigargin-insensitive non-mitochondrial intracellular Ca2+ store might be also involved in H2O2-induced Ca2+ mobilization.
Zheng
Yi
Y
Institute of Biophysics, Chinese Academy of Science, Graduate School of the Chinese Academy of Sciences, Beijing, P. R. China.
Shen
Xun
X
D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000502:physiology; D004730:Endothelium, Vascular / Q000187:drug effects / Q000502:physiology*; D006632:Histamine; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000502:physiology*; D019284:Thapsigargin / Q000494:pharmacology; D014471:Umbilical Veins
D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D019284:Thapsigargin; D006632:Histamine; D006861:Hydrogen Peroxide