We compared the Ca(2+) responses to reactive oxygen species (ROS) between mouse endothelial cells derived from large-sized arteries, aortas (aortic ECs), and small-sized arteries, mesenteric arteries (MAECs). Application of hydrogen peroxide (H(2)O(2)) caused an increase in cytosolic Ca(2+) levels ([Ca(2+)](i)) in both cell types. The [Ca(2+)](i) rises diminished in the presence of U73122, a phospholipase C inhibitor, or Xestospongin C (XeC), an inhibitor for inositol-1,4,5-trisphosphate (IP(3)) receptors. Removal of Ca(2+) from the bath also decreased the [Ca(2+)](i) rises in response to H(2)O(2). In addition, treatment of endothelial cells with H(2)O(2) reduced the [Ca(2+)](i) responses to subsequent challenge of ATP. The decreased [Ca(2+)](i) responses to ATP were resulted from a pre-depletion of intracellular Ca(2+) stores by H(2)O(2). Interestingly, we also found that Ca(2+) store depletion was more sensitive to H(2)O(2) treatment in endothelial cells of mesenteric arteries than those of aortas. Hypoxanthine-xanthine oxidase (HX-XO) was also found to induce [Ca(2+)](i) rises in both types of endothelial cells, the effect of which was mediated by superoxide anions and H(2)O(2) but not by hydroxyl radical. H(2)O(2) contribution in HX-XO-induced [Ca(2+)](i) rises were more significant in endothelial cells from mesenteric arteries than those from aortas. In summary, H(2)O(2) could induce store Ca(2+) release via phospholipase C-IP(3) pathway in endothelial cells. Resultant emptying of intracellular Ca(2+) stores contributed to the reduced [Ca(2+)](i) responses to subsequent ATP challenge. The [Ca(2+)](i) responses were more sensitive to H(2)O(2) in endothelial cells of small-sized arteries than those of large-sized arteries.