the possible role of free radical species secreted by endothelial cells in conditioning of smooth muscle responses to depolarization was supported by the results of three sets of experiments : 1 ) endothelial cells did respond to endotoxin with oxidative burst , 2 ) pretreatment of cocultured cells with catalase prevented endotoxin-induced downregulation of ca2+ transients , and 3 ) in isolated smooth muscle cells , the addition of hydrogen peroxide virtually abolished depolarization-induced ca2+ transients .
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