Agonist-induced calcium and oxidative stress responses in endothelial cells.

[Ca(2+)](i) (cytosolic [Ca(2+)]) and OS (oxidative stress) were measured simultaneously in calf pulmonary artery endothelial cells using fura-2 and carboxy-2',7'-dichlorodihydrofluorescein. ATP stimulated a [Ca(2+)](i) increase that was followed a few seconds later by an increase in OS. Pre-exposure to 5 microM H(2)O(2) potentiated these responses to ATP. Elevating or removing extracellular Ca(2+) increased or reduced the [Ca(2+)](i) response to ATP and caused parallel changes in the OS response, suggesting that this response was a consequence of the [Ca(2+)](i) response. Inhibition of mitochondria with rotenone or antimycin A affected the responses but not in a manner that allowed a simple interpretation of the role of mitochondria. These data show an intimate connection between [Ca(2+)](i) and OS that can be modulated by low levels of exogenously applied OS, allowing the possibility of positive feedback.