Agonist-induced calcium and oxidative stress responses in endothelial cells

[Ca²⁺]_i (cytosolic [Ca²⁺]) and OS (oxidative stress) were measured simultaneously in calf pulmonary artery endothelial cells using fura-2 and carboxy-2´,7´-dichlorodihydrofluorescein. ATP stimulated a [Ca²⁺]_i increase that was followed a few seconds later by an increase in OS. Pre-exposure to 5 μM H₂O₂ potentiated these responses to ATP. Elevating or removing extracellular Ca²⁺ increased or reduced the [Ca²⁺]_i response to ATP and caused parallel changes in the OS response, suggesting that this response was a consequence of the [Ca²⁺]_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 initimate connection between [Ca²⁺]_i and OS that can be modulated by low levels of exogenously applied OS, allowing the possibility of positive feedback.