Carmustine augments the effects of tert-butyl hydroperoxide on calcium signaling in cultured pulmonary artery endothelial cells

The effects of oxidant stress and inhibition of glutathione reductase on the bradykinin-stimulated changes in cytosolic free Ca2+ concentration (Ca2+]i) of calf pulmonary artery endothelial cells were determined using the intracellular fluorescent probe, fura-2. Changes in Ca2+]i upon stimulation with bradykinin were measured after incubation of cells with the chemical oxidant tert-butyl hydroperoxide (0.4 mM) for various times. After 60 min, bradykinin-stimulated Ca2+ influx was significantly decreased. With more prolonged incubations with the peroxide, bradykinin had little effect on cytosolic calcium concentration. Preincubation of cells with the glutathione reductase inhibitor, carmustine, led to elevated basal Ca2+]i, yet the cells remained responsive to bradykinin. However, incubation of carmustine-treated cells with tert-butyl hydroperoxide for 30 min dramatically reduced both bradykinin-stimulated release of Ca2+ from internal stores and influx of Ca2+ from the extracellular space. These results suggest that inhibition of glutathione reductase alters cytosolic Ca2+ homeostasis and enhances the effects of oxidative stress on signal transduction in vascular endothelial cells.