CYTOSOLIC CALCIUM INCREASE IN CORONARY ENDOTHELIAL-CELLS AFTER H2O2 EXPOSURE AND THE INHIBITORY EFFECT OF U78517F

1 Cytosolic calcium concentrations ([Ca2+]i were determined with fura-2 on both resting (unstimulated) and A23187-stimulated coronary endothelial cells following injury by hydrogen peroxide (H2O2). 2 Treatment of cells with H2O2 (10(-4) M) caused an increase in the resting [Ca2+]i, which reached a maximum of five fold after 3 h. 3 The increase in resting [Ca2+]i was significantly attenuated by treatment with U78517F, a potent inhibitor of lipid peroxidation, at a concentration of 10(-6) M or greater. Catalase (50 u ml-1) also markedly inhibited the H202-induced rise in [Ca2+]i. Pretreatment with verapamil (10(-5) M), nifedipine (10(-6) M) or diltiazem (10(-5) M) had no effect on the increase in [Ca2+]i following addition of H202. 4 A23187 produced a transient increase in [Ca2+]i followed by a sustained plateau. The initial peak and plateau phase responses to A23187 were augmented by H202. This augmentation of [Ca2+]i was suppressed by U78517F or catalase but not by Ca-entry blockers. 5 Thus, it is likely that lipid peroxidation plays a critical role in the sustained increase in [Ca2+]i that occurs following treatment with H2O2 and that this continues in the presence of agonists which stimulate the endothelium. Voltage-gated Ca2+ channels do not seem to be involved in the genesis of cellular damage associated with sustained large increases in [Ca2+]i.