HYDROGEN-PEROXIDE INDUCES INTRACELLULAR CALCIUM OSCILLATIONS IN HUMANAORTIC ENDOTHELIAL-CELLS

Background-Because the vascular endothelium is exposed to oxidant stre ss resulting from ischemia/reperfusion and from the products of polymo rphonuclear leukocytes or monocytes, studies were performed to examine the effect of hydrogen peroxide (1 mu mol/L to 10 mmol/L) on endothel ial Ca2+ signaling, Methods and Results-At low concentrations (1 to 10 mu mol/L), hydrogen peroxide did not affect intracellular Ca2+ concen tration in subconfluent, indo 1-loaded human aortic endothelial monola yers, At a concentration of 100 mu mol/L hydrogen peroxide, intracellu lar free Ca2+ gradually increased from 125.3 +/- 6.8 to 286.3 +/- 19.9 nmol/L over 4.2 +/- 0.9 minutes before repetitive Ca2+ oscillations w ere observed, consisting of an initial large, transient spike of appro ximate to 1 mu mol/L followed by several spikes of decreasing amplitud es at a frequency of 0.7 +/- 0.1 min(-1) over 12.0 +/- 1.1 minutes, Af ter these oscillations, intracellular Ca2+ reached a plateau of 543.4 +/- 64.0 nmol/L, which was maintained above baseline levels for > 5 mi nutes and then partially reversible on washout of hydrogen peroxide in most monolayers, Intracellular Ca2+ oscillations were typically obser ved when monolayers were exposed to 100 to 500 mu mol/L hydrogen perox ide. Higher concentrations of hydrogen peroxide (1 and 10 mmol/L) incr eased intracellular Ca2+ but only rarely (2 of 6 monolayers at 1 mmol/ L) or never (at 10 mmol/L) stimulated intracellular Ca2+ oscillations. Removal of Ca2+ from the buffer either before hydrogen peroxide stimu lation or during an established response did not block intracellular C a2+ oscillations in response to 100 mu mol/L hydrogen peroxide, but pr ior depletion of an intracellular Ca2+ store with either caffeine, his tamine, or thapsigargin abolished Ca2+ oscillations. Conclusions-Hydro gen peroxide induces concentration-dependent intracellular Ca2+ oscill ations in human endothelial cells, which results from release of an en doplasmic reticulum Ca2+ store. Because oxidant production appears to occur In the micromolar range in the postischemic/anoxic endothelium a nd is associated with impaired endothelium-dependent relaxation, the e ffects of micromolar concentrations of hydrogen peroxide on endothelia l Ca2+ signaling described in the present study maybe important in the pathogenesis of postischemic endothelial dysfunction.