Calcium influx-dependent differential actions of superoxide and hydrogen peroxide on microvessel permeability

Abstract

Our previous study demonstrated that reactive oxygen species (ROS) released from activated blood cells contribute significantly to the increased microvessel permeability during inflammation. This study aims to define the individual roles of hydrogen peroxide (H2O2) and superoxide in ROS-induced increases in permeability and endothelial intracellular Ca2+concentration ([Ca2+]i) in individually perfused rat mesenteric venules. Microvessel permeability was determined by measuring hydraulic conductivity ( Lp). Endothelial [Ca2+]iwas measured in fura-2 AM-loaded microvessels. Perfusing microvessels with superoxide generated by hypoxanthine and xanthine oxidase (HX/XO) induced immediate and transient increases in Lp. The mean peak value, which occurred within 5 min of HX/XO exposure, was 4.3 ± 0.6 times that of the control. In contrast, the perfusion of H2O2(100 and 500 μM) caused no immediate increases in Lp. A significant Lpincrease, 3.6 ± 0.6 times the control value, occurred 30 min after the perfusion of H2O2at 500 μM. The perfusion of H2O2at 100 or 500 μM for 1 h increased Lpto 6.6 ± 0.9 and 11.3 ± 3.6 times the control value, respectively. The increased endothelial [Ca2+]iin HX/XO or H2O2perfused vessels was correlated with the time course of the increases in Lp. Inhibiting Ca2+influx by LaCl3prevented the permeability increase induced by HX/XO or H2O2. These results demonstrated differential actions of superoxide and H2O2on microvessel permeability and endothelial [Ca2+]i. Superoxide-induced permeability increases were immediate and transient, whereas H2O2-induced permeability increases were progressive, demonstrating concentration and time dependence. Ca2+influx plays an essential role in both superoxide and H2O2-induced permeability increases.