The Effects of Peroxynitrite on eNOS Activation and Microvessel Permeability in Intact Venules

The increased peroxynitrite formation has been implicated in the pathogenesis of many cardiovascular diseases. This study aims to examine the effect of peroxynitrite on microvessel permeability and the involved cellular and molecular mechanisms in rat mesenteric venules. Permeability was determined by measuring hydraulic conductivity (Lp). NO and endothelial (EC) [Ca 2+ ] i were measured in DAF‐2 and Fura‐2 loaded vessels. Cell injury was detected by Annexin‐V staining. Perfusing vessels with peroxynitrite induced delayed and progressive increases in Lp, which correlated with the time courses of the increases in EC [Ca 2+ ] i and vascular cell injury. However, peroxynitrite induced immediate increases in EC NO production with an initial rate at 27±8%/min (13 min) followed by a continuous slower rate at 4±1%/min. Inhibition of NO production by L‐NMMA prevented peroxynitrite‐induced increase in microvessel Lp. Blocking Ca 2+ influx by LaCl 3 did not affect the initial NO but prevented the late phase NO production and the increases in Lp. Our results demonstrated that peroxynitrite, a product of NO reaction with superoxide, enables to activate eNOS and further increase NO production. The peroxynitrite‐triggered initial NO, occurred before the increases in EC [Ca 2+ ] i , is independent from the Ca 2+ signal but the late phase NO production is affected by the Ca 2+ influx. More importantly, peroxynitrite‐induced NO and the subsequent magnified peroxynitrite formation are essential for the Ca 2+ accumulation, vascular cell injury, and increases in microvessel permeability. Supported by HL56237 and HL084338.