Aquaporin-1 facilitates the transport of hydrogen peroxide and nitric oxide during endothelium-dependent vasorelaxation.

Aquaporins (AQPs) are transmembrane proteins that primarily transport water, but certain isoforms also facilitate the diffusion of small neutral signaling molecules, such as hydrogen peroxide (H2O2) and nitric oxide (NO). However, whether AQPs mediate vascular H2O2 and NO transport remains poorly understood. We investigated whether AQPs facilitate the transport of these endothelium-derived relaxing factors using relaxation assays in isolated male Wistar rat aortas. Incubation with diphenyleneiodonium (non-specific NADPH oxidase inhibitor), VAS2870 (pan-NADPH oxidase inhibitor), diethyldithiocarbamate (superoxide dismutase inhibitor), exogenous peroxidase, AgNO3 (non-selective AQP inhibitor), or bacopaside II (selective AQP1 inhibitor) significantly attenuated carbachol-stimulated endothelium-dependent relaxation. Vasorelaxation induced by exogenous H2O2 was reduced by AgNO3 or bacopaside II; however, in endothelium-denuded rings, AgNO3 - but not bacopaside II- attenuated this response. Furthermore, both AgNO3 and bacopaside II decreased relaxation mediated by the intracellular NO donor sodium nitroprusside. Concomitantly, in endothelium-denuded segments, vasorelaxation induced by the extracellular NO donor spermine NONOate was diminished by AgNO3, but was slightly increased by bacopaside II. Collectively, these findings suggest that during endothelium-dependent vasorelaxation, AQP1 facilitates endothelial H2O2 influx and subsequent NO efflux, rather than promoting their entry into vascular smooth muscle cells. Thus, our work uncovers a coordinated H2O2-NO signaling cascade that drives endothelium-dependent relaxation in the rat aorta via AQP1-mediated transport, providing novel insights into the biophysical mechanisms governing endothelial function.