Vascular biology: Localized TRPA1 channel Ca²⁺ signals stimulated by reactive oxygen species promote cerebral artery dilation

Reactive oxygen species (ROS) can have divergent effects in cerebral and peripheral circulations. We found that Ca²⁺-permeable transient receptor potential ankyrin 1 (TRPA1) channels were present and colocalized with NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase 2 (NOX2), a major source of ROS, in the endothelium of cerebral arteries but not in other vascular beds. We recorded and characterized ROS-triggered Ca²⁺ signals representing Ca²⁺ influx through single TRPA1 channels, which we called "TRPA1 sparklets." TRPA1 sparklet activity was low under basal conditions but was stimulated by NOX-generated ROS. Ca²⁺ entry during a single TRPA1 sparklet was twice that of a TRPV4 sparklet and ∼200 times that of an L-type Ca²⁺ channel sparklet. TRPA1 sparklets representing the simultaneous opening of two TRPA1 channels were more common in endothelial cells than in human embryonic kidney (HEK) 293 cells expressing TRPA1. The NOX-induced TRPA1 sparklets activated intermediate-conductance, Ca²⁺-sensitive K⁺ channels, resulting in smooth muscle hyperpolarization and vasodilation. NOX-induced activation of TRPA1 sparklets and vasodilation required generation of hydrogen peroxide and lipid-peroxidizing hydroxyl radicals as intermediates. 4-Hydroxy-nonenal, a metabolite of lipid peroxidation, also increased TRPA1 sparklet frequency and dilated cerebral arteries. These data suggest that in the cerebral circulation, lipid peroxidation metabolites generated by ROS activate Ca²⁺ influx through TRPA1 channels in the endothelium of cerebral arteries to cause dilation.