Both purinergic signaling through nucleotides such as ATP (adenosine 5′-triphosphate) and noradrenergic signaling through molecules such as norepinephrine regulate vascular tone and blood pressure. Pannexin1 (Panx1), which forms large-pore, ATP-releasing channels, is present in vascular smooth muscle cells in peripheral blood vessels and participates in noradrenergic responses. Using pharmacological approaches and mice conditionally lacking Panx1 in smooth muscle cells, we found that Panx1 contributed to vaso-constriction mediated by the α1 adrenoreceptor (α1AR), whereas vasoconstriction in response to serotonin or endothelin-1 was independent of Panx1. Analysis of the Panx1-deficient mice showed that Panx1 contributed to blood pressure regulation especially during the night cycle when sympathetic nervous activity is highest. Using mimetic peptides and site-directed mutagenesis, we identified a specific amino acid sequence in the Panx1 intracellular loop that is essential for activation by α1AR signaling. Collectively, these data describe a specific link between noradrenergic and purinergic signaling in blood pressure homeostasis.

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Transient receptor potential (TRP) channels of the vanilloid subfamily, mainly TRPV1 and TRPV4, are expressed in pulmonary artery smooth muscle cells (PASMC) and implicated in the remodeling of pulmonary artery, a landmark of pulmonary hypertension (PH). Among a variety of PH subtypes, PH of group 3 are mostly related to a prolonged hypoxia exposure occurring in a variety of chronic lung diseases. In the present study, we thus investigated the role of hypoxia on TRPV1 and TRPV4 channels independently of the increased pulmonary arterial pressure that occurs during PH. We isolated PASMC from normoxic rat and cultured these cells under in vitro hypoxia. Using microspectrofluorimetry and the patch-clamp technique, we showed that hypoxia (1 % O2 for 48 h) significantly increased stretch- and TRPV4-induced calcium responses. qRT-PCR, Western blotting, and immunostaining experiments revealed that the expression of TRPV1 and TRPV4 was not enhanced under hypoxic conditions, but we observed a membrane translocation of TRPV1. Furthermore, hypoxia induced a reorganization of the F-actin cytoskeleton, the tubulin, and intermediate filament networks (immunostaining experiments), associated with an enhanced TRPV1- and TRPV4-induced migratory response (wound-healing assay). Finally, as assessed by immunostaining, exposure to in vitro hypoxia elicited a significant increase in NFATc4 nuclear localization. Cyclosporin A and BAPTA-AM inhibited NFATc4 translocation, indicating the activation of the Ca(2+)/calcineurin/NFAT pathway. In conclusion, these data point out the effect of hypoxia on TRPV1 and TRPV4 channels in rat PASMC, suggesting that these channels can act as direct signal transducers in the pathophysiology of PH.