Evidence for a functional role of endothelial TRPV4 in shear stress‐induced vasodilatation

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Ca2+-influx through TRP channels is believed to play a role in the synthesis of endothelial vasodilators. Here, we investigated function and expression of the TRPV4 channel in endothelial cells (EC) by using the in situ patch-clamp technique, single-cell-RT-PCR, Ca2+-imaging, and pressure-myograph experiments. In EC in situ, TRPV4-like currents were activated by the selective TRPV4-opener 4α-phorbol-12,13-didecanoate (4αPDD), arachidonic acid (AA), moderate warmth, and hypotonic stress. Single-cell-RT-PCR revealed expression of TRPV4, but none of the other closely related TRPV1-3. Activation of this endothelial TRPV4 by 4αPDD increased intracellular [Ca2+]i to 250 nM. In pressure-myograph experiments in carotid artery (CA) and small A. gracilis, intraluminal application of 4αPDD caused a robust vasodilatation by ≈80% (at 1 uM; KD 0.3 uM) which was strictly endothelium-dependent and was suppressed by the TRPV4-inhibitor ruthenium red (RuR). Wall shear stress (WSS)-induced vasodilatation was similarly blocked by RuR and was also prevented by inhibition of phospholipase A2 by AACOCF3. In the presence of inhibitors of NO- and prostacyclin-synthesis, 4αPDD and WSS did not produce considerable vasodilatation of CA whereas 4αPDD but not WSS caused vasodilatation of small A. gracilis. In conclusion, Ca2+-entry through endothelial TRPV4 channels triggers NO- and EDHF-dependent vasodilatation in rat endothelium. Since blockage of TRPV4 suppressed WSS-induced vasodilatation, TRPV4 seems to play a role in endothelial mechanosensing of WSS.