Abstract 1307: TRPV4 Plays a Crucial Role in NO- and Prostacyclin-independent, Flow-induced Vasodilation
We previously reported that cytochrome P450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) activate the transient receptor potential (TRP)V4 channel in vascular endothelial cells. TRPV4 activation leads to an influx of Ca2+ that can then induce endothelial hyperpolarization via small and intermediate conductance Ca2+-activated potassium channels (SKCa and IKCa). In vitro studies have also shown activation of TRPV4 in response to mechanical stimuli, such as shear stress, which also elicits endothelium-dependent vasodilation via nitric oxide and prostacyclin-dependent, as well as -independent mechanisms. We therefore hypothesized that the TRPV4 channel is involved in the flow-induced vasodilation attributed to the endothelium derived hyperpolarization factor (EDHF). Carotid arteries from TRPV4-deficient mice and their wild-type littermates were constricted with phenylephrine and subjected to step-wise increases in luminal flow. In the presence of L-NAME and diclofenac, arteries from wild-type mice displayed a considerable flow-induced vasodilation (up to 70 ± 6%, n=7). This response to flow was markedly reduced in TRPV4 −/− mice in which maximal dilation reached only 41 ± 4% (n=8, P<0.001). Since in our hands activation of TRP channels was not associated with alterations in phosphorylation, we assessed whether translocation can explain their activation. In unstimulated human endothelial cells, TRPC3 and TRPC6 fusion proteins were detected around the nucleus, but not in the plasma membrane. Stimulation of these cells with ionomycin induced the translocation of TRP channels to the plasma membrane. When intracellular EET production was enhanced by overexpressing CYP2C9, however, agonist-induced TRP channel translocation was much more pronounced. We conclude that the TRPV4 channel is involved in flow-induced, endothelium-dependent vasodilation of murine carotid arteries. Moreover, flow-induced EET-production leads to activation of TRP channels by a mechanism involving their translocation and insertion into the plasma membrane.