TRPV4 (Transient Receptor Potential Vanilloid 4) Channel-Dependent Negative Feedback Mechanism Regulates G Protein-Coupled Receptor-Induced Vasoconstriction.

Objective: Several physiological stimuli activate smooth muscle cell (SMC) GPCRs (G protein-coupled receptors) to cause vasoconstriction. As a protective mechanism against excessive vasoconstriction, SMC GPCR stimulation invokes endothelial cell vasodilatory signaling. Whether Ca influx in endothelial cells contributes to the regulation of GPCR-induced vasoconstriction remains unknown. Ca influx through TRPV4 (transient receptor potential vanilloid 4) channels is a key regulator of endothelium-dependent vasodilation. We hypothesized that SMC GPCR stimulation engages endothelial TRPV4 channels to limit vasoconstriction.

Approach And Results: Using high-speed confocal microscopy to record unitary Ca influx events through TRPV4 channels (TRPV4 sparklets), we report that activation of SMC αARs (alpha-adrenergic receptors) with phenylephrine or thromboxane A receptors with U46619 stimulated TRPV4 sparklets in the native endothelium from mesenteric arteries. Activation of endothelial TRPV4 channels did not require an increase in Ca as indicated by the lack of effect of L-type Ca channel activator or chelator of intracellular Ca EGTA-AM. However, gap junction communication between SMCs and endothelial cells was required for phenylephrine activation or U46619 activation of endothelial TRPV4 channels. Lowering inositol 1,4,5-trisphosphate levels with phospholipase C inhibitor or lithium chloride suppressed phenylephrine activation of endothelial TRPV4 sparklets. Moreover, uncaging inositol 1,4,5-trisphosphate profoundly increased TRPV4 sparklet activity. In pressurized arteries, phenylephrine-induced vasoconstriction was followed by a slow, TRPV4-dependent vasodilation, reflecting activation of negative regulatory mechanism. Consistent with these data, phenylephrine induced a significantly higher increase in blood pressure in TRPV4 mice.

Conclusions: These results demonstrate that SMC GPCR stimulation triggers inositol 1,4,5-trisphosphate-dependent activation of endothelial TRPV4 channels to limit vasoconstriction.