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

Abstract

Objective Several physiological stimuli activate smooth muscle cell (SMC) G(q)PCRs (G(q) protein-coupled receptors) to cause vasoconstriction. As a protective mechanism against excessive vasoconstriction, SMC G(q)PCR stimulation invokes endothelial cell vasodilatory signaling. Whether Ca2+ influx in endothelial cells contributes to the regulation of G(q)PCR-induced vasoconstriction remains unknown. Ca2+ influx through TRPV4 (transient receptor potential vanilloid 4) channels is a key regulator of endothelium-dependent vasodilation. We hypothesized that SMC G(q)PCR stimulation engages endothelial TRPV4 channels to limit vasoconstriction. Approach and Results Using high-speed confocal microscopy to record unitary Ca2+ influx events through TRPV4 channels (TRPV4 sparklets), we report that activation of SMC (1)ARs (alpha(1)-adrenergic receptors) with phenylephrine or thromboxane A(2) receptors with U46619 stimulated TRPV4 sparklets in the native endothelium from mesenteric arteries. Activation of endothelial TRPV4 channels did not require an increase in Ca2+ as indicated by the lack of effect of L-type Ca2+ channel activator or chelator of intracellular Ca2+ 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 G(q)PCR stimulation triggers inositol 1,4,5-trisphosphate-dependent activation of endothelial TRPV4 channels to limit vasoconstriction.