Nitric Oxide–Dependent Feedback Loop Regulates Transient Receptor Potential Vanilloid 4 (TRPV4) Channel Cooperativity and Endothelial Function in Small Pulmonary Arteries

BACKGROUND: Recent studies demonstrate that spatially restricted, local Ca(2+) signals are key regulators of endothelium‐dependent vasodilation in systemic circulation. There are drastic functional differences between pulmonary arteries (PAs) and systemic arteries, but the local Ca(2+) signals that control endothelium‐dependent vasodilation of PAs are not known. Localized, unitary Ca(2+) influx events through transient receptor potential vanilloid 4 (TRPV4) channels, termed TRPV4 sparklets, regulate endothelium‐dependent vasodilation in resistance‐sized mesenteric arteries via activation of Ca(2+)‐dependent K(+) channels. The objective of this study was to determine the unique functional roles, signaling targets, and endogenous regulators of TRPV4 sparklets in resistance‐sized PAs. METHODS AND RESULTS: Using confocal imaging, custom image analysis, and pressure myography in fourth‐order PAs in conjunction with knockout mouse models, we report a novel Ca(2+) signaling mechanism that regulates endothelium‐dependent vasodilation in resistance‐sized PAs. TRPV4 sparklets exhibit distinct spatial localization in PAs when compared with mesenteric arteries, and preferentially activate endothelial nitric oxide synthase (eNOS). Nitric oxide released by TRPV4‐endothelial nitric oxide synthase signaling not only promotes vasodilation, but also initiates a guanylyl cyclase‐protein kinase G‐dependent negative feedback loop that inhibits cooperative openings of TRPV4 channels, thus limiting sparklet activity. Moreover, we discovered that adenosine triphosphate dilates PAs through a P2 purinergic receptor‐dependent activation of TRPV4 sparklets. CONCLUSIONS: Our results reveal a spatially distinct TRPV4‐endothelial nitric oxide synthase signaling mechanism and its novel endogenous regulators in resistance‐sized PAs.