Elementary Ca ²⁺ Signals Through Endothelial TRPV4 Channels Regulate Vascular Function

Abstract

Major features of the transcellular signaling mechanism responsible for endothelium-dependent regulation of vascular smooth muscle tone are unresolved. We identified local calcium (Ca2+) signals (“sparklets”) in the vascular endothelium of resistance arteries that represent Ca2+ influx through single TRPV4 cation channels. Gating of individual TRPV4 channels within a four-channel cluster was cooperative, with activation of as few as three channels per cell causing maximal dilation through activation of endothelial cell intermediate (IK)- and small (SK)-conductance, Ca2+-sensitive potassium (K+) channels. Endothelial-dependent muscarinic receptor signaling also acted largely through TRPV4 sparklet-mediated stimulation of IK and SK channels to promote vasodilation. These results support the concept that Ca2+ influx through single TRPV4 channels is leveraged by the amplifier effect of cooperative channel gating and the high Ca2+ sensitivity of IK and SK channels to cause vasodilation.

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

“…Endothelial denudation was performed by passing an air bubble through the artery for ≈60 s. Complete removal of the endothelial layer was verified by the absence of dilation to NS309. Changes in arterial diameter were recorded at a 60‐ms frame rate using a charge‐coupled device camera and edge‐detection software (IonOptix LLC, Westwood, MA) 4, 5. All drug treatments were incubated for 10 minutes.…”

“…Measurement of Ca 2+ events in the native ECs from PAs was performed as previously described 4, 5. Briefly, Andor Revolution WD (with Borealis) spinning‐disk confocal imaging system described above was used to record Ca 2+ influx events in en face PAs.…”

“…Recent studies in systemic arteries—including mesenteric, cremaster, and cerebral arteries—have demonstrated that endothelium‐dependent vasodilation is controlled by local, spatially restricted increases in endothelial Ca 2+ while the whole‐cell Ca 2+ level remains unchanged 1, 2, 3, 4, 5. In contrast to systemic arteries, pulmonary arteries (PAs) comprise a low‐pressure, high‐flow circulation.…”

“…In mesenteric arteries, local, unitary Ca 2+ influx events through endothelial TRPV4 channels, termed “TRPV4 sparklets,” activated endothelial IK/SK (Ca 2+ ‐activated intermediate and small conductance K + ) channels to cause vasodilation 4, 5. The biophysical properties, signaling targets, and endogenous regulators of TRPV4 sparklets in small PAs remain unknown.…”

“…Whether a specific local Ca 2+ signal can activate eNOS has not been elucidated. In this study, we explored the possibility that local, unitary Ca 2+ influx through TRPV4 channels activates eNOS in small PAs, a signaling mechanism different from small mesenteric/cremaster/cerebral arteries 1, 4, 7…”