Physiological levels of fluid shear stress modulate vascular function through TRPV4 sparklets

Endothelial calcium (Ca2+) signaling plays a major role in regulating vasodilation in response to fluid shear stress (FSS) generated by blood flow. Local Ca2+ influx through single transient receptor potential channel subfamily V member 4 (TRPV4) (termed "sparklets") activated by low concentrations of chemical and biological stimuli has been revealed to modulate vascular function. However, the range in which FSS can initiate TRPV4 sparklets to induce vasodilation is unknown. Here, we assess the activity of TPRV4 sparklets induced by various physiological levels of FSS and investigate the mechanisms involving these Ca2+ signals in FSS-induced vasodilation. Intact small mesenteric arteries are used for Cav imaging with a GCaMP2(TRPV4-KO) mouse model and high-speed confocal systems. Markedly increased local Ca2+ signals are observed in the endothelium under 4-8 dyne/cm(2) FSS, whereas FSS > 8 dyne/cm(2) causes global Ca2+ influx. Further analysis shows that TRPV4 channels form a four-channel group to mediate Ca2+ sparklets under certain levels of FSS. The large Ca2+ influx hyperpolarizes endothelial cells by stimulating intermediate (IK)- and small (SK)-conductance Ca2+-sensitive potassium channels, leading to hyperpolarization of the surrounding smooth muscle cells and ultimately causing endothelium-dependent vasodilation. In conclusion, Ca2+ influx transits through a small number of endothelial TRPV4 channels opened by certain levels of FSS, which activates the Ca2+-sensitive IK and SK channels to cause vasodilation.