The role of TRPV4 in flow-mediated inhibition of rat mesenteric collecting lymphatic vessel pumping

Abstract

Lymphatic contractility is modulated by transmural pressure and shear stress exerted by the lymph on the lymphatic vessel wall. It has previously been shown that in rat mesenteric collecting lymphatic vessels, lymph flow inhibits lymphatic contractility in an endothelial nitric oxide synthase (eNOS) dependent manner. However, the molecular elements responsible for the activation of this signaling pathway are not known. TRPV4 is a non-selective cation permeable channel ubiquitously expressed throughout the body. It promotes calcium entry and has been shown to contribute to blood flow dependent vasodilation but its role in lymphatics under conditions of flow has yet to be determined. It is expressed in lymphatic vessels and promotes the entry of Ca2+ upon stimulation with classical NO-dependent pathway agonists, resulting in endothelial cell depolarization. This is imperative since lymph flow and transport is required to maintain tissue fluid homeostasis within the body. In our study, we postulated that TRPV4 contributes to flow-induced collecting lymphatic relaxation in a NO-dependent, endothelium-dependent manner. In the current study qPCR was used to determine TRPV4 gene expression along with the expression levels of other mechanosensitive TRP channels. Immunofluorescence was used to determine TRPV4 protein expression within whole lymphatic vessels and in rat lymphatic endothelial cells. Pressure myography allowed for the determination of TRPV4 function under conditions of flow within lymphatic vessels and the implications of TRPV4 agonism under no flow conditions at a set transmural pressure. The results obtained implicate the expression of TRPV4 on both the smooth muscle and endothelial layers with agonism triggering a biphasic response. They also indicate a role for TRPV4, nitric oxide, and dilatory prostaglandins in rat mesenteric lymphatic vessels in modulating flow-induced decreases in contractile activity.