Abstract
Since its discovery in 2000, an increasing body of evidence has demonstrated the importance of the transient receptor potential vanilloid 4 (TRPV4) ion channel in regulating two critical components of endothelial function, namely the control of vascular tone and permeability. However, our understanding of both mechanisms is incomplete. TRPV4 modulates vascular tone by activating endothelial nitric oxide and endothelial-derived hyperpolarization factor pathways. In this thesis, evidence is provided linking TRPV4 activation to the release of vasoactive prostaglandins. Pharmacological TRPV4 activation elicited a striking release of prostaglandins both in vivo, in rats and in vitro from human umbilical vein endothelial cells (HUVECs). Prostaglandin release in vivo in rats contributed to the noted blood pressure reducing effect associated with the TRPV4 activator GSK1016790A. Moreover, TRPV4-mediated prostanoid release in rats also appeared to counteract the lung permeability increase , assessed by lung wet weight, also associated with this agent. In subsequent experiments, the mechanism by which TRPV4 mediates increases in vascular permeability were explored in vitro, using a HUVEC detachment assay. The results obtained demonstrate that two selective, structurally distinct TRPV4 activators, GSK1016790A and GSK634775, elicit divergent endothelial detachment responses in vitro, whereby both increase intracellular calcium levels but only GSK1016790A induced detachment. Surprisingly, the mechanism of GSK1016790A-mediated detachment was found to be independent of intracellular calcium or cytoskeletal modulation, but was mediated in part by activation of PKC and disruption of the plasma membrane. These findings demonstrate that TRPV4 couples to prostaglandin-generating pathways in endothelial cells. The release of these prostanoids may play a role in modulating blood pressure and endothelial permeability, which may be of relevance in hypertensive states. In addition, these studies also highlight an intriguing differential coupling of TRPV4 channels in isolated endothelial cells in response to structurally distinct agonists.