Abstract 1289: Activation of the Transient Receptor Potential V4 Channel Causes Cardiovascular Collapse Mediated by Endothelial Failure
Transient receptor potential V4 (TRPV4), is an osmo/mechano-sensitive ligand-gated non-selective cationic channel that contributes to intracellular Ca2+ homeostasis and regulation of cell volume. TRPV4 is highly expressed in endothelial and various epithelial cells and to a lesser extent in vascular smooth muscle. The purpose of the present study was to evaluate the cardiovascular effects of a potent novel small molecule TRPV4 activator (TRPV4A; EC50 = 19, 8 or 1 nM in mouse, rat or dog, respectively) and to examine its mechanism of action. In the three species (mouse, rat and dog) examined, the intravenous administration of TRPV4A in anesthetized preparations induced a dose-dependent reduction in blood pressure, followed by cardiovascular collapse at doses ≤300 ug/kg. TRPV4A had no acute cardiovascular effects in the TRPV4−/− null mouse (>5 mg/kg, iv). Hemodynamic analysis in the dog suggested that the terminal event was related to a profound reduction in cardiac output (decreased SV followed by decreased HR). However, TRPV4A had no effect on rate or contractility in the isolated, buffer-perfused rat heart. In contrast, TRPV4A produced potent endothelial-dependent relaxation of rodent isolated vascular ring segments that was abolished by NOS inhibition (L-NAME) and eNOS gene deletion. Surprisingly, the in vivo cardiovascular collapse induced by TRPV4A was not altered by NOS inhibition (L-NAME), eNOS gene deletion or by treatment with anticoagulant or antiplatelet agents. Cardiovascular collapse induced by TRPV4A was correlated (concentration and time appropriate) with profound fluid extravasation (Evans Blue) and tissue hemorrhage in the lung, intestine and kidney. Consistent with these results, TRPV4A induced a ruthenium-red sensitive non-selective cation current, reduction in cell volume and subsequent cell death in cultured endothelial cells. These results provide the first characterization of the cardiovascular effects of a potent and selective TRPV4 channel activator and suggest that inappropriate activation of TRPV4 produces acute cardiovascular collapse associated with endothelial activation/injury and failure of the microvascular permeability barrier.