Abstract 1287: TRPV4-Deficient Mice Exhibit Impaired Endothelium-Dependent Relaxation Induced by Acetylcholine in Vitro and in Vivo

Agonist-induced Ca 2+ entry in endothelial cells is important for the synthesis and release of vasoactive factors, although mechanisms of Ca 2+ entry remain largely unknown. Emerging evidence suggests that the transient receptor potential vanilloid 4 (TRPV4) channel, a Ca 2+ -permeant TRP channel, is expressed in endothelial cells and may be involved in the regulation of vascular tone. Here we investigated the potential role of TRPV4 channels in acetylcholine-induced vasodilation in vitro and in vivo using the TRPV4 knockout (TRPV4 −/− ) mice model. Carotid arteries were isolated and preconstricted with the thromboxane A2 mimetic U46619. Concentration-dependent relaxations to acetylcholine (10 −9 –10 −5 M) were markedly reduced in carotids of TRPV4 −/− vs. wild-type (WT) mice (maximal relaxations of 31±12% vs 53±4%, respectively; n=4 mice). There was no significant change in the ED50 for Ach. In both WT and TRPV4 −/− , acetylcholine-induced relaxations were blocked and converted to constrictions by the NO synthase inhibitor L-NAME (maximal relaxations of −25±6% and −24±7%, respectively). There was no difference in papaverine-induced relaxations between WT and TRPV4 −/− mice (maximal relaxations of 93±3% vs. 90±3%, respectively). U46619 caused similar contractions in carotid arteries from those mice. We also compared in vivo vasodilator effects of acetylcholine by measuring changes in blood pressure in those animals. Intravenous administration of acetylcholine (15 ng/gm bolus) decreased blood pressure by 32±6 mmHg in WT mice (from 90±15 to 57±10 mmHg; n=6), whereas blood pressure was reduced by only 10 mmHg in TRPV4 −/− mice (from 67±6 to 56±4 mmHg; n=12). Acetylcholine caused similar reductions in heart rate in WT and TRPV4 −/− mice, with mean changes of 365±57 and 292±40 beats/min, respectively. We conclude that the endothelium-dependent vasodilator response to acetylcholine is reduced both in vitro and in vivo in TRPV4 −/− mice, and these findings may provide novel insight into the mechanisms of Ca 2+ entry evoked by chemical agonists in endothelial cells. The paradoxically lower baseline blood pressure in TRPV4 −/− mice requires further investigation.