Abstract 11751: Multiple Mechanisms Are Involved in Enhanced Endothelium-Derived Hyperpolarizing Factor(EDHF)-Mediated Responses in Microvessels in Mice -A Clue for Novel Strategy for Vascular Protection
Background: Endothelium-derived hyperpolarizing factor (EDHF) plays an important role in organ protection by modulating vascular tone, especially in microvessels. We have demonstrated in animals and humans that endothelium-derived hydrogen peroxide (H2O2) is an EDHF and that endothelial nitric oxide synthase (eNOS) is a major source of EDHF/H2O2. We also have demonstrated that endothelial NOSs play diverse roles depending on vessel size, as a NO generating system in conduit arteries and as an EDHF/H2O2 generating system in resistance arteries. However, the molecular mechanisms for the enhanced EDHF-mediated responses in microvessels remain to be elucidated.
Methods: We used male wild-type (WT) mice and caveolin-1-deficient mice (Cav-1-/-). We used the aorta (Ao) and mesenteric arteries (MA) as conduit and resistance arteries. Isometric tension was recorded in organ chamber experiments and membrane potential by microelectrode technique.
Results: Both EDHF-mediated relaxations to acetylcholine (ACh) and vascular smooth muscle (VSM) relaxations to exogenous H2O2 were enhanced in MA as compared with Ao. Quantitatively, the contribution of the former to the enhanced EDHF-mediated responses in MA was much greater than the latter. In the endothelium, the extent of eNOS phosphorylation at Ser1177 (stimulatory site) was significantly decreased and that at Thr495(inhibitory site) was significantly enhanced in MA than in Ao, indicating functional inhibition of eNOS under physiological conditions. We then examined molecular mechanisms involved in the intracellular signaling for eNOS activation. STO-609, an inhibitor of CaMKKβ significantly reduced EDHF-mediated relaxations and hyperpolarizations to ACh in MA but not in Ao. In Cav-1-/- mice, EDHF-mediated relaxations and hyperpolarizations to ACh were significantly attenuated in MA but not in Ao. In VSM, the inhibition of protein kinase G1α (PKG1α) significantly reduced relaxations and hyperpolarizations to exogenous H2O2 in MA but not in Ao.
Conclusions: These results indicate that CaMKKβ and caveolin-1 (at endothelial level) and PKG1α (at VSMC level) are involved in enhanced EDHF-mediated responses in microvessels, providing clues for novel strategy for vascular protection.
- © 2011 by American Heart Association, Inc.