The endothelium controls vascular tone not only by releasing NO and prostacyclin, but also by other pathways causing hyperpolarization of the underlying smooth muscle cells. This characteristic was at the origin of the term ‘endothelium-derived hyperpolarizing factor’ (EDHF). However, this acronym includes different mechanisms. Arachidonic acid metabolites derived from the cyclo-oxygenases, lipoxygenases and cytochrome P450 pathways, H2O2, CO, H2S and various peptides can be released by endothelial cells. These factors activate different families of K+ channels and hyperpolarization of the vascular smooth muscle cells contribute to the mechanisms leading to their relaxation. Additionally, another pathway associated with the hyperpolarization of both endothelial and vascular smooth muscle cells contributes also to endothelium-dependent relaxations (EDHF-mediated responses). These responses involve an increase in the intracellular Ca2+ concentration of the endothelial cells, followed by the opening of SKCa and IKCa channels (small and intermediate conductance Ca2+-activated K+ channels respectively). These channels have a distinct subcellular distribution: SKCa are widely distributed over the plasma membrane, whereas IKCa are preferentially expressed in the endothelial projections toward the smooth muscle cells. Following SKCa activation, smooth muscle hyperpolarization is preferentially evoked by electrical coupling through myoendothelial gap junctions, whereas, following IKCa activation, K+ efflux can activate smooth muscle Kir2.1 and/or Na+/K+-ATPase. EDHF-mediated responses are altered by aging and various pathologies. Therapeutic interventions can restore these responses, suggesting that the improvement in the EDHF pathway contributes to their beneficial effect. A better characterization of EDHF-mediated responses should allow the determination of whether or not new drugable targets can be identified for the treatment of cardiovascular diseases.
- cell membrane potential
- endothelium-derived hyperpolarizing factor (EDHF)
- myoendothelial gap junction
- potassium channel
Abbreviations: AngII, angiotensin II; CaV channel, voltage-dependent Ca2+ channel; CNP, C-type natriuretic peptide; COX, cyclo-oxygenase; CSE, cystathionine γ-lyase; Cx, connexin; EBIO, ethyl-2-benzimidazolinone; EC, endothelial cell; EDHF, endothelium-derived hyperpolarizing factor; EET, epoxyeicosatrienoic acid; HETE, hydroxyeicosatetraenoic acid; HO, haem oxygenase; KATP channel, ATP-sensitive K+ channel; KCa channel, Ca2+-activated K+ channel; BKCa channel, large conductance KCa channel; IKCa channel, intermediate conductance KCa channel; IP receptor, PGI2 receptor; KIR channel, inward rectifier K+ channel; LOX, lipoxygenase; NOS, NO synthase; eNOS, endothelial NOS; NPR, natriuretic peptide receptor; O2−, superoxide anion; PGI2, prostacyclin; ROS, reactive oxygen species; SKCa channel, small conductance KCa channel; SMC, smooth muscle cell; SOD, superoxide dismutase; THETA, trihydroxyeicosatrienoic acid; TRPC, transient receptor potential canonical channel; TRPV, transient receptor potential vanilloid channel; VSMC, vascular SMC
- © The Authors Journal compilation © 2009 Biochemical Society