Our view of the endothelium was transformed around 30 years ago, from one of an inert barrier to that of a key endocrine organ central to cardiovascular function. This dramatic change followed the discoveries that endothelial cells (ECs) elaborate the vasodilators prostacyclin and nitric oxide. The key to these discoveries was the use of the quintessentially pharmacological technique of bioassay. Bioassay also revealed endothelium-derived hyperpolarizing factor (EDHF), particularly important in small arteries and influencing blood pressure and flow distribution. The basic idea of EDHF as a diffusible factor causing smooth muscle hyperpolarization (and thus vasodilatation) has evolved into one of a complex pathway activated by endothelial Ca 2+ opening two Ca 2+ -sensitive K + -channels, KCa2.3 and KCa3.1. Combined application of apamin and charybdotoxin blocked EDHF responses, revealing the critical role of these channels as iberiotoxin was unable to substitute for charybdotoxin. We showed these channels are arranged in endothelial microdomains, particularly within projections towards the adjacent smooth muscle, and close to interendothelial gap junctions. Activation of KCa channels hyperpolarizes ECs, and K + efflux through them can act as a diffusible 'EDHF' stimulating Na + /K + -ATPase and inwardly rectifying K-channels. In parallel, hyperpolarizing current can spread from the endothelium to the smooth muscle through myoendothelial gap junctions upon endothelial projections. The resulting radial hyperpolarization mobilized by EDHF is complemented by spread of hyperpolarization along arteries and arterioles, effecting distant dilatation dependent on the endothelium. So the complexity of the endothelium still continues to amaze and, as knowledge evolves, provides considerable potential for novel approaches to modulate blood pressure. LINKED ARTICLES AbbreviationsBKCa, large conductance Ca 2+ -sensitive K + -channels; CaSR, calcium-sensing receptors; Cx, connexin; CyPPA, N-cyclohexyl-N-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidinamine; EDH, endothelium-dependent hyperpolarization; EDRF, endothelium-derived relaxing factor; EET, epoxyeicosatetraenoic acid; EDHF, endotheliumdependent hyperpolarizing factor; IKCa, intermediate conductance Ca 2+ -sensitive K + -channels; InsP3, inositol trisphosphate; KCa, Ca 2+ -sensitive K + channels; NO, nitric oxide; KATP, ATP-sensitive K + -channels; KIR, inwardly-rectifying K + -channels; Kv, voltage-gated K + -channels; MEGJ, myoendothelial gap junctions; Na + /K + -ATPase, sodium and potassium dependent adenosine triphosphatase; PGI2, prostaglandin I2; SKCa, small conductance Ca 2+ -sensitive K + -channels; TRP, transient receptor potential This review was inspired by the 2009 JR Vane Lecture, delivered by the first author in the Summer of that year at the Edinburgh BPS meeting. It tracks our perspective of the key discoveries and the development of understanding of the pathway commonly referred to as endothelium-derived hyperpolarizing factor or EDHF. As such, it i...
Relaxation of the methoxamine‐precontracted rat small mesenteric artery by endothelium‐derived hyperpolarizing factor (EDHF) was compared with relaxation to the cannabinoid, anandamide (arachidonylethanolamide). EDHF was produced in a concentration‐ and endothelium‐dependent fashion in the presence of NG‐nitro‐l‐arginine methyl ester (l‐NAME, 100 μm) by either carbachol (pEC50 [negative logarithm of the EC50]=6.19±0.01, Rmax [maximum response]=93.2±0.4%; n=14) or calcium ionophore A23187 (pEC50=6.46±0.02, Rmax=83.6±3.6%; n=8). Anandamide responses were independent of the presence of endothelium or l‐NAME (control with endothelium: pEC50=6.31±0.06, Rmax=94.7±4.6%; n=10; with l‐NAME: pEC50=6.33±0.04, Rmax=93.4±6.0%; n=4). The selective cannabinoid receptor antagonist, SR 141716A (1 μm) caused rightward shifts of the concentration‐response curves to both carbachol (2.5 fold) and A23187 (3.3 fold). It also antagonized anandamide relaxations in the presence or absence of endothelium giving a 2 fold shift in each case. SR 141716A (10 μm) greatly reduced the Rmax values for EDHF‐mediated relaxations to carbachol (control, 93.2±0.4%; SR 141716A, 10.7±2.5%; n=5; P<0.001) and A23187 (control, 84.8±2.1%; SR 141716A, 3.5±2.3%; n=6; P<0.001) but caused a 10 fold parallel shift in the concentration‐relaxation curve for anandamide without affecting Rmax. Precontraction with 60 mm KCl significantly reduced (P<0.01; n=4 for all) relaxations to 1 μm carbachol (control 68.8±5.6% versus 17.8±7.1%), A23187 (control 71.4±6.1% versus 3.9±0.45%) and anandamide (control 71.1±7.0% versus 5.2±3.6%). Similar effects were seen in the presence of 25 mm K+. Incubation of vessels with pertussis toxin (PTX; 400 ng ml−1, 2 h) also reduced (P<0.01; n=4 for all) relaxations to 1 μm carbachol (control 63.5±7.5% versus 9.0±3.2%), A23187 (control 77.0±5.8% versus 16.2±7.1%) and anandamide (control 89.8±2.2% versus 17.6±8.7%). Incubation of vessels with the protease inhibitor phenylmethylsulphonyl fluoride (PMSF; 200 μm) significantly potentiated (P<0.01), to a similar extent (∼2 fold), relaxation to A23187 (pEC50: control, 6.45±0.04; PMSF, 6.74±0.10; n=4) and anandamide (pEC50: control, 6.31±0.02; PMSF, 6.61±0.08; n=8). PMSF also potentiated carbachol responses both in the presence (pEC50: control, 6.25±0.01; PMSF, 7.00±0.01; n=4; P<0.01) and absence (pEC50: control, 6.41±0.04; PMSF, 6.88±0.04; n=4; P<0.001) of l‐NAME. Responses to the nitric oxide donor S‐nitroso‐N‐acetylpenicillamine (SNAP) were also potentiated by PMSF (pEC50: control, 7.51±0.06; PMSF, 8.00±0.05, n=4, P<0.001). EDHF‐mediated relaxation to carbachol was significantly attenuated by the K+ channel blocker tetraethylammonium (TEA; 1 mm) (pEC50: control, 6.19±0.01; TEA, 5.61±0.01; n=6; P<0.01). In contrast, TEA (1 mm) had no effect on EDHF‐mediated relaxation to A23187 (pEC50: control, 6.47±0.04; TEA, 6.41±0.02, n=4) or on anandamide (pEC50: control, 6.28±0.06; TEA, 6.09±0.02; n=5). TEA (10 mm) significantly (P<0.01) reduced the Rmax for anandamide (control, 94.3±4.0%; 10 mm TEA, 60.7...
Nitric oxide (NO • ) competitively inhibits oxygen consumption by mitochondria at cytochrome c oxidase and S-nitrosates thiol proteins. We developed mitochondria-targeted S-nitrosothiols (MitoSNOs) that selectively modulate and protect mitochondrial function. The exemplar MitoSNO1, produced by covalently linking an Snitrosothiol to the lipophilic triphenylphosphonium cation, was rapidly and extensively accumulated within mitochondria, driven by the membrane potential, where it generated NO • and Snitrosated thiol proteins. MitoSNO1-induced NO • production reversibly inhibited respiration at cytochrome c oxidase and increased extracellular oxygen concentration under hypoxic conditions. MitoSNO1 also caused vasorelaxation due to its NO • generation. Infusion of MitoSNO1 during reperfusion was protective against heart ischemia-reperfusion injury, consistent with a functional modification of mitochondrial proteins, such as complex I, following S-nitrosation. These results support the idea that selectively targeting NO • donors to mitochondria is an effective strategy to reversibly modulate respiration and to protect mitochondria against ischemia-reperfusion injury.nitric oxide ͉ S-nitrosation
The binding of one irreversible and two reversible radioactive antagonists to muscarinic receptors in synaptosome preparations of rat cerebral cortex has been studied. The ligands all bind to the same receptor pool and directly and competitively yield self-consistent binding constants closely similar to those obtained by pharmacological methods on intact smooth muscle. The binding process for antagonists seems to be a simple mass action-determined process with a Hill slope of 1.0. The quantitative correlations strongly support the view that the receptor studied by ligand binding corresponds to the receptor studied by pharmacological methods. Inhibition of antagonist binding by most agonists shows a reduced Hill slope which also applies to direct binding studies of [3H] acetylcholine. Mechansims that might account for the behavior of agonists are discussed but do not conclusively point to any single mechanism.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.