Endothelium-Dependent Hyperpolarization: The Evolution of Myoendothelial Microdomains

Nitric oxide, endothelium-derived hyperpolarizing factor, and smooth muscle-dependent mechanisms contribute to magnesium-dependent vascular relaxation in mouse arteries

AIM

Magnesium (Mg2+ ) is a vasorelaxant. The underlying physiological mechanisms driving this vasorelaxation remain unclear. Studies were designed to test the hypothesis that multiple signaling pathways including nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) in endothelial cells as well as Ca2+ antagonization and TRPM7 channels in vascular smooth muscle cells mediate Mg2+ -dependent vessel relaxation.

METHODS

To uncover these mechanisms, force development was measured ex vivo in aorta rings from mice using isometric wire myography. Concentration responses to Mg2+ were studied in intact and endothelium-denuded aortas. Key findings were confirmed in second-order mesenteric resistance arteries perfused ex vivo using pressure myography. Effects of Mg2+ on NO formation were measured in Chinese Hamster Ovary (CHO) cells, isolated mesenteric vessels, and mouse urine.

RESULTS

Mg2+ caused a significant concentration-dependent relaxation of aorta rings. This relaxation was attenuated significantly in endothelium-denuded aortas. The endothelium-dependent portion was inhibited by NO and cGMP blockade but not by cyclooxygenase inhibition. Mg2+ stimulated local NO formation in CHO cells and isolated mesenteric vessels without changing urinary NOx levels. High extracellular Mg2+ augmented acetylcholine-induced relaxation. SKCa and IKCa channel blockers apamin and TRAM34 inhibited Mg2+ -dependent relaxation. The endothelium-independent relaxation in aorta rings was inhibited by high extracellular Ca2+ . Combined blockade of NO, SKCa , and IKCa channels significantly reduced Mg2+ -dependent dilatation in mesenteric resistance vessels.

CONCLUSIONS

In mouse conductance and resistance arteries Mg2+ -induced relaxation is contributed by endothelial NO formation, EDHF pathways, antagonism of Ca2+ in smooth muscle cells, and additional unidentified mechanisms.

Cardiac energy depletion in a rat model of polycystic ovarian syndrome is reversed by acetate and associated with inhibitory effect of HDAC2/mTOR

In addition to the clinical manifestation of polycystic ovarian syndrome (PCOS), life-threatening diseases, especially hypertension and cardiovascular disease (CVD) are emerging critical complications of PCOS. Changes in cardiac energy remains an independent risk factor of CVD. Histone deacetylase (HDAC) inhibitors, including acetate has received attention for its beneficial role in energy regulation. Herein we hypothesized that acetate improves cardiac energy homeostasis in experimentally induced PCOS. Female Wistar rats (8-week-old) were divided into groups. To induce PCOS, 1 mg/kg of letrozole was given for 21 days. After confirmation of PCOS, acetate (200 mg/kg) was administered for 6 weeks. Rats with PCOS showed multiple ovarian cysts with androgen excess and decreased SHBG. The rats also manifested impaired glucose tolerance/hyperinsulinemia and hypertriglyceridemia. Increased systemic oxidative stress (malondialdehyde)/inflammatory (NF-kB/SDF-1) markers and nitric oxide deficiency (NO/eNOS) were observed. Though, the body weight was increased without affecting the cardiac mass index of PCOS rats. Nevertheless, there was an increase in cardiac triglyceride and oxidative stress/inflammatory markers with consequent cardiac injury, revealed by decreased levels of SIRT-1/HIF-1α and increased levels of CTGF/TGFβ-1 and plasma troponin T. These led to cardiac ATP depletion with increased AMP and AMP/ATP ratio. These alterations were accompanied by elevated levels of mTOR and HDAC2, which were reversed when treated with acetate. The present results interestingly suggest that HDAC2 inhibition by acetate reversed cardiac energy depletion and attendant cardiomorbidities in experimental PCOS model. A beneficial effect that is accompanied by suppressed expression of mTOR.

Cracking the Endothelial Calcium (Ca2+) Code: A Matter of Timing and Spacing

A monolayer of endothelial cells lines the innermost surface of all blood vessels, thereby coming into close contact with every region of the body and perceiving signals deriving from both the bloodstream and parenchymal tissues. An increase in intracellular Ca2+ concentration ([Ca2+]i) is the main mechanism whereby vascular endothelial cells integrate the information conveyed by local and circulating cues. Herein, we describe the dynamics and spatial distribution of endothelial Ca2+ signals to understand how an array of spatially restricted (at both the subcellular and cellular levels) Ca2+ signals is exploited by the vascular intima to fulfill this complex task. We then illustrate how local endothelial Ca2+ signals affect the most appropriate vascular function and are integrated to transmit this information to more distant sites to maintain cardiovascular homeostasis. Vasorelaxation and sprouting angiogenesis were selected as an example of functions that are finely tuned by the variable spatio-temporal profile endothelial Ca2+ signals. We further highlighted how distinct Ca2+ signatures regulate the different phases of vasculogenesis, i.e., proliferation and migration, in circulating endothelial precursors.

Impact of aging on vascular ion channels: perspectives and knowledge gaps across major organ systems

Individuals aged ≥65 yr will comprise ∼20% of the global population by 2030. Cardiovascular disease remains the leading cause of death in the world with age-related endothelial "dysfunction" as a key risk factor. As an organ in and of itself, vascular endothelium courses throughout the mammalian body to coordinate blood flow to all other organs and tissues (e.g., brain, heart, lung, skeletal muscle, gut, kidney, skin) in accord with metabolic demand. In turn, emerging evidence demonstrates that vascular aging and its comorbidities (e.g., neurodegeneration, diabetes, hypertension, kidney disease, heart failure, and cancer) are "channelopathies" in large part. With an emphasis on distinct functional traits and common arrangements across major organs systems, the present literature review encompasses regulation of vascular ion channels that underlie blood flow control throughout the body. The regulation of myoendothelial coupling and local versus conducted signaling are discussed with new perspectives for aging and the development of chronic diseases. Although equipped with an awareness of knowledge gaps in the vascular aging field, a section has been included to encompass general feasibility, role of biological sex, and additional conceptual and experimental considerations (e.g., cell regression and proliferation, gene profile analyses). The ultimate goal is for the reader to see and understand major points of deterioration in vascular function while gaining the ability to think of potential mechanistic and therapeutic strategies to sustain organ perfusion and whole body health with aging.

Cooling-induced cutaneous vasodilatation is mediated by small-conductance, calcium-activated potassium channels in tail arteries from male mice

Cooling causes cutaneous dilatation to restrain cold-induced constriction and prevent tissue injury. Cooling increases communication through myoendothelial gap junctions (MEGJs), thereby increasing endothelium-derived hyperpolarization (EDH)-type dilatation. EDH is initiated by calcium-activated potassium channels (KCa ) activated by endothelial stimuli or muscle-derived mediators traversing MEGJs (myoendothelial feedback). The goal of this study was to determine the individual roles of KCa with small (SK3) and intermediate (IK1) conductance in cooling-induced dilatation. Vasomotor responses of mice isolated cutaneous tail arteries were analyzed by pressure myography at 37°C and 28°C. Cooling increased acetylcholine-induced EDH-type dilatation during inhibition of NO and prostacyclin production. IK1 inhibition did not affect dilatations to acetylcholine, whereas SK3 inhibition inhibited dilatation at both temperatures. Cooling uncovered myoendothelial feedback to inhibit constrictions in U46619. IK1 inhibition did not affect U46619 constrictions, whereas SK3 inhibition abolished the inhibitory effect of cooling without affecting U46619 constriction at 37°C. Immunoblots confirmed SK3 expression, which was localized (immunofluorescence) to holes in the internal elastic lamina consistent with myoendothelial projections. Immunoblots and Immunofluorescence did not detect IK1. Studies in non-cutaneous arteries have highlighted the predominant role of IK1 in EDH-type dilatation. Cutaneous arteries are distinctly reliant on SK3, which may enable EDH-type dilation to be amplified by cooling.

Codonopsis lanceolata Extract Restores Smooth Muscle Vasorelaxation in Rat Carotid Arteries Even under High Extracellular K+ Concentrations

Recent studies showed that Codonopsis lanceolata (CL) has antihypertensive effects. However, to date, no study has examined the effects of CL on vascular tone under a high extracellular K+ concentration ([K+]o). Thus, the present study examined the effect of an extract of Codonopsis lanceolata (ECL) on the vascular tension of rat carotid arteries exposed to high [K+]o. We used myography to investigate the effect of an ECL on the vascular tension of rat carotid arteries exposed to high [K+]o and the underlying mechanism of action. In arteries with intact endothelia, the ECL (250 μg/mL) had no effect on vascular tension in arteries exposed to normal or high [K+]o. In contrast, the ECL significantly increased vasorelaxation in endothelium-impaired arteries exposed to a physiologically normal or high [K+]o compared with control arteries exposed to the same [K+]o conditions in the absence of ECL. This vasorelaxing action was unaffected by a broad-spectrum K+ channel blocker and an ATP-sensitive K+ channel blocker. The ECL significantly inhibited the vasoconstriction induced by Ca2+ influx through voltage-dependent Ca2+ channels (VDCCs) but not Ca2+ influx induced via receptor-operated Ca2+ channels or the release of Ca2+ from the sarcoplasmic reticulum in the vascular smooth muscle. In summary, our study reveals that the ECL acts through VDCCs in vascular smooth muscle to promote the recovery of vasorelaxation even in arteries exposed to high [K+]o in the context of endothelial dysfunction and provides further evidence of the vascular-protective effects of ECL.

Effects of Hydroxytyrosol in Endothelial Functioning: A Comprehensive Review

Pharmacologists have been emphasizing and applying plant and herbal-based treatments in vascular diseases for decades now. Olives, for example, are a traditional symbol of the Mediterranean diet. Hydroxytyrosol is an olive-derived compound known for its antioxidant and cardioprotective effects. Acknowledging the merit of antioxidants in maintaining endothelial function warrants the application of hydroxytyrosol in endothelial dysfunction salvage and recovery. Endothelial dysfunction (ED) is an impairment of endothelial cells that adversely affects vascular homeostasis. Disturbance in endothelial functioning is a known precursor for atherosclerosis and, subsequently, coronary and peripheral artery disease. However, the effects of hydroxytyrosol on endothelial functioning were not extensively studied, limiting its value either as a nutraceutical supplement or in clinical trials. The action of hydroxytyrosol in endothelial functioning at a cellular and molecular level is gathered and summarized in this review. The favorable effects of hydroxytyrosol in the improvement of endothelial functioning from in vitro and in vivo studies were scrutinized. We conclude that hydroxytyrosol is capable to counteract oxidative stress, inflammation, vascular aging, and arterial stiffness; thus, it is beneficial to preserve endothelial function both in vitro and in vivo. Although not specifically for endothelial dysfunction, hydroxytyrosol safety and efficacy had been demonstrated via in vivo and clinical trials for cardiovascular-related studies.

Renal Sympathetic Hyperactivity in Diabetes Is Modulated by 5-HT1D Receptor Activation via NO Pathway

Renal vasculature, which is highly innervated by sympathetic fibers, contributes to cardiovascular homeostasis. This renal sympathetic outflow is inhibited by 5-HT in normoglycaemic rats. Considering that diabetes induces cardiovascular complications, we aimed to determine whether diabetic state modifies noradrenergic input at renal level and its serotonergic modulation in rats. Alloxan diabetic rats were anaesthetized (pentobarbital; 60 mg/kg i.p.) and prepared for in situ autoperfusion of the left kidney to continuously measure systemic blood pressure (SBP), heart rate (HR), and renal perfusion pressure (RPP). Electrical stimulation of renal sympathetic outflow induces frequency-dependent increases (Δ) in RPP (23.9 ± 2.1, 59.5 ± 1.9, and 80.5 ± 3.5 mm Hg at 2, 4, and 6 Hz, respectively), which were higher than in normoglycaemic rats, without modifying HR or SBP. Intraarterial bolus of 5-HT and 5-CT (5-HT_1/5/7 agonist) reduced electrically induced ΔRPP. Only L-694,247 (5-HT_1D agonist) reproduced 5-CT inhibition on sympathetic-induced vasoconstrictions, whereas it did not modify exogenous noradrenaline-induced ΔRPP. 5-CT inhibition was exclusively abolished by i.v. bolus of LY310762 (5-HT_1D antagonist). An inhibitor of guanylyl cyclase, ODQ (i.v.), completely reversed the L-694,247 inhibitory effect. In conclusion, diabetes induces an enhancement in sympathetic-induced vasopressor responses at the renal level. Prejunctional 5-HT_1D receptors, via the nitric oxide pathway, inhibit noradrenergic-induced vasoconstrictions in diabetic rats.

Ca2+-Activated K+ Channels and the Regulation of the Uteroplacental Circulation

Adequate uteroplacental blood supply is essential for the development and growth of the placenta and fetus during pregnancy. Aberrant uteroplacental perfusion is associated with pregnancy complications such as preeclampsia, fetal growth restriction (FGR), and gestational diabetes. The regulation of uteroplacental blood flow is thus vital to the well-being of the mother and fetus. Ca²⁺-activated K⁺ (K_Ca) channels of small, intermediate, and large conductance participate in setting and regulating the resting membrane potential of vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) and play a critical role in controlling vascular tone and blood pressure. K_Ca channels are important mediators of estrogen/pregnancy-induced adaptive changes in the uteroplacental circulation. Activation of the channels hyperpolarizes uteroplacental VSMCs/ECs, leading to attenuated vascular tone, blunted vasopressor responses, and increased uteroplacental blood flow. However, the regulation of uteroplacental vascular function by K_Ca channels is compromised in pregnancy complications. This review intends to provide a comprehensive overview of roles of K_Ca channels in the regulation of the uteroplacental circulation under physiological and pathophysiological conditions.

Physiological and Pathophysiological Role of Large-Conductance Calcium-Activated Potassium Channels (BKCa) in HUVECs and Placenta

BKCa channels (large-conductance Ca2+-activated K+ channels) play a critical role in regulating vascular tone and blood pressure. These channels are present in the smooth muscle cells of blood vessels and are activated by voltage and increased intracellular Ca2+ concentration. More recently, the expression and activity of BKCa have been proposed to be relevant in endothelial cells, too, specifically in human umbilical vein endothelial cells (HUVECs), the more studied cell type in the fetoplacental circulation. The role of BKCa in endothelial cells is not well understood, but in HUVECs or placental endothelium, these channels could be crucial for vascular tone regulation during pregnancy as part of endothelium-derived hyperpolarization (EDH), a key mechanism for an organ that lacks nervous system innervation like the placenta.In this review, we will discuss the evidence about the role of BKCa (and other Ca2+-activated K+ channels) in HUVECs and the placenta to propose a physiological mechanism for fetoplacental vascular regulation and a pathophysiological role of BKCa, mainly associated with pregnancy pathologies that present maternal hypertension and/or placental hypoxia, like preeclampsia.

Endothelial dysfunction due to the inhibition of the synthesis of nitric oxide: Proposal and characterization of an in vitro cellular model

The vascular endothelium plays a pivotal role in the maintenance of vascular homeostasis, mediated by vasoactive molecules produced by endothelial cells. The balance between vasoconstrictor and vasodilator biomolecules is what guarantees this equilibrium. Therefore, an increase in the bioavailability of vasoconstrictors along with a reduction in vasodilators may indicate a condition known as endothelial dysfunction. Endothelial dysfunction is marked by an inflammatory process and reduced activity of vasoprotective enzymes, being characterized by some factors like the reduction of the bioavailability of nitric oxide (NO) and increase in the production of reactive oxygen species (ROS), pro-inflammatory and vasoconstrictor molecules. This condition is a predictive marker of several cardiovascular diseases (e.g., atherosclerosis, hypertension, and diabetes). Research is affected by the scarcity of suitable in vitro models that simulate endothelial dysfunction. The goal of this study was to induce an in vitro condition to mimic endothelial dysfunction by inhibiting NO synthesis in cells. Thymus-derived endothelial cells (tEnd.1) were treated with different concentrations of L-NAME (from 1 to 1,000 μM) for different times (12, 24, 48, 72, 96, and 120 h without and with retreatment every 24 h). Cell viability, nitrite concentration, p22phox, NOX2, NOX4, IL-6, and ACE genes expression and lipid peroxidation were evaluated. The results indicate that the treatment with 100 μM L-NAME for 72 h without retreatment reduced NO concentration and NOX4 gene expression while increasing ACE expression, thus mimicking reduced vascular protection and possibly increased vasoconstriction. On the other hand, treatment with 100 μM L-NAME for 96 h with retreatment reduced the concentration of NO and the expression of the p22phox gene while increasing the expression of the IL-6 and ACE genes, mimicking the increase in inflammation and vasoconstriction parameters. Based on these results, we thus propose that both 100 μM L-NAME for 72 h without retreatment and 100 μM L-NAME for 96 h with retreatment may be used as models for in vitro endothelial dysfunction according to the purpose of the study to be conducted.