We suggest that KCNQ channel opening is a powerful mechanism to produce vasorelaxation of systemic arteries in rats and mice. Furthermore, KCNQ channels play a major role in the paracrine control of vascular tone by perivascular adipose tissue, which is at least in part mediated or modulated by H2S. In conditions of reduced H2S release from perivascular adipose tissue, these paracrine effects can be mimicked by synthetic KCNQ channel openers.

High blood pressure is the leading risk factor for death worldwide. One of the hallmarks is a rise of peripheral vascular resistance, which largely depends on arteriole tone. Ca 2+ -activated chloride currents (CaCCs) in vascular smooth muscle cells (VSMCs) are candidates for increasing vascular contractility. We analyzed the vascular tree and identified substantial CaCCs in VSMCs of the aorta and carotid arteries. CaCCs were small or absent in VSMCs of medium-sized vessels such as mesenteric arteries and larger retinal arterioles. In small vessels of the retina, brain, and skeletal muscle, where contractile intermediate cells or pericytes gradually replace VSMCs, CaCCs were particularly large. Targeted disruption of the calcium-activated chloride channel TMEM16A, also known as ANO1, in VSMCs, intermediate cells, and pericytes eliminated CaCCs in all vessels studied. Mice lacking vascular TMEM16A had lower systemic blood pressure and a decreased hypertensive response following vasoconstrictor treatment. There was no difference in contractility of medium-sized mesenteric arteries; however, responsiveness of the aorta and small retinal arterioles to the vasoconstrictioninducing drug U46619 was reduced. TMEM16A also was required for peripheral blood vessel contractility, as the response to U46619 was attenuated in isolated perfused hind limbs from mutant mice. Out data suggest that TMEM16A plays a general role in arteriolar and capillary blood flow and is a promising target for the treatment of hypertension.

Wall stretch is a major stimulus for the myogenic response of small arteries to pressure. Recent findings suggest that G protein‐coupled receptors can elicit a stretch response. Our aim was to determine if angiotensin II type 1 receptors (AT1R) in vascular smooth muscle cells (VSMC) exert mechanosensitivity and identify the downstream ion channel mediators of myogenic vasoconstriction. We used mice deficient in AT1R signaling molecules and putative ion channel targets, namely AT1R, angiotensinogen, TRPC6 channels or subtypes of the KCNQ (Kv7) gene family (KCNQ3, 4 or 5). We identified a mechano‐sensing mechanism in mesenteric arteries and the renal circulation that relies on coupling of the AT1R subtype a (AT1aR) to a Gq/11‐protein as a critical event to accomplish the myogenic response. The mechano‐activation occurs after block of AT1R, and in the absence of angiotensinogen or TRPC6. Activation of AT1aR suppresses XE991‐sensitive Kv channel currents in VSMCs, blocking these channels enhances mesenteric and renal myogenic tone. Although KCNQ3, 4 and 5 are expressed in VSMCs, XE991‐sensitive K+ current and myogenic contractions persist in arteries deficient in these channels. Our results provide evidence that myogenic responses of mouse mesenteric and renal arteries rely on ligand‐independent mechano‐activation of AT1aR. This signal relies on an ion channel distinct from TRPC6 or KCNQ3, 4 or 5. Grant Funding Source: Supported by Deutsche Forschungsgemeinschaft (DFG)

KCNQ channels have been identified in arterial smooth muscle. However, their role in vasoregulation and chronic vascular diseases remains elusive. We tested the hypothesis that KCNQ channels contribute to periadventitial vasoregulation in peripheral skeletal muscle arteries by perivascular adipose tissue and that they represent novel targets to rescue periadventitial vascular dysfunction. Two models, spontaneously hypertensive rats and New Zealand obese mice, were studied using quantitative polymerase chain reaction, the patch-clamp technique, membrane potential measurements, myography of isolated vessels, and blood pressure telemetry. In rat Gracilis muscle arteries, anticontractile effects of perivascular fat were inhibited by the KCNQ channel blockers XE991 and linopirdine but not by other selective K + channel inhibitors. Accordingly, XE991 and linopirdine blocked noninactivating K + currents in freshly isolated Gracilis artery smooth muscle cells. mRNAs of several KCNQ channel subtypes were detected in those arteries, with KCNQ4 channels being dominant. In spontaneously hypertensive rats, the anticontractile effect of perivascular fat in Gracilis muscle arteries was largely reduced compared with Wistar rats. However, the vasodilator effects of KCNQ channel openers and mRNA expression of KCNQ channels were normal. Furthermore, KCNQ channel openers restored the diminished anticontractile effects of perivascular fat in spontaneously hypertensive rats. Moreover, KCNQ channel openers reduced arterial blood pressure in both models of hypertension independent of ganglionic blockade. Thus, our data suggest that KCNQ channels play a pivotal role in periadventitial vasoregulation of peripheral skeletal muscle arteries, and KCNQ channel opening may be an effective mechanism to improve impaired periadventitial vasoregulation and associated hypertension.

SUMMARYArteriogenesis requires growth of pre-existing arteriolar collateral networks and determines clinical outcome in arterial occlusive diseases. Factors responsible for the development of arteriolar collateral networks are poorly understood. The Notch ligand Deltalike 4 (Dll4) promotes arterial differentiation and restricts vessel branching. We hypothesized that Dll4 may act as a genetic determinant of collateral arterial networks and functional recovery in stroke and hind limb ischemia models in mice. Genetic lossand gain-of-function approaches in mice showed that Dll4-Notch signaling restricts pial collateral artery formation by modulating arterial branching morphogenesis during embryogenesis. Adult Dll4 +/− mice showed increased pial collateral numbers, but stroke volume upon middle cerebral artery occlusion was not reduced compared with wild-type littermates. Likewise, Dll4 +/− mice showed reduced blood flow conductance after femoral artery occlusion, and, despite markedly increased angiogenesis, tissue ischemia was more severe. In peripheral arteries, loss of Dll4 adversely affected excitation-contraction coupling in arterial smooth muscle in response to vasopressor agents and arterial vessel wall adaption in response to increases in blood flow, collectively contributing to reduced flow reserve. We conclude that Dll4-Notch signaling modulates native collateral formation by acting on vascular branching morphogenesis during embryogenesis. Dll4 furthermore affects tissue perfusion by acting on arterial function and structure. Loss of Dll4 stimulates collateral formation and angiogenesis, but in the context of ischemic diseases such beneficial effects are overruled by adverse functional changes, demonstrating that ischemic recovery is not solely determined by collateral number but rather by vessel functionality.

BackgroundHydrogen sulfide (H2S) is a potent vasodilator. However, the complex mechanisms of vasoregulation by H2S are not fully understood. We tested the hypotheses that (1) H2S exerts vasodilatory effects by opening KCNQ-type voltage-dependent (Kv) K+ channels and (2) that H2S-producing cystathionine-γ-lyase (CSE) in perivascular adipose tissue plays a major role in this pathway.Methodology/Principal FindingsWire myography of rat and mouse aortas was used. NaHS and 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione (ADTOH) were used as H2S donors. KCNQ-type Kv channels were blocked by XE991. 4-Propargylglycine (PPG) and ß-cyano-l-alanine (BCA), or 2-(aminooxy)-acetic acid (AOAA) were used as inhibitors of CSE or cystathionine-ß-synthase (CBS), respectively. NaHS and ADTOH produced strong vasorelaxation in rat and mouse aortas, which were abolished by KCNQ channel inhibition with XE991. Perivascular adipose tissue (PVAT) exerted an anticontractile effect in these arteries. CSE inhibition by PPG and BCA reduced this effect in aortas from rats but not from mice. CBS inhibition with AOAA did not inhibit the anticontractile effects of PVAT. XE991, however, almost completely suppressed the anticontractile effects of PVAT in both species. Exogenous l-cysteine, substrate for the endogenous production of H2S, induced vasorelaxation only at concentrations >5 mmol/l, an effect unchanged by CSE inhibition.Conclusions/SignficanceOur results demonstrate potent vasorelaxant effects of H2S donors in large arteries of both rats and mice, in which XE991-sensitive KCNQ-type channel opening play a pivotal role. CSE-H2S seems to modulate the effect of adipocyte-derived relaxing factor in rat but not in mouse aorta. The present study provides novel insight into the interaction of CSE-H2S and perivascular adipose tissue. Furthermore, with additional technical advances, a future clinical approach targeting vascular H2S/KCNQ pathways to influence states of vascular dysfunction may be possible.

Abstract-Perivascular adipose tissue has been recognized unequivocally as a major player in the pathology of metabolic and cardiovascular diseases. Through its production of adipokines and the release of other thus far unidentified factors, this recently discovered adipose tissue modulates vascular regulation and the myogenic response. After the discovery of its ability to diminish the vessel's response to vasoconstrictors, a new paradigm established adipose-derived relaxing factor (ADRF) as a paracrine smooth muscle cells' potassium channel opener that could potentially help combat vascular dysfunction. This review will discuss the role of ADRF in vascular dysfunction in obesity and hypertension, the different potassium channels that can be activated by this factor, and describes new pharmacological tools that can mimic the ADRF effect and thus can be beneficial against vascular dysfunction in cardiovascular disease. [19][20][21][22] and are also observable on veins. 23 The release of ADRF from PVAT is strongly dependent on the concentration of Ca 2+ and seems to be dependent on the activation of intracellular pathways involving tyrosine kinase and protein kinase A. In contrast, perivascular nerve endings, notably presynaptic neuronal N-type Ca 2+ , Na + channels, calcitonin gene-related peptide, cannabinoid, and vanilloid receptors, do not play an important role in this process.4 Importantly, recent experiments have shown a dual role of PVAT in the initiation and progression of obesity. In effect, PVAT (similarly to endothelium) in animal and human models of hypertension, obesity, and metabolic syndrome becomes dysfunctional and loses its anticontractile properties, likely because of a decrease in PVRF release. 16,[24][25][26][27] It is, therefore, of utmost importance to determine the nature of PVRFs as well as its targets for the paracrine regulation of PVAT. PVRF: Potential CandidatesSeveral studies have tried to pinpoint the nature of PVRFs. The role of adiponectin as PVRF has been thus far inconclusive. Vessels from the aorta and mesenteric arteries of adiponectin-knockout mice have been initially shown to maintain their anticontractile properties. 16 In contrast, recent studies in mesenteric vessels of wild-type mice advance that the vasorelaxing and hyperpolarizing effects of adiponectin rely on the opening of maxi Ca 2+ -activated K + (BK Ca ) channels. 28,29 In addition, a factor that might be adiponectin is released after stimulation of rat and murine mesenteric arteries with β3 adrenoreceptor. This latter factor seems to exert its paracrine effect by activation of AMPK and opening of BK ca channels. 30 Similarly to adiponectin, leptin has also been proposed as a candidate for PVRF in a hypertension mouse model. 31 Leptin, however, is perhaps not ADRF in the systemic circulation because the PVAT of Zucker fa/fa rats that lack the leptin receptor still display anticontractile properties. 3 As mentioned above, angiotensin-1 to 7 and methyl palmitate are also proposed as PVRF. A study using aortas from...

Background Hypertension is the major risk factor for cardiovascular disease, the most common cause of death worldwide. Resistance arteries are capable of adapting their diameter independently in response to pressure and flow‐associated shear stress. Ryanodine receptors (RyRs) are major Ca 2+ ‐release channels in the sarcoplasmic reticulum membrane of myocytes that contribute to the regulation of contractility. Vascular smooth muscle cells exhibit 3 different RyR isoforms (RyR1, RyR2, and RyR3), but the impact of individual RyR isoforms on adaptive vascular responses is largely unknown. Herein, we generated tamoxifen‐inducible smooth muscle cell–specific RyR2‐deficient mice and tested the hypothesis that vascular smooth muscle cell RyR2s play a specific role in elementary Ca 2+ signaling and adaptive vascular responses to vascular pressure and/or flow. Methods and Results Targeted deletion of the Ryr2 gene resulted in a complete loss of sarcoplasmic reticulum–mediated Ca 2+ ‐release events and associated Ca 2+ ‐activated, large‐conductance K + channel currents in peripheral arteries, leading to increased myogenic tone and systemic blood pressure. In the absence of RyR2, the pulmonary artery pressure response to sustained hypoxia was enhanced, but flow‐dependent effects, including blood flow recovery in ischemic hind limbs, were unaffected. Conclusions Our results establish that RyR2‐mediated Ca 2+ ‐release events in VSCM s specifically regulate myogenic tone (systemic circulation) and arterial adaptation in response to changes in pressure (hypoxic lung model), but not flow. They further suggest that vascular smooth muscle cell–expressed RyR2 deserves scrutiny as a therapeutic target for the treatment of vascular responses in hypertension and chronic vascular diseases.