Transcriptional upregulation of α2δ-1 elevates arterial smooth muscle cell voltage-dependent Ca2+ channel surface expression and cerebrovascular constriction in genetic hypertension

Exercise training affects calcium ion transport by downregulating the CACNA2D1 protein to reduce hypertension-induced myocardial injury in mice

Hypertension is a risk factor for cardiovascular disease, and exercise has cardioprotective effects on the heart. However, the mechanism by which exercise affects hypertension-induced myocardial injury remains unclear. Exercise response model of hypertension-induced myocardial injury in mice was analyzed using multiomics data to identify potential factors. The study found that serum Ca2+ and brain natriuretic peptide concentrations were significantly higher in the HTN (hypertension) group than in the control, HTN+MICT (moderate intensity continuous exercise), and HTN+HIIT (high intensity intermittent exercise) groups. Cardiac tissue damage and fibrosis increased in the HTN group, but exercise training reduced pathological changes, with more improvement in the HTN+HIIT group. Transcriptomic and proteomic studies showed significant differences in CACNA2D1 expression between the different treatment groups. HIIT ameliorated HTN-induced myocardial injury in mice by decreasing Ca2+ concentration and diastolizing vascular smooth muscle by downregulating CACNA2D1 via exercise.

Physiological functions and pathological involvement of ion channel trafficking in the vasculature

A variety of ion channels regulate membrane potential and calcium influx in arterial smooth muscle and endothelial cells to modify vascular functions, including contractility. The current (I) generated by a population of ion channels is equally dependent upon their number (N), open probability (Po) and single channel current (i), such that I = N.PO .i. A conventional view had been that ion channels traffic to the plasma membrane in a passive manner, resulting in a static surface population. It was also considered that channels assemble with auxiliary subunits prior to anterograde trafficking of the multimeric complex to the plasma membrane. Recent studies have demonstrated that physiological stimuli can regulate the surface abundance (N) of several different ion channels in arterial smooth muscle and endothelial cells to control arterial contractility. Physiological stimuli can also regulate the number of auxiliary subunits present in the plasma membrane to modify the biophysical properties, regulatory mechanisms and physiological functions of some ion channels. Furthermore, ion channel trafficking becomes dysfunctional in the vasculature during hypertension, which negatively impacts the regulation of contractility. The temporal kinetics of ion channel and auxiliary subunit trafficking can also vary depending on the signalling mechanisms and proteins involved. This review will summarize recent work that has uncovered the mechanisms, functions and pathological modifications of ion channel trafficking in arterial smooth muscle and endothelial cells.

Endothelial cell TRPA1 activity exacerbates cerebral hemorrhage during severe hypertension

Introduction: Hypoxia-induced dilation of cerebral arteries orchestrated by Ca2+-permeable transient receptor potential ankyrin 1 (TRPA1) cation channels on endothelial cells is neuroprotective during ischemic stroke, but it is unknown if the channel has a similar impact during hemorrhagic stroke. TRPA1 channels are endogenously activated by lipid peroxide metabolites generated by reactive oxygen species (ROS). Uncontrolled hypertension, a primary risk factor for the development of hemorrhagic stroke, is associated with increased ROS production and oxidative stress. Therefore, we hypothesized that TRPA1 channel activity is increased during hemorrhagic stroke. Methods: Severe, chronic hypertension was induced in control (Trpa1 fl/fl) and endothelial cell-specific TRPA1 knockout (Trpa1-ecKO) mice using a combination of chronic angiotensin II administration, a high-salt diet, and the addition of a nitric oxide synthase inhibitor to drinking water. Blood pressure was measured in awake, freely-moving mice using surgically placed radiotelemetry transmitters. TRPA1-dependent cerebral artery dilation was evaluated with pressure myography, and expression of TRPA1 and NADPH oxidase (NOX) isoforms in arteries from both groups was determined using PCR and Western blotting techniques. In addition, ROS generation capacity was evaluated using a lucigenin assay. Histology was performed to examine intracerebral hemorrhage lesion size and location. Results: All animals became hypertensive, and a majority developed intracerebral hemorrhages or died of unknown causes. Baseline blood pressure and responses to the hypertensive stimulus did not differ between groups. Expression of TRPA1 in cerebral arteries from control mice was not altered after 28 days of treatment, but expression of three NOX isoforms and the capacity for ROS generation was increased in hypertensive animals. NOX-dependent activation of TRPA1 channels dilated cerebral arteries from hypertensive animals to a greater extent compared with controls. The number of intracerebral hemorrhage lesions in hypertensive animals did not differ between control and Trpa1-ecKO animals but were significantly smaller in Trpa1-ecKO mice. Morbidity and mortality did not differ between groups. Discussion: We conclude that endothelial cell TRPA1 channel activity increases cerebral blood flow during hypertension resulting in increased extravasation of blood during intracerebral hemorrhage events; however, this effect does not impact overall survival. Our data suggest that blocking TRPA1 channels may not be helpful for treating hypertension-associated hemorrhagic stroke in a clinical setting.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Functional tuning of Vascular L-type Ca2+ channels

Vascular smooth muscle contraction is intimately tied to membrane potential and the rise in intracellular Ca2+ enabled by the opening of L-type Ca2+ channels. While voltage is often viewed as the single critical factor gating these channels, research is starting to reveal a more intricate scenario whereby their function is markedly tuned. This emerging concept will be the focus of this three-part review, the first part articulating the mechanistic foundation of contractile development in vascular smooth muscle. Part two will extend this foundational knowledge, introducing readers to functional coupling and how neighboring L-type Ca2+ channels work cooperatively through signaling protein complexes, to facilitate their open probability. The final aspect of this review will discuss the impact of L-type Ca2+ channel trafficking, a process tied to cytoskeleton dynamics. Cumulatively, this brief manuscript provides new insight into how voltage, along with channel cooperativity and number, work in concert to tune Ca2+ responses and smooth muscle contraction.

Vascular CaV1.2 channels in diabetes

Diabetic vasculopathy is a significant cause of morbidity and mortality in the diabetic population. Hyperglycemia, one of the central metabolic abnormalities in diabetes, has been associated with vascular dysfunction due to endothelial cell damage. However, studies also point toward vascular smooth muscle as a locus for hyperglycemia-induced vascular dysfunction. Emerging evidence implicates hyperglycemia-induced regulation of vascular L-type Ca²⁺ channels Ca_V1.2 as a potential mechanism for vascular dysfunction during diabetes. This chapter summarizes our current understanding of vascular Ca_V1.2 channels and their regulation during physiological and hyperglycemia/diabetes conditions. We will emphasize the role of Ca_V1.2 in vascular smooth muscle, the effects of elevated glucose on Ca_V1.2 function, and the mechanisms underlying its dysregulation in hyperglycemia and diabetes. We conclude by examining future directions and gaps in knowledge regarding Ca_V1.2 regulation in health and during diabetes.

Ion channel molecular complexes in vascular smooth muscle

Ion channels that influence membrane potential and intracellular calcium concentration control vascular smooth muscle excitability. Voltage-gated calcium channels (VGCC), transient receptor potential (TRP) channels, voltage (K_V), and Ca²⁺-activated K⁺ (BK) channels are key regulators of vascular smooth muscle excitability and contractility. These channels are regulated by various signaling cues, including protein kinases and phosphatases. The effects of these ubiquitous signaling molecules often depend on the formation of macromolecular complexes that provide a platform for targeting and compartmentalizing signaling events to specific substrates. This manuscript summarizes our current understanding of specific molecular complexes involving VGCC, TRP, and K_V and BK channels and their contribution to regulating vascular physiology.

Novel Smooth Muscle Ca2+-Signaling Nanodomains in Blood Pressure Regulation

BACKGROUND

Ca2+ signals in smooth muscle cells (SMCs) contribute to vascular resistance and control blood pressure. Increased vascular resistance in hypertension has been attributed to impaired SMC Ca2+ signaling mechanisms. In this regard, transient receptor potential vanilloid 4 (TRPV4SMC) ion channels are a crucial Ca2+ entry pathway in SMCs. However, their role in blood pressure regulation has not been identified.

METHODS

We used SMC-specific TRPV4-/- (TRPV4SMC-/-) mice to assess the role of TRPV4SMC channels in blood pressure regulation. We determined the contribution of TRPV4SMC channels to the constrictor effect of α1 adrenergic receptor (α1AR) stimulation and elevated intraluminal pressure: 2 main physiologic stimuli that constrict resistance-sized arteries. The contribution of spatially separated TRPV4SMC channel subpopulations to elevated blood pressure in hypertension was evaluated in angiotensin II-infused mice and patients with hypertension.

RESULTS

We provide first evidence that TRPV4SMC channel activity elevates resting blood pressure in normal mice. α1AR stimulation activated TRPV4SMC channels through PKCα (protein kinase Cα) signaling, which contributed significantly to vasoconstriction and blood pressure elevation. Intraluminal pressure-induced TRPV4SMC channel activity opposed vasoconstriction through activation of Ca2+-sensitive K+ (BK) channels, indicating functionally opposite pools of TRPV4SMC channels. Superresolution imaging of SMCs revealed spatially separated α1AR:TRPV4 and TRPV4:BK nanodomains in SMCs. These data suggest that spatially separated α1AR-TRPV4SMC and intraluminal pressure-TRPV4SMC-BK channel signaling have opposite effects on blood pressure, with α1AR-TRPV4SMC signaling dominating under resting conditions. Furthermore, in patients with hypertension and a mouse model of hypertension, constrictor α1AR-PKCα-TRPV4 signaling was upregulated, whereas dilator pressure-TRPV4-BK channel signaling was disrupted, thereby increasing vasoconstriction and elevating blood pressure.

CONCLUSIONS

Our data identify novel smooth muscle Ca2+-signaling nanodomains that regulate blood pressure and demonstrate their impairment in hypertension.

Gabapentinoid-induced peripheral edema and acute heart failure: A translational study combining pharmacovigilance data and in vitro animal experiments

INTRODUCTION

Gabapentinoids are ligands of the α2-δ subunit of voltage-gated calcium channels (Cav) that have been associated with a risk of peripheral edema and acute heart failure in connection with a potentially dual mechanism, vascular and cardiac.

OBJECTIVES & METHODS

All cases of peripheral edema or heart failure involving gabapentin or pregabalin reported to the French Pharmacovigilance Centers between January 1, 1994 and April 30, 2020 were included to describe their onset patterns (e.g., time to onset). Based on these data, we investigated the impact of gabapentinoids on the myogenic tone of rat third-order mesenteric arteries and on the electrophysiological properties of rat ventricular cardiomyocytes.

RESULTS

A total of 58 reports were included (gabapentin n = 5, pregabalin n = 53). The female-to-male ratio was 4:1 and the median age was 77 years (IQR 57-85, range 32-95). The median time to onset were 23 days (IQR 10-54) and 17 days (IQR 3-30) for non-cardiogenic edema and acute heart failure, respectively. Cardiogenic and non-cardiogenic peripheral edema occurred frequently after a dose escalation (27/45, 60%), and the course was rapidly favorable after discontinuation of gabapentinoid (median 7 days, IQR 5-13). On rat mesenteric arteries, gabapentinoids significantly decreased the myogenic tone to the same extent as verapamil and nifedipine. Acute application of gabapentinoids had no significant effect on Ca_v1.2 currents of ventricular cardiomyocytes.

CONCLUSION

Gabapentinoids can cause concentration-dependent peripheral edema of early onset. The primary mechanism of non-cardiogenic peripheral edema is vasodilatory edema secondary to altered myogenic tone, independent of Ca_v1.2 blockade under the experimental conditions tested.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

TMEM16A channel upregulation in arterial smooth muscle cells produces vasoconstriction during diabetes

The pathological involvement of anion channels in vascular dysfunction that occurs during type 2 diabetes (T2D) is unclear. Here, we tested the hypothesis that TMEM16A, a calcium-activated chloride (Cl-) channel, contributes to modifications in arterial contractility during T2D. Our data indicate that T2D increased TMEM16A mRNA in arterial smooth muscle cells and total and surface TMEM16A protein in resistance-size cerebral and hindlimb arteries of mice. To examine vascular cell types in which TMEM16A protein increased and the functional consequences of TMEM16A upregulation during T2D, we generated tamoxifen-inducible, smooth muscle cell-specific TMEM16A knockout (TMEM16A smKO) mice. T2D increased both TMEM16A protein and Cl- current density in arterial smooth muscle cells of control (TMEM16Afl/fl) mice. In contrast, T2D did not alter arterial TMEM16A protein or Cl- current density in smooth muscle cells of TMEM16A smKO mice. Intravascular pressure stimulated greater vasoconstriction (myogenic tone) in the arteries of T2D TMEM16Afl/fl mice than in the arteries of nondiabetic TMEM16Afl/fl mice. This elevation in myogenic tone in response to T2D was abolished in the arteries of T2D TMEM16A smKO mice. T2D also reduced Akt2 protein and activity in the arteries of T2D mice. siRNA-mediated knockdown of Akt2, but not Akt1, increased arterial TMEM16A protein in nondiabetic mice. In summary, data indicate that T2D is associated with an increase in TMEM16A expression and currents in arterial smooth muscle cells that produces vasoconstriction. Data also suggest that a reduction in Akt2 function drives these pathological alterations during T2D.NEW & NOTEWORTHY We investigated the involvement of TMEM16A channels in vascular dysfunction during type 2 diabetes (T2D). TMEM16A message, protein, and currents were higher in smooth muscle cells of resistance-size arteries during T2D. Pressure stimulated greater vasoconstriction in the arteries of T2D mice that was abolished in the arteries of TMEM16A smKO mice. Akt2 protein and activity were both lower in T2D arteries, and Akt2 knockdown elevated TMEM16A protein. We propose that a decrease in Akt2 function stimulates TMEM16A expression in arterial smooth muscle cells, leading to vasoconstriction during T2D.

Drug-induced peripheral oedema: An aetiology-based review

Many drugs are responsible, through different mechanisms, for peripheral oedema. Severity is highly variable, ranging from slight oedema of the lower limbs to anasarca pictures as in the capillary leak syndrome. Although most often noninflammatory and bilateral, some drugs are associated with peripheral oedema that is readily erythematous (eg, pemetrexed) or unilateral (eg, sirolimus). Thus, drug-induced peripheral oedema is underrecognized and misdiagnosed, frequently leading to a prescribing cascade. Four main mechanisms are involved, namely precapillary arteriolar vasodilation (vasodilatory oedema), sodium/water retention (renal oedema), lymphatic insufficiency (lymphedema) and increased capillary permeability (permeability oedema). The underlying mechanism has significant impact on treatment efficacy. The purpose of this review is to provide a comprehensive analysis of the main causative drugs by illustrating each pathophysiological mechanism and their management through an example of a drug.

Age-dependent increase in activity of eukaryotic elongation factor 2 kinase in mesenteric arteries from spontaneously hypertensive rats

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) negatively regulates protein translation through the phosphorylation of its specific substrate, eEF2. We previously found that expression of eEF2K was increased in arteries from 13-15-week-old spontaneously hypertensive rats (SHR) as well as in left ventricles of cardiac hypertrophy models. Furthermore, we demonstrated that eEF2K mediates the development of essential hypertension and pulmonary arterial hypertension in animal models. Protein expression changes with age during development of hypertension in SHR. In the present study, we examined whether activity and expression of eEF2K change in isolated mesenteric arteries dependent on the age. After superior mesenteric arteries were isolated from 4-10-week-old Wistar Kyoto rats (WKY) and SHR, Western blotting was performed. The phosphorylation of eEF2K at Ser500, an activating phosphorylation site, was increased in the arteries from 10-week-old SHR, whereas the phosphorylation of eEF2K at Ser366, an inactivating phosphorylation site, was increased in the arteries from 4-5-week-old SHR compared with WKY. The expression of eEF2K was increased in the arteries from 10-week-old SHR compared with WKY. The phosphorylation of eEF2 at Thr56 was decreased in the arteries from 4-5-week-old SHR, whereas it was increased in the arteries from 10-week-old SHR compared with WKY. We for the first time revealed that eEF2K activity is lower in prehypertensive stage but higher in hypertensive stage in SHR, suggesting that an inhibition of eEF2K activity may be a potential therapeutic strategy for the treatment of essential hypertension.

A paradoxical increase of force development in saphenous and tail arteries from heterozygous ANO1 knockout mice

A Ca²⁺‐activated Cl⁻ channel protein, ANO1, is expressed in vascular smooth muscle cells where Cl⁻ current is thought to potentiate contraction by contributing to membrane depolarization. However, there is an inconsistency between previous knockout and knockdown studies on ANO1’s role in small arteries. In this study, we assessed cardiovascular function of heterozygous mice with global deletion of exon 7 in the ANO1 gene. We found decreased expression of ANO1 in aorta, saphenous and tail arteries from heterozygous ANO1 knockout mice in comparison with wild type. Accordingly, ANO1 knockdown reduced the Ca²⁺‐activated Cl⁻ current in smooth muscle cells. Consistent with conventional hypothesis, the contractility of aorta from ANO1 heterozygous mice was reduced. Surprisingly, we found an enhanced contractility of tail and saphenous arteries from ANO1 heterozygous mice when stimulated with noradrenaline, vasopressin, and K⁺‐induced depolarization. This difference was endothelium‐independent. The increased contractility of ANO1 downregulated small arteries was due to increased Ca²⁺ influx. The expression of L‐type Ca²⁺ channels was not affected but expression of the plasma membrane Ca²⁺ ATPase 1 and the Piezo1 channel was increased. Expressional analysis of tail arteries further suggested changes of ANO1 knockdown smooth muscle cells toward a pro‐contractile phenotype. We did not find any difference between genotypes in blood pressure, heart rate, pressor response, and vasorelaxation in vivo. Our findings in tail and saphenous arteries contrast with the conventional hypothesis and suggest additional roles for ANO1 as a multifunctional protein in the vascular wall that regulates Ca²⁺ homeostasis and smooth muscle cell phenotype.

METTL3 Induces AAA Development and Progression by Modulating N6-Methyladenosine-Dependent Primary miR34a Processing

Identifying effective drugs to delay the progression of aortic aneurysms is a formidable challenge in vascular medicine. Methyltransferase-like 3 (METTL3) plays a key role in catalyzing the formation of N6-methyladenosine (m⁶A), but despite the functional importance of METTL3 and m⁶A in various fundamental biological processes, their roles in abdominal aortic aneurysm (AAA) are unknown. Here, we found that METTL3 knockdown in apolipoprotein E-deficient (ApoE^−/−) mice treated with angiotensin II suppressed the formation of AAAs, while METTL3 overexpression exerted the opposite effects. Similar results were obtained in a calcium chloride (CaCl₂)-induced mouse AAA model. Mechanistically, METTL3-dependent m⁶A methylation promoted primary microRNA-34a (miR-34a, pri-miR34a) maturation through DGCR8. Moreover, miR-34a overexpression significantly decreased SIRT1 expression and aggravated AAA formation, while miR-34a deficiency produced the opposite effects. In a rescue experiment, miR-34a knockdown or forced expression of SIRT1 partially attenuated the protective effects of METTL3 deficiency against AAA formation. Our studies reveal an important role for METTL3/m⁶A-mediated miR-34a maturation in AAA formation and provide a novel therapeutic target and diagnostic biomarker for AAA treatment.

HIIT sensitizes the arterial baroreflex by activating GSH-Px and downregulating calcium channel

BACKGROUND

High-intensity intermittent training (HIIT) is an emerging strategy for controlling blood pressure (BP) requiring intermittent exercise. However, few studies were focused on clinical test or related mechanisms. Here we compared the detailed aspects of HIIT on rat blood pressure control and explored its possible molecular mechanisms.

METHODS

Thirty-six spontaneous hypertensive rats (SHR) were recruited to complete 8 weeks of different training pattern using treadmill. Measurements of BP, bradycardia reflex, tachycardia reflex, plasma oxidative stress biomarkers and protein expression were acquired at the end of training.

RESULTS

After the 8-week training, HIIT can significantly downregulate the rest heart rate (HR) and blood pressure of SHR. The bradycardia reflex induced by phenylephrine and tachycardia response to sodium nitroprusside (SNP) were both improved in the HIIT group compared with control group. By testing the plasma metabolites, we found no statistically alteration on levels of malondialdehyde (MDA) or superoxide dismutase (SOD). However, HIIT increased the plasma glutathione peroxidase (GSH-Px) activity. Besides, HIIT attenuated the vasoconstriction induced by norepinephrine while has little effect on potassium chloride stimulation. Similarly, the sensitivity of vasorelaxation induced by SNP was upregulated after HIIT. Finally, we identified a decrease of of calcium channel CaV 1.2 on blood vessel in HIIT group.

CONCLUSIONS

HIIT provides a better control of BP and higher sensitivity to vasorelaxation, which may be related to higher GSH-Px activity and lower CaV 1.2 expression.

Therapeutic effect of pregabalin on radiotherapy-induced trismus in nasopharyngeal carcinoma patients

AIMS

To evaluate the effect of pregabalin on radiotherapy-induced trismus in patients with nasopharyngeal carcinoma, a hospital-based, clinical retrospective cohort study was conducted.

MATERIALS AND METHODS

Data were collected on patients diagnosed with radiotherapy-induced trismus from March 2014 and March 2016 in the department of neurology in our hospital. Patients in the treatment group were administrated pregabalin for 8 weeks combined with rehabilitation, while the control group only received rehabilitation. The clinical therapeutic effects were observed and evaluated by mandibular motion, severity of trismus measured by late effects of normal tissues/subjective and objective medical analysis (LENT/SOMA) scales, and quality of life (QOL) assessed using the World Health Organization QOL instrument (WHOQOL-BREF) at baseline, week 4 and week 8 during treatment in these two groups, respectively.

RESULTS

In the treatment group, the number of patients with improvement on maximal vertical dimension (MVD) was significantly more than controls at week 4 and week 8 (P=0.013, P=0.004, respectively). Moreover, at week 4 and week 8, the severity of trismus was both significantly improved on LENT/SOMA grade in treatment group (P=0.047, P=0.032, respectively). And at week 8, the physical health and the whole life domain of the WHOQOL-BREF score were significantly increased (P=0.037, P=0.034, respectively). In the treatment group, 11 patients (36.7%) presented dizziness, and 7 patients (23.3%) presented somnolence.

CONCLUSIONS

Administration of pregabalin, in adjunct to rehabilitation, might provide a better outcome in patients with radiotherapy-induced trismus.

Prenatal hypoxia plus postnatal high-fat diet exacerbated vascular dysfunction via up-regulated vascular Cav1.2 channels in offspring rats

Background

This study aimed to examine whether and how postnatal high‐fat diet had additional impact on promoting vascular dysfunction in the offspring exposed to prenatal hypoxia.

Methods and Results

Pregnant Sprague‐Dawley rats were randomly assigned to hypoxia (10.5% oxygen) or normoxia (21% O₂) groups from gestation days 5‐21. A subset of male offspring was placed on a high‐fat diet (HF, 45% fat) from 4‐16 weeks of age. Prenatal hypoxia induced a decrease in birth weight. In offspring‐fed HF diet, prenatal hypoxia was associated with increased fasting plasma triglyceride, total cholesterol, free fatty acids, and low‐density lipoprotein‐cholesterol. Compared with the other three groups, prenatal hypoxic offspring with high‐fat diet showed a significant increase in blood pressure, phenylephrine‐mediated vasoconstrictions, L‐type voltage‐gated Ca2+ (Cav1.2) channel currents, and elevated mRNA and protein expression of Cav1.2 α1 subunit in mesenteric arteries or myocytes. The large‐conductance Ca2+‐activated K+ (BK) channels currents and the BK channel units (β1, not α‐subunits) were significantly increased in mesenteric arteries or myocytes in HF offspring independent of prenatal hypoxia factor.

Conclusion

The results demonstrated that prenatal hypoxia followed by postnatal HF caused vascular dysfunction through ion channel remodelling in myocytes.

Mutations in voltage-gated L-type calcium channel: implications in cardiac arrhythmia

The voltage-gated L-type calcium channel (LTCC) is essential for multiple cellular processes. In the heart, calcium influx through LTCC plays an important role in cardiac electrical excitation. Mutations in LTCC genes, including CACNA1C, CACNA1D, CACNB2 and CACNA2D, will induce the dysfunctions of calcium channels, which result in the abnormal excitations of cardiomyocytes, and finally lead to cardiac arrhythmias. Nevertheless, the newly found mutations in LTCC and their functions are continuously being elucidated. This review summarizes recent findings on the mutations of LTCC, which are associated with long QT syndromes, Timothy syndromes, Brugada syndromes, short QT syndromes, and some other cardiac arrhythmias. Indeed, we describe the gain/loss-of-functions of these mutations in LTCC, which can give an explanation for the phenotypes of cardiac arrhythmias. Moreover, we present several challenges in the field at present, and propose some diagnostic or therapeutic approaches to these mutation-associated cardiac diseases in the future.

Alternative Splicing of L-type CaV1.2 Calcium Channels: Implications in Cardiovascular Diseases

L-type Ca_V1.2 calcium channels are the major pathway for Ca²⁺ influx to initiate the contraction of smooth and cardiac muscles. Alteration of Ca_V1.2 channel function has been implicated in multiple cardiovascular diseases, such as hypertension and cardiac hypertrophy. Alternative splicing is a post-transcriptional mechanism that expands Ca_V1.2 channel structures to modify function, pharmacological and biophysical property such as calcium/voltage-dependent inactivation (C/VDI), or to influence its post-translational modulation by interacting proteins such as Galectin-1. Alternative splicing has generated functionally diverse Ca_V1.2 isoforms that can be developmentally regulated in the heart, or under pathophysiological conditions such as in heart failure. More importantly, alternative splicing of certain exons of Ca_V1.2 has been reported to be regulated by splicing factors such as RNA-binding Fox-1 homolog 1/2 (Rbfox 1/2), polypyrimidine tract-binding protein (PTBP1) and RNA-binding motif protein 20 (RBM20). Understanding how Ca_V1.2 channel function is remodelled in disease will provide better information to guide the development of more targeted approaches to discover therapeutic agents for cardiovascular diseases.

Negatively charged residues in the first extracellular loop of the L-type CaV1.2 channel anchor the interaction with the CaVα2δ1 auxiliary subunit

Voltage-gated L-type Ca_V1.2 channels in cardiomyocytes exist as heteromeric complexes. Co-expression of Ca_Vα2δ1 with Ca_Vβ/Ca_Vα1 proteins reconstitutes the functional properties of native L-type currents, but the interacting domains at the Ca_V1.2/Ca_Vα2δ1 interface are unknown. Here, a homology-based model of Ca_V1.2 identified protein interfaces between the extracellular domain of Ca_Vα2δ1 and the extracellular loops of the Ca_Vα1 protein in repeats I (IS1S2 and IS5S6), II (IIS5S6), and III (IIIS5S6). Insertion of a 9-residue hemagglutinin epitope in IS1S2, but not in IS5S6 or in IIS5S6, prevented the co-immunoprecipitation of Ca_V1.2 with Ca_Vα2δ1. IS1S2 contains a cluster of three conserved negatively charged residues Glu-179, Asp-180, and Asp-181 that could contribute to non-bonded interactions with Ca_Vα2δ1. Substitutions of Ca_V1.2 Asp-181 impaired the co-immunoprecipitation of Ca_Vβ/Ca_V1.2 with Ca_Vα2δ1 and the Ca_Vα2δ1-dependent shift in voltage-dependent activation gating. In contrast, single substitutions in Ca_V1.2 in neighboring positions in the same loop (179, 180, and 182–184) did not significantly alter the functional up-regulation of Ca_V1.2 whole-cell currents. However, a negatively charged residue at position 180 was necessary to convey the Ca_Vα2δ1-mediated shift in the activation gating. We also found a more modest contribution from the positively charged Arg-1119 in the extracellular pore region in repeat III of Ca_V1.2. We conclude that Ca_V1.2 Asp-181 anchors the physical interaction that facilitates the Ca_Vα2δ1-mediated functional modulation of Ca_V1.2 currents. By stabilizing the first extracellular loop of Ca_V1.2, Ca_Vα2δ1 may up-regulate currents by promoting conformations of the voltage sensor that are associated with the channel's open state.

Pregabalin and heart failure: A population-based study

PURPOSE

The anticonvulsant pregabalin is increasingly prescribed for pain, seizures, and psychiatric disorders. Although evidence suggests pregabalin can cause edema and heart failure, its cardiac safety profile in clinical practice is unknown. We sought to examine the risk of heart failure among older patients receiving pregabalin compared to those receiving gabapentin.

METHODS

We conducted a population-based cohort study of Ontarians aged 66 and older with a history of seizure who received pregabalin or gabapentin between April 2013 and March 2014. We used propensity scores to match patients commencing pregabalin to those commencing gabapentin. The primary outcome was an emergency department visit or hospitalization for heart failure within 90 days.

RESULTS

We studied 9855 patients who initiated pregabalin and an equal number treated with gabapentin. In the primary analysis, we found no difference in the risk of heart failure with pregabalin compared to gabapentin (1.2% versus 1.3%, hazard ratio of 0.77; 95% CI 0.58-1.03). Secondary analyses stratified for baseline history of heart failure yielded similar findings.

CONCLUSION

In a large cohort of older patients with a seizure disorder, pregabalin was not associated with an increased risk of heart failure relative to gabapentin.

Proteolytic cleavage of the hydrophobic domain in the CaVα2δ1 subunit improves assembly and activity of cardiac CaV1.2 channels

Voltage-gated L-type Ca_V1.2 channels in cardiomyocytes exist as heteromeric complexes with the pore-forming Ca_Vα1, Ca_Vβ, and Ca_Vα2δ1 subunits. The full complement of subunits is required to reconstitute the native-like properties of L-type Ca²⁺ currents, but the molecular determinants responsible for the formation of the heteromeric complex are still being studied. Enzymatic treatment with phosphatidylinositol-specific phospholipase C, a phospholipase C specific for the cleavage of glycosylphosphatidylinositol (GPI)-anchored proteins, disrupted plasma membrane localization of the cardiac Ca_Vα2δ1 prompting us to investigate deletions of its hydrophobic transmembrane domain. Patch-clamp experiments indicated that the C-terminally cleaved Ca_Vα2δ1 proteins up-regulate Ca_V1.2 channels. In contrast, deleting the residues before the single hydrophobic segment (Ca_Vα2δ1 Δ1059-1063) impaired current up-regulation. Ca_Vα2δ1 mutants G1060I and G1061I nearly eliminated the cell-surface fluorescence of Ca_Vα2δ1, indicated by two-color flow cytometry assays and confocal imaging, and prevented Ca_Vα2δ1-mediated increase in peak current density and modulation of the voltage-dependent gating of Ca_V1.2. These impacts were specific to substitutions with isoleucine residues because functional modulation was partially preserved in Ca_Vα2δ1 G1060A and G1061A proteins. Moreover, C-terminal fragments exhibited significantly altered mobility in denatured immunoblots of Ca_Vα2δ1 G1060I and Ca_Vα2δ1 G1061I, suggesting that these mutant proteins were impaired in proteolytic processing. Finally, Ca_Vα2δ1 Δ1059-1063, but not Ca_Vα2δ1 G1060A, failed to co-immunoprecipitate with Ca_V1.2. Altogether, our data support a model in which small neutral hydrophobic residues facilitate the post-translational cleavage of the Ca_Vα2δ1 subunit at the predicted membrane interface and further suggest that preventing GPI anchoring of Ca_Vα2δ1 averts its cell-surface expression, its interaction with Ca_Vα1, and modulation of Ca_V1.2 currents.

Membrane depolarization activates BK channels through ROCK-mediated β1 subunit surface trafficking to limit vasoconstriction

Membrane depolarization of smooth muscle cells (myocytes) in the small arteries that regulate regional organ blood flow leads to vasoconstriction. Membrane depolarization also activates large-conductance calcium (Ca²⁺)-activated potassium (BK) channels, which limits Ca²⁺ channel activity that promotes vasoconstriction, thus leading to vasodilation. We showed that in human and rat arterial myocytes, membrane depolarization rapidly increased the cell surface abundance of auxiliary BK β1 subunits but not that of the pore-forming BKα channels. Membrane depolarization stimulated voltage-dependent Ca²⁺ channels, leading to Ca²⁺ influx and the activation of Rho kinase (ROCK) 1 and 2. ROCK1/2-mediated activation of Rab11A promoted the delivery of β1 subunits to the plasma membrane by Rab11A-positive recycling endosomes. These additional β1 subunits associated with BKα channels already at the plasma membrane, leading to an increase in apparent Ca²⁺ sensitivity and activation of the channels in pressurized arterial myocytes and vasodilation. Thus, membrane depolarization activates BK channels through stimulation of ROCK- and Rab11A-dependent trafficking of β1 subunits to the surface of arterial myocytes.

Unravelling the complexities of vascular smooth muscle ion channels: Fine tuning of activity by ancillary subunits

Which ion channel is the most important for regulating vascular tone? Which one is responsible for controlling the resting membrane potential or repolarization? Which channels are recruited by different intracellular signalling pathways or change in certain vascular diseases? Many different ion channels have been identified in the vasculature over the years and claimed as future therapeutic targets. Unfortunately, several of these ion channels are not just found in the vasculature, with many of them also found to have prominent functional roles in different organs of the body, which then leads to off-target effects. As cardiovascular diseases are expected to increase worldwide to epidemic proportions, ion channel research and the hunt for the next major therapeutic target to treat different vascular diseases has never been more important. However, I believe that the question we should now be asking is: which ancillary subunits are involved in regulating specific ion channels in the vasculature and do they have the potential to be new therapeutic targets?

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Angiotensin II reduces the surface abundance of KV 1.5 channels in arterial myocytes to stimulate vasoconstriction

KEY POINTS

Several different voltage-dependent K⁺ (K_V ) channel isoforms are expressed in arterial smooth muscle cells (myocytes). Vasoconstrictors inhibit K_V currents, but the isoform selectivity and mechanisms involved are unclear. We show that angiotensin II (Ang II), a vasoconstrictor, stimulates degradation of K_V 1.5, but not K_V 2.1, channels through a protein kinase C- and lysosome-dependent mechanism, reducing abundance at the surface of mesenteric artery myocytes. The Ang II-induced decrease in cell surface K_V 1.5 channels reduces whole-cell K_V 1.5 currents and attenuates K_V 1.5 function in pressurized arteries. We describe a mechanism by which Ang II stimulates protein kinase C-dependent K_V 1.5 channel degradation, reducing the abundance of functional channels at the myocyte surface.

ABSTRACT

Smooth muscle cells (myocytes) of resistance-size arteries express several different voltage-dependent K⁺ (K_V ) channels, including K_V 1.5 and K_V 2.1, which regulate contractility. Myocyte K_V currents are inhibited by vasoconstrictors, including angiotensin II (Ang II), but the mechanisms involved are unclear. Here, we tested the hypothesis that Ang II inhibits K_V currents by reducing the plasma membrane abundance of K_V channels in myocytes. Angiotensin II (applied for 2 h) reduced surface and total K_V 1.5 protein in rat mesenteric arteries. In contrast, Ang II did not alter total or surface K_V 2.1, or K_V 1.5 or K_V 2.1 cellular distribution, measured as the percentage of total protein at the surface. Bisindolylmaleimide (BIM; a protein kinase C blocker), a protein kinase C inhibitory peptide or bafilomycin A (a lysosomal degradation inhibitor) each blocked the Ang II-induced decrease in total and surface K_V 1.5. Immunofluorescence also suggested that Ang II reduced surface K_V 1.5 protein in isolated myocytes; an effect inhibited by BIM. Arteries were exposed to Ang II or Ang II plus BIM (for 2 h), after which these agents were removed and contractility measurements performed or myocytes isolated for patch-clamp electrophysiology. Angiotensin II reduced both whole-cell K_V currents and currents inhibited by Psora-4, a K_V 1.5 channel blocker. Angiotensin II also reduced vasoconstriction stimulated by Psora-4 or 4-aminopyridine, another K_V channel inhibitor. These data indicate that Ang II activates protein kinase C, which stimulates K_V 1.5 channel degradation, leading to a decrease in surface K_V 1.5, a reduction in whole-cell K_V 1.5 currents and a loss of functional K_V 1.5 channels in myocytes of pressurized arteries.

Calcium Channels in Vascular Smooth Muscle

Calcium (Ca²⁺) plays a central role in excitation, contraction, transcription, and proliferation of vascular smooth muscle cells (VSMs). Precise regulation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) is crucial for proper physiological VSM function. Studies over the last several decades have revealed that VSMs express a variety of Ca²⁺-permeable channels that orchestrate a dynamic, yet finely tuned regulation of [Ca²⁺]_i. In this review, we discuss the major Ca²⁺-permeable channels expressed in VSM and their contribution to vascular physiology and pathology.

Identification of Glycosylation Sites Essential for Surface Expression of the CaVα2δ1 Subunit and Modulation of the Cardiac CaV1.2 Channel Activity

Alteration in the L-type current density is one aspect of the electrical remodeling observed in patients suffering from cardiac arrhythmias. Changes in channel function could result from variations in the protein biogenesis, stability, post-translational modification, and/or trafficking in any of the regulatory subunits forming cardiac L-type Ca(2+) channel complexes. CaVα2δ1 is potentially the most heavily N-glycosylated subunit in the cardiac L-type CaV1.2 channel complex. Here, we show that enzymatic removal of N-glycans produced a 50-kDa shift in the mobility of cardiac and recombinant CaVα2δ1 proteins. This change was also observed upon simultaneous mutation of the 16 Asn sites. Nonetheless, the mutation of only 6/16 sites was sufficient to significantly 1) reduce the steady-state cell surface fluorescence of CaVα2δ1 as characterized by two-color flow cytometry assays and confocal imaging; 2) decrease protein stability estimated from cycloheximide chase assays; and 3) prevent the CaVα2δ1-mediated increase in the peak current density and voltage-dependent gating of CaV1.2. Reversing the N348Q and N812Q mutations in the non-operational sextuplet Asn mutant protein partially restored CaVα2δ1 function. Single mutation N663Q and double mutations N348Q/N468Q, N348Q/N812Q, and N468Q/N812Q decreased protein stability/synthesis and nearly abolished steady-state cell surface density of CaVα2δ1 as well as the CaVα2δ1-induced up-regulation of L-type currents. These results demonstrate that Asn-663 and to a lesser extent Asn-348, Asn-468, and Asn-812 contribute to protein stability/synthesis of CaVα2δ1, and furthermore that N-glycosylation of CaVα2δ1 is essential to produce functional L-type Ca(2+) channels.

Expression of Calcium Channel Subunit Variants in Small Mesenteric Arteries of WKY and SHR

BACKGROUND

Enhanced function of dihydropyridine-sensitive Ca2+ channels (CaV) in hypertensive arterial myocytes (HAM) is well accepted. Increased protein expression of pore forming α1-subunits contributes to this effect, but cannot explain all of the differences in CaV properties in HAM. We hypothesized that differences in expression of CaV subunits and/or their splice variants also contribute.

METHODS

RNA, protein, and myocytes were isolated from small mesenteric arteries (SMA) of 20-week-old male WKY and SHR and analyzed by polymerase chain reaction (PCR), sequencing, immunoblotting, and patch clamp methods.

RESULTS

Cav1.2 α1, β2c, and α2δ1d were the dominant subunits expressed in both WKY and SHR with a smaller amount of β3a. Real-time PCR indicated that the mRNA abundance of β3a and α2δ1 but not total Cav1.2 α1 or β2c were significantly larger in SHR. Analysis of alternative splicing of Cav1.2 α1 showed no differences in abundance of mutually exclusive exons1b, 8, 21 and 32 or alternative exons33 and 45. However, inclusion of exon9* was higher and a 73 nucleotide (nt) deletion in exon15 (exon15Δ73) was lower in SHR. Immunoblot analysis showed higher protein levels of Cav1.2 α1 (1.61±0.05), β3 (1.80±0.32), and α2δ1 (1.80±0.24) but not β2 in SHR.

CONCLUSIONS

The lower abundance of exon15Δ73 transcripts in SHR results in a larger fraction of total Cav1.2 mRNA coding for full-length CaV protein, and the higher abundance of exon9* transcripts and CaVβ3a protein likely contribute to differences in gating and kinetics of CaV currents in SHR. Functional studies of Ca2+ currents in native SMA myocytes and HEK cells transiently transfected with CaV subunits support these conclusions.

Intravascular pressure enhances the abundance of functional Kv1.5 channels at the surface of arterial smooth muscle cells

Voltage-dependent potassium (K(v)) channels are present in various cell types, including smooth muscle cells (myocytes) of resistance-sized arteries that control systemic blood pressure and regional organ blood flow. Intravascular pressure depolarizes arterial myocytes, stimulating calcium (Ca(2+)) influx through voltage-dependent Ca(2+) (Ca(v)) channels that results in vasoconstriction and also K(+) efflux through K(v) channels that oppose vasoconstriction. We hypothesized that pressure-induced depolarization may not only increase the open probability of plasma membrane-resident K(v) channels but also increase the abundance of these channels at the surface of arterial myocytes to limit vasoconstriction. We found that K(v)1.5 and K(v)2.1 proteins were abundant in the myocytes of resistance-sized mesenteric arteries. K(v)1.5, but not K(v)2.1, continuously recycled between the intracellular compartment and the plasma membrane in contractile arterial myocytes. Using ex vivo preparations of intact arteries, we showed that physiological intravascular pressure through membrane depolarization or membrane depolarization in the absence of pressure inhibited the degradation of internalized K(v)1.5 and increased recycling of K(v)1.5 to the plasma membrane. Accordingly, by stimulating the activity of Ca(v)1.2, membrane depolarization increased whole-cell K(v)1.5 current density in myocytes and K(v)1.5 channel activity in pressurized arteries. In contrast, the total amount and cell surface abundance of K(v)2.1 were independent of intravascular pressure or membrane potential. Thus, our data indicate that intravascular pressure-induced membrane depolarization selectively increased K(v)1.5 surface abundance to increase K(v) currents in arterial myocytes, which would limit vasoconstriction.

Enhanced parenchymal arteriole tone and astrocyte signaling protect neurovascular coupling mediated parenchymal arteriole vasodilation in the spontaneously hypertensive rat

Functional hyperemia is the regional increase in cerebral blood flow upon increases in neuronal activity which ensures that the metabolic demands of the neurons are met. Hypertension is known to impair the hyperemic response; however, the neurovascular coupling mechanisms by which this cerebrovascular dysfunction occurs have yet to be fully elucidated. To determine whether altered cortical parenchymal arteriole function or astrocyte signaling contribute to blunted neurovascular coupling in hypertension, we measured parenchymal arteriole reactivity and vascular smooth muscle cell Ca(2+) dynamics in cortical brain slices from normotensive Wistar Kyoto (WKY) and spontaneously hypertensive (SHR) rats. We found that vasoconstriction in response to the thromboxane A2 receptor agonist U46619 and basal vascular smooth muscle cell Ca(2+) oscillation frequency were significantly increased in parenchymal arterioles from SHR. In perfused and pressurized parenchymal arterioles, myogenic tone was significantly increased in SHR. Although K(+)-induced parenchymal arteriole dilations were similar in WKY and SHR, metabotropic glutamate receptor activation-induced parenchymal arteriole dilations were enhanced in SHR. Further, neuronal stimulation-evoked parenchymal arteriole dilations were similar in SHR and WKY. Our data indicate that neurovascular coupling is not impaired in SHR, at least at the level of the parenchymal arterioles.

Impaired P2X signalling pathways in renal microvascular myocytes in genetic hypertension

AIMS

P2X receptors (P2XRs) mediate sympathetic control and autoregulation of renal circulation triggering preglomerular vasoconstriction, which protects glomeruli from elevated pressures. Although previous studies established a casual link between glomerular susceptibility to hypertensive injury and decreased preglomerular vascular reactivity to P2XR activation, the mechanisms of attenuation of the P2XR signalling in hypertension remained unknown. We aimed to analyse molecular mechanisms of the impairment of P2XR signalling in renal vascular smooth muscle cells (RVSMCs) in genetic hypertension.

METHODS AND RESULTS

We compared the expression of pertinent genes and P2XR-linked Ca(2+) entry and Ca(2+) release mechanisms in RVSMCs of spontaneously hypertensive rats (SHRs) and their normotensive controls, Wistar Kyoto (WKY) rats. We found that, in SHR RVSMCs, P2XR-linked Ca(2+) entry and Ca(2+) release from the sarcoplasmic reticulum (SR) are both significantly reduced. The former is due to down-regulation of the P2X1 subunit. The latter is caused by a decrease of the SR Ca(2+) load. The SR Ca(2+) load reduction is caused by attenuated Ca(2+) uptake via down-regulated sarco-/endoplasmic reticulum Ca(2+)-ATPase 2b and elevated Ca(2+) leak from the SR via ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors. Spontaneous activity of these Ca(2+)-release channels is augmented due to up-regulation of RyR type 2 and elevated IP3 production by up-regulated phospholipase C-β1.

CONCLUSIONS

Our study unravels the cellular and molecular mechanisms of attenuation of P2XR-mediated preglomerular vasoconstriction that elevates glomerular susceptibility to harmful hypertensive pressures. This provides an important impetus towards understanding of the pathology of hypertensive renal injury.

Nifedipine-Sensitive Blood Pressure Component in Hypertensive Models Characterized by High Activity of Either Sympathetic Nervous System or Renin-Angiotensin System

High blood pressure (BP) of spontaneously hypertensive rats (SHR) is maintained by enhanced activity of sympathetic nervous system (SNS), whereas that of Ren-2 transgenic rats (Ren-2 TGR) by increased activity of renin-angiotensin system (RAS). However, both types of hypertension are effectively attenuated by chronic blockade of L-type voltage-dependent calcium channel (L-VDCC). The aim of our study was to evaluate whether the magnitude of BP response elicited by acute nifedipine administration is proportional to the alterations of particular vasoactive systems (SNS, RAS, NO) known to modulate L-VDCC activity. We therefore studied these relationships not only in SHR, in which mean arterial pressure was modified in a wide range of 100-210 mm Hg by chronic antihypertensive treatment (captopril or hydralazine) or its withdrawal, but also in rats with augmented RAS activity such as homozygous Ren-2 TGR, pertussis toxin-treated SHR or L-NAME-treated SHR. In all studied groups the magnitude of BP response to nifedipine was proportional to actual BP level and it closely correlated with BP changes induced by acute combined blockade of RAS and SNS. BP response to nifedipine is also closely related to the degree of relative NO deficiency. This was true for both SNS- and RAS-dependent forms of genetic hypertension, suggesting common mechanisms responsible for enhanced L-VDCC opening and/or their upregulation in hypertensive animals. In conclusions, BP response to nifedipine is proportional to the vasoconstrictor activity exerted by both SNS and RAS, indicating a key importance of these two pressor systems for actual L-VDCC opening necessary for BP maintenance.

Expression of microRNAs is essential for arterial myogenic tone and pressure-induced activation of the PI3-kinase/Akt pathway

AIMS

The myogenic response is the intrinsic ability of small arteries to constrict in response to increased intraluminal pressure. Although microRNAs have been shown to play a role in vascular smooth muscle function, their importance in the regulation of the myogenic response is not known. In this study, we investigate the role of microRNAs in the regulation of myogenic tone by using smooth muscle-specific and tamoxifen-inducible deletion of the endonuclease Dicer in mice.

METHODS AND RESULTS

In order to avoid effects of Dicer deletion on smooth muscle differentiation and growth, we used an early time point (5 weeks) after the tamoxifen-induction of Dicer knockout (KO). At this time point, we found that myogenic tone was completely absent in the mesenteric arteries of Dicer KO mice. This was associated with a reduced pressure-induced Akt-phosphorylation, possibly via increased phosphatase and tensin homologue (PTEN) expression, which was found to be a target of miR-26a. Furthermore, loss of myogenic tone was associated with a decreased depolarization-induced calcium influx, and was restored by the L-type channel agonist Bay K 8644 or by transient stimulation with angiotensin II (Ang II). The effect of Ang II was dependent on AT1-receptors and activation of the PI3-kinase/Akt pathway.

CONCLUSION

In this study we have identified novel mechanisms that regulate myogenic tone in resistance arteries, which involves microRNA-dependent control of PI3-kinase/Akt signalling and L-type calcium influx. Furthermore, we have demonstrated that transient stimulation by Ang II can have long-lasting effects by potentiating myogenic tone.

Down-regulation of CaV1.2 channels during hypertension: how fewer CaV1.2 channels allow more Ca(2+) into hypertensive arterial smooth muscle

Hypertension is a clinical syndrome characterized by increased arterial tone. Although the mechanisms are varied, the generally accepted view is that increased CaV1.2 channel function is a common feature of this pathological condition. Here, we investigated the mechanisms underlying vascular dysfunction in a mouse model of genetic hypertension. Contrary to expectation, we found that whole-cell CaV1.2 currents (ICa) were lower in hypertensive (BPH line) than normotensive (BPN line) myocytes. However, local CaV1.2 sparklet activity was higher in BPH cells, suggesting that the relatively low ICa in these cells was produced by a few hyperactive CaV1.2 channels. Furthermore, our data suggest that while the lower expression of the pore-forming α1c subunit of CaV1.2 currents underlies the lower ICa in BPH myocytes, the increased sparklet activity was due to a different composition in the auxiliary subunits of the CaV1.2 complexes. ICa currents in BPN cells were produced by channels composed of α1c/α2δ/β3 subunits, while in BPH myocytes currents were probably generated by the opening of channels formed by α1c/α2δ/β2 subunits. In addition, Ca(2+) sparks evoked large conductance, Ca(2+)-activated K(+) (BK) currents of lower magnitude in BPH than in BPN myocytes, because BK channels were less sensitive to Ca(2+). Our data are consistent with a model in which a decrease in the global number of CaV1.2 currents coexist with the existence of a subpopulation of highly active channels that dominate the resting Ca(2+) influx. The decrease in BK channel activity makes the hyperpolarizing brake ineffective and leads BPH myocytes to a more contracted resting state.

The voltage-dependent L-type Ca2+ (CaV1.2) channel C-terminus fragment is a bi-modal vasodilator

Voltage-dependent L-type Ca(2+) channels (CaV1.2) are the primary Ca(2+) entry pathway in vascular smooth muscle cells (myocytes). CaV1.2 channels control systemic blood pressure and organ blood flow and are pathologically altered in vascular diseases, which modifies vessel contractility. The CaV1.2 distal C-terminus is susceptible to proteolytic cleavage, which yields a truncated CaV1.2 subunit and a cleaved C-terminal fragment (CCt). Previous studies in cardiac myocytes and neurons have identified CCt as both a transcription factor and CaV1.2 channel inhibitor, with different signalling mechanisms proposed to underlie some of these effects. CCt existence and physiological functions in arterial myocytes are unclear, but important to study given the functional significance of CaV1.2 channels. Here, we show that CCt exists in myocytes of both rat and human resistance-size cerebral arteries, where it locates to both the nucleus and plasma membrane. Recombinant CCt expression in arterial myocytes inhibited CaV1.2 transcription and reduced CaV1.2 protein. CCt induced a depolarizing shift in the voltage dependence of both CaV1.2 current activation and inactivation, and reduced non-inactivating current in myocytes. Recombinant truncated CCt lacking a putative nuclear localization sequence (92CCt) did not locate to the nucleus and had no effect on arterial CaV1.2 transcription or protein. However, 92CCt shifted the voltage dependence of CaV1.2 activation and inactivation similarly to CCt. CCt and 92CCt both inhibited pressure- and depolarization-induced vasoconstriction, although CCt was a far more effective vasodilator. These data demonstrate that endogenous CCt exists and reduces both CaV1.2 channel expression and voltage sensitivity in arterial myocytes. Thus, CCt is a bi-modal vasodilator.

An elevation in physical coupling of type 1 inositol 1,4,5-trisphosphate (IP3) receptors to transient receptor potential 3 (TRPC3) channels constricts mesenteric arteries in genetic hypertension

Hypertension is associated with an elevation in agonist-induced vasoconstriction, but mechanisms involved require further investigation. Many vasoconstrictors bind to phospholipase C-coupled receptors, leading to an elevation in inositol 1,4,5-trisphosphate (IP(3)) that activates sarcoplasmic reticulum IP(3) receptors. In cerebral artery myocytes, IP(3) receptors release sarcoplasmic reticulum Ca(2+) and can physically couple to canonical transient receptor potential 3 (TRPC3) channels in a caveolin-1-containing macromolecular complex, leading to cation current activation that stimulates vasoconstriction. Here, we investigated mechanisms by which IP(3) receptors control vascular contractility in systemic arteries and IP(3)R involvement in elevated agonist-induced vasoconstriction during hypertension. Total and plasma membrane-localized TRPC3 protein was ≈2.7- and 2-fold higher in mesenteric arteries of spontaneously hypertensive rats (SHRs) than in Wistar-Kyoto (WKY) rat controls, respectively. In contrast, IP(3)R1, TRPC1, TRPC6, and caveolin-1 expression was similar. TRPC3 expression was also similar in arteries of pre-SHRs and WKY rats. Control, IP(3)-induced and endothelin-1 (ET-1)-induced fluorescence resonance energy transfer between IP3R1 and TRPC3 was higher in SHR than WKY myocytes. IP3-induced cation current was ≈3-fold larger in SHR myocytes. Pyr3, a selective TRPC3 channel blocker, and calmodulin and IP(3) receptor binding domain peptide, an IP(3)R-TRP physical coupling inhibitor, reduced IP(3)-induced cation current and ET-1-induced vasoconstriction more in SHR than WKY myocytes and arteries. Thapsigargin, a sarcoplasmic reticulum Ca(2+)-ATPase blocker, did not alter ET-1-stimulated vasoconstriction in SHR or WKY arteries. These data indicate that ET-1 stimulates physical coupling of IP(3)R1 to TRPC3 channels in mesenteric artery myocytes, leading to vasoconstriction. Furthermore, an elevation in IP(3)R1 to TRPC3 channel molecular coupling augments ET-1-induced vasoconstriction during hypertension.