Impaired Trafficking of β1 Subunits Inhibits BK Channels in Cerebral Arteries of Hypertensive Rats

Arterial Smooth Muscle Cell AKAP150 Mediates Exercise-Induced Repression of CaV1.2 Channel Function in Cerebral Arteries of Hypertensive Rats

BACKGROUND

Hypertension is a major, prevalent risk factor for the development and progression of cerebrovascular disease. Regular exercise has been recommended as an excellent choice for the large population of individuals with mild-to-moderate elevations in blood pressure, but the mechanisms that underlie its vascular-protective and antihypertensive effects remain unknown. Here, we describe a mechanism by which myocyte AKAP150 (A-kinase anchoring protein 150) inhibition induced by exercise training alleviates voltage-dependent L-type Ca2+ channel (CaV1.2) activity and restores cerebral arterial function in hypertension.

METHODS

Spontaneously hypertensive rats and newly generated smooth muscle-specific AKAP150 knockin mice were used to assess the role of myocyte AKAP150/CaV1.2 channel in regulating cerebral artery function after exercise intervention.

RESULTS

Activation of the AKAP150/PKCα (protein kinase Cα) signaling increased CaV1.2 activity and Ca2+ influx of cerebral arterial myocyte, thus enhancing vascular tone in spontaneously hypertensive rats. Smooth muscle-specific AKAP150 knockin mice were hypertensive with higher CaV1.2 channel activity and increased vascular tone. Furthermore, treatment of Ang II (angiotensin II) resulted in a more pronounced increase in blood pressure in smooth muscle-specific AKAP150 knockin mice. Exercise training significantly reduced arterial myocyte AKAP150 expression and alleviated CaV1.2 channel activity, thus restoring cerebral arterial function in spontaneously hypertensive rats and smooth muscle-specific AKAP150 knockin mice. AT1R (AT1 receptor) and AKAP150 were interacted closely in arterial myocytes. Exercise decreased the circulating Ang II and Ang II-involved AT1R-AKAP150 association in myocytes of hypertension.

CONCLUSIONS

The current study demonstrates that aerobic exercise ameliorates CaV1.2 channel function via inhibiting myocyte AKAP150, which contributes to reduced cerebral arterial tone in hypertension.

Milestone Papers on Signal Transduction Mechanisms of Hypertension and Its Complications

To celebrate 100 years of American Heart Association-supported cardiovascular disease research, this review article highlights milestone papers that have significantly contributed to the current understanding of the signaling mechanisms driving hypertension and associated cardiovascular disorders. This article also includes a few of the future research directions arising from these critical findings. To accomplish this important mission, 4 principal investigators gathered their efforts to cover distinct yet intricately related areas of signaling mechanisms pertaining to the pathogenesis of hypertension. The renin-angiotensin system, canonical and novel contractile and vasodilatory pathways in the resistance vasculature, vascular smooth muscle regulation by membrane channels, and noncanonical regulation of blood pressure and vascular function will be described and discussed as major subjects.

Extracellular glucose and dysfunctional insulin receptor signaling independently upregulate arterial smooth muscle TMEM16A expression

Diabetes alters the function of ion channels responsible for regulating arterial smooth muscle membrane potential, resulting in vasoconstriction. Our prior research demonstrated an elevation of TMEM16A in diabetic arteries. Here, we explored the mechanisms involved in Transmembrane protein 16A (TMEM16A) gene expression. Our data indicate that a Snail-mediated repressor complex regulates arterial TMEM16A gene transcription. Snail expression was reduced in diabetic arteries while TMEM16A expression was upregulated. The TMEM16A promoter contained three canonical E-box sites. Electrophoretic mobility and super shift assays revealed that the -154 nt E-box was the binding site of the Snail repressor complex and binding of the repressor complex decreased in diabetic arteries. High glucose induced a biphasic contractile response in pressurized nondiabetic mouse hindlimb arteries incubated ex vivo. Hindlimb arteries incubated in high glucose also showed decreased phospho-protein kinase D1 and TMEM16A expression. In hindlimb arteries from nondiabetic mice, administration of a bolus dose of glucose activated protein kinase D1 signaling to induce Snail degradation. In both in vivo and ex vivo conditions, Snail expression exhibited an inverse relationship with the expression of protein kinase D1 and TMEM16A. In diabetic mouse arteries, phospho-protein kinase D1 increased while Akt2 and pGSK3β levels declined. These results indicate that in nondiabetic mice, high glucose triggers a transient deactivation of the Snail repressor complex to increase arterial TMEM16A expression independently of insulin signaling. Conversely, insulin resistance activates GSK3β signaling and enhances arterial TMEM16A channel expression. These data have uncovered the Snail-mediated regulation of arterial TMEM16A expression and its dysfunction during diabetes.NEW & NOTEWORTHY The calcium-activated chloride channel, TMEM16A, is upregulated in the diabetic vasculature to cause increased vasoconstriction. In this paper, we have uncovered that the TMEM16A gene expression is controlled by a Snail-mediated repressor complex that uncouples with both insulin-dependent and -independent pathways to allow for upregulated arterial protein expression thereby causing vasoconstriction. The paper highlights the effect of short- and long-term glucose-induced dysfunction of an ion channel expression as a causative factor in diabetic vascular disease.

Hyperoside ameliorates cerebral ischaemic-reperfusion injury by opening the TRPV4 channel in vivo through the IP3-PKC signalling pathway

CONTEXT

Hyperoside (Hyp), one of the active flavones from Rhododendron (Ericaceae), has beneficial effects against cerebrovascular disease. However, the effect of Hyp on vasodilatation has not been elucidated.

OBJECTIVE

To explore the effect of Hyp on vasodilatation in the cerebral basilar artery (CBA) of Sprague-Dawley (SD) rats suffering with ischaemic-reperfusion (IR) injury.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into sham, model, Hyp, Hyp + channel blocker and channel blocker groups. Hyp (50 mg/kg, IC₅₀ = 18.3 μg/mL) and channel blocker were administered via tail vein injection 30 min before ischaemic, followed by 20 min of ischaemic and 2 h of reperfusion. The vasodilation, hyperpolarization, ELISA assay, haematoxylin-eosin (HE), Nissl staining and channel-associated proteins and qPCR were analysed. Rat CBA smooth muscle cells were isolated to detect the Ca²⁺ concentration and endothelial cells were isolated to detect apoptosis rate.

RESULTS

Hyp treatment significantly ameliorated the brain damage induced by IR and evoked endothelium-dependent vasodilation rate (47.93 ± 3.09% vs. 2.99 ± 1.53%) and hyperpolarization (-8.15 ± 1.87 mV vs. -0.55 ± 0.42 mV) by increasing the expression of IP3R, PKC, transient receptor potential vanilloid channel 4 (TRPV4), IK_Ca and SK_Ca in the CBA. Moreover, Hyp administration significantly reduced the concentration of Ca²⁺ (49.08 ± 7.74% vs. 83.52 ± 6.93%) and apoptosis rate (11.27 ± 1.89% vs. 23.44 ± 2.19%) in CBA. Furthermore, these beneficial effects of Hyp were blocked by channel blocker.

DISCUSSION AND CONCLUSIONS

Although Hyp showed protective effect in ischaemic stroke, more clinical trial certification is needed due to the difference between animals and humans.

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.

Vasodilators mobilize SK3 channels in endothelial cells to produce arterial relaxation

Endothelial cells (ECs) line the lumen of all blood vessels and regulate functions, including contractility. Physiological stimuli, such as acetylcholine (ACh) and intravascular flow, activate transient receptor potential vanilloid 4 (TRPV4) channels, which stimulate small (SK3)- and intermediate (IK)-conductance Ca2+-activated potassium channels in ECs to produce vasodilation. Whether physiological vasodilators also modulate the surface abundance of these ion channels in ECs to elicit functional responses is unclear. Here, we show that ACh and intravascular flow stimulate rapid anterograde trafficking of an intracellular pool of SK3 channels in ECs of resistance-size arteries, which increases surface SK3 protein more than two-fold. In contrast, ACh and flow do not alter the surface abundance of IK or TRPV4 channels. ACh triggers SK3 channel trafficking by activating TRPV4-mediated Ca2+ influx, which stimulates Rab11A, a Rab GTPase associated with recycling endosomes. Superresolution microscopy data demonstrate that SK3 trafficking specifically increases the size of surface SK3 clusters which overlap with TRPV4 clusters. We also show that Rab11A-dependent trafficking of SK3 channels is an essential contributor to vasodilator-induced SK current activation in ECs and vasorelaxation. In summary, our data demonstrate that vasodilators activate Rab11A, which rapidly delivers an intracellular pool of SK3 channels to the vicinity of surface TRPV4 channels in ECs. This trafficking mechanism increases surface SK3 cluster size, elevates SK3 current density, and produces vasodilation. These data also demonstrate that SK3 and IK channels are differentially regulated by trafficking-dependent and -independent signaling mechanisms in endothelial cells.

Loss of IP3R-BKCa Coupling Is Involved in Vascular Remodeling in Spontaneously Hypertensive Rats

Mechanisms by which BK_Ca (large-conductance calcium-sensitive potassium) channels are involved in vascular remodeling in hypertension are not fully understood. Vascular smooth muscle cell (VSMC) proliferation and vascular morphology were compared between hypertensive and normotensive rats. BK_Ca channel activity, protein expression, and interaction with IP3R (inositol 1,4,5-trisphosphate receptor) were examined using patch clamp, Western blot analysis, and coimmunoprecipitation. On inside-out patches of VSMCs, the Ca²⁺-sensitivity and voltage-dependence of BK_Ca channels were similar between hypertensive and normotensive rats. In whole-cell patch clamp configuration, treatment of cells with the IP3R agonist, Adenophostin A (AdA), significantly increased BK_Ca channel currents in VSMCs of both strains of rats, suggesting IP3R-BK_Ca coupling; however, the AdA-induced increases in BK_Ca currents were attenuated in VSMCs of hypertensive rats, indicating possible IP3R-BK_Ca decoupling, causing BK_Ca dysfunction. Co-immunoprecipitation and Western blot analysis demonstrated that BK_Ca and IP3R proteins were associated together in VSMCs; however, the association of BK_Ca and IP3R proteins was dramatically reduced in VSMCs of hypertensive rats. Genetic disruption of IP3R-BK_Ca coupling using junctophilin-2 shRNA dramatically augmented Ang II-induced proliferation in VSMCs of normotensive rats. Subcutaneous infusion of NS1619, a BK_Ca opener, to reverse BK_Ca dysfunction caused by IP3R-BK_Ca decoupling significantly attenuated vascular hypertrophy in hypertensive rats. In summary, the data from this study demonstrate that loss of IP3R-BK_Ca coupling in VSMCs induces BK_Ca channel dysfunction, enhances VSMC proliferation, and thus, may contribute to vascular hypertrophy in hypertension.

Histamine Potentiates SARS-CoV-2 Spike Protein Entry Into Endothelial Cells

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which causes coronavirus disease (COVID-19) is one of the most serious global health crises in recent history. COVID-19 patient symptoms range from life-threatening to mild and asymptomatic, which presents unique problems in identifying, quarantining, and treating the affected individuals. The emergence of unusual symptoms among survivors, now referred to as “Long COVID”, is concerning, especially since much about the condition and the treatment of it is still relatively unknown. Evidence so far also suggests that some of these symptoms can be attributed to vascular inflammation. Although famotidine, the commonly used histamine H2 receptor (H2R) blocker, was shown to have no antiviral activity, recent reports indicate that it could prevent adverse outcomes in COVID-19 patients. Histamine is a classic proinflammatory mediator, the levels of which increase along with other cytokines during COVID-19 infection. Histamine activates H2R signaling, while famotidine specifically blocks H2R activation. Investigating the effects of recombinant SARS-CoV-2 spike protein S1 Receptor-Binding Domain (Spike) on ACE2 expression in cultured human coronary artery endothelial cells, we found that the presence of histamine potentiated spike-mediated ACE2 internalization into endothelial cells. This effect was blocked by famotidine, protein kinase A inhibition, or by H2 receptor protein knockdown. Together, these results indicate that histamine and histamine receptor signaling is likely essential for spike protein to induce ACE2 internalization in endothelial cells and cause endothelial dysfunction and that this effect can be blocked by the H2R blocker, famotidine.

Downregulation of large-conductance Ca2+-activated K+ channels in human umbilical arterial smooth muscle cells in gestational diabetes mellitus

AIMS

We investigated the changes in large-conductance Ca²⁺-activated K⁺ (BK_Ca) channels from human umbilical arterial smooth muscle cells experiencing gestational diabetes mellitus (GDM).

MAIN METHODS

Whole-cell patch-clamp technique, arterial tone measurement, RT-PCR, Quantitative real-time PCR, western blot were performed in human umbilical arterial smooth muscle cells.

KEY FINDINGS

Whole-cell BK_Ca current density was decreased in the GDM group compared with the normal group. The vasorelaxant effects of the synthetic BK_Ca channel activator NS-1619 (10 μM) were impaired in the GDM group compared with the normal group. Reverse-transcription polymerase chain reaction (RT-PCR), real-time RT-PCR, and western blot analyses suggested that the mRNA, total RNA, and protein expression levels of the BK_Ca channel were decreased in the GDM group relative to the normal group. In addition, the expression levels of protein kinase A and protein kinase G, which regulate BK_Ca channel activity, remained unchanged between the groups. Applying the BK_Ca channel inhibitor paxilline (10 μM) induced vasoconstriction and membrane depolarization of isolated umbilical arteries in the normal group but showed less of an effect on umbilical arteries in the GDM group.

SIGNIFICANCE

Our results demonstrate for the first time impaired BK_Ca current and BK_Ca channel-induced vasorelaxation activities that were not caused by impaired BK_Ca channel-regulated protein kinases, but by decreased expression of the BK_Ca channels, in the umbilical arteries of GDM patients.

KV1.5-KVβ1.3 Recycling Is PKC-Dependent

K_V1.5 channel function is modified by different regulatory subunits. K_Vβ1.3 subunits assemble with K_V1.5 channels and induce a fast and incomplete inactivation. Inhibition of PKC abolishes the K_Vβ1.3-induced fast inactivation, decreases the amplitude of the current K_V1.5–K_Vβ1.3 and modifies their pharmacology likely due to changes in the traffic of K_V1.5–K_Vβ1.3 channels in a PKC-dependent manner. In order to analyze this hypothesis, HEK293 cells were transfected with K_V1.5–K_Vβ1.3 channels, and currents were recorded by whole-cell configuration of the patch-clamp technique. The presence of K_V1.5 in the membrane was analyzed by biotinylation techniques, live cell imaging and confocal microscopy approaches. PKC inhibition resulted in a decrease of 33 ± 7% of channels in the cell surface due to reduced recycling to the plasma membrane, as was confirmed by confocal microscopy. Live cell imaging indicated that PKC inhibition almost abolished the recycling of the K_V1.5–K_Vβ1.3 channels, generating an accumulation of channels into the cytoplasm. All these results suggest that the trafficking regulation of K_V1.5–K_Vβ1.3 channels is dependent on phosphorylation by PKC and, therefore, they could represent a clinically relevant issue, mainly in those diseases that exhibit modifications in PKC activity.

Clinical Importance of the Human Umbilical Artery Potassium Channels

Potassium (K⁺) channels are usually predominant in the membranes of vascular smooth muscle cells (SMCs). These channels play an important role in regulating the membrane potential and vessel contractility-a role that depends on the vascular bed. Thus, the activity of K⁺ channels represents one of the main mechanisms regulating the vascular tone in physiological and pathophysiological conditions. Briefly, the activation of K⁺ channels in SMC leads to hyperpolarization and vasorelaxation, while its inhibition induces depolarization and consequent vascular contraction. Currently, there are four different types of K⁺ channels described in SMCs: voltage-dependent K⁺ (K_V) channels, calcium-activated K⁺ (K_Ca) channels, inward rectifier K⁺ (Kir) channels, and 2-pore domain K⁺ (K_2P) channels. Due to the fundamental role of K⁺ channels in excitable cells, these channels are promising therapeutic targets in clinical practice. Therefore, this review discusses the basic properties of the various types of K⁺ channels, including structure, cellular mechanisms that regulate their activity, and new advances in the development of activators and blockers of these channels. The vascular functions of these channels will be discussed with a focus on vascular SMCs of the human umbilical artery. Then, the clinical importance of K⁺ channels in the treatment and prevention of cardiovascular diseases during pregnancy, such as gestational hypertension and preeclampsia, will be explored.

Targeting BKCa Channels in Migraine: Rationale and Perspectives

Large (big)-conductance calcium-activated potassium (BK_Ca) channels are expressed in migraine-related structures such as the cranial arteries, trigeminal ganglion and trigeminal spinal nucleus, and they play a substantial role in vascular tonus and neuronal excitability. Using synthetic BK_Ca channels openers was associated with headache as a frequent adverse effect in healthy volunteers. Additionally, BK_Ca channels are downstream molecules in migraine signalling pathways that are activated by several compounds known to provoke migraine, including calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP) and glyceryl trinitrate (GTN). Also, there is a high affinity and a close coupling between BK_Ca channels and ATP-sensitive potassium (K_ATP) channels, the role of which has recently been established in migraine pathophysiology. These observations raise the question as to whether direct BK_Ca channel activation can provoke migraine in migraine patients, and whether the BK_Ca channel could be a potential novel anti-migraine target. Hence, randomized and placebo-controlled clinical studies on BK_Ca channel openers or blockers in migraine patients are needed.

Potassium channels in vascular smooth muscle: a pathophysiological and pharmacological perspective

Potassium (K⁺ ) ion channel activity is an important determinant of vascular tone by regulating cell membrane potential (MP). Activation of K⁺ channels leads to membrane hyperpolarization and subsequently vasodilatation, while inhibition of the channels causes membrane depolarization and then vasoconstriction. So far five distinct types of K⁺ channels have been identified in vascular smooth muscle cells (VSMCs): Ca⁺² -activated K⁺ channels (BK_{C a} ), voltage-dependent K⁺ channels (K_V ), ATP-sensitive K⁺ channels (K_ATP ), inward rectifier K⁺ channels (K_ir ), and tandem two-pore K⁺ channels (K₂ P). The activity and expression of vascular K⁺ channels are changed during major vascular diseases such as hypertension, pulmonary hypertension, hypercholesterolemia, atherosclerosis, and diabetes mellitus. The defective function of K⁺ channels is commonly associated with impaired vascular responses and is likely to become as a result of changes in K⁺ channels during vascular diseases. Increased K⁺ channel function and expression may also help to compensate for increased abnormal vascular tone. There are many pharmacological and genotypic studies which were carried out on the subtypes of K⁺ channels expressed in variable amounts in different vascular beds. Modulation of K⁺ channel activity by molecular approaches and selective drug development may be a novel treatment modality for vascular dysfunction in the future. This review presents the basic properties, physiological functions, pathophysiological, and pharmacological roles of the five major classes of K⁺ channels that have been determined in VSMCs.