Coupling of c-Src to large conductance voltage- and Ca2+-activated K+ channels as a new mechanism of agonist-induced vasoconstriction

Vascular smooth muscle BK channels limit ouabain-induced vasocontraction: Dual role of the Na/K-ATPase as a hub for Src-kinase and the Na/Ca-exchanger

Large-conductance, calcium-activated potassium channels (BK channels) and the Na/K-ATPase are expressed universally in vascular smooth muscle. The Na/K-ATPase may act via changes in the intracellular Ca2+ concentration mediated by the Na/Ca exchanger (NCX) and via Src kinase. Both pathways are known to regulate BK channels. Whether BK channels functionally interact in vascular smooth muscle cells with the Na/K-ATPase remains to be elucidated. Thus, this study addressed the hypothesis that BK channels limit ouabain-induced vasocontraction. Rat mesenteric arteries were studied using isometric myography, FURA-2 fluorimetry and proximity ligation assay. The BK channel blocker iberiotoxin potentiated methoxamine-induced contractions. The cardiotonic steroid, ouabain (10-5 M), induced a contractile effect of IBTX at basal tension prior to methoxamine administration and enhanced the pro-contractile effect of IBTX on methoxamine-induced contractions. These facilitating effects of ouabain were prevented by the inhibition of either NCX or Src kinase. Furthermore, inhibition of NCX or Src kinase reduced the BK channel-mediated negative feedback regulation of arterial contraction. The effects of NCX and Src kinase inhibition were independent of each other. Co-localization of the Na/K-ATPase and the BK channel was evident. Our data suggest that BK channels limit ouabain-induced vasocontraction by a dual mechanism involving the NCX and Src kinase signaling. The data propose that the NCX and the Src kinase pathways, mediating the ouabain-induced activation of the BK channel, act in an independent manner.

Receptor-specific contributions of caveolae, PKC, and Src tyrosine kinase to serotonergic and adrenergic regulation of Kv channels and vasoconstriction

AIMS

Caveolae are invaginated, Ω-shaped membrane structures. They are now recognized as portals for signal transduction of multiple chemical and mechanical stimuli. Notably, the contribution of caveolae has been reported to be receptor-specific. However, details of how they differentially contribute to receptor signaling remain unclear.

MAIN METHODS

Using isometric tension measurements, patch-clamping, and western blotting, we examined the contribution of caveolae and their related signaling pathways to serotonergic (5-HT2A receptor-mediated) and adrenergic (α1-adrenoceptor-mediated) signaling in rat mesenteric arteries.

KEY FINDINGS

Disruption of caveolae by methyl-β-cyclodextrin effectively blocked vasoconstriction mediated by the 5-HT2A receptor (5-HT2AR), but not by the α1-adrenoceptor. Caveolar disruption selectively impaired 5-HT2AR-mediated voltage-dependent K+ channel (Kv) inhibition, but not α1-adrenoceptor-mediated Kv inhibition. In contrast, both serotonergic and α1-adrenergic effects on vasoconstriction, as well as Kv currents, were similarly blocked by the Src tyrosine kinase inhibitor PP2. However, inhibition of protein kinase C (PKC) by either GO6976 or chelerythrine selectively attenuated the effects mediated by the α1-adrenoceptor, but not by 5-HT2AR. Disruption of caveolae decreased 5-HT2AR-mediated Src phosphorylation, but not α1-adrenoceptor-mediated Src phosphorylation. Finally, the PKC inhibitor GO6976 blocked Src phosphorylation by the α1-adrenoceptor, but not by 5-HT2AR.

SIGNIFICANCE

5-HT2AR-mediated Kv inhibition and vasoconstriction are dependent on caveolar integrity and Src tyrosine kinase, but not on PKC. In contrast, α1-adrenoceptor-mediated Kv inhibition and vasoconstriction are not dependent on caveolar integrity, but rather on PKC and Src tyrosine kinase. Caveolae-independent PKC is upstream of Src activation for α1-adrenoceptor-mediated Kv inhibition and vasoconstriction.

β3 Receptor Signaling in Pregnant Human Myometrium Suggests a Role for β3 Agonists as Tocolytics

Preterm labor leading to preterm birth is the leading cause of infant morbidity and mortality. At the present time, nothing can reliably halt labor once it begins. The knowledge that agonists of the β2 adrenergic receptor relax airway smooth muscle and are effective in the treatment of asthma led to the notion that β2 mimetics would prevent preterm birth by relaxing uterine smooth muscle. The activation of cAMP-dependent protein kinase by β2 receptors is unable to provide meaningful tocolysis. The failure of β2 agonists such as ritodrine and terbutaline to prevent preterm birth suggests that the regulation of uterine smooth muscle is disparate from that of airway. Other smooth muscle quiescent-mediating molecules, such as nitric oxide, relax vascular smooth muscle in a cGMP-protein kinase G-dependent manner; however, nitric oxide activation of protein kinase G fails to explain the relaxation of the myometrium to nitric oxide. Moreover, nitric oxide-mediated relaxation is blunted in preterm labor, and thus, for this reason and because of the fall in maternal blood pressure, nitric oxide cannot be employed as a tocolytic. The β3 adrenergic receptor-mediated relaxation of the human myometrium is claimed to be cAMP-dependent protein kinase-dependent. This is scientifically displeasing given the failure of β2 agonists as tocolytics and suggests a non-canonical signaling role for β3AR in myometrium. The addition of the β3 agonist mirabegron to pregnant human myometrial strips in the tissue bath relaxes oxytocin-induced contractions. Mirabegron stimulates nitric oxide production in myometrial microvascular endothelial cells, and the relaxation of uterine tissue in vitro is partially blocked by the addition of the endothelial nitric oxide synthase blocker Nω-Nitro-L-arginine. Recent data suggest that both endothelial and smooth muscle cells respond to β3 stimulation and contribute to relaxation through disparate signaling pathways. The repurposing of approved medications such as mirabegron (Mybetriq™) tested in human myometrium as uterine tocolytics can advance the prevention of preterm birth.

G Protein-Coupled Receptor 75 (GPR75) As a Novel Molecule for Targeted Therapy of Cancer and Metabolic Syndrome

In recent years, molecular targeted therapy has attracted more attention from researchers due to its high efficiency and fewer side effects. Researchers are attempting to find more specific ways to treat diseases. It has been found that there are different targets for the treatment of diseases such as cancer, obesity, and metabolic syndrome. It is important to find a potential target in order to lessen the side effects of current treatments. G Protein-coupled receptors (GPCRs) are a large family of transmembrane proteins that are expressed in many organs, leading to the activation of internal signal transduction cascades through the binding of different ligands, including neurotransmitters, peptides, and lipids. Due to the critical role of GPCRs in cells, it could be a potential target. G protein-coupled receptor 75 (GPR75) is a novel member of the GPCR family that has an important role in many diseases, such as obesity, cancer, and metabolic syndrome. Until now, three ligands have been detected for GPR75, including 20-HETE, CCL5, and RANTES. Recent studies suggest that 20-HETE, through GPR75, triggers signaling pathways including PI3K/Akt and RAS/MAPK, leading to a more aggressive phenotype in prostate cancer cells. Additionally, the PI3K/Akt and RAS/MAPK signaling pathways activate NF-κB, which is significant in various pathways of cancer development such as proliferation, migration, and apoptosis. The findings indicate that inhibiting GPR75 in humans leads to an increase in insulin sensitivity and glucose tolerance, as well as a reduction in body fat storage. According to these discoveries, GPR75 could be a potential target for drug treatment of diseases such as obesity, metabolic syndrome, and cancer. In this review, we aimed to discuss the therapeutic impact of GPR75 in cancer, metabolic syndrome, and obesity and underscore the possible pathways.

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

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

Coronary Large Conductance Ca2+-Activated K+ Channel Dysfunction in Diabetes Mellitus

Diabetes mellitus (DM) is an independent risk of macrovascular and microvascular complications, while cardiovascular diseases remain a leading cause of death in both men and women with diabetes. Large conductance Ca2+-activated K+ (BK) channels are abundantly expressed in arteries and are the key ionic determinant of vascular tone and organ perfusion. It is well established that the downregulation of vascular BK channel function with reduced BK channel protein expression and altered intrinsic BK channel biophysical properties is associated with diabetic vasculopathy. Recent efforts also showed that diabetes-associated changes in signaling pathways and transcriptional factors contribute to the downregulation of BK channel expression. This manuscript will review our current understandings on the molecular, physiological, and biophysical mechanisms that underlie coronary BK channelopathy in diabetes mellitus.

Angiotensin-II Modulates GABAergic Neurotransmission in the Mouse Substantia Nigra

GABAergic projections neurons of the substantia nigra reticulata (SNr), through an extensive network of dendritic arbors and axon collaterals, provide robust inhibitory input to neighboring dopaminergic neurons in the substantia nigra compacta (SNc). Angiotensin-II (Ang-II) receptor signaling increases SNc dopaminergic neuronal sensitivity to insult, thus rendering these cells susceptible to dysfunction and destruction. However, the mechanisms by which Ang-II regulates SNc dopaminergic neuronal activity are unclear. Given the complex relationship between SN dopaminergic and GABAergic neurons, we hypothesized that Ang-II could regulate SNc dopaminergic neuronal activity directly and indirectly by modulating SNr GABAergic neurotransmission. Here, using transgenic mice, slice electrophysiology, and optogenetics, we provide evidence of an AT₁ receptor-mediated signaling mechanism in SNr GABAergic neurons where Ang-II suppresses electrically-evoked neuronal output by facilitating postsynaptic GABA_A receptors (GABA_ARs) and prolonging the action potential (AP) duration. Unexpectedly, Ang-II had no discernable effects on the electrical properties of SNc dopaminergic neurons. Also, and indicating a nonlinear relationship between electrical activity and neuronal output, following phasic photoactivation of SNr GABAergic neurons, Ang-II paradoxically enhanced the feedforward inhibitory input to SNc dopaminergic neurons. In sum, our observations describe an increasingly complex and heterogeneous response of the SN to Ang-II by revealing cell-specific responses and nonlinear effects on intranigral GABAergic neurotransmission. Our data further implicate the renin-angiotensin-system (RAS) as a functionally relevant neuromodulator in the substantia nigra, thus underscoring a need for additional inquiry.

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.

Smooth muscle Ca2+ sensitization causes hypercontractility of middle cerebral arteries in mice bearing the familial hemiplegic migraine type 2 associated mutation

Familial hemiplegic migraine type 2 (FHM2) is associated with inherited point-mutations in the Na,K-ATPase α2 isoform, including G301R mutation. We hypothesized that this mutation affects specific aspects of vascular function, and thus compared cerebral and systemic arteries from heterozygote mice bearing the G301R mutation (Atp1a2^+/-G301R) with wild type (WT). Middle cerebral (MCA) and mesenteric small artery (MSA) function was compared in an isometric myograph. Cerebral blood flow was assessed with Laser speckle analysis. Intracellular Ca²⁺ and membrane potential were measured simultaneously. Protein expression was semi-quantified by immunohistochemistry. Protein phosphorylation was analysed by Western blot. MSA from Atp1a2^+/-G301R and WT showed similar contractile responses. The Atp1a2^+/-G301R MCA constricted stronger to U46619, endothelin and potassium compared to WT. This was associated with an increased depolarization, although the Ca²⁺ change was smaller than in WT. The enhanced constriction of Atp1a2^+/-G301R MCA was associated with increased cSrc activation, stronger sensitization to [Ca²⁺]_i and increased MYPT1 phosphorylation. These differences were abolished by cSrc inhibition. Atp1a2^+/-G301R mice had reduced resting blood flow through MCA in comparison with WT mice. FHM2-associated mutation leads to elevated contractility of MCA due to sensitization of the contractile machinery to Ca²⁺, which is mediated via Na,K-ATPase/Src-kinase/MYPT1 signalling.

The Na,K-ATPase in vascular smooth muscle cells

The Na,K-ATPase is an enzyme essential for ion homeostasis in all cells. Over the last decades, it has been well-established that in addition to the transport of Na⁺/K⁺ over the cell membrane, the Na,K-ATPase acts as a receptor transducing humoral signals intracellularly. It has been suggested that ouabain-like compounds serve as endogenous modulators of this Na,K-ATPase signal transduction. The molecular mechanisms underlying Na,K-ATPase signaling are complicated and suggest the confluence of divergent biological pathways. This review discusses recent updates on the Na,K-ATPase signaling pathways characterized or suggested in vascular smooth muscle cells. The conventional view on this signaling is based on a microdomain structure where the Na,K-ATPase controls the Na,Ca-exchanger activity via modulation of intracellular Na⁺ in the spatially restricted submembrane space. This, in turn, affects intracellular Ca²⁺ and Ca²⁺ load in the sarcoplasmic reticulum leading to modulation of contractility as well as gene expression. An ion-transport-independent signal transduction from the Na,K-ATPase is based on molecular interactions. This was primarily characterized in other cell types but recently also demonstrated in vascular smooth muscles. The downstream signaling from the Na,K-ATPase includes Src and phosphatidylinositol-4,5-bisphosphate 3 kinase signaling pathways and generation of reactive oxygen species. Moreover, in vascular smooth muscle cells the interaction between the Na,K-ATPase and proteins responsible for Ca²⁺ homeostasis, e.g., phospholipase C and inositol triphosphate receptors, contributes to an integration of the signaling pathways. Recent update on the Na,K-ATPase dependent intracellular signaling and the significance for physiological functions and pathophysiological changes are discussed in this review.

The α2 isoform Na,K-ATPase modulates contraction of rat mesenteric small artery via cSrc-dependent Ca2+ sensitization

AIMS

The Na,K-ATPase is involved in a large number of regulatory activities including cSrc-dependent signalling. Upon inhibition of the Na,K-ATPase with ouabain, cSrc activation is shown to occur in many cell types. This study tests the hypothesis that acute potentiation of agonist-induced contraction by ouabain is mediated through Na,K-ATPase-cSrc signalling-dependent sensitization of vascular smooth muscle cells to Ca²⁺ .

METHODS

Agonist-induced rat mesenteric small artery contraction was examined in vitro under isometric conditions and in vivo in anaesthetized rats. Arterial wall tension and [Ca²⁺ ]_i in vascular smooth muscle cells were measured simultaneously. Changes in cSrc and myosin phosphatase targeting protein 1 (MYPT1) phosphorylation were analysed by Western blot. Protein expression was examined with immunohistochemistry. The α1 and α2 isoforms of the Na,K-ATPase were transiently downregulated by siRNA transfection in vivo.

RESULTS

Ten micromolar ouabain, but not digoxin, potentiated contraction to noradrenaline. This effect was not endothelium-dependent. Ouabain sensitized smooth muscle cells to Ca²⁺ , and this was associated with increased phosphorylation of cSrc and MYPT1. Inhibition of tyrosine kinase by genistein, PP2 or pNaKtide abolished the potentiating effect of ouabain on arterial contraction and Ca²⁺ sensitization. Downregulation of the Na,K-ATPase α2 isoform made arterial contraction insensitive to ouabain and tyrosine kinase inhibition.

CONCLUSION

Data suggest that micromolar ouabain potentiates agonist-induced contraction of rat mesenteric small artery via Na,K-ATPase-dependent cSrc activation, which increases Ca²⁺ sensitization of vascular smooth muscle cells by MYPT1 phosphorylation. This mechanism may be critical for acute control of vascular tone.

G protein pathway suppressor 2 enhanced the renal large-conductance Ca2+-activated potassium channel expression via inhibiting ERK1/2 signaling pathway

G protein pathway suppressor 2 (GPS2) is a multifunctional protein and transcriptional regulation factor that is involved in the G protein MAPK signaling pathway. It has been shown that the MAPK signaling pathway plays an important role in the regulation of renal large-conductance Ca²⁺-activated potassium (BK) channels. In this study, we investigated the effects of GPS2 on BK channel activity and protein expression. In human embryonic kidney (HEK) BK stably expressing cells transfected with either GPS2 or its vector control, a single-cell recording showed that GPS2 significantly increased BK channel activity ( NP_o), increasing BK open probability ( P_o), and channel number ( N) compared with the control. In Cos-7 cells and HEK 293 T cells, GPS2 overexpression significantly enhanced the total protein expression of BK in a dose-dependent manner. Knockdown of GPS2 expression significantly decreased BK protein expression, while increasing ERK1/2 phosphorylation. Knockdown of ERK1/2 expression reversed the GPS2 siRNA-mediated inhibition of BK protein expression in Cos-7 cells. Pretreatments of Cos-7 cells with either the lysosomal inhibitor bafilomycin A1 or the proteasomal inhibitor MG132 partially reversed the inhibitory effects of GPS2 siRNA on BK protein expression. In addition, feeding a high-potassium diet significantly increased both GPS2 and BK protein abundance in mice. These data suggest that GPS2 enhances BK channel activity and its protein expression by reducing ERK1/2 signaling-mediated degradation of the channel.

The Unexpected Role of Calcium-Activated Potassium Channels: Limitation of NO-Induced Arterial Relaxation

BACKGROUND

Multiple studies have shown that an NO-induced activation of vascular smooth muscle BK channels contributes to the NO-evoked dilation in many blood vessels. In vivo, NO is released continuously. NO attenuates vessel constrictions and, therefore, exerts an anticontractile effect. It is unknown whether the anticontractile effect of continuously present NO is mediated by BK channels.

METHODS AND RESULTS

This study tested the hypothesis that BK channels mediate the vasodilatory effect of continuously present NO. Experiments were performed on rat and mouse tail and rat saphenous arteries using isometric myography and FURA-2 fluorimetry. Continuously present NO donors, as well as endogenous NO, attenuated methoxamine-induced vasoconstrictions. This effect was augmented in the presence of the BK channel blocker iberiotoxin. Moreover, the contractile effect of iberiotoxin was reduced in the presence of NO donors. The effect of the NO donor sodium nitroprusside was abolished by an NO scavenger and by a guanylyl cyclase inhibitor. In addition, the effect of sodium nitroprusside was reduced considerably by a protein kinase G inhibitor, but was not altered by inhibition of H2S generation. Sodium nitroprusside attenuated the intracellular calcium concentration response to methoxamine. Furthermore, sodium nitroprusside strongly reduced methoxamine-induced calcium influx, which depends entirely on L-type calcium channels. It did not affect methoxamine-induced calcium release.

CONCLUSIONS

In summary, this study demonstrates the following: (1) continuously present NO evokes a strong anticontractile effect on rat and mouse arteries; (2) the iberiotoxin-induced augmentation of the effect of NO is associated with an NO-induced reduction of the effect of iberiotoxin; and (3) NO evoked a reduction of calcium influx via L-type calcium channels.

JAK2 mediates lung fibrosis, pulmonary vascular remodelling and hypertension in idiopathic pulmonary fibrosis: an experimental study

BACKGROUND

Pulmonary hypertension (PH) is a common disorder in patients with idiopathic pulmonary fibrosis (IPF) and portends a poor prognosis. Recent studies using vasodilators approved for PH have failed in improving IPF mainly due to ventilation (V)/perfusion (Q) mismatching and oxygen desaturation. Janus kinase type 2 (JAK2) is a non-receptor tyrosine kinase activated by a broad spectrum of profibrotic and vasoactive mediators, but its role in PH associated to PH is unknown.

OBJECTIVE

The study of JAK2 as potential target to treat PH in IPF.

METHODS AND RESULTS

JAK2 expression was increased in pulmonary arteries (PAs) from IPF (n=10; 1.93-fold; P=0.0011) and IPF+PH (n=9; 2.65-fold; P<0.0001) compared with PA from control subjects (n=10). PA remodelling was evaluated in human pulmonary artery endothelial cells (HPAECs) and human pulmonary artery smooth muscle cells (HPASMCs) from patients with IPF in vitro treated with the JAK2 inhibitor JSI-124 or siRNA-JAK2 and stimulated with transforming growth factor beta. Both JSI-124 and siRNA-JAK2 inhibited the HPAEC to mesenchymal transition and the HPASMCs to myofibroblast transition and proliferation. JAK2 inhibition induced small PA relaxation in precision-cut lung slice experiments. PA relaxation was dependent of the large conductance calcium-activated potassium channel (BK_Ca). JAK2 inhibition activated BK_Ca channels and reduced intracellular Ca²⁺. JSI-124 1 mg/kg/day, reduced bleomycin-induced lung fibrosis, PA remodelling, right ventricular hypertrophy, PA hypertension and V/Q mismatching in rats. The animal studies followed the ARRIVE guidelines.

CONCLUSIONS

JAK2 participates in PA remodelling and tension and may be an attractive target to treat IPF associated to PH.

Na-K-ATPase regulates intercellular communication in the vascular wall via cSrc kinase-dependent connexin43 phosphorylation

Communication between vascular smooth muscle cells (VSMCs) is dependent on gap junctions and is regulated by the Na-K-ATPase. The Na-K-ATPase is therefore important for synchronized VSMC oscillatory activity, i.e., vasomotion. The signaling between the Na-K-ATPase and gap junctions is unknown. We tested here the hypothesis that this signaling involves cSrc kinase. Intercellular communication was assessed by membrane capacitance measurements of electrically coupled VSMCs. Vasomotion in isometric myograph, input resistance, and synchronized [Ca2+]i transients were used as readout for intercellular coupling in rat mesenteric small arteries in vitro. Phosphorylation of cSrc kinase and connexin43 (Cx43) were semiquantified by Western blotting. Micromole concentration of ouabain reduced the amplitude of norepinephrine-induced vasomotion and desynchronized Ca2+ transients in VSMC in the arterial wall. Ouabain also increased input resistance in the arterial wall. These effects of ouabain were antagonized by inhibition of tyrosine phosphorylation with genistein, PP2, and by an inhibitor of the Na-K-ATPase-dependent cSrc activation, pNaKtide. Moreover, inhibition of cSrc phosphorylation increased vasomotion amplitude and decreased the resistance between cells in the vascular wall. Ouabain inhibited the electrical coupling between A7r5 cells, but pNaKtide restored the electrical coupling. Ouabain increased cSrc autophosphorylation of tyrosine 418 (Y418) required for full catalytic activity whereas pNaKtide antagonized it. This cSrc activation was associated with Cx43 phosphorylation of tyrosine 265 (Y265). Our findings demonstrate that Na-K-ATPase regulates intercellular communication in the vascular wall via cSrc-dependent Cx43 tyrosine phosphorylation.

20-HETE Signals Through G-Protein-Coupled Receptor GPR75 (Gq) to Affect Vascular Function and Trigger Hypertension

RATIONALE

20-Hydroxyeicosatetraenoic acid (20-HETE), one of the principle cytochrome P450 eicosanoids, is a potent vasoactive lipid whose vascular effects include stimulation of smooth muscle contractility, migration, and proliferation, as well as endothelial cell dysfunction and inflammation. Increased levels of 20-HETE in experimental animals and in humans are associated with hypertension, stroke, myocardial infarction, and vascular diseases.

OBJECTIVE

To date, a receptor/binding site for 20-HETE has been implicated based on the use of specific agonists and antagonists. The present study was undertaken to identify a receptor to which 20-HETE binds and through which it activates a signaling cascade that culminates in many of the functional outcomes attributed to 20-HETE in vitro and in vivo.

METHODS AND RESULTS

Using crosslinking analogs, click chemistry, binding assays, and functional assays, we identified G-protein receptor 75 (GPR75), currently an orphan G-protein-coupled receptor (GPCR), as a specific target of 20-HETE. In cultured human endothelial cells, 20-HETE binding to GPR75 stimulated Gα_q/11 protein dissociation and increased inositol phosphate accumulation and GPCR-kinase interacting protein-1-GPR75 binding, which further facilitated the c-Src-mediated transactivation of epidermal growth factor receptor. This results in downstream signaling pathways that induce angiotensin-converting enzyme expression and endothelial dysfunction. Knockdown of GPR75 or GPCR-kinase interacting protein-1 prevented 20-HETE-mediated endothelial growth factor receptor phosphorylation and angiotensin-converting enzyme induction. In vascular smooth muscle cells, GPR75-20-HETE pairing is associated with Gα_q/11- and GPCR-kinase interacting protein-1-mediated protein kinase C-stimulated phosphorylation of MaxiKβ, linking GPR75 activation to 20-HETE-mediated vasoconstriction. GPR75 knockdown in a mouse model of 20-HETE-dependent hypertension prevented blood pressure elevation and 20-HETE-mediated increases in angiotensin-converting enzyme expression, endothelial dysfunction, smooth muscle contractility, and vascular remodeling.

CONCLUSIONS

This is the first report to identify a GPCR target for an eicosanoid of this class. The discovery of 20-HETE-GPR75 pairing presented here provides the molecular basis for the signaling and pathophysiological functions mediated by 20-HETE in hypertension and cardiovascular diseases.

Tyrphostin AG556 increases the activity of large conductance Ca2+ -activated K+ channels by inhibiting epidermal growth factor receptor tyrosine kinase

The present study was designed to investigate whether large conductance Ca²⁺‐activated K⁺ (BK) channels were regulated by epidermal growth factor (EGF) receptor (EGFR) tyrosine kinase. BK current and channel tyrosine phosphorylation level were measured in BK‐HEK 293 cells expressing both functional α‐subunits and the auxiliary β1‐subunits using electrophysiology, immunoprecipitation and Western blotting approaches, respectively, and the function of rat cerebral basilar arteries was determined with a wire myography system. We found that BK current in BK‐HEK 293 cells was increased by the broad spectrum protein tyrosine kinase (PTK) inhibitor genistein and the selective EGFR tyrosine kinase inhibitor AG556, one of the known tyrphostin. The effect of genistein or AG556 was antagonized by the protein tyrosine phosphatase (PTP) inhibitor orthovanadate. On the other hand, orthovanadate or EGF decreased BK current, and the effect was counteracted by AG556. The tyrosine phosphorylation level of BK channels (α‐ and β1‐subunits) was increased by EGF and orthovanadate, while decreased by genistein and AG556, and the reduced tyrosine phosphorylation of BK channels by genistein or AG556 was reversed by orthovanadate. Interestingly, AG556 induced a remarkable enhancement of BK current in rat cerebral artery smooth muscle cells and relaxation of pre‐contracted rat cerebral basilar arteries with denuded endothelium, and these effects were antagonized by the BK channel blocker paxilline or orthovanadate. These results demonstrate that tyrosine phosphorylation of BK channels by EGFR kinase decreases the channel activity, and inhibition of EGFR kinase by AG556 enhances the channel activity and dilates rat cerebral basilar arteries.

Specialized Functional Diversity and Interactions of the Na,K-ATPase

Na,K-ATPase is a protein ubiquitously expressed in the plasma membrane of all animal cells and vitally essential for their functions. A specialized functional diversity of the Na,K-ATPase isozymes is provided by molecular heterogeneity, distinct subcellular localizations, and functional interactions with molecular environment. Studies over the last decades clearly demonstrated complex and isoform-specific reciprocal functional interactions between the Na,K-ATPase and neighboring proteins and lipids. These interactions are enabled by a spatially restricted ion homeostasis, direct protein-protein/lipid interactions, and protein kinase signaling pathways. In addition to its "classical" function in ion translocation, the Na,K-ATPase is now considered as one of the most important signaling molecules in neuronal, epithelial, skeletal, cardiac and vascular tissues. Accordingly, the Na,K-ATPase forms specialized sub-cellular multimolecular microdomains which act as receptors to circulating endogenous cardiotonic steroids (CTS) triggering a number of signaling pathways. Changes in these endogenous cardiotonic steroid levels and initiated signaling responses have significant adaptive values for tissues and whole organisms under numerous physiological and pathophysiological conditions. This review discusses recent progress in the studies of functional interactions between the Na,K-ATPase and molecular microenvironment, the Na,K-ATPase-dependent signaling pathways and their significance for diversity of cell function.

Posttranscriptional and Posttranslational Regulation of BK Channels

Large conductance calcium- and voltage-activated potassium (BK) channels are ubiquitously expressed and play an important role in the regulation of an eclectic array of physiological processes. Their diverse functional role requires channels with a wide variety of properties even though the pore-forming α-subunit is encoded by a single gene, KCNMA1. To achieve this, BK channels exploit some of the most fundamental posttranscriptional and posttranslational mechanisms that allow proteomic diversity to be generated from a single gene. These include mechanisms that diversify mRNA variants and abundance such as alternative pre-mRNA splicing, editing, and control by miRNA. The BK channel is also subject to a diverse array of posttranslational modifications including protein phosphorylation, lipidation, glycosylation, and ubiquitination to control the number, properties, and regulation of BK channels in specific cell types. Importantly, "cross talk" between these posttranscriptional and posttranslational modifications typically converge on disordered domains of the BK channel α-subunit. This allows both wide physiological diversity to be generated and a diversity of mechanisms to allow conditional regulation of BK channels and is emerging as an important determinant of BK channel function in health and disease.

Calcium-Activated Potassium Channels: Potential Target for Cardiovascular Diseases

Ca(2+)-activated K(+) channels (KCa) are classified into three subtypes: big conductance (BKCa), intermediate conductance (IKCa), and small conductance (SKCa) KCa channels. The three types of KCa channels have distinct physiological or pathological functions in cardiovascular system. BKCa channels are mainly expressed in vascular smooth muscle cells (VSMCs) and inner mitochondrial membrane of cardiomyocytes, activation of BKCa channels in these locations results in vasodilation and cardioprotection against cardiac ischemia. IKCa channels are expressed in VSMCs, endothelial cells, and cardiac fibroblasts and involved in vascular smooth muscle proliferation, migration, vessel dilation, and cardiac fibrosis. SKCa channels are widely expressed in nervous and cardiovascular system, and activation of SKCa channels mainly contributes membrane hyperpolarization. In this chapter, we summarize the physiological and pathological roles of the three types of KCa channels in cardiovascular system and put forward the possibility of KCa channels as potential target for cardiovascular diseases.

An unexpected journey: conceptual evolution of mechanoregulated potassium transport in the distal nephron

Flow-induced K secretion (FIKS) in the aldosterone-sensitive distal nephron (ASDN) is mediated by large-conductance, Ca(2+)/stretch-activated BK channels composed of pore-forming α-subunits (BKα) and accessory β-subunits. This channel also plays a critical role in the renal adaptation to dietary K loading. Within the ASDN, the cortical collecting duct (CCD) is a major site for the final renal regulation of K homeostasis. Principal cells in the ASDN possess a single apical cilium whereas the surfaces of adjacent intercalated cells, devoid of cilia, are decorated with abundant microvilli and microplicae. Increases in tubular (urinary) flow rate, induced by volume expansion, diuretics, or a high K diet, subject CCD cells to hydrodynamic forces (fluid shear stress, circumferential stretch, and drag/torque on apical cilia and presumably microvilli/microplicae) that are transduced into increases in principal (PC) and intercalated (IC) cell cytoplasmic Ca(2+) concentration that activate apical voltage-, stretch- and Ca(2+)-activated BK channels, which mediate FIKS. This review summarizes studies by ourselves and others that have led to the evolving picture that the BK channel is localized in a macromolecular complex at the apical membrane, composed of mechanosensitive apical Ca(2+) channels and a variety of kinases/phosphatases as well as other signaling molecules anchored to the cytoskeleton, and that an increase in tubular fluid flow rate leads to IC- and PC-specific responses determined, in large part, by the cell-specific composition of the BK channels.

Rottlerin-induced BKCa channel activation impairs specific contractile responses and promotes vasodilation

BACKGROUND

Activation of large conductance calcium-activated potassium (BKCa) channels is cardioprotective for ischemic injury and can enhance vasorelaxation. Rottlerin has recently been identified as a potent BKCa activator. We demonstrated that rottlerin improves cardiac function and increases coronary flow when used as a cardioplegia additive in rat and mouse models of cardioplegic arrest and reperfusion. In this study we examined the effectiveness and specificity of the putative BKCa activator rottlerin on vascular reactivity in response to specific contractile and dilatory agonists.

METHODS

Aortic rings from wild-type (wt) and BKCa knock-out (KO) mice were mounted in a tissue bath with force transducers. The vasodilatory effect of rottlerin was evaluated after pre-constriction with U46619. Dose responses to the contractile agonists U46619 and phenylephrine (PE), and vasodilation responses to rottlerin, hydrogen sulfide (H2S), and sodium nitroprusside (SNP) were performed after pretreatment with rottlerin. Similar studies were performed in pig coronary vessels.

RESULTS

The BKCa KO mouse aortic rings exhibited spontaneous contraction and had greater contractile responses to U46619 and reduced vasodilation to SNP compared with wt mice. The wt and KO responses to phenylephrine were similar. Rottlerin dose dependently dilated wild-type vessels, but not in BKCa KO animals. Pretreatment with rottlerin caused depressed U46619 responses, but had no effect on PE, SNP, or H2S-mediated responses. However, pig coronary vessels pretreated with rottlerin exhibited reduced contractile responses and enhanced nitric oxide-dependent dilation.

CONCLUSIONS

Rottlerin directly causes vasodilation through BKCa channel dependent mechanisms. The BKCa channel activator pretreatment enhances vasodilatory responses and impairs specific vasoconstrictive agonists.

Control of vascular smooth muscle function by Src-family kinases and reactive oxygen species in health and disease

Reactive oxygen species (ROS) are now recognised as second messenger molecules that regulate cellular function by reversibly oxidising specific amino acid residues of key target proteins. Amongst these are the Src-family kinases (SrcFKs), a multi-functional group of non-receptor tyrosine kinases highly expressed in vascular smooth muscle (VSM). In this review we examine the evidence supporting a role for ROS-induced SrcFK activity in normal VSM contractile function and in vascular remodelling in cardiovascular disease. VSM contractile responses to G-protein-coupled receptor stimulation, as well as hypoxia in pulmonary artery, are shown to be dependent on both ROS and SrcFK activity. Specific phosphorylation targets are identified amongst those that alter intracellular Ca(2+) concentration, including transient receptor potential channels, voltage-gated Ca(2+) channels and various types of K(+) channels, as well as amongst those that regulate actin cytoskeleton dynamics and myosin phosphatase activity, including focal adhesion kinase, protein tyrosine kinase-2, Janus kinase, other focal adhesion-associated proteins, and Rho guanine nucleotide exchange factors. We also examine a growing weight of evidence in favour of a key role for SrcFKs in multiple pro-proliferative and anti-apoptotic signalling pathways relating to oxidative stress and vascular remodelling, with a particular focus on pulmonary hypertension, including growth-factor receptor transactivation and downstream signalling, hypoxia-inducible factors, positive feedback between SrcFK and STAT3 signalling and positive feedback between SrcFK and NADPH oxidase dependent ROS production. We also discuss evidence for and against the potential therapeutic targeting of SrcFKs in the treatment of pulmonary hypertension.

Mechanisms underlying vasorelaxation induced in rat aorta by galetin 3,6-dimethyl ether, a flavonoid from Piptadenia stipulacea (Benth.) Ducke

In this study, we investigated the relaxant action of galetin 3,6-dimethyl ether (FGAL) on rat aorta. The flavonoid relaxed both PMA‑ and phenylephrine (Phe)-induced contractions (pD₂ = 5.36 ± 0.11 and 4.17 ± 0.10, respectively), suggesting the involvement of PKC and Phe pathways or α₁ adrenergic receptor blockade. FGAL inhibited and rightward shifted Phe-induced cumulative concentration‑response curves, indicating a noncompetitive antagonism of α₁ adrenergic receptors. The flavonoid was more potent in relaxing 30 mM KCl- than 80 mM KCl-induced contractions (pD₂ = 5.50 ± 0.22 and 4.37 ± 0.12). The vasorelaxant potency of FGAL on Phe-induced contraction was reduced in the presence of 10 mM TEA⁺. Furthermore, in the presence of apamin, glibenclamide, BaCl₂ or 4-AP, FGAL-induced relaxation was attenuated, indicating the participation of small conductance calcium-activated K⁺ channels (SK_Ca), ATP-sensitive K⁺ channels (K_ATP), inward rectifier K⁺ channels (K_ir) and voltage-dependent K⁺ channels (K_V), respectively. FGAL inhibited and rightward shifted CaCl₂-induced cumulative concentration-response curves in both depolarizing medium (high K⁺) and in the presence of verapamil and phenylephrine, suggesting inhibition of Ca²⁺ influx through voltage-gated calcium channels (Ca_V) and receptor operated channels (ROCs), respectively. Likewise, FGAL inhibited Phe-induced contractions in Ca²⁺-free medium, indicating inhibition of Ca²⁺ release from the sarcoplasmic reticulum (SR). FGAL potentiated the relaxant effect of aminophylline and sildenafil but not milrinone, suggesting the involvement of phosphodiesterase V (PDE V). Thus, the FGAL vasorelaxant mechanism involves noncompetitive antagonism of α₁ adrenergic receptors, the non-selective opening of K⁺ channels, inhibition of Ca²⁺ influx through Ca_V or ROCs and the inhibition of intracellular Ca²⁺ release. Additionally, there is the involvement of cyclic nucleotide pathway, particularly through PDE V inhibition.

Large conductance voltage- and Ca2+-gated potassium (BK) channel β4 subunit influences sensitivity and tolerance to alcohol by altering its response to kinases

Tolerance is a well described component of alcohol abuse and addiction. The large conductance voltage- and Ca(2+)-gated potassium channel (BK) has been very useful for studying molecular tolerance. The influence of association with the β4 subunit can be observed at the level of individual channels, action potentials in brain slices, and finally, drinking behavior in the mouse. Previously, we showed that 50 mm alcohol increases both α and αβ4 BK channel open probability, but only α BK develops acute tolerance to this effect. Currently, we explore the possibility that the influence of the β4 subunit on tolerance may result from a striking effect of β4 on kinase modulation of the BK channel. We examine the influence of the β4 subunit on PKA, CaMKII, and phosphatase modulation of channel activity, and on molecular tolerance to alcohol. We record from human BK channels heterologously expressed in HEK 293 cells composed of its core subunit, α alone (Insertless), or co-expressed with the β4 BK auxiliary subunit, as well as, acutely dissociated nucleus accumbens neurons using the cell-attached patch clamp configuration. Our results indicate that BK channels are strongly modulated by activation of specific kinases (PKA and CaMKII) and phosphatases. The presence of the β4 subunit greatly influences this modulation, allowing a variety of outcomes for BK channel activity in response to acute alcohol.

The regulation of BK channel activity by pre- and post-translational modifications

Large conductance, Ca²⁺-activated K⁺ (BK) channels represent an important pathway for the outward flux of K⁺ ions from the intracellular compartment in response to membrane depolarization, and/or an elevation in cytosolic free [Ca²⁺]. They are functionally expressed in a range of mammalian tissues (e.g., nerve and smooth muscles), where they can either enhance or dampen membrane excitability. The diversity of BK channel activity results from the considerable alternative mRNA splicing and post-translational modification (e.g., phosphorylation) of key domains within the pore-forming α subunit of the channel complex. Most of these modifications are regulated by distinct upstream cell signaling pathways that influence the structure and/or gating properties of the holo-channel and ultimately, cellular function. The channel complex may also contain auxiliary subunits that further affect channel gating and behavior, often in a tissue-specific manner. Recent studies in human and animal models have provided strong evidence that abnormal BK channel expression/function contributes to a range of pathologies in nerve and smooth muscle. By targeting the upstream regulatory events modulating BK channel behavior, it may be possible to therapeutically intervene and alter BK channel expression/function in a beneficial manner.

WNK1 activates large-conductance Ca2+-activated K+ channels through modulation of ERK1/2 signaling

With no lysine (WNK) kinases are members of the serine/threonine kinase family. We previously showed that WNK4 inhibits renal large-conductance Ca(2+)-activated K(+) (BK) channel activity by enhancing its degradation through a lysosomal pathway. In this study, we investigated the effect of WNK1 on BK channel activity. In HEK293 cells stably expressing the α subunit of BK (HEK-BKα cells), siRNA-mediated knockdown of WNK1 expression significantly inhibited both BKα channel activity and open probability. Knockdown of WNK1 expression also significantly inhibited BKα protein expression and increased ERK1/2 phosphorylation, whereas overexpression of WNK1 significantly enhanced BKα expression and decreased ERK1/2 phosphorylation in a dose-dependent manner in HEK293 cells. Knockdown of ERK1/2 prevented WNK1 siRNA-mediated inhibition of BKα expression. Similarly, pretreatment of HEK-BKα cells with the lysosomal inhibitor bafilomycin A1 reversed the inhibitory effects of WNK1 siRNA on BKα expression in a dose-dependent manner. Knockdown of WNK1 expression also increased the ubiquitination of BKα channels. Notably, mice fed a high-K(+) diet for 10 days had significantly higher renal protein expression levels of BKα and WNK1 and lower levels of ERK1/2 phosphorylation compared with mice fed a normal-K(+) diet. These data suggest that WNK1 enhances BK channel function by reducing ERK1/2 signaling-mediated lysosomal degradation of the channel.

The angiotensin II type 1 receptor (AT1R) closely interacts with large conductance voltage- and Ca2+-activated K+ (BK) channels and inhibits their activity independent of G-protein activation

Angiotensin II (ANG-II) and BK channels play important roles in the regulation of blood pressure. In arterial smooth muscle, ANG-II inhibits BK channels, but the underlying molecular mechanisms are unknown. Here, we first investigated whether ANG-II utilizes its type 1 receptor (AT1R) to modulate BK activity. Pharmacological, biochemical, and molecular evidence supports a role for AT1R. In renal arterial myocytes, the AT1R antagonist losartan (10 μM) abolished the ANG-II (1 μM)-induced reduction of whole cell BK currents, and BK channels and ANG-II receptors were found to co-localize at the cell periphery. We also found that BK inhibition via ANG-II-activated AT1R was independent of G-protein activation (assessed with 500 μM GDPβS). In BK-expressing HEK293T cells, ANG-II (1 μM) also induced a reduction of BK currents, which was contingent on AT1R expression. The molecular mechanisms of AT1R and BK channel coupling were investigated in co-transfected cells. Co-immunoprecipitation showed formation of a macromolecular complex, and live immunolabeling demonstrated that both proteins co-localized at the plasma membrane with high proximity indexes as in arterial myocytes. Consistent with a close association, we discovered that the sole AT1R expression could decrease BK channel voltage sensitivity. Truncated BK proteins revealed that the voltage-sensing conduction cassette is sufficient for BK-AT1R association. Finally, C-terminal yellow and cyan fluorescent fusion proteins, AT1R-YFP and BK-CFP, displayed robust co-localized Förster resonance energy transfer, demonstrating intermolecular interactions at their C termini. Overall, our results strongly suggest that AT1R regulates BK channels through a close protein-protein interaction involving multiple BK regions and independent of G-protein activation.

Antispasmodic and myorelaxant effects of the flavoring agent methyl cinnamate in gut: potential inhibition of tyrosine kinase

Methyl cinnamate (MC) is a safe flavoring agent useful to food industry. Although chemically analog to tyrosine kinase inhibitors, there is little information regarding its biological actions. Here, we aimed at assessing the MC effects on gastrointestinal contractility and the putative involvement of tyrosine kinase in the mediation of these effects. Isometric contractions were recorded in rat isolated strips from stomach, duodenum and colon segments. In gastric strips, MC (3-3000 µM) showed antispasmodic effects against carbachol-induced contractions, which remained unchanged by either l-NAME or tetraethylammonium pretreatment and occurred with potency similar to that obtained against contractions evoked by potassium or U-46619. In colon strips, MC was four times more potent than in gastric ones. MC and the positive control genistein inhibited phasic contractions induced by acetylcholine in Ca2+-free medium, an effect fully prevented by sodium orthovanadate. Both MC and genistein decreased the spontaneous contractions of duodenal strips and shortened the time necessary for gastric fundic tissues to reach 50% of maximal relaxation. In freshly isolated colon myocytes, MC decreased the basal levels of cytoplasmic Ca2+, but not the potassium-elicited cytoplasmic Ca2+ elevation. Colon strips obtained from rats subjected to intracolonic acetic acid instillation showed reduced contractility to potassium, which was partially recovered in MC-treated rats. Inhibitory effect of nifedipine against cholinergic contractions, blunted in acetic acid-induced colitis, was also recovered in MC-treated rats. In conclusion, MC inhibited the gastrointestinal contractility with a probable involvement of tyrosine kinase pathways. In vivo, it was effective to prevent the deleterious effects of colitis resulting from acetic acid injury.

Physiological and ultrastructural features of human induced pluripotent and embryonic stem cell-derived skeletal myocytes in vitro

Progress has recently been made toward the production of human skeletal muscle cells from induced pluripotent stem (iPS) cells. However, the functional and ultrastructural characterization, which is crucial for disease modeling and drug discovery, remains to be documented. We show, for the first time to our knowledge, that the electrophysiological properties of human iPS-derived skeletal myocytes are strictly similar to those of their embryonic stem (ES) cell counterparts, and both are typical of aneural mammalian skeletal muscle. In both cell types, intracellular calcium signaling that links membrane depolarization to contraction occurs in the absence of extracellular Ca(2+), a unique feature of skeletal muscle. Detailed analysis of the Ca(2+) signal revealed diverse kinetics of the rising phase, and hence various rates in the release of Ca(2+) from the sarcoplasmic reticulum. This was mirrored by ultrastructural evidence of Ca(2+) release units, which varied in location, shape, and size. Thus, the excitation-contraction coupling machinery of both iPS- and ES-derived skeletal myocytes was functional and specific, but did not reach full maturity in culture. This is in contrast with the myofibrillar network, which displayed the same organization as in adult skeletal muscle. Overall, the present study validates the human iPS-based skeletal myocyte model in comparison with the embryonic system, and provides the functional and ultrastructural basis for its application to human skeletal muscle diseases.

Gestational hypoxia up-regulates protein kinase C and inhibits calcium-activated potassium channels in ovine uterine arteries

OBJECTIVE

The present study tested the hypothesis that gestational hypoxia up-regulates protein kinase C (PKC) and inhibits calcium-activated potassium channels (KCa)-mediated relaxations of uterine arteries in pregnancy.

STUDY DESIGN

Uterine arteries were isolated from nonpregnant (NPUA) and pregnant (PUA) (~140 day gestation) sheep maintained at either sea level or high altitude (3,820 m for 110 days, PaO2: 60 mmHg). Contractions of uterine arteries were determined.

KEY FINDINGS

In normoxic PUA, selective inhibition of large-conductance KCa (BK) channels significantly enhanced PKC activator phorbol 12, 13-dibutyrate (PDBu)-induced contractions. This effect was abrogated by chronic hypoxia in gestation. Unlike BK channels, inhibition of small-conductance KCa (SK) channels had no significant effect on PDBu-mediated contractions. In normoxic PUA, activation of both BK with NS1619 or SK with NS309 produced concentration-dependent relaxations, which were not altered by the addition of PDBu. However, in uterine arteries treated with chronic hypoxia (10.5% O2 for 48 h), both NS1619- and NS309-induced relaxations were significantly attenuated by PDBu. In NPUAs, inhibition of BK channels significantly enhanced PDBu-induced contractions in both normoxic and hypoxic animals.

CONCLUSION

The results suggest that in the normoxic condition BK inhibits PKC activity and uterine vascular contractility, which is selectively attenuated by chronic hypoxia during gestation. In addition, hypoxia induces PKC-mediated inhibition of BK and SK activities and relaxations of uterine arteries in pregnancy.

Neferine exerts its antithrombotic effect by inhibiting platelet aggregation and promoting dissociation of platelet aggregates

INTRODUCTION

Neferine, a kind of isoquinoline alkaloid, extracted from the seed embryo of Nelumbo nucifera Gaertn, has long been recognized in traditional medicine as a medicinal plant with various usages. Neferine has many biological activities, including anti-hypertensive, anti-arrhythmic, negative inotropic effect and relaxation on vascular smooth muscle. Although previous studies have reported its antithrombotic effect, the mechanisms by which it exerts antithrombotic effect have not been thoroughly studied.

METHOD

Washed mice platelets and mice platelet-rich-plasma (PRP) were used to investigate the effects of neferine on platelet aggregation, secretion induced by various agonists and dissociation of agonist-formed platelet aggregates. Bioflux plates coated with collagen were used to investigate the effect of neferine on platelet adhesion and thrombosis in vitro. With collagen-epinephrine-induced acute pulmonary thrombus formation mouse model, the effect of neferine on thrombosis in vivo was also examined.

RESULTS

Neferine, significantly and dose-dependently, inhibited collagen-, thrombin-, U46619-induced platelet aggregation in mice washed platelets, or ADP-induced platelet aggregation in PRP. Neferine treatment decreased platelet dense granule secretion initiated by collagen, thrombin and U46619. Also, Neferine dramatically and dose-dependently promoted the dissociation of platelet aggregates pre-formed by various agonists including collagen, thrombin, U46619 or ADP. Neferine can significantly reduce the area of mice platelets adhesion to the collagen and inhibit thrombosis in vitro. In collagen-epinephrine-induced acute pulmonary thrombus mouse model, neferine, at 6 mg/kg, significantly attenuated thrombus formation.

CONCLUSIONS

Neferine remarkably prevents thrombus formation by inhibiting platelet activation, adhesion and aggregation, as well as promoting disassembly of pre-formed platelet aggregates. The inhibitory effects of neferine on platelet activation might be relevant in cases involving aberrant platelet activation where neferine could be used as an anti-platelet and antithrombotic agent.

Function and regulation of large conductance Ca(2+)-activated K+ channel in vascular smooth muscle cells

Large conductance Ca(2+)-activated K(+) (BK(Ca)) channels are abundantly expressed in vascular smooth muscle cells. Activation of BK(Ca) channels leads to hyperpolarization of cell membrane, which in turn counteracts vasoconstriction. Therefore, BK(Ca) channels have an important role in regulation of vascular tone and blood pressure. The activity of BK(Ca) channels is subject to modulation by various factors. Furthermore, the function of BK(Ca) channels are altered in both physiological and pathophysiological conditions, such as pregnancy, hypertension and diabetes, which has dramatic impacts on vascular tone and hemodynamics. Consequently, compounds and genetic manipulation that alter activity and expression of the channel might be of therapeutic interest.

Multifaceted modulation of K+ channels by protein-tyrosine phosphatase ε tunes neuronal excitability

Non-receptor-tyrosine kinases (protein-tyrosine kinases) and non-receptor tyrosine phosphatases (PTPs) have been implicated in the regulation of ion channels, neuronal excitability, and synaptic plasticity. We previously showed that protein-tyrosine kinases such as Src kinase and PTPs such as PTPα and PTPε modulate the activity of delayed-rectifier K(+) channels (I(K)). Here we show cultured cortical neurons from PTPε knock-out (EKO) mice to exhibit increased excitability when compared with wild type (WT) mice, with larger spike discharge frequency, enhanced fast after-hyperpolarization, increased after-depolarization, and reduced spike width. A decrease in I(K) and a rise in large-conductance Ca(2+)-activated K(+) currents (mBK) were observed in EKO cortical neurons compared with WT. Parallel studies in transfected CHO cells indicate that Kv1.1, Kv1.2, Kv7.2/7.3, and mBK are plausible molecular correlates of this multifaceted modulation of K(+) channels by PTPε. In CHO cells, Kv1.1, Kv1.2, and Kv7.2/7.3 K(+) currents were up-regulated by PTPε, whereas mBK channel activity was reduced. The levels of tyrosine phosphorylation of Kv1.1, Kv1.2, Kv7.3, and mBK potassium channels were increased in the brain cortices of neonatal and adult EKO mice compared with WT, suggesting that PTPε in the brain modulates these channel proteins. Our data indicate that in EKO mice, the lack of PTPε-mediated dephosphorylation of Kv1.1, Kv1.2, and Kv7.3 leads to decreased I(K) density and enhanced after-depolarization. In addition, the deficient PTPε-mediated dephosphorylation of mBK channels likely contributes to enhanced mBK and fast after-hyperpolarization, spike shortening, and consequent increase in neuronal excitability observed in cortical neurons from EKO mice.

The complex contribution of NOS interneurons in the physiology of cerebrovascular regulation

Following the discovery of the vasorelaxant properties of nitric oxide (NO) by Furchgott and Ignarro, the finding by Bredt and coll. of a constitutively expressed NO synthase in neurons (nNOS) led to the presumption that neuronal NO may control cerebrovascular functions. Consequently, numerous studies have sought to determine whether neuraly-derived NO is involved in the regulation of cerebral blood flow (CBF). Anatomically, axons, dendrites, or somata of NO neurons have been found to contact the basement membrane of blood vessels or perivascular astrocytes in all segments of the cortical microcirculation. Functionally, various experimental approaches support a role of neuronal NO in the maintenance of resting CBF as well as in the vascular response to neuronal activity. Since decades, it has been assumed that neuronal NO simply diffuses to the local blood vessels and produce vasodilation through a cGMP-PKG dependent mechanism. However, NO is not the sole mediator of vasodilation in the cerebral microcirculation and is known to interact with a myriad of signaling pathways also involved in vascular control. In addition, cerebrovascular regulation is the result of a complex orchestration between all components of the neurovascular unit (i.e., neuronal, glial, and vascular cells) also known to produce NO. In this review article, the role of NO interneuron in the regulation of cortical microcirculation will be discussed in the context of the neurovascular unit.

Regulation of voltage-gated sodium current by endogenous Src family kinases in cochlear spiral ganglion neurons in culture

Voltage-gated sodium (Na+) and potassium (K+)channels have been found to be regulated by Src family kinases(SFKs).However, how these channels are regulated by SFKs in cochlear spiral ganglion neurons (SGNs) remains unknown.Here, we report that altering the activity of endogenous SFKs modulated voltage-gated Na+, but not K+, currents recorded in embryonic SGNs in culture. Voltage-gated Na+ current was suppressed by inhibition of endogenous SFKs or just Src and potentiated by the activation of these enzymes. Detailed investigations showed that under basal conditions, SFK inhibitor application did not significantly affect the voltage-dependent activation, but shifted the steady-state inactivation curves of Na+ currents and delayed the recovery of Na+ currents from inactivation. Application of Src specific inhibitor, Src40–58,not only shifted the inactivation curve but also delayed the recovery of Na+ currents and moved the voltage-dependent activation curve towards the left. The pre-inhibition of SFKs occluded all the effects induced by Src40–58 application, except the left shift of the activation curve. The activation of SFKs did not change either steady-state inactivation or recovery of Na+ currents, but caused the left shift of the activation curve.SFK inhibitor application effectively prevented all the effects induced by SFK activation, suggesting that both the voltage-dependent activation and steady-state inactivation of Na+ current are subjects of SFK regulation. The different effects induced by activation versus inhibition of SFKs implied that under basal conditions, endogenously active and inactive SFKs might be differentially involved in the regulation of voltage-gated Na+ channels in SGNs.

Hair cell BK channels interact with RACK1, and PKC increases its expression on the cell surface by indirect phosphorylation

Large conductance (BK) calcium activated potassium channels (Slo) are ubiquitous and implicated in a number of human diseases including hypertension and epilepsy. BK channels consist of a pore forming α-subunit (Slo) and a number of accessory subunits. In hair cells of nonmammalian vertebrates these channels play a critical role in electrical resonance, a mechanism of frequency selectivity. Hair cell BK channel clusters on the surface and currents increase along the tonotopic axis and contribute significantly to the responsiveness of these hair cells to sounds of high frequency. In contrast, messenger RNA levels encoding the Slo gene show an opposite decrease in high frequency hair cells. To understand the molecular events underlying this paradox, we used a yeast two-hybrid screen to isolate binding partners of Slo. We identified Rack1 as a Slo binding partner and demonstrate that PKC activation increases Slo surface expression. We also establish that increased Slo recycling of endocytosed Slo is at least partially responsible for the increased surface expression of Slo. Moreover, analysis of several PKC phosphorylation site mutants confirms that the effects of PKC on Slo surface expression are likely indirect. Finally, we show that Slo clusters on the surface of hair cells are also increased by increased PKC activity and may contribute to the increasing amounts of channel clusters on the surface of high-frequency hair cells.

Dehydroepiandrosterone inhibits the Src/STAT3 constitutive activation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an obstructive vasculopathy characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation and suppressed apoptosis. This phenotype is sustained by the activation of the Src/signal transducer and activator of transcription 3 (STAT3) axis, maintained by a positive feedback loop involving miR-204 and followed by an aberrant expression/activation of its downstream targets such as Pim1 and nuclear factor of activated T-cells (NFATc2). Dehydroepiandrosterone (DHEA) is a steroid hormone shown to reverse vascular remodeling in systemic vessels. Since STAT3 has been described as modulated by DHEA, we hypothesized that DHEA reverses human pulmonary hypertension by inhibiting Src/STAT3 constitutive activation. Using PASMCs isolated from patients with PAH (n = 3), we demonstrated that DHEA decreases both Src and STAT3 activation (Western blot and nuclear translocation assay), resulting in a significant reduction of Pim1, NFATc2 expression/activation (quantitative RT-PCR and Western blot), as well as Survivin and upregulation of bone morphogenetic protein receptor 2 (BMPR2) and miR-204. Src/STAT3 axis inhibition by DHEA is associated with 1) mitochondrial membrane potential (tetramethylrhodamine methyl-ester perchlorate; n = 150; P < 0.05) depolarization increasing apoptosis by 25% (terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling; n = 150; P < 0.05); and 2) decreased intracellular Ca(2+) concentration (fluo-3 AM; n = 150; P < 0.05) and proliferation by 30% (PCNA). Finally, in vivo similarly to STAT3 inhibition DHEA improves experimental PAH (monocrotaline rats) by decreasing mean PA pressure and right ventricle hypertrophy. These effects were associated with the inhibition of Src, STAT3, Pim1, NFATc2, and Survivin and the upregulation of BMPR2 and miR-204. We demonstrated that DHEA reverses pulmonary hypertension in part by inhibiting the Src/STAT3.

Distinct transcriptional regulation of human large conductance voltage- and calcium-activated K+ channel gene (hSlo1) by activated estrogen receptor alpha and c-Src tyrosine kinase

Estrogen receptor α (ERα) regulates gene transcription via "genomic" (binding directly or indirectly, typically via Sp1 or AP-1 sites, to target genes) and/or "nongenomic" (signaling) mechanisms. ERα activation by estrogen up-regulates the murine Ca(2+)-activated K(+) channel α subunit gene (mSlo1) via genomic mechanisms. Here, we investigated whether ERα also drives transcription of the human (hSlo1) gene. Consistent with this view, estrogen increased hSlo1 transcript levels in primary human smooth muscle cells. Promoter studies revealed that estrogen/hERα-mediated hSlo1 transcription was nearly 6-fold more efficient than for mSlo1 (EC(50), 0.07 versus 0.4 nM). Unlike the genomic transcriptional mechanism employed by mSlo1, hSlo1 exhibits a nongenomic hERα-mediated regulatory mechanism. This is supported by the following: 1) efficient hSlo1 transcription after disruption of the DNA-binding domain of hERα or knockdown of Sp1, and 2) lack of AP-1 sites in the hSlo1 promoter. Three nongenomic signaling pathways were explored: Src, Rho, and PI3K. Inhibition of Src with 10 μM PP2, and reported downstream ERK with 25 μM PD98059 did not prevent estrogen action but caused an increase in hSlo1 basal transcription; conversely, constitutively active c-Src (Y527F) decreased hSlo1 basal transcription even preventing its estrogen/hERα-mediated transcriptional activation. Rho inhibition by coexpressed Clostridium botulinum C3 transferase did not alter estrogen action. In contrast, inhibition of PI3K activity with 10 μM LY294002 decreased estrogen-stimulated hSlo1 transcription by ∼40%. These results indicate that the nongenomic PI3K signaling pathway plays a role in estrogen/hERα-stimulated hSlo1 gene expression; whereas c-Src activity leads to hSlo1 gene tonic repression independently of estrogen, likely through ERK activation.

WNK4 kinase inhibits Maxi K channel activity by a kinase-dependent mechanism

WNK [with no lysine (k)] kinase is a serine/threonine kinase subfamily. Mutations in two of the WNK kinases result in pseudohypoaldosteronism type II (PHA II) characterized by hypertension, hyperkalemia, and metabolic acidosis. Recent studies showed that both WNK1 and WNK4 inhibit ROMK activity. However, little is known about the effect of WNK kinases on Maxi K, a large-conductance Ca(2+) and voltage-activated potassium (K) channel. Here, we report that WNK4 wild-type (WT) significantly inhibits Maxi K channel activity in HEK αBK stable cell lines compared with the control group. However, a WNK4 dead-kinase mutant, D321A, has no inhibitory effect on Maxi K activity. We further found that WNK4 inhibits total and cell surface protein expression of Maxi K equally compared with control groups. A dominant-negative dynamin mutant, K44A, did not alter the WNK4-mediated inhibitory effect on Maxi K surface expression. Treatment with bafilomycin A1 (a proton pump inhibitor) and leupeptin (a lysosomal inhibitor) reversed WNK4 WT-mediated inhibition of Maxi K total protein expression. These findings suggest that WNK4 WT inhibits Maxi K activity by reducing Maxi K protein at the membrane, but that the inhibition is not due to an increase in clathrin-mediated endocytosis of Maxi K, but likely due to enhancing its lysosomal degradation. Also, WNK4's inhibitory effect on Maxi K activity is dependent on its kinase activity.

Thromboxane A2 receptor and MaxiK-channel intimate interaction supports channel trans-inhibition independent of G-protein activation

Large conductance voltage- and calcium-activated potassium channels (MaxiK, BK(Ca)) are well known for sustaining cerebral and coronary arterial tone and for their linkage to vasodilator β-adrenergic receptors. However, how MaxiK channels are linked to counterbalancing vasoconstrictor receptors is unknown. Here, we show that vasopressive thromboxane A2 receptors (TP) can intimately couple with and inhibit MaxiK channels. Activation of the receptor with its agonist trans-inhibits MaxiK independently of G-protein activation. This unconventional mechanism is supported by independent lines of evidence: (i) inhibition of MaxiK current by thromboxane A2 mimetic, U46619, occurs even when G-protein activity is suppressed; (ii) MaxiK and TP physically associate and display a high degree of proximity; and (iii) Förster resonance energy transfer occurs between fluorescently labeled MaxiK and TP, supporting a direct interaction. The molecular mechanism of MaxiK-TP intimate interaction involves the receptor's first intracellular loop and C terminus, and it entails the voltage-sensing conduction cassette of MaxiK channel. Further, physiological evidence of MaxiK-TP physical interaction is given in human coronaries and rat aorta, and by confirming TP role (with antagonist SQ29,548) in the U46619-induced MaxiK inhibition in human coronaries. We propose that vasoconstrictor TP receptor and MaxiK-channel direct interaction facilitates G-protein-independent TP to MaxiK trans-inhibition, which would promote vasoconstriction.

Enhancement of mesenteric artery contraction to 5-HT depends on Rho kinase and Src kinase pathways in the ob/ob mouse model of type 2 diabetes

BACKGROUND AND PURPOSE

Arteries from hypertensive subjects are reportedly hyperresponsive to 5-hydroxytryptamine (5-HT), but it remains unclear whether this is true in chronic type 2 diabetes. We have assessed responses to 5-HT shown by mesenteric arteries from type 2 diabetic ob/ob mice (27-32 weeks old) and have identified the molecular mechanisms involved.

EXPERIMENTAL APPROACH

Contractions of mesenteric rings to 5-HT were examined in vitro. Activation of mesenteric RhoA, Rho kinase and Src was measured by Western blotting or by modified enzyme-linked immunosorbent assay.

KEY RESULTS

Concentration-dependent contractions to 5-HT were greater in mesenteric rings from the ob/ob than in those from the age-matched control ('Lean') group. In each group, there was no significant change in the 5-HT-induced contractions after inhibition of nitric oxide synthase (with N(G)-nitro-L-arginine), of cyclooxygenase (with indomethacin) or of protein kinase C (with chelerythrine). However inhibition of the MEK/ERK pathway (with PD98059) decreased the response to 5-HT. Although the diabetes-related enhancement of the 5-HT response was preserved with each of these inhibitors, enhancement was abolished by a Rho kinase inhibitor (Y27632) and by Src kinase inhibitors (PP1 analogue or Src kinase inhibitor I). 5-HT-induced activation of RhoA, Rho kinase and Src kinase in mesenteric arteries was greater in the ob/ob than in the Lean group, but the expression of RhoA, Rho kinase isoforms and Src did not differ between these groups.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the enhancement of 5-HT-induced contraction in mesenteric arteries from ob/ob mice may be attributable to increased activation of RhoA/Rho kinase and Src kinase.

Ca2+-activated K channels in parotid acinar cells: The functional basis for the hyperpolarized activation of BK channels

Fluid secretion relies on a close interplay between Ca(2+)-activated Cl and K channels. Salivary acinar cells contain both large conductance, BK, and intermediate conductance, IK1, K channels. Physiological fluid secretion occurs with only modest (<500 nM) increases in intracellular Ca(2+) levels but BK channels in many cell types and in heterologous expression systems require very high concentrations for significant activation. We report here our efforts to understand this apparent contradiction. We determined the Ca(2+) dependence of IK1 and BK channels in mouse parotid acinar cells. IK1 channels activated with an apparent Ca(2+) affinity of about 350 nM and a Hill coefficient near 3. Native parotid BK channels activated at similar Ca(2+) levels unlike the BK channels in other cell types. Since the parotid BK channel is encoded by an uncommon splice variant, we examined this clone in a heterologous expression system. In contrast to the native parotid channel, activation of this expressed "parSlo" channel required very high levels of Ca(2+). In order to understand the functional basis for the special properties of the native channels, we analyzed the parotid BK channel in the context of the Horrigan-Aldrich model of BK channel gating. We found that the shifted activation of parotid BK channels resulted from a hyperpolarizing shift of the voltage dependence of voltage sensor activation and channel opening and included a large change in the coupling of these two processes.

Large conductance, Ca2+-activated K+ channels (BKCa) and arteriolar myogenic signaling

Myogenic, or pressure-induced, vasoconstriction is critical for local blood flow autoregulation. Underlying this vascular smooth muscle (VSM) response are events including membrane depolarization, Ca(2+) entry and mobilization, and activation of contractile proteins. Large conductance, Ca(2+)-activated K(+) channel (BK(Ca)) has been implicated in several of these steps including, (1) channel closure causing membrane depolarization, and (2) channel opening causing hyperpolarization to oppose excessive pressure-induced vasoconstriction. As multiple mechanisms regulate BK(Ca) activity (subunit composition, membrane potential (Em) and Ca(2+) levels, post-translational modification) tissue level diversity is predicted. Importantly, heterogeneity in BK(Ca) channel activity may contribute to tissue-specific differences in regulation of myogenic vasoconstriction, allowing local hemodynamics to be matched to metabolic requirements. Knowledge of such variability will be important to exploiting the BK(Ca) channel as a therapeutic target and understanding systemic effects of its pharmacological manipulation.

Regulation of coronary arterial BK channels by caveolae-mediated angiotensin II signaling in diabetes mellitus

RATIONALE

The large conductance Ca(2+)-activated K(+) (BK) channel, a key determinant of vascular tone, is regulated by angiotensin II (Ang II) type 1 receptor signaling. Upregulation of Ang II functions and downregulation of BK channel activities have been reported in diabetic vessels. However, the molecular mechanisms underlying Ang II-mediated BK channel modulation, especially in diabetes mellitus, have not been thoroughly examined.

OBJECTIVES

The aim in this study was to determine whether caveolae-targeting facilitates BK channel dysfunction in diabetic vessels.

METHODS AND RESULTS

Using patch clamp techniques and molecular biological approaches, we found that BK channels, Ang II type 1 receptor, G(alphaq/11) (G protein q/11 alpha subunit), nonphagocytic NAD(P)H oxidases (NOX-1), and c-Src kinases (c-Src) were colocalized in the caveolae of rat arterial smooth muscle cells and the integrity of caveolae in smooth muscle cells was critical for Ang II-mediated BK channel regulation. Most importantly, membrane microdomain targeting of these proteins was upregulated in the caveolae of streptozotocin-induced rat diabetic vessels, leading to enhanced Ang II-induced redox-mediated BK channel modification and causing BK channel and coronary dysfunction. The absence of caveolae abolished the effects of Ang II on vascular BK channel activity and preserved BK channel function in diabetes.

CONCLUSIONS

These results identified a molecular scheme of receptor/enzyme/channel/caveolae microdomain complex that facilitates the development of vascular BK channel dysfunction in diabetes.

Mechanisms involved in the regulation of bovine pulmonary vascular tone by the 5-HT1B receptor

BACKGROUND AND PURPOSE

5-HT(1B) receptors may have a role in pulmonary hypertension. Their relationship with the activity of BK(Ca,) a T-type voltage-operated calcium channel (VOCC) and cyclic nucleotide-mediated relaxation was examined.

EXPERIMENTAL APPROACH

Ring segments of bovine pulmonary arteries were mounted in organ baths in modified Krebs-Henseleit buffer (37 degrees C) under a tension of 20 mN and gassed with 95% O(2)/5% CO(2). Isometric recordings were made using Chart 5 software.

KEY RESULTS

Contractile responses to 5-HT (10 nM-300 microM) were inhibited similarly by the 5-HT(1B) receptor antagonist SB216641 (100 nM) and the T-type VOCC blockers mibefradil (10 microM) and NNC550396 (10 microM) with no additive effect between SB216641 and mibefradil. Inhibition by SB216641 was prevented by the potassium channel blocker, charybdotoxin (100 nM). 5-HT(1B) receptor activation and charybdotoxin produced a mibefradil-sensitive potentiation of responses to U46619. Bradykinin (0.1 nM-30 microM), sodium nitroprusside (0.01 nM-3 microM), zaprinast (1 nM-3 microM), isoprenaline (0.1 nM-10 microM) and rolipram (1 nM-3 microM) produced 50% relaxation of arteries constricted with 5-HT (1-3 microM) or U46619 (30-50 nM) in the presence of 5-HT(1B) receptor activation, but full relaxation of arteries constricted with U46619, the 5-HT(2A) receptor agonist 2,5 dimethoxy-4 iodoamphetamine (1 microM) or 5-HT in the presence of 5-HT(1B) receptor antagonism. Enhanced relaxation of 5-HT-constricted arteries by cGMP-dependent pathways, seen in the presence of the 5-HT(1B) receptor antagonist, was reversed by charybdotoxin whereas cAMP-dependent relaxation was only partly reversed by charybdotoxin.

CONCLUSIONS AND IMPLICATIONS

5-HT(1B) receptors couple to inhibition of BK(Ca), thus increasing tissue sensitivity to contractile agonists by activating a T-type VOCC and impairing cGMP-mediated relaxation. Impaired cAMP-mediated relaxation was only partly mediated by inhibition of BK(Ca).

IL-1beta modulate the Ca(2+)-activated big-conductance K channels (BK) via reactive oxygen species in cultured rat aorta smooth muscle cells

The large conductance Ca(2+)-activated K(+) (BK) channel, abundantly expressed in vascular smooth muscle cells, plays a critical role in controlling vascular tone. Activation of BK channels leads to membrane hyperpolarization and promotes vasorelaxation. BK channels are activated either by elevation of the intracellular Ca(2+) concentration or by membrane depolarization. It is also regulated by a diversity of vasodilators and vasoconstrictors. Interleukin-1beta (IL-1beta) is one of the cytokines that play important roles in the development and progression of a variety of cardiovascular diseases. The effects of IL-1beta on vascular reactivity are controversial, and little is known about the modulation of BK channel function by IL-1beta. In this study, we investigated how IL-1beta modulates BK channel function in cultured arterial smooth muscle cells (ASMCs), and examined the role of H(2)O(2) in the process. We demonstrated that IL-1beta had biphasic effects on BK channel function and membrane potential of ASMCs, that is both concentration and time dependent. IL-1beta increased BK channel-dependent K(+) current and hyperpolarized ASMCs when applied for 30 min. While long-term (24-48 h) treatment of IL-1beta resulted in decreased expression of alpha-subunit of BK channel, suppressed BK channel activity, decreased BK channel-dependent K(+) current and depolarization of the cells. H(2)O(2) scavenger catalase completely abolished the early effect of IL-1beta, while it only partly diminished the long-term effect of IL-1beta. These results may provide important molecular mechanisms for therapeutic strategies targeting BK channel in inflammation-related diseases.