Endothelin-1 acts via protein kinase C to block KATP channels in rabbit coronary and pulmonary arterial smooth muscle cells

Mechanisms and treatment of pulmonary arterial hypertension

Substantial progress has been made in the management of pulmonary arterial hypertension (PAH) in the past 25 years, but the disease remains life-limiting. Established therapies for PAH are mostly limited to symptomatic relief by correcting the imbalance of vasoactive factors. The tyrosine kinase inhibitor imatinib, the first predominantly non-vasodilatory drug to be tested in patients with PAH, improved exercise capacity and pulmonary haemodynamics compared with placebo but at the expense of adverse events such as subdural haematoma. Given that administration by inhalation might reduce the risk of systemic adverse effects, inhaled formulations of tyrosine kinase inhibitors are currently in clinical development. Other novel therapeutic approaches for PAH include suppression of activin receptor type IIA signalling with sotatercept, which has shown substantial efficacy in clinical trials and was approved for use in the USA in 2024, but the long-term safety of the drug remains unclear. Future advances in the management of PAH will focus on right ventricular function and involve deep phenotyping and the development of a personalized medicine approach. In this Review, we summarize the mechanisms underlying PAH, provide an overview of available PAH therapies and their limitations, describe the development of newer, predominantly non-vasodilatory drugs that are currently being tested in phase II or III clinical trials, and discuss future directions for PAH research.

Capillary regression leads to sustained local hypoperfusion by inducing constriction of upstream transitional vessels

In the brain, a microvascular sensory web coordinates oxygen delivery to regions of neuronal activity. This involves a dense network of capillaries that send conductive signals upstream to feeding arterioles to promote vasodilation and blood flow. Although this process is critical to the metabolic supply of healthy brain tissue, it may also be a point of vulnerability in disease. Deterioration of capillary networks is a feature of many neurological disorders and injuries and how this web is engaged during vascular damage remains unknown. We performed in vivo two-photon microscopy on young adult mural cell reporter mice and induced focal capillary injuries using precise two-photon laser irradiation of single capillaries. We found that ~59% of the injuries resulted in regression of the capillary segment 7 to 14 d following injury, and the remaining repaired to reestablish blood flow within 7 d. Injuries that resulted in capillary regression induced sustained vasoconstriction in the upstream arteriole-capillary transition (ACT) zone at least 21 days postinjury in both awake and anesthetized mice. The degree of vasomotor dynamics was chronically attenuated in the ACT zone consequently reducing blood flow in the ACT zone and in secondary, uninjured downstream capillaries. These findings demonstrate how focal capillary injury and regression can impair the microvascular sensory web and contribute to cerebral hypoperfusion.

Capillary regression leads to sustained local hypoperfusion by inducing constriction of upstream transitional vessels

In the brain, a microvascular sensory web coordinates oxygen delivery to regions of neuronal activity. This involves a dense network of capillaries that send conductive signals upstream to feeding arterioles to promote vasodilation and blood flow. Although this process is critical to the metabolic supply of healthy brain tissue, it may also be a point of vulnerability in disease. Deterioration of capillary networks is a hallmark of many neurological disorders and how this web is engaged during vascular damage remains unknown. We performed in vivo two-photon microscopy on young adult mural cell reporter mice and induced focal capillary injuries using precise two-photon laser irradiation of single capillaries. We found that ∼63% of the injuries resulted in regression of the capillary segment 7-14 days following injury, and the remaining repaired to re-establish blood flow within 7 days. Injuries that resulted in capillary regression induced sustained vasoconstriction in the upstream arteriole-capillary transition (ACT) zone at least 21 days post-injury in both awake and anesthetized mice. This abnormal vasoconstriction involved attenuation of vasomotor dynamics and uncoupling from mural cell calcium signaling following capillary regression. Consequently, blood flow was reduced in the ACT zone and in secondary, uninjured downstream capillaries. These findings demonstrate how capillary injury and regression, as often seen in age-related neurological disease, can impair the microvascular sensory web and contribute to cerebral hypoperfusion.

SIGNIFICANCE

Deterioration of the capillary network is a characteristic of many neurological diseases and can exacerbate neuronal dysfunction and degeneration due to poor blood perfusion. Here we show that focal capillary injuries can induce vessel regression and elicit sustained vasoconstriction in upstream transitional vessels that branch from cortical penetrating arterioles. This reduces blood flow to broader, uninjured regions of the same microvascular network. These findings suggest that widespread and cumulative damage to brain capillaries in neurological disease may broadly affect blood supply and contribute to hypoperfusion through their remote actions.

The mechanism of ions in pulmonary hypertension

Pulmonary hypertension（PH）is a kind of hemodynamic and pathophysiological state, in which the pulmonary artery pressure (PAP) rises above a certain threshold. The main pathological manifestation is pulmonary vasoconstriction and remodelling progressively. More and more studies have found that ions play a major role in the pathogenesis of PH. Many vasoactive substances, inflammatory mediators, transcription-inducing factors, apoptosis mediators, redox substances and translation modifiers can control the concentration of ions inside and outside the cell by regulating the activity of ion channels, which can regulate vascular contraction, cell proliferation, migration, apoptosis, inflammation and other functions. We all know that there are no effective drugs to treat PH. Ions are involved in the occurrence and development of PH, so it is necessary to clarify the mechanism of ions in PH as a therapeutic target for PH. The main ions involved in PH are calcium ion (Ca2+), potassium ion (K+), sodium ion (Na+) and chloride ion (Cl-). Here, we mainly discuss the distribution of these ions and their channels in pulmonary arteries and their role in the pathogenesis of PH.

2-Deoxy-D-Glucose Exhibits Anti-seizure Effects by Mediating the Netrin-G1-KATP Signaling Pathway in Epilepsy

Epilepsy is a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures. The glycolytic inhibitor 2-deoxy-D-glucose (2-DG) has been reported to exert antiepileptic effects by upregulating KATP subunits (kir6.1 and kir6.2). We evaluated whether 2-DG exhibits anti-seizure effect by mediating the netrin-G1-KATP signaling pathway in epilepsy. In a mouse epilepsy model induced by lithium chloride-pilocarpine, 2-DG intervention increased the mRNA and protein expression levels of kir6.1 and kir6.2, and these increases were significantly reversed after knocking down netrin-G1 expression. Similarly, in cultured neurons with a magnesium-free medium, we found that the frequency of spontaneous postsynaptic potentials (SP) was increased, and in the meanwhile, expression levels of kir6.1 and kir6.2 were increased after pretreatment with 2DG. These effects were remarkably reversed after knocking down netrin-G1. Thus, our findings show that 2DG exhibits anti-seizure effects through the netrin-G1-KATP signaling pathway.

Linoleic Acid Attenuates the Toxic Dose of Bupivacaine-Mediated Reduction of Vasodilation Evoked by the Activation of Adenosine Triphosphate-Sensitive Potassium Channels

The goal of this study was to investigate the effect of lipid emulsion on a toxic dose of local anesthetic-mediated reduction of vasodilation evoked by the ATP-sensitive potassium (K_ATP) channel agonist levcromakalim. The effect of lipid emulsion (LE) and linoleic acid on the local anesthetic-mediated reduction of vasodilation and membrane hyperpolarization evoked by levcromakalim was assessed in isolated endothelium-denuded vessels (rat aorta and mesenteric artery) and aortic vascular smooth muscle cells. The effect of LE and linoleic acid on K_ATP channel activity in transfected HEK-293 cells was investigated, as was the effect of LE on bupivacaine concentration. The efficacy of LE in attenuating the local anesthetic-mediated reduction of vasodilation evoked by levcromakalim was correlated with the lipid solubility of the local anesthetic. Linoleic acid attenuated the bupivacaine-mediated reduction of vasodilation evoked by levcromakalim. LE decreased the bupivacaine-mediated reduction of membrane hyperpolarization evoked by levcromakalim but did not significantly alter the mepivacaine-mediated reduction. LE and linoleic acid both reversed the bupivacaine-mediated decrease of K_ATP activity and enhanced K_ATP activity. LE decreased the bupivacaine concentration. Linoleic acid may be the major contributor to LE-induced attenuation of bupivacaine-mediated reduction of vasodilation evoked by levcromakalim via the direct activation of K_ATP channels and indirect effects.

ATP-sensitive K+ channels maintain resting membrane potential in interstitial cells of Cajal from the mouse colon

To investigate the role of ATP-sensitive K⁺(K_ATP) channels on pacemaker activity in interstitial cells of Cajal (ICC), whole-cell patch clamping, RT-PCR, and intracellular Ca²⁺([Ca²⁺]_i) imaging were performed in cultured colonic ICC. Pinacidil (a K⁺ channel opener) hyperpolarized the membrane and inhibited the generation of pacemaker potential, and this effect was reversed by glibenclamide (a K_ATP channel blocker). RT-PCR showed that K_ir 6.1 and SUR2B were expressed in Ano-1 positive colonic ICC. Glibenclamide depolarized the membrane and increased pacemaker potential frequency. However, 5-hydroxydecanoic acid (a mitochondrial K_ATP channel blocker) had no effects on pacemaker potentials. Phorbol 12-myristate 13-acetate (PMA; a protein kinase C activator) blocked the pinacidil-induced effects, and PMA alone depolarized the membrane and increased pacemaker potential frequency. Cell-permeable 8-bromo-cyclic AMP also increased pacemaker potential frequency. Recordings of spontaneous intracellular Ca²⁺([Ca²⁺]_i) oscillations showed that glibenclamide increased the frequency of [Ca²⁺]_i oscillations. In small intestinal ICC, glibenclamide alone did not alter the generation of pacemaker potentials, and K_ir 6.2 and SUR2B were expressed in Ano-1 positive ICC. Therefore, K_ATP channels in colonic ICC are activated in resting state and play an important role in maintaining resting membrane potential.

Mepivacaine attenuates vasodilation induced by ATP-sensitive potassium channels in rat aorta

The goal of this in vitro study was to investigate the effect of mepivacaine on vasodilation induced by the ATP-sensitive potassium (K_ATP) channel opener levcromakalim in isolated endothelium-denuded rat aortas. The effects of mepivacaine and the K_ATP channel inhibitor glibenclamide, alone or in combination, on levcromakalim-induced vasodilation were assessed in the isolated aortas. The effects of mepivacaine or combined treatment with a protein kinase C (PKC) inhibitor, GF109203X, and mepivacaine on this vasodilation were also investigated. Levcromakalim concentration-response curves were generated for isolated aortas precontracted with phenylephrine or a PKC activator, phorbol 12,13-dibutyrate (PDBu). Further, the effects of mepivacaine and glibenclamide on levcromakalim-induced hyperpolarization were assessed in rat aortic vascular smooth muscle cells. Mepivacaine attenuated levcromakalim-induced vasodilation, whereas it had no effect on this vasodilation in isolated aortas pretreated with glibenclamide. Combined treatment with GF109203X and mepivacaine enhanced levcromakalim-induced vasodilation compared with pretreatment with mepivacaine alone. This vasodilation was attenuated in aortas precontracted with PDBu compared with those precontracted with phenylephrine. Mepivacaine and glibenclamide, alone or in combination, attenuated levcromakalim-induced membrane hyperpolarization. Taken together, these results suggest that mepivacaine attenuates vasodilation induced by K_ATP channels, which appears to be partly mediated by PKC.

Ion channels and transporters as therapeutic targets in the pulmonary circulation

Pulmonary circulation is a low pressure, low resistance, high flow system. The low resting vascular tone is maintained by the concerted action of ion channels, exchangers and pumps. Under physiological as well as pathophysiological conditions, they are targets of locally secreted or circulating vasodilators and/or vasoconstrictors, leading to changes in expression or to posttranslational modifications. Both structural changes in the pulmonary arteries and a sustained increase in pulmonary vascular tone result in pulmonary vascular remodeling contributing to morbidity and mortality in pediatric and adult patients. There is increasing evidence demonstrating the pivotal role of ion channels such as K(+) and Cl(-) or transient receptor potential channels in different cell types which are thought to play a key role in vasoconstrictive remodeling. This review focuses on ion channels, exchangers and pumps in the pulmonary circulation and summarizes their putative pathophysiological as well as therapeutic role in pulmonary vascular remodeling. A better understanding of the mechanisms of their actions may allow for the development of new options for attenuating acute and chronic pulmonary vasoconstriction and remodeling treating the devastating disease pulmonary hypertension.

Alteration of ATP-sensitive K+ channels in rabbit aortic smooth muscle during left ventricular hypertrophy

We investigated the impairment of ATP-sensitive K(+) (K(ATP)) channels in aortic smooth muscle cells (ASMCs) from isoproterenol-induced hypertrophied rabbits. The amplitude of K(ATP) channels induced by the K(ATP) channel opener pinacidil (10 μM) was greater in ASMCs from control than from hypertrophied animals. In phenylephrine-preconstricted aortic rings, pinacidil induced relaxation in a dose-dependent manner. The dose-dependent curve was shifted to the right in the hypertrophied (EC(50): 17.80 ± 3.28 μM) compared with the control model (EC(50): 6.69 ± 2.40 μM). Although the level of Kir6.2 subtype expression did not differ between ASMCs from the control and hypertrophied models, those of the Kir6.1 and SUR2B subtypes were decreased in the hypertrophied model. Application of the calcitonin-gene related peptide (100 nM) and adenylyl cyclase activator forskolin (10 μM), which activates protein kinase A (PKA) and consequently K(ATP) channels, induced a K(ATP) current in both control and hypertrophied animals; however, the K(ATP) current amplitude did not differ between the two groups. Furthermore, PKA expression was not altered between the control and hypertrophied animals. These results suggests that the decreased K(ATP) current amplitude and K(ATP) channel-induced vasorelaxation in the hypertrophied animals were attributable to the reduction in K(ATP) channel expression but not to changes in the intracellular signaling mechanism that activates the K(ATP) current.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Regulation of the ATP-sensitive potassium channel subunit, Kir6.2, by a Ca2+-dependent protein kinase C

The activity of ATP-sensitive potassium (K(ATP)) channels is governed by the concentration of intracellular ATP and ADP and is thus responsive to the metabolic status of the cell. Phosphorylation of K(ATP) channels by protein kinase A (PKA) or protein kinase C (PKC) results in the modulation of channel activity and is particularly important in regulating smooth muscle tone. At the molecular level the smooth muscle channel is composed of a sulfonylurea subunit (SUR2B) and a pore-forming subunit Kir6.1 and/or Kir6.2. Previously, Kir6.1/SUR2B channels have been shown to be inhibited by PKC, and Kir6.2/SUR2B channels have been shown to be activated or have no response to PKC. In this study we have examined the modulation of channel complexes formed of the inward rectifier subunit, Kir6.2, and the sulfonylurea subunit, SUR2B. Using a combination of biochemical and electrophysiological techniques we show that this complex can be inhibited by protein kinase C in a Ca(2+)-dependent manner and that this inhibition is likely to be as a result of internalization. We identify a residue in the distal C terminus of Kir6.2 (Ser-372) whose phosphorylation leads to down-regulation of the channel complex. This inhibitory effect is distinct from activation which is seen with low levels of channel activity.

Role of KATP and L-type Ca2+ channel activities in regulation of ovine uterine vascular contractility: effect of pregnancy and chronic hypoxia

OBJECTIVE

Our objective was to determine whether the pregnancy and high altitude long-term hypoxia-mediated changes in uterine artery contractility were regulated by K(ATP) and L-type Ca(2+) channel activities.

STUDY DESIGN

Uterine arteries were isolated from nonpregnant and near-term pregnant ewes that had been maintained at sea level (∼300 m) or exposed to high altitude (3801 m) for 110 days. Isometric tension was measured in a tissue bath.

RESULTS

Pregnancy increased diazoxide, but not verapamil-induced relaxations. Long-term hypoxia attenuated diazoxide-induced relaxations in near-term pregnant uterine arteries, but enhanced verapamil-induced relaxations in nonpregnant uterine arteries. Diazoxide decreased the maximal response (E(max)) of phenylephrine-induced contractions in near-term pregnant uterin arteries but not nonpregnant uterine arteries in normoxic sheep. In contrast, diazoxide had no effect on phenylephrine-induced E(max) in near-term pregnant uterine arteries but decreased it in nonpregnant uterine arteries in long-term hypoxia animals. Verapamil decreased the E(max) and pD(2) (-logEC(50)) of phenylephrine-induced contractions in both nonpregnant uterine arteries and near-term pregnant uterine arteries in normoxic and long-term hypoxia animals, except nonpregnant uterine arteries of normoxic animals in which verapamil showed no effect on the pD(2).

CONCLUSION

The results suggest that pregnancy selectively increases K(ATP), but not L-type Ca(2+) channel activity. Long-term hypoxia decreases the K(ATP) channel activity, which may contribute to the enhanced uterine vascular myogenic tone observed in pregnant sheep at high altitude hypoxia.

The guanylyl cyclase activator YC-1 directly inhibits the voltage-dependent K+ channels in rabbit coronary arterial smooth muscle cells

We investigated the effects of YC-1, an activator of soluble guanylyl cyclase (sGC), on voltage-dependent K+ (Kv) channels in smooth muscle cells from freshly isolated rabbit coronary arteries by using the whole-cell patch clamp technique. YC-1 inhibited the Kv current in a dose-dependent fashion with an apparent K(d) of 9.67 microM. It accelerated the decay rate of Kv channel inactivation without altering the kinetics of current activation. The rate constants of association and dissociation for YC-1 were 0.36 +/- 0.01 microM(-1) x s(-1) and 3.44 +/- 0.22 s(-1), respectively. YC-1 did not have a significant effect on the steady-state activation and inactivation curves. The recovery time constant from inactivation was decreased in the presence of YC-1, and application of train pulses (1 or 2 Hz) caused a progressive increase in the YC-1 blockade, indicating that YC-1-induced inhibition of Kv currents is use-dependent. Pretreatment with Bay 41-2272 (also a sGC activator), ODQ (a sGC inhibitor), or Rp-8-Br-PET-cGMPs (a protein kinase G inhibitor) did not affect the basal Kv current and also did not significantly alter the inhibitory effect of YC-1. From these results, we suggest that YC-1 directly inhibits the Kv current independently of sGC activation and in a state-, time-, and use-dependent fashion.

Muscle KATP channels: recent insights to energy sensing and myoprotection

ATP-sensitive potassium (K(ATP)) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of K(ATP) channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle K(ATP) channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle K(ATP) activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.

Targeting TASK-1 channels as a therapeutic approach

The voltage-independent background two-pore domain K(+) channel TASK-1 sets the resting membrane potential in excitable cells and renders these cells sensitive to a variety of vasoactive factors. There is clear evidence for TASK-1 in human pulmonary artery smooth muscle cells and TASK-1 channels are likely to regulate the pulmonary vascular tone through their regulation by hypoxia, pH, inhaled anesthetics, and G protein-coupled pathways. Furthermore, TASK-1 is a strong candidate to play a role in hypoxic pulmonary vasoconstriction. On the other hand, consistent with the activation of TASK-1 channels by volatile anesthetics, TASK-1 contributes to the anesthetic-induced pulmonary vasodilation. TASK-1 channels are unique among K(+) channels because they are regulated by both, increases and decreases from physiological pH, thus contributing to their protective effect on the pulmonary arteries. Moreover, TASK-1 may also have a critical role in mediating the vasoactive response of G protein-coupled pathways in resistance arteries which can offer promising therapeutic solutions to target diseases of the pulmonary circulation.

Endothelin-1 inhibits background two-pore domain channel TASK-1 in primary human pulmonary artery smooth muscle cells

Endothelin (ET)-1 causes long-lasting vasoconstriction and vascular remodeling by interacting with specific G-protein-coupled receptors in pulmonary artery smooth muscle cells (PASMCs), and thus plays an important role in the pathophysiology of pulmonary arterial hypertension. The two-pore domain K(+) channel, TASK-1, controls the resting membrane potential in human PASMCs (hPASMCs), and renders these cells sensitive to a variety of vasoactive factors, as previously shown. ET-1 may exert its vasoconstrictive effects in part by targeting TASK-1. To clarify this, we analyzed the ET-1 signaling pathway related to TASK-1 in primary hPASMCs. We employed the whole-cell patch-clamp technique combined with TASK-1 small interfering RNA (siRNA) in hPASMC and the isolated, perfused, and ventilated mouse lung model. We found that ET-1 depolarized primary hPASMCs by phosphorylating TASK-1 at clinically relevant concentrations. The ET sensitivity of TASK-1 required ET(A) receptors, phospholipase C, phosphatidylinositol 4,5-biphosphate, diacylglycerol, and protein kinase C in primary hPASMCs. The ET-1 effect on membrane potential and TASK-1 was abrogated using TASK-1 siRNA. This is the first time that the background K(+) channel, TASK-1, has been identified in the ET-1-mediated depolarization in native hPASMC, and might represent a novel pathologic mechanism related to pulmonary arterial hypertension.

Proteomic analysis of the effect of iptakalim on human pulmonary arterial smooth muscle cell proliferation

AIM

To investigate the anti-proliferative effect of iptakalim (Ipt), a newly selective K(ATP) channel opener, in endothelin-1 (ET-1)-induced human pulmonary arterial smooth muscle cells (PASMCs) using proteomic analysis.

METHODS

Human PASMCs were incubated with ET-1 (10(-8) mol/L) and ET-1 (10(-8) mol/L) plus iptaklim (10(-5) mol/L) for 24 h. Analysis via 2-DE gel electrophoresis and MALDI-TOF-MS was employed to display the different protein profiles of whole-cell protein from cultures of control, ET-1 treatment alone, and treatment with ET-1 and iptaklim combined. Real time RT-PCR and Western blot analysis were used to confirm the proteomic analysis.

RESULTS

When iptakalim inhibited the proliferative effect of ET-1 in human PASMCs by opening the K(ATP) channels, the expression of different groups of cellular proteins was changed, including cytoskeleton-associated proteins, plasma membrane proteins and receptors, chaperone proteins, ion transport-associated proteins, and glycolytic and metabolism-associated proteins. We found that iptakalim could inhibit the proliferation of human PASMCs partly by affecting the expression of Hsp60, vimentin, nucleoporin P54 (NUP54) and Bcl-X(L) by opening the K(ATP) channel.

CONCLUSION

The data suggest that a wide range of signaling pathways may be involved in abolishing ET-1-induced proliferation of human PASMCs following iptakalim treatment.

Calcium-activated potassium channels and endothelial dysfunction: therapeutic options?

The three subtypes of calcium-activated potassium channels (K(Ca)) of large, intermediate and small conductance (BK(Ca), IK(Ca) and SK(Ca)) are present in the vascular wall. In healthy arteries, BK(Ca) channels are preferentially expressed in vascular smooth muscle cells, while IK(Ca) and SK(Ca) are preferentially located in endothelial cells. The activation of endothelial IK(Ca) and SK(Ca) contributes to nitric oxide (NO) generation and is required to elicit endothelium-dependent hyperpolarizations. In the latter responses, the hyperpolarization of the smooth muscle cells is evoked either via electrical coupling through myo-endothelial gap junctions or by potassium ions, which by accumulating in the intercellular space activate the inwardly rectifying potassium channel Kir2.1 and/or the Na(+)/K(+)-ATPase. Additionally, endothelium-derived factors such as cytochrome P450-derived epoxyeicosatrienoic acids and under some circumstances NO, prostacyclin, lipoxygenase products and hydrogen peroxide (H(2)O(2)) hyperpolarize and relax the underlying smooth muscle cells by activating BK(Ca). In contrast, cytochrome P450-derived 20-hydroxyeicosatetraenoic acid and various endothelium-derived contracting factors inhibit BK(Ca). Aging and cardiovascular diseases are associated with endothelial dysfunctions that can involve a decrease in NO bioavailability, alterations of EDHF-mediated responses and/or enhanced production of endothelium-derived contracting factors. Because potassium channels are involved in these endothelium-dependent responses, activation of endothelial and/or smooth muscle K(Ca) could prevent the occurrence of endothelial dysfunction. Therefore, direct activators of these potassium channels or compounds that regulate their activity or their expression may be of some therapeutic interest. Conversely, blockers of IK(Ca) may prevent restenosis and that of BK(Ca) channels sepsis-dependent hypotension.

A short motif in Kir6.1 consisting of four phosphorylation repeats underlies the vascular KATP channel inhibition by protein kinase C

Vascular ATP-sensitive K(+) channels are inhibited by multiple vasoconstricting hormones via the protein kinase C (PKC) pathway. However, the molecular substrates for PKC phosphorylation remain unknown. To identify the PKC sites, Kir6.1/SUR2B and Kir6.2/SUR2B were expressed in HEK293 cells. Following channel activation by pinacidil, the catalytic fragment of PKC inhibited the Kir6.1/SUR2B currents but not the Kir6.2/SUR2B currents. Phorbol 12-myristate 13-acetate (a PKC activator) had similar effects. Using Kir6.1-Kir6.2 chimeras, two critical protein domains for the PKC-dependent channel inhibition were identified. The proximal N terminus of Kir6.1 was necessary for channel inhibition. Because there was no PKC phosphorylation site in the N-terminal region, our results suggest its potential involvement in channel gating. The distal C terminus of Kir6.1 was crucial where there are several consensus PKC sites. Mutation of Ser-354, Ser-379, Ser-385, Ser-391, or Ser-397 to nonphosphorylatable alanine reduced PKC inhibition moderately but significantly. Combined mutations of these residues had greater effects. The channel inhibition was almost completely abolished when 5 of them were jointly mutated. In vitro phosphorylation assay showed that 4 of the serine residues were necessary for the PKC-dependent (32)P incorporation into the distal C-terminal peptides. Thus, a motif containing four phosphorylation repeats is identified in the Kir6.1 subunit underlying the PKC-dependent inhibition of the Kir6.1/SUR2B channel. The presence of the phosphorylation motif in Kir6.1, but not in its close relative Kir6.2, suggests that the vascular K(ATP) channel may have undergone evolutionary optimization, allowing it to be regulated by a variety of vasoconstricting hormones and neurotransmitters.

Endothelin-1 accentuates the proatherosclerotic effects associated with C-reactive protein

OBJECTIVES

The proinflammatory marker C-reactive protein has been demonstrated to play a role in the development of atherosclerosis. Endothelin-1 and nitric oxide homeostasis is crucial for normal vasomotor function, limiting inflammatory activation and maintaining a nonthrombogenic endothelial surface. In addition to its vasoactive properties, endothelin-1 is also an inflammatory cytokine. We have previously demonstrated that C-reactive protein impairs endothelial cell nitric oxide production. Protein kinase C, an important signal transducer within the cell, is involved in several cellular responses to external stimuli. We therefore sought to determine whether endothelin-1 exposure modulates C-reactive protein's effects on nitric oxide production via protein kinase C.

METHODS

Endothelial cells were incubated with C-reactive protein (200 microg), endothelin-1 (100 nM), C-reactive protein + endothelin-1, or phosphate-buffered saline solution (control) for 24 hours. After exposure, endothelial nitric oxide synthase expression was determined in addition to total nitric oxide production and protein kinase C translocation and activity.

RESULTS

Endothelial nitric oxide synthase protein expression was reduced following incubation with C-reactive protein and endothelin-1 treatment compared with baseline by 40% and 45%, respectively (P = .04); however, no additive effects were seen with coincubation. C-reactive protein produced a 47% decrease in nitric oxide production compared with control. Coincubation with endothelin-1 resulted in a synergistic 70% reduction in nitric oxide production (P = .001). C-reactive protein exposure inhibited translocation of protein kinase C lambda compared with control (P = .01). Furthermore, coincubation of C-reactive protein with endothelin-1 led to a synergistic inhibition of protein kinase C lambda translocation (P = .01). C-reactive protein exposure reduced protein kinase C activity by 40% compared with control (P = .02), although coincubation with endothelin-1 had a synergistic reduction in activity (P = .02).

CONCLUSIONS

Our results indicate that endothelin-1 exposure accentuated C-reactive protein's impairment of endothelial nitric oxide production via synergistic inhibition of protein kinase C lambda translocation and activity. Our investigations suggest that endothelin-1 inhibition and protein kinase C stimulation may provide a novel therapeutic strategy to improve vascular nitric oxide homeostasis and mitigate the proatherosclerotic effects of C-reactive protein.

Interaction of KATP channels and endothelin-1 in lambs with persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn is a life-threatening condition in which half of infants fail to respond to inhaled nitric oxide. Development of new therapeutic pathways is crucial. The adenosine triphosphate (ATP)-sensitive potassium channels (K(ATP)) may be important in this condition. Concentration-response curves to the K(ATP) channel opener (SR47063) were performed in isolated pulmonary arterial rings from normal newborn lambs (n = 8) and pulmonary hypertensive lambs (n = 7) induced by intrauterine ductus arteriosus ligation. The effect of endothelin (ET) receptor antagonists was analyzed. Expression in the lung of the subunit Kir 6.1 of the K(ATP) channel and of ET were analyzed using Western blot and immunohistochemistry. Relaxation to SR47063 was increased in ligated animals compared with the control group. Endothelium removal enhanced this response in ligated animals (p < 0.01). The inhibitory effect of the endothelium was reversed by the Endothelin-A receptor (ET-A) antagonist BQ 123 (p < 0.01). Kir 6.1 expression was not different between groups and that of endothelin-1 (ET-1) was increased threefold in ligated animals (p = 0.007). In pulmonary hypertensive lambs, vasodilation to K(ATP) channel openers was enhanced compared with controls and further potentiated by ET-A blockade. These data might lead to new therapeutic strategies in infants with pulmonary hypertension.

Elevated endothelin-1 levels impair nitric oxide homeostasis through a PKC-dependent pathway

BACKGROUND

Endothelin-1 (ET-1) plays an important role in the maintenance of vascular tone and pathological states such as ischemia/reperfusion (I/R) injury, coronary vasospasm, and cardiac allograft vasculopathy. We assessed the effects of elevated ET-1 levels as seen after I/R to determine if ET-1 modulates nitric oxide (NO) production via the translocation of specific protein kinase C (PKC) isoforms.

METHODS AND RESULTS

Human saphenous vein endothelial cells (HSVECs) (n=8) were incubated with ET-1 or phosphate-buffered saline (PBS) for 24 hours. NO production was determined in the supernatant by measuring nitrate/nitrite levels. Protein expression of endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), caveolin-1 and PKC were determined. Lastly, PKC translocation and activity were assessed after exposure to the drug of interest. HSVECs exposed to ET-1 displayed decreased NO production. PKC inhibition reduced NO production, whereas PKC activation increased production. NO production was maintained when HSVECs exposed to ET-1 were treated with the PKC agonist, PMA. eNOS protein expression was reduced after ET-1 treatment. PKC inhibition also downregulated eNOS protein expression, whereas PMA upregulated expression. ET-1 exposure led to a significant increase in PKCdelta and PKCalpha translocation compared with control, whereas translocation of PKClambda was inhibited. ET-1 exposure significantly reduced overall PKC activity compared with control.

CONCLUSIONS

Our study demonstrates that high levels of ET-1 impair endothelial NO production via an isoform-specific PKC-mediated inhibition of eNOS expression. ET-1 antagonism with bosentan stimulates translocation of PKClambda and leads to increased PKC activity and NO production. ET-1 antagonism may provide a novel therapeutic strategy to improve vascular homeostasis.

Glucose reduces endothelin inhibition of voltage-gated potassium channels in rat arterial smooth muscle cells

Prolonged hyperglycaemia impairs vascular reactivity and inhibits voltage-activated K(+) (Kv) channels. We examined acute effects of altering glucose concentration on the activity and inhibition by endothelin-1 (ET-1) of Kv currents of freshly isolated rat arterial myocytes. Peak Kv currents recorded in glucose-free solution were reversibly reduced within 200 s by increasing extracellular glucose to 4 mm. This inhibitory effect of glucose was abolished by protein kinase C inhibitor peptide (PKC-IP), and Kv currents were further reduced in 10 mm glucose. In current-clamped cells, membrane potentials were more negative in 4 than in 10 mm glucose. In 4 mm d-glucose, 10 nm ET-1 decreased peak Kv current amplitude at +60 mV from 23.5 +/- 3.3 to 12.1 +/- 3.1 pA pF(-1) (n = 6, P < 0.001) and increased the rate of inactivation, decreasing the time constant around fourfold. Inhibition by ET-1 was prevented by PKC-IP. When d-glucose was increased to 10 mm, ET-1 no longer inhibited Kv current (n = 6). Glucose metabolism was required for prevention of ET-1 inhibition of Kv currents, since fructose mimicked the effects of d-glucose, while l-glucose, sucrose or mannitol were without effect. Endothelin receptors were still functional in 10 mm d-glucose, since pinacidil-activated ATP-dependent K(+) (K(ATP)) currents were reduced by 10 nm ET-1. This inhibition was nearly abolished by PKC-IP, indicating that endothelin receptors could still activate PKC in 10 mm d-glucose. These results indicate that changes in extracellular glucose concentration within the physiological range can reduce Kv current amplitude and can have major effects on Kv channel modulation by vasoconstrictors.

Expression and function of potassium channels in the human placental vasculature

In the placental vasculature, where oxygenation may be an important regulator of vascular reactivity, there is a paucity of data on the expression of potassium (K) channels, which are important mediators of vascular smooth muscle tone. We therefore addressed the expression and function of several K channel subtypes in human placentas. The expression of voltage-gated (Kv)2.1, KV9.3, large-conductance Ca2+-activated K channel (BKCa), inward-rectified K+ channel (KIR)6.1, and two-pore domain inwardly rectifying potassium channel-related acid-sensitive K channels (TASK)1 in chorionic plate arteries, veins, and placental homogenate was assessed by RT-PCR and Western blot analysis. Functional activity of K channels was assessed pharmacologically in small chorionic plate arteries and veins by wire myography using 4-aminopyridine, iberiotoxin, pinacidil, and anandamide. Experiments were performed at 20, 7, and 2% oxygen to assess the effect of oxygenation on the efficacy of K channel modulators. KV2.1, KV9.3, BKCa, KIR6.1, and TASK1 channels were all demonstrated to be expressed at the message level. KV2.1, BKCa, KIR6.1, and TASK1 were all demonstrated at the protein level. Pharmacological manipulation of voltage-gated and ATP-sensitive channels produced the most marked modifications in vascular tone, in both arteries and veins. We conclude that K channels play an important role in controlling placental vascular function.

Endothelin-1 inhibits inward rectifier K+ channels in rabbit coronary arterial smooth muscle cells through protein kinase C

We studied inward rectifier K+ (Kir) channels in smooth muscle cells isolated from rabbit coronary arteries. In cells from small- (<100 microm, SCASMC) and medium-diameter (100 approximately 200 microm, MCASMC) coronary arteries, Kir currents were clearly identified (11.2 +/- 0.6 and 4.2 +/- 0.6 pA pF at -140 mV in SCASMC and MCASMC, respectively) that were inhibited by Ba(2+) (50 microm). By contrast, a very low Kir current density (1.6 +/- 0.4 pA pF) was detected in cells from large-diameter coronary arteries (>200 microm, LCASMC). The presence of Kir2.1 protein was confirmed in SCASMC in a Western blot assay. Endothelin-1 (ET-1) inhibited Kir currents in a dose-dependent manner. The inhibition of Kir currents by ET-1 was abolished by pretreatment with the protein kinase C (PKC) inhibitor staurosporine (100 nM) or GF 109203X (1 microm). The PKC activators phorbol 12,13-dibutyrate (PDBu) and 1-oleoyl-2-acetyl-sn-glycerol (OAG) reduced Kir currents. The ETA-receptor inhibitor BQ-123 prevented the ET-1-induced inhibition of Kir currents. The amplitudes of the ATP-dependent K+ (KATP), Ca(2+)-activated K+ (BKCa), and voltage-dependent K+ (KV) currents, and effects of ET-1 on these channels did not differ between SCASMC and LCASMC. From these results, we conclude that Kir channels are expressed at a higher density in SCASMC than in larger arteries and that the Kir channel activity is negatively regulated by the stimulation of ETA-receptors via the PKC pathway.

Angiotensin II inhibits inward rectifier K+ channels in rabbit coronary arterial smooth muscle cells through protein kinase Calpha

We investigated the effects of the vasoconstrictor angiotensin (Ang) II on the whole cell inward rectifier K(+) (Kir) current enzymatically isolated from small-diameter (<100 microm) coronary arterial smooth muscle cells (CASMCs). Ang II inhibited the Kir current in a dose-dependent manner (half inhibition value: 154 nM). Pretreatment with phospholipase C inhibitor and protein kinase C (PKC) inhibitors prevented the Ang II-induced inhibition of the Kir current. The PKC activator reduced the Kir currents. The inhibitory effect of Ang II was reduced by intracellular and extracellular Ca(2+) free condition and by Gö6976, which inhibits Ca(2+)-dependent PKC isoforms alpha and beta. However, the inhibitory effect of Ang II was unaffected by a peptide that selectively inhibits the translocation of the epsilon isoform of PKC. Western blot analysis confirmed that PKCalpha, and not PKCbeta, was expressed in small-diameter CASMCs. The Ang II type 1 (AT(1))-receptor antagonist CV-11974 prevented the Ang II-induced inhibition of the Kir current. From these results, we conclude that Ang II inhibits Kir channels through AT(1) receptors by the activation of PKCalpha.

Glibenclamide Reveals Role for Endothelin in Hypoxia-Induced Vasoconstriction in Rat Intrapulmonary Arteries

The present study investigated whether activation of vasodilatory mechanisms masks the involvement of endothelin in hypoxic pulmonary vasoconstriction. Rat intrapulmonary arteries were mounted in microvascular myographs. In arteries with endothelium and contracted with phenylephrine, hypoxia, evoked by exchanging 5% CO2 in air for CO2 in N2, caused a transient contraction followed by a sustained contraction. Hypoxia evoked relaxation in preparations without endothelium. An inhibitor of ATP-sensitive K+ channels (KATP), glibenclamide (10 microM), blunted hypoxic relaxation in arteries without endothelium and enhanced the sustained hypoxic vasoconstriction in arteries with endothelium. Hypoxic contraction was more pronounced in endothelin compared with phenylephrine-contracted preparations in the absence, but not in the presence of glibenclamide. Antagonism of the endothelin ETA and ETB receptors with SB217242 or the combination of BQ123 and BQ788 inhibited endothelin and hypoxic contraction, but the latter only in the presence of glibenclamide. An inhibitor of nitric oxide (NO) synthase, N-nitro-L-arginine (100 microM), evoked contractions, which were left unaltered by SB217242 in hypoxic conditions. In conclusion, hypoxic contraction is mediated in part by an unknown endothelium-derived contractile factor and incubation with glibenclamide shows endothelin enhances hypoxic contraction in part through inhibition of KATP channels. Moreover, inhibition of NO formation in pulmonary arteries does not change endothelin receptor activation in severe hypoxia.

KATP channel conductance of descending vasa recta pericytes

Using nystatin-perforated patch-clamp and whole cell recording, we tested the hypothesis that K(ATP) channels contribute to resting conductance of rat descending vasa recta (DVR) pericytes and are modulated by vasoconstrictors. The K(ATP) blocker glybenclamide (Glb; 10 microM) depolarized pericytes and inhibited outward currents of cells held at -40 mV. K(ATP) openers pinacidil (Pnc; 10 microM) and P-1075 (1 microM) hyperpolarized pericytes and transiently augmented outward currents. All effects of Pnc and P-1075 were fully reversed by Glb. Inward currents of pericytes held at -60 mV in symmetrical 140 mM K(+) were markedly augmented by Pnc and fully reversed by Glb. Ramp depolarizations in symmetrical K(+), performed in Pnc and Pnc + Glb, yielded a Pnc-induced, Glb-sensitive K(ATP) difference current that lacked rectification and reversed at 0 mV. Immunostaining identified both K(IR)6.1, K(IR)6.2 inward rectifier subunits and sulfonurea receptor subtype 2B. ANG II (1 and 10 nM) and endothelin-1 (10 nM) but not vasopressin (100 nM) significantly lowered holding current at -40 mV and abolished Pnc-stimulated outward currents. We conclude that DVR pericytes express K(ATP) channels that make a significant contribution to basal K(+) conductance and are inhibited by ANG II and endothelin-1.