Endothelin-1 increases intracellular Ca(2+) in rabbit pulmonary artery smooth muscle cells through phospholipase C

ASIC1-mediated calcium entry stimulates NFATc3 nuclear translocation via PICK1 coupling in pulmonary arterial smooth muscle cells

The development of chronic hypoxia (CH)-induced pulmonary hypertension is associated with increased pulmonary arterial smooth muscle cell (PASMC) Ca(2+) influx through acid-sensing ion channel-1 (ASIC1) and activation of the Ca(2+)/calcineurin-dependent transcription factor known as nuclear factor of activated T-cells isoform c3 (NFATc3). Whether Ca(2+) influx through ASIC1 contributes to NFATc3 activation in the pulmonary vasculature is unknown. Furthermore, both ASIC1 and calcineurin have been shown to interact with the scaffolding protein known as protein interacting with C kinase-1 (PICK1). In the present study, we tested the hypothesis that ASIC1 contributes to NFATc3 nuclear translocation in PASMC in a PICK1-dependent manner. Using both ASIC1 knockout (ASIC1(-/-)) mice and pharmacological inhibition of ASIC1, we demonstrate that ASIC1 contributes to CH-induced (1 wk at 380 mmHg) and endothelin-1 (ET-1)-induced (10(-7) M) Ca(2+) responses and NFATc3 nuclear import in PASMC. The interaction between ASIC1/PICK1/calcineurin was shown using a Duolink in situ Proximity Ligation Assay. Inhibition of PICK1 by using FSC231 abolished ET-1-induced and ionomycin-induced NFATc3 nuclear import, but it did not alter ET-1-mediated Ca(2+) responses, suggesting that PICK1 acts downstream of Ca(2+) influx. The key findings of the present work are that 1) Ca(2+) influx through ASIC1 mediates CH- and ET-1-induced NFATc3 nuclear import and 2) the scaffolding protein PICK1 is necessary for NFATc3 nuclear import. Together, these data provide an essential link between CH-induced ASIC1-mediated Ca(2+) influx and activation of the NFATc3 transcription factor. Identification of this ASIC1/PICK1/NFATc3 signaling complex increases our understanding of the mechanisms contributing to the vascular remodeling and increased vascular contractility that are associated with CH-induced pulmonary hypertension.

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.

Adaptive regulation of endothelin receptor type-A and type-B in vascular smooth muscle cells during pregnancy in rats

Normal pregnancy is associated with systemic vasodilation and decreased vascular contraction, partly due to increased release of endothelium-derived vasodilator substances. Endothelin-1 (ET-1) is an endothelium-derived vasoconstrictor acting via endothelin receptor type A (ETA R) and possibly type B (ETB R) in vascular smooth muscle cells (VSMCs), with additional vasodilator effects via endothelial ETB R. However, the role of ET-1 receptor subtypes in the regulation of vascular function during pregnancy is unclear. We investigated whether the decreased vascular contraction during pregnancy reflects changes in the expression/activity of ETAR and ETBR. Contraction was measured in single aortic VSMCs isolated from virgin, mid-pregnant (mid-Preg, day 12), and late-Preg (day 19) Sprague-Dawley rats, and the mRNA expression, protein amount, tissue and cellular distribution of ETAR and ETBR were examined using RT-PCR, Western blots, immunohistochemistry, and immunofluorescence. Phenylephrine (Phe, 10(-5)  M), KCl (51 mM), and ET-1 (10(-6)  M) caused VSMC contraction that was in late-Preg < mid-Preg and virgin rats. In VSMCs treated with ETB R antagonist BQ788, ET-1 caused significant contraction that was still in late-Preg < mid-Preg and virgin rats. In VSMCs treated with the ETAR antagonist BQ123, ET-1 caused a small contraction; and the ETBR agonists IRL-1620 and sarafotoxin 6c (S6c) caused similar contraction that was in late-Preg < mid-Preg and virgin rats. RT-PCR revealed similar ETAR, but greater ETBR mRNA expression in pregnant versus virgin rats. Western blots revealed similar ETAR, and greater protein amount of ETBR in endothelium-intact vessels, but reduced ETBR in endothelium-denuded vessels of pregnant versus virgin rats. Immunohistochemistry revealed prominent ETBR staining in the intima, but reduced ETAR and ETBR in the aortic media of pregnant rats. Immunofluorescence signal for ETAR and ETBR was less in VSMCs of pregnant versus virgin rats. The pregnancy-associated decrease in ETAR- and ETBR-mediated VSMC contraction appears to involve downregulation of ETAR and ETBR expression/activity in VSM, and may play a role in the adaptive vasodilation during pregnancy.

Functional characterization of voltage-dependent Ca(2+) channels in mouse pulmonary arterial smooth muscle cells: divergent effect of ROS

Electromechanical coupling via membrane depolarization-mediated activation of voltage-dependent Ca(2+) channels (VDCC) is an important mechanism in regulating pulmonary vascular tone, while mouse is an animal model often used to study pathogenic mechanisms of pulmonary vascular disease. The function of VDCC in mouse pulmonary artery (PA) smooth muscle cells (PASMC), however, has not been characterized, and their functional role in reactive oxygen species (ROS)-mediated regulation of vascular function remains unclear. In this study, we characterized the electrophysiological and pharmacological properties of VDCC in PASMC and the divergent effects of ROS produced by xanthine oxidase (XO) and hypoxanthine (HX) on VDCC in PA and mesenteric artery (MA). Our data show that removal of extracellular Ca(2+) or application of nifedipine, a dihydropyridine VDCC blocker, both significantly inhibited 80 mM K(+)-mediated PA contraction. In freshly dissociated PASMC, the maximum inward Ca(2+) currents were -2.6 ± 0.2 pA/pF at +10 mV (with a holding potential of -70 mV). Window currents were between -40 and +10 mV with a peak at -15.4 mV. Nifedipine inhibited currents with an IC(50) of 0.023 μM, and 1 μM Bay K8644, a dihydropyridine VDCC agonist, increased the inward currents by 61%. XO/HX attenuated 60 mM K(+)-mediated increase in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) due to Ca(2+) influx through VDCC in PASMC. Exposure to XO/HX caused relaxation in PA preconstricted by 80 mM K(+) but not in aorta and MA. In contrast, H(2)O(2) inhibited high K(+)-mediated increase in [Ca(2+)](cyt) and caused relaxation in both PA and MA. Indeed, RT-PCR and Western blot analysis revealed significantly lower expression of Ca(V)1.3 in MA compared with PA. Thus our study characterized the properties of VDCC and demonstrates that ROS differentially regulate vascular contraction by regulating VDCC in PA and systemic arteries.

Vardenafil ameliorates calcium mobilization in pulmonary artery smooth muscle cells from hypoxic pulmonary hypertensive mice

BACKGROUND AND AIMS

Vardenafil has been found to be potent in pulmonary hypertension; however, the underlying mechanisms remain poorly understood. To address this issue, we investigated the underlying mechanisms of vardenafil in the contribution of Ca(2+) signaling and mobilization in modifying vasoconstriction of pulmonary arteries in hypoxic mice.

METHODS

Hemodynamic measurements and morphological studies were performed. Muscle tension was measured by PowerLab system. I(Ca,L) was recorded using a perforated patch-clamp technique. [Ca(2+)](i) was measured using a fluorescence imaging system.

RESULTS

Vardenafil greatly inhibited RVSP increases, RV hypertrophy and ameliorated pulmonary artery remodeling in response to chronic hypoxia. Membrane depolarization following 50 mM high K(+)-caused muscle contraction significantly decreased from 101.7 ± 10.1 in the hypoxia group to 81.8 ± 5.0 mg in hypoxia plus vardenafil arteries. Fifty mM high K(+)-elicited increase [Ca(2+)](i) was markedly decreased from 610.6 ± 71.8 in hypoxia cells to 400.3 ± 47.2 nM in hypoxia plus vardenafil cells. Application of vardenafil greatly inhibited the density of I(Ca,L) by 37.7% compared with that in the hypoxia group. Administration of 1 μM phenylephrine to stimulate α(1)-adrenergic receptor resulted in a smaller increase in [Ca(2+)](i) in hypoxia plus vardenafil cells than that in hypoxia cells. One hundred μM ATP-mediated increase in [Ca(2+)](i) was also inhibited in vardenafil-hypoxia group (from 625.8 ± 62.3 to 390.9 ± 38.1 nM), suggesting that internal calcium reserves contribute to neurotransmitter-induced Ca(2+) release from the SR through IP(3)Rs in PASMCs.

CONCLUSIONS

Vardenafil may effectively block Ca(2+) influx through L-type Ca(2+) channel and inhibit the Ca(2+) release from SR through IP(3)Rs, thus enhancing its vasorelaxation of pulmonary arteries under hypoxia conditions.

Vascular endothelin receptor type B: structure, function and dysregulation in vascular disease

Endothelin-1 (ET-1) is a major regulator of vascular function, acting via both endothelin receptor type A (ET(A)R) and type B (ET(B)R). Although the role of ET(A)R in vascular smooth muscle (VSM) contraction has been studied, little is known about ET(B)R. ET(B)R is a G-protein coupled receptor with a molecular mass of ~50 kDa and 442 amino acids arranged in seven transmembrane domains. Alternative splice variants of ET(B)R and heterodimerization and cross-talk with ET(A)R may affect the receptor function. ET(B)R has been identified in numerous blood vessels with substantial effects in the systemic, renal, pulmonary, coronary and cerebral circulation. ET(B)R in the endothelium mediates the release of relaxing factors such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, and could also play a role in ET-1 clearance. ET(B)R in VSM mediates increases in [Ca(2+)](i), protein kinase C, mitogen-activated protein kinase and other pathways of VSM contraction and cell growth. ET-1/ET(A)R signaling has been associated with salt-sensitive hypertension (HTN) and pulmonary arterial hypertension (PAH), and ET(A)R antagonists have shown some benefits in these conditions. In search for other pathogenetic factors and more effective approaches, the role of alterations in endothelial ET(B)R and VSM ET(B)R in vascular dysfunction, and the potential benefits of modulators of ET(B)R in treatment of HTN and PAH are being examined. Combined ET(A)R/ET(B)R antagonists could be more efficacious in the management of conditions involving upregulation of ET(A)R and ET(B)R in VSM. Combined ET(A)R antagonist with ET(B)R agonist may need to be evaluated in conditions associated with decreased endothelial ET(B)R expression/activity.

Inositol trisphosphate receptors in smooth muscle cells

Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) are a family of tetrameric intracellular calcium (Ca(2+)) release channels that are located on the sarcoplasmic reticulum (SR) membrane of virtually all mammalian cell types, including smooth muscle cells (SMC). Here, we have reviewed literature investigating IP(3)R expression, cellular localization, tissue distribution, activity regulation, communication with ion channels and organelles, generation of Ca(2+) signals, modulation of physiological functions, and alterations in pathologies in SMCs. Three IP(3)R isoforms have been identified, with relative expression and cellular localization of each contributing to signaling differences in diverse SMC types. Several endogenous ligands, kinases, proteins, and other modulators control SMC IP(3)R channel activity. SMC IP(3)Rs communicate with nearby ryanodine-sensitive Ca(2+) channels and mitochondria to influence SR Ca(2+) release and reactive oxygen species generation. IP(3)R-mediated Ca(2+) release can stimulate plasma membrane-localized channels, including transient receptor potential (TRP) channels and store-operated Ca(2+) channels. SMC IP(3)Rs also signal to other proteins via SR Ca(2+) release-independent mechanisms through physical coupling to TRP channels and local communication with large-conductance Ca(2+)-activated potassium channels. IP(3)R-mediated Ca(2+) release generates a wide variety of intracellular Ca(2+) signals, which vary with respect to frequency, amplitude, spatial, and temporal properties. IP(3)R signaling controls multiple SMC functions, including contraction, gene expression, migration, and proliferation. IP(3)R expression and cellular signaling are altered in several SMC diseases, notably asthma, atherosclerosis, diabetes, and hypertension. In summary, IP(3)R-mediated pathways control diverse SMC physiological functions, with pathological alterations in IP(3)R signaling contributing to disease.

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.

Endothelium-dependent vasoconstriction in isolated vessel grafts: a novel mechanism of vasospasm?

BACKGROUND

YC-1 (3-(5'-hydroxymethyl-2'furyl)-1-benzyl-indazole) is an allosteric activator of soluble guanylyl cyclase (sGC) and a vasodilator. This study describes a paradoxical action of YC-1 in isolated vessels of patients with coronary artery disease (CAD) that appears to trigger an endothelium-dependent vasoconstrictor pathway present in vessels with endothelial dysfunction.

METHODS

Effects of YC-1 on the tensions of isolated vessels were investigated in an organ bath. Vasoconstrictors released from the vessels were quantified through enzyme-linked immunosorbent assay.

RESULTS

YC-1 elicited long-lasting constriction in saphenous veins and radial arteries from patients with CAD, but not in human umbilical veins. The half-maximal effective dose was 1.0 μmol/L. Constriction was attenuated by nifedipine (an L-type Ca(2+)-channel blocker), bosentan (an endothelin [ET](A)/ET(B) inhibitor), BQ-788 (N-[(cis-2,6-Dimethyl-1-piperidinyl)carbonyl]-4-methyl-L-leucyl-1-(methoxycarbonyl)-D-tryptophyl-D-norleucine; an ET(B) inhibitor), and by denuding, but not by ODQ (1H-(1,2,4)oxadiazolo[4,3-a]quinoxalin-1-one; an inhibitor of sGC), BQ-123 (cyclo(-D-Trp-D-Asp-Pro-D-Val-Leu); an ET(A) inhibitor), or phosphoramidon (an endothelin converting enzyme inhibitor). Indomethacin (an inhibitor of cyclooxygenase-1 and -2) and SQ29,548 ([1S-[1α,2α(Z),3α,4α]]-7-[3-[[2-[(phenylamino)carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1]hept-2-yl]-5-heptenoic acid; a thromboxane receptor antagonist) suppressed YC-1-induced constriction, whereas DFU (5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone; a cyclooxygenase-2 inhibitor) had no effect. Rings of saphenous vein released significantly more endothelin-1 in the presence than in the absence of YC-1.

CONCLUSIONS

YC-1-induced vasoconstriction demonstrates the existence of an endothelium-dependent vasoconstrictor pathway in the blood vessels of patients with CAD that to date has been described only in animal models of hypertension. Patients with CAD who have elevated plasma levels of endothelin-1 are thus prone to endothelium-dependent vasoconstriction, which may also play a role in vasospasm in vascular grafts.

Tension Measurement in Isolated Rat and Mouse Pulmonary Artery

Arterial vasoconstriction is an important physiological process in regulating blood pressure, and is involved in pathologies. The isolation of arteries from rats and mice, as well as the measurement of vascular tension in an ex vivo preparation, are important methods in studying the physiology of arteries and the pathophysiology associated with arterials. Three major methods to measure vascular tension are organ bath, wire myograph, and pressurized arterial myograph. The major method to measure vascular remodeling is by observing the zero-stress state of an artery.

The functional expression of extracellular calcium-sensing receptor in rat pulmonary artery smooth muscle cells

BACKGROUND

The extracellular calcium-sensing receptor (CaSR) belongs to family C of the G protein coupled receptors. Whether the CaSR is expressed in the pulmonary artery (PA) is unknown.

METHODS

The expression and distribution of CaSR were detected by RT-PCR, Western blotting and immunofluorescence. PA tension was detected by the pulmonary arterial ring technique, and the intracellular calcium concentration ([Ca2+]i) was detected by a laser-scanning confocal microscope.

RESULTS

The expressions of CaSR mRNA and protein were found in both rat pulmonary artery smooth muscle cells (PASMCs) and PAs. Increased levels of [Ca2+]o (extracellular calcium concentration) or Gd3+ (an agonist of CaSR) induced an increase of [Ca2+]i and PAs constriction in a concentration-dependent manner. In addition, the above-mentioned effects of Ca2+ and Gd3+ were inhibited by U73122 (specific inhibitor of PLC), 2-APB (specific antagonist of IP3 receptor), and thapsigargin (blocker of sarcoplasmic reticulum calcium ATPase).

CONCLUSIONS

CaSR is expressed in rat PASMCs, and is involved in regulation of PA tension by increasing [Ca2+]i through G-PLC-IP3 pathway.

Voltage-independent calcium channels mediate lipopolysaccharide-induced hyporeactivity to endothelin-1 in the rat aorta

The roles of intracellular calcium concentration ([Ca(2+)](i)) and Ca(2+) sensitization in lipopolysaccharide (LPS)-induced vascular smooth muscle (VSM) hyporesponsiveness are incompletely understood. To investigate these roles, contraction responses to endothelin-1 (ET-1) and 80 mM KCl; relaxation responses to nifedipine; the expression levels of mRNAs of ET-1 and its receptors (ET(A) or ET(B)); the expression levels of protein kinase C (PKC) and phosphorylation of Rho kinase (ROKalpha), CPI-17, and myosin phosphatase target subunit-1 (MYPT1); and changes in aortic VSM cell [Ca(2+)](i) were measured in LPS-treated aortic rings from male Wistar rats (250-300 g). LPS (10 mug/ml, 20 h) decreased contraction induced by ET-1 (0.3-100 nM) or 80 mM KCl. LPS-induced hypocontractility was not observed in the absence of external Ca(2+), but LPS-treated aorta remained hypocontractile on subsequent stepwise restoration of extracellular Ca(2+) (0.01-10 mM). Vascular relaxation to nifedipine; mRNA expression levels of ET-1, ET(A), or ET(B); protein expression levels of PKC; and phosphorylation levels of ROKalpha, CPI-17, and MYPT1 were not affected by LPS. In isolated aortic VSM cells, ET-1 caused a transient initial increase in [Ca(2+)](i), followed by a maintained tonic increase in [Ca(2+)](i), which was decreased by LPS pretreatment and was dependent on external Ca(2+). Subsequent restoration of extracellular Ca(2+) increased [Ca(2+)](i), but this increase was lower in the LPS-treated group. This difference in response to extracellular Ca(2+) addition was not affected by diltiazem, but was abolished by SKF-96365. Therefore, LPS induces hyporeactivity to ET-1 in rat aorta that depends on external Ca(2+) influx through non-voltage-operated Ca(2+) channels, but not on ET-1 receptor expression or Ca(2+) sensitization.

Endothelin-induced contraction of bronchiole and pulmonary arteriole smooth muscle cells is regulated by intracellular Ca2+ oscillations and Ca2+ sensitization

Endothelin-1 (ET) induces increases in intracellular Ca(2+) concentration ([Ca(2+)](i)), Ca(2+) sensitization, and contraction of both bronchiole and pulmonary arteriole smooth muscle cells (SMCs) and may play an important role in the pathophysiology of asthma and pulmonary hypertension. However, because it remains unclear how changes in [Ca(2+)](i) and the Ca(2+) sensitivity regulate SMC contraction, we have studied mouse lung slices with phase-contrast and confocal microscopy to correlate the ET-induced contraction with the changes in [Ca(2+)](i) and Ca(2+) sensitivity of bronchiole and arteriole SMCs. In comparison with acetylcholine (ACh) or serotonin (5-HT), ET induced a stronger and long-lasting contraction of both bronchioles and arterioles. This ET-induced contraction was associated with prominent asynchronous Ca(2+) oscillations that were propagated as Ca(2+) waves along the SMCs. These Ca(2+) oscillations were mediated by cyclic intracellular Ca(2+) release and required external Ca(2+) for their maintenance. Importantly, as the frequency of the Ca(2+) oscillations increased, the extent of contraction increased. ET-induced contraction was also associated with an increase in Ca(2+) sensitivity. In "model" slices in which the [Ca(2+)](i) was constantly maintained at an elevated level by pretreatment of slices with caffeine and ryanodine, the addition of ET increased bronchiole and arteriole contraction. These results indicate that ET-induced contraction of bronchiole and arteriole SMCs is regulated by the frequency of Ca(2+) oscillations and by increasing the sensitivity of the contractile machinery to Ca(2+).