Rho-dependent kinase is involved in agonist-activated calcium entry in rat arteries

SIRT-associated attenuation of cellular senescence in vascular wall

This review focuses on the vital function that SIRT1 and other sirtuins play in promoting cellular senescence in vascular smooth muscle cells, which is a key element in the pathogenesis of vascular aging and associated cardiovascular diseases. Vascular aging is a gradual process caused by the accumulation of senescent cells, which results in increased vascular remodeling, stiffness, and diminished angiogenic ability. Such physiological alterations are characterized by a complex interplay of environmental and genetic variables, including oxidative stress and telomere attrition, which affect gene expression patterns and trigger cell growth arrest. SIRT1 has been highlighted for its potential to reduce cellular senescence through modulation of multiple signaling cascades, particularly the endothelial nitric oxide (eNOS)/NO signaling pathway. It also modulates cell cycle through p53 inactivation and suppresses NF-κB mediated expression of adhesive molecules at the vascular level. The study also examines the therapeutic potential of sirtuin modulation in vascular health, identifying SIRT1 and its sirtuin counterparts as potential targets for reducing vascular aging. This study sheds light on the molecular basis of vascular aging and the beneficial effects of sirtuins, paving the way for the development of tailored therapies aimed at enhancing vascular health and prolonging life.

Calcium handling coupled to the endothelin ETA and ETB receptor-mediated vasoconstriction in resistance arteries: Differential regulation by PI3K, PKC and RhoK

Abnormal endothelin-1 (ET-1) activity is involved in the pathogenesis of vascular diseases such as essential and pulmonary arterial hypertension, coronary artery disease, and cerebrovascular disease, blockade of ET receptors having shown efficacy in clinical assays and experimental models of hypertension. Augmented Ca2+ influx and changes in Ca2+ sensitization associated with arterial vasoconstriction underlie increased systemic vascular resistance in hypertension. Since peripheral resistance arteries play a key role in blood pressure regulation, we aimed to determine here the specific Ca2+ signaling mechanisms linked to the ET receptor-mediated vasoconstriction in resistance arteries and their selective regulation by protein kinase C (PKC), Rho kinase (RhoK), the phosphatidylinositol 3-kinase (PI3K) and the mitogen-activated protein kinase (MAPK). ET-1-induced contraction was mediated by the endothelin ETA receptor with a minor contribution of vascular smooth muscle (VSM) endothelin ETB receptors. ET receptor activation elicited Ca2+ mobilization from intracellular stores, extracellular Ca2+ influx and Ca2+ sensitization associated with contraction in resistance arteries. Vasoconstriction induced by ET-1 was largely dependent on activation of canonical transient receptor potential channel 3 (TRPC3) and extracellular Ca2+ influx through nifedipine-sensitive voltage-dependent Ca2+ channels. PI3K inhibition reduced intracellular Ca2+ mobilization and Ca2+ entry without altering vasoconstriction elicited by ET-1, while PKC has dual opposite actions by enhancing Ca2+ influx associated with contraction, and by inhibiting Ca2+ release from intracellular stores. RhoK was a major determinant of the enhanced sensitivity of the contractile filaments underlying ET-1 vasoconstriction, with also a modulatory positive action on Ca2+ influx and intracellular Ca2+ release. Augmented RhoK and PKC activities are involved in vascular dysfunction in hypertension and vascular complications of insulin-resistant states, and these kinases are thus potential pharmacological targets in vascular diseases in which the ET pathway is impaired.

Senescent murine femoral arteries undergo vascular remodelling associated with accelerated stress-induced contractility and reactivity to nitric oxide

This work explored the mechanism of augmented stress-induced vascular reactivity of senescent murine femoral arteries (FAs). Mechanical and pharmacological reactivity of young (12-25 weeks, y-FA) and senescent (>104 weeks, s-FAs) femoral arteries was measured by wire myography. Expression and protein phosphorylation of selected regulatory proteins were studied by western blotting. Expression ratio of the Exon24 in/out splice isoforms of the regulatory subunit of myosin phosphatase, MYPT1 (MYPT1-Exon24 in/out), was determined by polymerase chain reaction (PCR). While the resting length-tension relationship showed no alteration, the stretch-induced-tone increased to 8.3 ± 0.9 mN in s-FA versus only 4.6 ± 0.3 mN in y-FAs. Under basal conditions, phosphorylation of the regulatory light chain of myosin at S19 was 19.2 ± 5.8% in y-FA versus 49.2 ± 12.6% in s-FA. Inhibition of endogenous NO release raised tone additionally to 10.4 ± 1.2 mN in s-FA, whereas this treatment had a negligible effect in y-FAs (4.8 ± 0.3 mN). In s-FAs, reactivity to NO donor was augmented (pD₂  = -4.5 ± 0.3 in y-FA vs. -5.2 ± 0.1 in senescent). Accordingly, in s-FAs, MYPT1-Exon24-out-mRNA, which is responsible for expression of the more sensitive to protein-kinase G, leucine-zipper-positive MYPT1 isoform, was increased. The present work provides evidence that senescent murine s-FA undergoes vascular remodelling associated with increases in stretch-activated contractility and sensitivity to NO/cGMP/PKG system.

Involvement of G proteins and Rho kinase in α1-adrenoceptor mediated contractions of the rat portal vein

Contractions of the rat portal vein in response to the α1-adrenoceptor agonist phenylephrine consist of phasic contractions at low concentrations, with tonic contractions superimposed at higher concentrations. The α1D-adrenoceptor antagonist BMY7378 (7.0, -log M) did not affect phasic or tonic contractions to phenylephrine. The relatively nonselective α1-adrenoceptor antagonist prazosin (7.5) shifted equally the potencies of phenylephrine at producing phasic and tonic contractions, with pKB values of 8.85 and 8.83 (-log M), respectively. The α1A-adrenoceptor antagonist RS100329 (8.5) produced a significantly greater shift in phenylephrine potency for phasic (pKB of 10.51) than tonic contractions (pKB of 9.78). Prazosin was less effective than RS100329 at reducing the effects of phenylephrine on frequency of phasic contractions. The Rho kinase inhibitor fasudil (5.0) did not affect phasic contractions to phenylephrine, but significantly reduced tonic contractions. It is concluded that there is no evidence for involvement of α1D-adrenoceptors in responses of the rat portal vein to phenylephrine, but phasic responses involve predominantly α1A-adrenoceptors. Tonic responses may involve predominantly α1B-adrenoceptors and are at least partly mediated by mechanisms involving Rho kinase sensitive to fasudil.

Fasudil Dichloroacetate Alleviates SU5416/Hypoxia-Induced Pulmonary Arterial Hypertension by Ameliorating Dysfunction of Pulmonary Arterial Smooth Muscle Cells

Background

Pulmonary arterial hypertension (PAH) is an incurable disease that urgently needs therapeutic approaches. Based on the therapeutic effects of fasudil and dichloroacetate (DCA) on PAH, we aimed to explore the effects and potential mechanism of a new salt, fasudil dichloroacetate (FDCA), in a SU5416 plus hypoxia (SuHx)-induced rat model of PAH.

Methods

The rat model of PAH was established by a single subcutaneous injection of SU5416 (20 mg/kg) followed by hypoxia (10% O₂) exposure for 3 weeks. FDCA (15, 45, or 135 mg/kg i.g. daily) or the positive control, bosentan (100 mg/kg i.g. daily), were administered from the first day after SU5416 injection. After 3-week hypoxia, hemodynamic parameters, and histological changes of the pulmonary arterial vessels and right ventricle (RV) were assessed. Additionally, in vitro, the effects of FDCA (50 μM), compared with equimolar doses of fasudil, DCA, or fasudil+DCA, on the proliferation, migration, and contraction of human pulmonary arterial smooth muscle cell (PASMC) under hypoxia (1% O₂) were evaluated.

Results

FDCA dose-dependently attenuated SuHx-induced PAH, with significant reductions in RV systolic pressure, pulmonary artery wall thickness, pulmonary vessel muscularization, perivascular fibrosis, as well as RV hypertrophy and fibrosis. In vitro, FDCA inhibited hypoxia-induced PASMC proliferation, migration, and contraction to a greater degree than fasudil or DCA alone by restoring mitochondrial function, reducing intracellular Ca²⁺, and inhibiting calcium/calmodulin-dependent kinase (Ca²⁺/CaMK) activity as well as Rho-kinase activity.

Conclusion

FDCA ameliorates hypoxia-induced PASMC dysfunction by inhibiting both Ca²⁺/CaMK and Rho-kinase signaling pathways, as well as maintaining mitochondrial homeostasis, thus alleviating SuHx-induced PAH.

Rho kinase inhibitors reduce voltage-dependent Ca2+ channel signaling in aortic and renal microvascular smooth muscle cells

Voltage-dependent L-type Ca²⁺ channels (L-VDCCs) and the RhoA/Rho kinase pathway are two predominant intracellular signaling pathways that regulate renal microvascular reactivity. Traditionally, these two pathways have been thought to act independently; however, recent evidence suggests that these pathways could be convergent. We hypothesized that Rho kinase inhibitors can influence L-VDCC signaling. The effects of Rho kinase inhibitors Y-27632 or RKI-1447 on KCl-induced depolarization or the L-VDCC agonist Bay K8644 were assessed in afferent arterioles using an in vitro blood-perfused rat juxtamedullary nephron preparation. Superfusion of KCl (30-90 mM) led to concentration-dependent vasoconstriction of afferent arterioles. Administration of Y-27632 (1, 5, and 10 µM) or RKI-1447 (0.1, 1, and 10 µM) significantly increased the starting diameter by 16-65%. KCl-induced vasoconstriction was markedly attenuated with 5 and 10 µM Y-27632 and with 10 µM RKI-1447 (P < 0.05 vs. KCl alone). Y-27632 (5 µM) also significantly attenuated Bay K8644-induced vasoconstriction (P < 0.05). Changes in intracellular Ca²⁺ concentration ([Ca²⁺]_i) were estimated by fura-2 fluorescence during KCl-induced depolarization in cultured A7r5 cells and in freshly isolated preglomerular microvascular smooth muscle cells. Administration of 90 mM KCl significantly increased fura-2 fluorescence in both cell types. KCl-mediated elevation of [Ca²⁺]_i in A7r5 cells was suppressed by 1-10 µM Y-27632 (P < 0.05), but 10 µM Y-27632 was required to suppress Ca²⁺ responses in preglomerular microvascular smooth muscle cells. RKI-1447, however, significantly attenuated KCl-mediated elevation of [Ca²⁺]_i. Y-27632 markedly inhibited Bay K8644-induced elevation of [Ca²⁺]_i in both cell types. The results of the present study indicate that the Rho kinase inhibitors Y-27632 and RKI-1447 can partially inhibit L-VDCC function and participate in L-VDCC signaling.

Role of Phosphatidylinositol 3-Kinase (PI3K), Mitogen-Activated Protein Kinase (MAPK), and Protein Kinase C (PKC) in Calcium Signaling Pathways Linked to the α1-Adrenoceptor in Resistance Arteries

Insulin resistance plays a key role in the pathogenesis of type 2 diabetes and is also related to other health problems like obesity, hypertension, and metabolic syndrome. Imbalance between insulin vascular actions via the phosphatidylinositol 3-Kinase (PI3K) and the mitogen activated protein kinase (MAPK) signaling pathways during insulin resistant states results in impaired endothelial PI3K/eNOS- and augmented MAPK/endothelin 1 pathways leading to endothelial dysfunction and abnormal vasoconstriction. The role of PI3K, MAPK, and protein kinase C (PKC) in Ca²⁺ handling of resistance arteries involved in blood pressure regulation is poorly understood. Therefore, we assessed here whether PI3K, MAPK, and PKC play a role in the Ca²⁺ signaling pathways linked to adrenergic vasoconstriction in resistance arteries. Simultaneous measurements of intracellular calcium concentration ([Ca²⁺]_i) in vascular smooth muscle (VSM) and tension were performed in endothelium-denuded branches of mesenteric arteries from Wistar rats mounted in a microvascular myographs. Responses to CaCl₂ were assessed in arteries activated with phenylephrine (PE) and kept in Ca²⁺-free solution, in the absence and presence of the selective antagonist of L-type Ca²⁺ channels nifedipine, cyclopiazonic acid (CPA) to block sarcoplasmic reticulum (SR) intracellular Ca²⁺ release or specific inhibitors of PI3K, ERK-MAPK, or PKC. Activation of α₁-adrenoceptors with PE stimulated both intracellular Ca²⁺ mobilization and Ca²⁺ entry along with contraction in resistance arteries. Both [Ca²⁺]_i and contractile responses were inhibited by nifedipine while CPA abolished intracellular Ca²⁺ mobilization and modestly reduced Ca²⁺ entry suggesting that α₁-adrenergic vasoconstriction is largely dependent Ca²⁺ influx through L-type Ca²⁺ channel and to a lesser extent through store-operated Ca²⁺ channels. Inhibition of ERK-MAPK did not alter intracellular Ca²⁺ mobilization but largely reduced L-type Ca²⁺ entry elicited by PE without altering vasoconstriction. The PI3K blocker LY-294002 moderately reduced intracellular Ca²⁺ release, Ca²⁺ entry and contraction induced by the α₁-adrenoceptor agonist, while PKC inhibition decreased PE-elicited Ca²⁺ entry and to a lesser extent contraction without affecting intracellular Ca²⁺ mobilization. Under conditions of ryanodine receptor (RyR) blockade to inhibit Ca²⁺-induced Ca²⁺-release (CICR), inhibitors of PI3K, ERK-MAPK, or PKC significantly reduced [Ca²⁺]_i increases but not contraction elicited by high K⁺ depolarization suggesting an activation of L-type Ca²⁺ entry in VSM independent of RyR. In summary, our results demonstrate that PI3K, ERK-MAPK, and PKC regulate Ca²⁺ handling coupled to the α₁-adrenoceptor in VSM of resistance arteries and related to both contractile and non-contractile functions. These kinases represent potential pharmacological targets in pathologies associated to vascular dysfunction and abnormal Ca²⁺ handling such as obesity, hypertension and diabetes mellitus, in which these signaling pathways are profoundly impaired.

Higher Ca2+ -sensitivity of arterial contraction in 1-week-old rats is due to a greater Rho-kinase activity

AIM

During early post-natal development, arterial contraction depends less on Ca²⁺ -signalling pathways but more on changes in Ca²⁺ -sensitivity compared to adult animals. Whether this difference is related to Rho-kinase, one of the major players affecting Ca²⁺ -sensitivity, is unknown for intact vessels. Thus, we tested the hypothesis that Rho-kinase critically contributes to the higher Ca²⁺ -sensitivity of contraction in intact arteries of 1-week-old rats.

METHODS

We studied 1-week-old, 4- to 5-week-old and 10- to 12-week-old rats performing isometric myography, Ca²⁺ -fluorimetry and Western blotting using intact saphenous arteries and arterial pressure measurements under urethane anaesthesia.

RESULTS

In 10- to 12-week-old rats, methoxamine (MX) produced vasoconstriction associated with an increase in [Ca²⁺ ]_i and Ca²⁺ -sensitivity. In contrast, in 1-week-old rats these contractions were accompanied only by an increase in Ca²⁺ -sensitivity. All MX-induced effects were reduced by the Rho-kinase inhibitor Y-27632; this reduction was complete only in 1-week-old rats. The Rho-kinase specific site Thr⁸⁵⁵ on MYPT1 was increasingly phosphorylated by MX in vessels of 1-week-old, but not 10- to 12-week-old rats; this effect was also inhibited completely by Y-27632. The Rho-kinase inhibitor fasudil in a dose not affecting the pressor response to MX in 4- to 5-week-old rats reduced it considerably in 1-week-old rats.

CONCLUSION

Our results suggest that the higher Ca²⁺ -sensitivity of arterial contraction in 1-week-old compared to 10- to 12-week-old rats is due to a greater Rho-kinase activity. Constitutively active Rho-kinase contributes to MX-induced contraction in 10- to 12-week-old rats. In 1-week-old rats, additional Rho-kinase activation is involved. This remodelling of the Rho-kinase pathway is associated with its increased contribution to adrenergic arterial pressure responses.

Mechanisms of sphingosine-1-phosphate-mediated vasoconstriction of rat afferent arterioles

AIM

Sphingosine-1-phosphate (S1P) influences resistance vessel function and is implicated in renal pathological processes. Previous studies revealed that S1P evoked potent vasoconstriction of the pre-glomerular microvasculature, but the underlying mechanisms remain incompletely defined. We postulated that S1P-mediated pre-glomerular microvascular vasoconstriction involves activation of voltage-dependent L-type calcium channels (L-VDCC) and the rho/rho kinase pathway.

METHODS

Afferent arteriolar reactivity was assessed in vitro using the blood-perfused rat juxtamedullary nephron preparation, and diameter was measured during exposure to physiological and pharmacological agents.

RESULTS

Exogenous S1P (10^-9 -10^-5 mol L^-1 ) evoked concentration-dependent vasoconstriction of afferent arterioles. Superfusion with nifedipine, a L-VDCC blocker, increased arteriolar diameter by 39 ± 18% of baseline and significantly attenuated the S1P-induced vasoconstriction. Superfusion with the rho kinase inhibitor, Y-27632, increased diameter by 60 ± 12% of baseline and also significantly blunted vasoconstriction by S1P. Combined nifedipine and Y-27632 treatment significantly inhibited S1P-induced vasoconstriction over the entire concentration range tested. In contrast, depletion of intracellular Ca²⁺ stores with the Ca²⁺ -ATPase inhibitors, thapsigargin or cyclopiazonic acid, did not alter the S1P-mediated vasoconstrictor profile. Scavenging reactive oxygen species (ROS) or inhibition of nicotinamide adenine dinucleotide phosphate oxidase activity significantly attenuated S1P-mediated vasoconstriction.

CONCLUSION

Exogenous S1P elicits potent vasoconstriction of rat afferent arterioles. These data also demonstrate that S1P-mediated pre-glomerular vasoconstriction involves activation of L-VDCC, the rho/rho kinase pathway and ROS. Mobilization of Ca²⁺ from intracellular stores is not required for S1P-mediated vasoconstriction. These studies reveal a potential role for S1P in the modulation of renal microvascular tone.

Regional Heterogeneity in the Regulation of Vasoconstriction in Arteries and Its Role in Vascular Mechanics

Vasoconstriction and vasodilation play important roles in the circulatory system and can be regulated through different pathways that depend on myriad biomolecules. These different pathways reflect the various functions of smooth muscle cell (SMC) contractility within the different regions of the arterial tree and how they contribute to both the mechanics and the mechanobiology. Here, we review the primary regulatory pathways involved in SMC contractility and highlight their regional differences in elastic, muscular, and resistance arteries. In this way, one can begin to assess how these properties affect important biomechanical and mechanobiological functions in the circulatory system in health and disease.

Regional heterogeneity in the mechanisms of myogenic tone in hamster arterioles

Myogenic tone is an important feature of arterioles and resistance arteries, but the mechanisms responsible for this hallmark characteristic remain unclear. We used pharmacological inhibitors to compare the roles played by phospholipase C (PLC; 10 μM U73122), inositol 1,4,5-trisphosphate receptors (IP₃Rs; 100 μM 2-aminoethoxydiphenylborane), protein kinase C (10 μM bisindolylmaleimide I), angiotensin II type 1 receptors (1 μM losartan), Rho kinase (10 nM-30 μM Y27632 or 300 nM H1152), stretch-activated ion channels (10 nM-1 μM Gd³⁺ or 5 μM spider venom toxin GsMTx-4) and L-type voltage-gated Ca²⁺ channels (0.3-100 μM diltiazem) in myogenic tone of cannulated, pressurized (80 cmH₂O), second-order hamster cremaster or cheek pouch arterioles. Effective inhibition of either PLC or IP₃Rs dilated cremaster arterioles, inhibited Ca²⁺ waves, and reduced global Ca²⁺ levels. In contrast, cheek pouch arterioles did not display Ca²⁺ waves and inhibition of PLC or IP₃Rs had no effect on myogenic tone or intracellular Ca²⁺ levels. Inhibition of Rho kinase dilated both cheek pouch and cremaster arterioles with equal efficacy and potency but also reduced intracellular Ca²⁺ signals in both arterioles. Similarly, inhibition of mechanosensitive ion channels with Gd²⁺ or GsMTx-4 produced comparable dilation in both arterioles. Inhibition of L-type Ca²⁺ channels with diltiazem was more effective in dilating cremaster (86 ± 5% dilation, n = 4) than cheek pouch arterioles (54 ± 4% dilation, n = 6, P < 0.05). Thus, there are substantial differences in the mechanisms underlying myogenic tone in hamster cremaster and cheek pouch arterioles. Regional heterogeneity in myogenic mechanisms could provide new targets for drug development to improve regional blood flow in a tissue-specific manner.NEW & NOTEWORTHY Regional heterogeneity in the mechanisms of pressure-induced myogenic tone implies that resistance vessels may be able to alter myogenic signaling pathways to adapt to their environment. A better understanding of the spectrum of myogenic mechanisms could provide new targets to treat diseases that affect resistance artery and arteriolar function.

Peroxynitrite formed during a transient episode of brain ischaemia increases endothelium-derived hyperpolarization-type dilations in thromboxane/prostaglandin receptor-stimulated rat cerebral arteries

AIM

Increased thromboxane A₂ and peroxynitrite are hallmarks of cerebral ischaemia/reperfusion (I/R). Stimulation of thromboxane/prostaglandin receptors (TP) attenuates endothelium-derived hyperpolarization (EDH). We investigated whether EDH-type middle cerebral artery (MCA) relaxations following TP stimulation are altered after I/R and the influence of peroxynitrite.

METHODS

Vascular function was determined by wire myography after TP stimulation with the thromboxane A₂ mimetic 9,11-dideoxy-9α, 11α -methano-epoxy prostaglandin F2α (U46619) in MCA of Sprague Dawley rats subjected to MCA occlusion (90 min)/reperfusion (24 h) or sham operation, and in non-operated (control) rats. Some rats were treated with saline or the peroxynitrite decomposition catalyst 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) (20 mg kg^-1 ). Protein expression was evaluated in MCA and in human microvascular endothelial cells submitted to hypoxia (overnight)/reoxygenation (24 h) (H/R) using immunofluorescence and immunoblotting.

RESULTS

In U46619-pre-constricted MCA, EDH-type relaxation by the proteinase-activated receptor 2 agonist serine-leucine-isoleucine-glycine-arginine-leucine-NH₂ (SLIGRL) was greater in I/R than sham rats due to an increased contribution of small-conductance calcium-activated potassium channels (SK_Ca ), which was confirmed by the enlarged relaxation to the SK_Ca activator N-cyclohexyl-N-2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-4-pyrimidinamine. I/R and H/R induced endothelial protein tyrosine nitration and filamentous-actin disruption. In control MCA, either cytochalasin D or peroxynitrite disrupted endothelial filamentous-actin and augmented EDH-type relaxation. Furthermore, peroxynitrite decomposition during I/R prevented the increase in EDH-type responses.

CONCLUSION

Following TP stimulation in MCA, EDH-type relaxation to SLIGRL is greater after I/R due to endothelial filamentous-actin disruption by peroxynitrite, which prevents TP-induced block of SK_Ca input to EDH. These results reveal a novel mechanism whereby peroxynitrite could promote post-ischaemic brain injury.

Chemerin-induced arterial contraction is Gi- and calcium-dependent

Chemerin is an adipokine associated with increased blood pressure, and may link obesity with hypertension. We tested the hypothesis that chemerin-induced contraction of the vasculature occurs via calcium flux in smooth muscle cells. Isometric contraction of rat aortic rings was performed in parallel with calcium kinetics of rat aortic smooth muscle cells to assess the possible signaling pathway. Chemerin-9 (nonapeptide of the chemerin S¹⁵⁷ isoform) caused a concentration-dependent contraction of isolated aorta (EC₅₀ 100nM) and elicited a concentration-dependent intracellular calcium response (EC₅₀ 10nM). Pertussis toxin (G_i inhibitor), verapamil (L-type Ca²⁺ channel inhibitor), PP1 (Src inhibitor), and Y27632 (Rho kinase inhibitor) reduced both calcium influx and isometric contraction to chemerin-9 but PD098059 (Erk MAPK inhibitor) and U73122 (PLC inhibitor) had little to no effect on either measure of chemerin signaling. Although our primary aim was to examine chemerin signaling, we also highlight differences in the mechanisms of chemerin-9 and recombinant chemerin S¹⁵⁷. These data support a chemerin-induced contractile mechanism in vascular smooth muscle that functions through G_i proteins to activate L-type Ca²⁺ channels, Src, and Rho kinase. There is mounting evidence linking chemerin to hypertension and this mechanism brings us closer to targeting chemerin as a form of therapy.

Effects of 1-(2-trifluoromethylphenyl)-imidazole (TRIM) on receptor-independent and -dependent contractile responses in rat aorta

BACKGROUND/AIM

This study investigates whether 1-(2-trifluoromethylphenyl)-imidazole (TRIM), originally proposed as a nitric oxide synthase inhibitor and also suggested to be an inhibitor of store-operated calcium entry in mouse anococcygeal muscle, inhibits receptor-independent and -dependent responses in rat thoracic aorta.

MATERIALS AND METHODS

Cyclopiazonic acid- and serotonin-induced vascular responses were investigated in aortic segments isolated from male Sprague Dawley rats using isolated tissue experiments. Changes in intracellular calcium levels were also monitored via front surface fluorescence measurements in fura-2-loaded embryonic rat vascular smooth muscle cell line A7r5.

RESULTS

TRIM inhibited serotonin-mediated vascular contractions without affecting cyclopiazonic acid-induced responses. In addition, TRIM caused a nonlinear rightward shift in the serotonin concentration-response curve, possibly via serotonin receptor modulation.

CONCLUSION

TRIM may have an impact on investigation of tissue-specific receptor-independent and -dependent vascular responses. It may also be used as a lead compound in the development of selective serotonin receptor modulators.

Excitation-Contraction Coupling and Excitation-Transcription Coupling in Blood Vessels: Their Possible Interactions in Hypertensive Vascular Remodeling

Vascular smooth muscle cells (VSMC) display considerable phenotype plasticity which can be studied in vivo on vascular remodeling which occurs during acute or chronic vascular injury. In differentiated cells, which represent contractile phenotype, there are characteristic rapid transient changes of intracellular Ca2+ concentration ([Ca2+]i), while the resting cytosolic [Ca2+]i concentration is low. It is mainly caused by two components of the Ca2+ signaling pathways: Ca2+ entry via L-type voltage-dependent Ca2+ channels and dynamic involvement of intracellular stores. Proliferative VSMC phenotype is characterized by long-lasting [Ca2+]i oscillations accompanied by sustained elevation of basal [Ca2+]i. During the switch from contractile to proliferative phenotype there is a general transition from voltage-dependent Ca2+ entry to voltage-independent Ca2+ entry into the cell. These changes are due to the altered gene expression which is dependent on specific transcription factors activated by various stimuli. It is an open question whether abnormal VSMC phenotype reported in rats with genetic hypertension (such as spontaneously hypertensive rats) might be partially caused by a shift from contractile to proliferative VSMC phenotype.

Calcium Sensitization Mechanisms in Gastrointestinal Smooth Muscles

An increase in intracellular Ca²⁺ is the primary trigger of contraction of gastrointestinal (GI) smooth muscles. However, increasing the Ca²⁺ sensitivity of the myofilaments by elevating myosin light chain phosphorylation also plays an essential role. Inhibiting myosin light chain phosphatase activity with protein kinase C-potentiated phosphatase inhibitor protein-17 kDa (CPI-17) and myosin phosphatase targeting subunit 1 (MYPT1) phosphorylation is considered to be the primary mechanism underlying myofilament Ca²⁺ sensitization. The relative importance of Ca²⁺ sensitization mechanisms to the diverse patterns of GI motility is likely related to the varied functional roles of GI smooth muscles. Increases in CPI-17 and MYPT1 phosphorylation in response to agonist stimulation regulate myosin light chain phosphatase activity in phasic, tonic, and sphincteric GI smooth muscles. Recent evidence suggests that MYPT1 phosphorylation may also contribute to force generation by reorganization of the actin cytoskeleton. The mechanisms responsible for maintaining constitutive CPI-17 and MYPT1 phosphorylation in GI smooth muscles are still largely unknown. The characteristics of the cell-types comprising the neuroeffector junction lead to fundamental differences between the effects of exogenous agonists and endogenous neurotransmitters on Ca²⁺ sensitization mechanisms. The contribution of various cell-types within the tunica muscularis to the motor responses of GI organs to neurotransmission must be considered when determining the mechanisms by which Ca²⁺ sensitization pathways are activated. The signaling pathways regulating Ca²⁺ sensitization may provide novel therapeutic strategies for controlling GI motility. This article will provide an overview of the current understanding of the biochemical basis for the regulation of Ca²⁺ sensitization, while also discussing the functional importance to different smooth muscles of the GI tract.

Mechanisms Involved in Thromboxane A2 -induced Vasoconstriction of Rat Intracavernous Small Penile Arteries

Diabetes is associated with erectile dysfunction and with hypercontractility in erectile tissue and this is in part ascribed to increased formation of thromboxane. Rho kinase (ROCK) is a key regulator of calcium sensitization and contraction in vascular smooth muscle. This study investigated the role of calcium and ROCK in contraction evoked by activation of the thromboxane receptors. Rat intracavernous penile arteries were mounted for isometric tension and intracellular calcium ([Ca²⁺ ]_i ) recording and corpus cavernosum for measurements of MYPT1 phosphorylation. In penile arteries, U46619 by activation of thromboxane receptors concentration dependently increased calcium and contraction. U46619-induced calcium influx was blocked by nifedipine, a blocker of L-type calcium channels, and by 2-aminoethoxydiphenyl borate, a blocker of transient receptor potential (TRP) channels. Inhibitors of ROCK, Y27632 and glycyl-H1152P, concentration dependently reduced U46619-induced contraction, but only Y27632 reduced [Ca²⁺ ]_i levels in the penile arteries activated with either high extracellular potassium or U46619. MYPT-Thr⁸⁵⁰ phosphorylation in corpus cavernous strips was increased in response to U46619 through activation of TP receptors and was found to be a direct result of phosphorylation by ROCK. Y27632 induced less relaxation in mesenteric arteries, H1152P induced equipotent relaxations, and a protein kinase C inhibitor, Ro-318220, failed to relax intracavernous penile arteries, but induced full relaxation in rat mesenteric arteries. Our findings suggest that U46619 contraction depends on Ca²⁺ influx through L-type and TRP channels, and ROCK-dependent mechanisms in penile arteries. Inhibition of the ROCK pathway is a potential approach for the treatment of erectile dysfunction associated with hypertension and diabetes.

Effects of ethanol on RhoA/Rho-kinase-mediated calcium sensitization in mouse lung parenchymal tissue

Calcium sensitization by the RhoA/Rho-kinase (ROCK) pathway contributes to the contraction in smooth muscle. Contractile stimuli can sensitize myosin to Ca(2+) by activating RhoA/Rho-kinase that inhibits myosin light chain phosphatase activity. The present study was aimed at investigating the possible involvement of RhoA/Rho-kinase pathway in contractile responses to agonist (phenylephrine) and depolarizing (KCl) of mouse lung parenchymal tissues. Also, we investigated the effect of ethanol on RhoA/Rho-kinase pathway. Phenylephrine (10(-8)-10(-4) M) and KCl (10-80 mM) induced sustained contractions in parenchymal strips. Ethanol significantly attenuated the contractions to phenylephrine and KCl. The Rho-kinase inhibitors fasudil (5×10(-5) M) and Y-27632 (5×10(-5) M) inhibited contractions to in both control and ethanol-treated parenchymal strips. In addition, the relaxations induced by fasudil (10(-4) M) and Y-27632 (5×10(-4) M) on parenchymal strips contracted by phenylephrine but not KCl was decreased in ethanol-treatment group. Also, RhoA, ROCK1 and ROCK2 expressions were detected in mouse lung parenchymal tissue. In ethanol-treated group, expression of RhoA and ROCK1 but not ROCK2 decreased compared to control. Furthermore, ethanol causes apoptotic changes in alveolar type I epithelial cells of parenchymal tissue. These results suggest that RhoA/Rho-kinase signaling pathway plays an important role in phenylephrine- and KCl-induced Ca(2)(+) sensitization in mouse lung parenchymal tissue. Also, ethanol may be decrease phenylephrine- and KCl-induced contraction due to lowering the RhoA/Rho-kinase-mediated Ca(2+)-sensitizing by inhibiting RhoA/Rho-kinase pathway in parenchymal tissue. These results may be lead to important insights into the mechanisms of lung diseases due to alcohol consumption.

Regulation of calcium channels in smooth muscle: new insights into the role of myosin light chain kinase

Smooth muscle myosin light chain kinase (MLCK) plays a crucial role in artery contraction, which regulates blood pressure and blood flow distribution. In addition to this role, MLCK contributes to Ca(2+) flux regulation in vascular smooth muscle (VSM) and in non-muscle cells, where cytoskeleton has been suggested to help Ca(2+) channels trafficking. This conclusion is based on the use of pharmacological inhibitors of MLCK and molecular and cellular techniques developed to down-regulate the enzyme. Dissimilarities have been observed between cells and whole tissues, as well as between large conductance and small resistance arteries. A differential expression in MLCK and ion channels (either voltage-dependent Ca(2+) channels or non-selective cationic channels) could account for these observations, and is in line with the functional properties of the arteries. A potential involvement of MLCK in the pathways modulating Ca(2+) entry in VSM is described in the present review.

In vivo roles for myosin phosphatase targeting subunit-1 phosphorylation sites T694 and T852 in bladder smooth muscle contraction

KEY POINTS

Force production and maintenance in smooth muscle is largely controlled by myosin regulatory light chain (RLC) phosphorylation, which relies on a balance between Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) activities. MYPT1 is the regulatory subunit of MLCP that biochemically inhibits MLCP activity via T694 or T852 phosphorylation in vitro. Here we separately investigated the contribution of these two phosphorylation sites in bladder smooth muscles by establishing two single point mutation mouse lines, T694A and T852A, and found that phosphorylation of MYPT1 T694, but not T852, mediates force maintenance via inhibition of MLCP activity and enhancement of RLC phosphorylation in vivo. Our findings reveal the role of MYPT1 T694/T852 phosphorylation in vivo in regulation of smooth muscle contraction.

ABSTRACT

Force production and maintenance in smooth muscle is largely controlled by different signalling modules that fine tune myosin regulatory light chain (RLC) phosphorylation, which relies on a balance between Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) activities. To investigate the regulation of MLCP activity in vivo, we analysed the role of two phosphorylation sites on MYPT1 (regulatory subunit of MLCP) that biochemically inhibit MLCP activity in vitro. MYPT1 is constitutively phosphorylated at T694 by unidentified kinases in vivo, whereas the T852 site is phosphorylated by RhoA-associated protein kinase (ROCK). We established two mouse lines with alanine substitution of T694 or T852. Isolated bladder smooth muscle from T852A mice displayed no significant changes in RLC phosphorylation or force responses, but force was inhibited with a ROCK inhibitor. In contrast, smooth muscles containing the T694A mutation showed a significant reduction of force along with reduced RLC phosphorylation. The contractile responses of T694A mutant smooth muscle were also independent of ROCK activation. Thus, phosphorylation of MYPT1 T694, but not T852, is a primary mechanism contributing to inhibition of MLCP activity and enhancement of RLC phosphorylation in vivo. The constitutive phosphorylation of MYPT1 T694 may provide a mechanism for regulating force maintenance of smooth muscle.

Potential benefits of rho-kinase inhibition in arterial hypertension

Arterial hypertension is a major health problem, accounting for 12 % of the global death rate. A large proportion of patients treated for high blood pressure do not reach target blood pressure values. The question arises if new antihypertensive drugs could improve present hypertension treatment. Rho-kinases (ROCKs) are ubiquitously expressed serine/threonine kinases and involved in a variety of cell functions. They contribute to the pathogenesis of human and experimental hypertension. Pharmacological ROCK inhibition has been shown to effectively lower blood pressure in patients and experimental animals. Progress has been made towards the understanding on how non-selective ROCK inhibitors lower arterial pressure and efforts are currently undertaken to develop ROCK inhibitors to improve their specificity and isoenzyme selectivity. If introduction of ROCK inhibitors for the treatment of high blood pressure can significantly advance currently available options of antihypertensive pharmacotherapy awaits further experimental and clinical research.

Myosin light chain kinase controls voltage-dependent calcium channels in vascular smooth muscle

The Ca(2+)-dependent kinase myosin light chain kinase (MLCK) is the activator of smooth muscle contraction. In addition, it has been reported to be involved in Ca(2+) channel regulation in cultured cells, and we previously showed that the MLCK inhibitor ML-7 decreases arginine vasopressin (AVP)-induced Ca(2+) influx in rat aorta. This study was designed to investigate whether MLCK is involved in Ca(2+) regulation in resistance artery smooth muscle cell, which plays a major role in the control of blood pressure. As ML compounds were shown to have off-target effects, MLCK was downregulated by transfection with a small interfering RNA targeting MLCK (MLCK-siRNA) in rat small resistance mesenteric artery (RMA) and in the rat embryonic aortic cell line A7r5. Noradrenaline-induced contraction and Ca(2+) signal were significantly depressed in MLCK-siRNA compared to scramble-siRNA-transfected RMA. Contraction and Ca(2+) signal induced by high KCl and voltage-activated Ca(2+) current were also significantly decreased in MLCK-siRNA-transfected RMA, suggesting that MLCK depletion modifies voltage-operated Ca(2+) channels. KCl- and AVP-induced Ca(2+) signals and voltage-activated Ca(2+) current were decreased in MLCK-depleted A7r5 cells. Eventually, real-time quantitative PCR analysis indicated that in A7r5, MLCK controlled mRNA expression of CaV1.2 (L-type) and CaV3.1 (T-type) voltage-dependent Ca(2+) channels. Our results suggest that MLCK controls the transcription of voltage-dependent Ca(2+) channels in vascular smooth muscle cells.

Ionic Conductance(s) in Response to Post-junctional Potentials

The gastrointestinal motility is regulated by extrinsic and intrinsic neural regulation. Intrinsic neural pathways are controlled by sensory input, inter-neuronal relay and motor output. Enteric motor neurons release many transmitters which affect post-junctional responses. Post-junctional responses can be excitatory and inhibitory depending on neurotransmitters. Excitatory neurotransmitters induce depolarization and contraction. In contrast, inhibitory neurotransmitters hyperpolarize and relaxe the gastrointestinal smooth muscle. Smooth muscle syncytium is composed of smooth muscle cells, interstitial cells of Cajal and platelet-derived growth factor receptor α-positive (PDGFRα(+)) cells (SIP syncytium). Specific expression of receptors and ion channels in these cells can be affected by neurotransmitters. In recent years, molecular reporter expression techniques are able to study the properties of ion channels and receptors in isolated specialized cells. In this review, we will discuss the mechanisms of ion channels to interpret the post-junctional responses in the gastrointestinal smooth muscles.

Regulator of G-protein signaling 5 controls blood pressure homeostasis and vessel wall remodeling

RATIONALE

Regulator of G-protein signaling 5 (RGS5) modulates G-protein-coupled receptor signaling and is prominently expressed in arterial smooth muscle cells. Our group first reported that RGS5 is important in vascular remodeling during tumor angiogenesis. We hypothesized that RGS5 may play an important role in vessel wall remodeling and blood pressure regulation.

OBJECTIVE

To demonstrate that RGS5 has a unique and nonredundant role in the pathogenesis of hypertension and to identify crucial RGS5-regulated signaling pathways.

METHODS AND RESULTS

We observed that arterial RGS5 expression is downregulated with chronically elevated blood pressure after angiotensin II infusion. Using a knockout mouse model, radiotelemetry, and pharmacological inhibition, we subsequently showed that loss of RGS5 results in profound hypertension. RGS5 signaling is linked to the renin-angiotensin system and directly controls vascular resistance, vessel contractility, and remodeling. RGS5 deficiency aggravates pathophysiological features of hypertension, such as medial hypertrophy and fibrosis. Moreover, we demonstrate that protein kinase C, mitogen-activated protein kinase/extracellular signal-regulated kinase, and Rho kinase signaling pathways are major effectors of RGS5-mediated hypertension.

CONCLUSIONS

Loss of RGS5 results in hypertension. Loss of RGS5 signaling also correlates with hyper-responsiveness to vasoconstrictors and vascular stiffening. This establishes a significant, distinct, and causal role of RGS5 in vascular homeostasis. RGS5 modulates signaling through the angiotensin II receptor 1 and major Gαq-coupled downstream pathways, including Rho kinase. So far, activation of RhoA/Rho kinase has not been associated with RGS molecules. Thus, RGS5 is a crucial regulator of blood pressure homeostasis with significant clinical implications for vascular pathologies, such as hypertension.

Different effect of Rho kinase inhibition on calcium signaling in rat isolated large and small arteries

In addition to its role in the regulation of artery contraction, Rho kinase (ROCK) was reported to be involved in the cytosolic calcium response to vasoconstrictor agonists in rat aorta and superior mesenteric artery (SMA). However, it remains to be determined whether ROCK also contributes to calcium signaling in resistance arteries, which play a major role in blood pressure regulation. The investigation of the effect of ROCK inhibition on the calcium and contractile responses of rat resistance mesenteric artery (RMA), in comparison with aorta and SMA, indicated that the calcium response to noradrenaline was inhibited by the ROCK inhibitor Y-27632 in aorta and SMA but not in RMA. The effect of Y-27632 on the calcium signal was unaffected by cytochalasin-D. ROCK activation in noradrenaline-stimulated arteries was confirmed by the inhibition of myosin light chain phosphorylation by Y-27632. Moreover, noradrenaline-induced calcium signaling was similarly inhibited by nimodipine in aorta, SMA and RMA, but nimodipine sensitivity of the contraction increased from the aorta to the RMA, suggesting that the contraction was controlled by different sources of calcium. In pressurized RMA, Y-27632 and H-1152 depressed pressure-induced calcium responses and abolished myogenic contraction. These results stress the important differences in calcium signaling between conductance and resistance arteries.

Rho kinase regulation of vasopressin-induced calcium entry in vascular smooth muscle cell: comparison between rat isolated aorta and cultured aortic cells

In addition to its role in artery contraction, Rho kinase (ROCK) is reported to be involved in the Ca(2+) response to vasoconstrictor agonist in rat aorta. However the signaling pathway mediated by ROCK had not been investigated so far and it was not known whether ROCK also contributed to Ca(2+) signaling in cultured vascular smooth muscle cells (VSMC), which undergo profound phenotypic changes. Our results showed that in VSMC, ROCK inhibition by Y-27632 or H-1152 had no effect on the Ca(2+) response to vasopressin, while in aorta the vasopressin-induced Ca(2+) entry was significantly decreased. The inhibition of myosin light chain kinase (MLCK) by ML-7 depressed the vasopressin-induced Ca(2+) signal in aorta but not in VSMC. The difference in ROCK sensitivity of vasopressin-induced Ca(2+) entry between aorta and VSMC was not related to an alteration of the RhoA/ROCK pathway. However, MLCK expression and activity were depressed in cultured cells compared to aorta. We concluded that the regulation of vasopressin-induced Ca(2+) entry by ROCK in aorta could involve the myosin cytoskeleton and could be prevented by the downregulation of MLCK in VSMC. These results underline the important differences in Ca(2+) regulation between whole tissue and cultured cells.

Caffeine relaxes smooth muscle through actin depolymerization

Caffeine is sometimes used in cell physiological studies to release internally stored Ca(2+). We obtained evidence that caffeine may also act through a different mechanism that has not been previously described and sought to examine this in greater detail. We ruled out a role for phosphodiesterase (PDE) inhibition, since the effect was 1) not reversed by inhibiting PKA or adenylate cyclase; 2) not exacerbated by inhibiting PDE4; and 3) not mimicked by submillimolar caffeine nor theophylline, both of which are sufficient to inhibit PDE. Although caffeine is an agonist of bitter taste receptors, which in turn mediate bronchodilation, its relaxant effect was not mimicked by quinine. After permeabilizing the membrane using β-escin and depleting the internal Ca(2+) store using A23187, we found that 10 mM caffeine reversed tone evoked by direct application of Ca(2+), suggesting it functionally antagonizes the contractile apparatus. Using a variety of molecular techniques, we found that caffeine did not affect phosphorylation of myosin light chain (MLC) by MLC kinase, actin-filament motility catalyzed by MLC kinase, phosphorylation of CPI-17 by either protein kinase C or RhoA kinase, nor the activity of MLC-phosphatase. However, we did obtain evidence that caffeine decreased actin filament binding to phosphorylated myosin heads and increased the ratio of globular to filamentous actin in precontracted tissues. We conclude that, in addition to its other non-RyR targets, caffeine also interferes with actin function (decreased binding by myosin, possibly with depolymerization), an effect that should be borne in mind in studies using caffeine to probe excitation-contraction coupling in smooth muscle.

Possible Involvement of Sphingosine-1-Phosphate/G(i)/RhoA pathways in adherence of eosinophils to pulmonary endothelium

BACKGROUND

Sphingosine-1-phosphate (S1P), a lysophospholipid released from inflammatory cells, causes cell migration by increasing cytokines and chemokines. This study was designed to determine whether S1P causes adherence of eosinophils to pulmonary endothelial cells via enhancement of adhesion molecule expression.

METHODS

Expression of VCAM-1 and ICAM-1 was assessed by RT-PCR and Western blot analysis in human pulmonary microvasucular endothelial cells (HPMVECs). The number of adherent eosinophils to HPMVECs was calculated according to adhesion assay.

RESULTS

Pre-treatment of HPMVECs with S1P increased mRNA and protein expression of VCAM-1, in contrast, did not dramatically increase those expression of ICAM-1. The maximal expression of these adhesion molecules in mRNA and protein was observed 4 and 8h after exposure to S1P, respectively. Pre-treatment with S1P also activated RhoA, a monomeric G protein; the ability of S1P to enhance the expression of VCAM-1 was attenuated by RhoA related inhibitors such as Y-27632, C3 exoenzyme, and GGTI-286. The effects of S1P on VCAM-1 were attenuated by pre-incubation with pertussis toxin, which catalyzes the ADP-ribosylation of G(i), a heterotrimeric G protein. After HPMVECs were treated with S1P, adhesion of human eosinophilic leukemic cell line (EoL-1) cells to HPMVECs was enhanced in a concentration-dependent manner. Augmented adherence of EoL-1 cells by S1P was also attenuated by Y-27632 and pertussis toxin. S1P causes adherence of eosinophils to pulmonary endothelium via RhoA activation.

CONCLUSIONS

S1P may act as a lipid mediator in asthma. The RhoA/Rho-kinase pathway may be a therapeutic target for preventing eosinophil infiltration to the airway.

Impaired Ca2+ handling in penile arteries from prediabetic Zucker rats: involvement of Rho kinase

Diabetes is associated with an increased vascular tone usually involved in the pathogenesis of diabetic cardiovascular complications such as hypertension, stroke, coronary artery disease, or erectile dysfunction (ED). Enhanced contractility of penile erectile tissue has been associated with augmented activity of the RhoA/Rho kinase (RhoK) pathway in models of diabetes-associated ED. The present study assessed whether abnormal vasoconstriction in penile arteries from prediabetic obese Zucker rats (OZRs) is due to changes in the intracellular Ca2+ concentration ([Ca2+]i) and/or in myofilament Ca2+ sensitivity. Penile arteries from OZRs and lean Zucker rats (LZRs) were mounted on microvascular myographs for simultaneous measurements of [Ca2+]i and tension. The relationships between [Ca2+]i and contraction for the α1-adrenergic vasoconstrictor phenylephrine (PE) were left shifted and steeper in OZRs compared with LZRs, although the magnitude of the contraction was similar in both groups. In contrast, the vasoconstriction induced by the thromboxane A2 receptor agonist U-46619 was augmented in arteries from OZRs, and this increase was associated with an increase in both the sensitivity and maximum responses to Ca2+. The RhoK inhibitor Y-27632 (10 μM) reduced the vasoconstriction induced by PE to a greater extent in OZRs than in LZRs, without altering Ca2+. Y-27632 inhibited with a greater potency the contraction elicited by high KCl in arteries from OZRs compared with LZRs without changing [Ca2+]i. RhoK-II expression was augmented in arteries from OZRs. These results suggest receptor-specific changes in the Ca2+ handling of penile arteries under conditions of metabolic syndrome. Whereas augmented vasoconstriction upon activation of the thromboxane A2 receptor is coupled to enhanced Ca2+ entry, a RhoK-mediated enhancement of myofilament Ca2+ sensitivity is coupled with the α1-adrenergic vasoconstriction in penile arteries from OZRs.

Thrombin-induced endothelin-1 synthesis and secretion in retinal pigment epithelial cells is rho kinase dependent

PURPOSE

The retinal pigment epithelium (RPE) is a major source for endothelin-1 (ET-1), a potent vasoactive peptide, at the outer blood–retinal barrier. Factors that regulate ET-1 synthesis at this site may help identify its normal function and its role in pathologic states accompanying retinal injury. Thrombin is one such factor that might act on the RPE after injury and breakdown of the blood–retinal barrier. The present study was conducted to identify signaling intermediates in thrombin-induced ET-1 synthesis and secretion in primary human RPE (hRPE) and transformed RPE cells (ARPE-19) and a possible pharmacological strategy to block excess release of ET-1.

METHODS

Cultured hRPE cells were treated with different concentrations of thrombin and thrombin receptor agonists, and a time course to measure levels of preproET-1 (ppET-1) mRNA and secreted mature ET-1 was performed. Levels of secondary messengers [Ca²+]i and RhoA were measured and pharmacologically inhibited to determine how receptor-mediated thrombin activity lead to changes in ET-1 levels.

RESULTS

Thrombin primarily acts via the protease-activated receptor-1 (PAR-1) subtype in RPE to induce ET-1 synthesis. Thrombin and other receptor agonists increased both [Ca²+]<]i and active RhoA. PAR-1-dependent rho/Rho kinase activation led to increase in ppET-1 mRNA and mature ET-1 secretion.

CONCLUSIONS

Transient intracellular calcium mobilization and protein kinase C activation by thrombin play a minor role, if any, in ET-1 synthesis in RPE. Instead, rho/Rho kinase activation after PAR-1 stimulation strongly increased ppET-1 mRNA and ET-1 secretion in hRPE cells.

Identification and functional implication of a Rho kinase-dependent moesin-EBP50 interaction in noradrenaline-stimulated artery

Ezrin, radixin, and moesin (ERM) proteins are known to be substrates of Rho kinase (ROCK), a key player in vascular smooth muscle regulation. Their function in arteries remains to be elucidated. The objective of the present study was to investigate ERM phosphorylation and function in rat aorta and mesenteric artery and the influence of ERM-binding phosphoprotein 50 (EBP50), a scaffold partner of ERM proteins in several cell types. In isolated arteries, ERM proteins are phosphorylated by PKC and ROCK with different kinetics after either agonist stimulation or KCl-induced depolarization. Immunoprecipitation of EBP50 in noradrenaline-stimulated arteries allowed identification of its interaction with moesin and several other proteins involved in cytoskeleton regulation. This interaction was inhibited by Y27632, a ROCK inhibitor. Moesin or EBP50 depletion after small interfering RNA transfection by reverse permeabilization in intact mesenteric arteries both potentiated the contractility in response to agonist stimulation without any effect on contractile response induced by high KCl. This effect was preserved in ionomycin-permeabilized arteries. These results indicate that, in agonist-stimulated arteries, the activation of ROCK leads to the binding of moesin to EBP50, which interacts with several components of the cytoskeleton, resulting in a decrease in the contractile response.

Key role of the RhoA/Rho kinase system in pulmonary hypertension

Pulmonary hypertension (PH) is a general term comprising a spectrum of pulmonary hypertensive disorders which have in common an elevation of mean pulmonary arterial pressure (mPAP). The prototypical form of the disease, termed pulmonary arterial hypertension (PAH), is a rare but lethal syndrome with a complex aetiology characterised by increased pulmonary vascular resistance (PVR) and progressive elevation of mPAP; patients generally die from heart failure. Current therapies are inadequate and median survival is less than three years. PH due to chronic hypoxia (CH) is a condition separate from PAH and is strongly associated with chronic obstructive pulmonary disease (COPD). An early event in the pathogenesis of this form of PH is hypoxic pulmonary vasoconstriction (HPV), an acute homeostatic process that maintains the ventilation-perfusion ratio during alveolar hypoxia. The mechanisms underlying HPV remain controversial, but RhoA/Rho kinase (ROK)-mediated Ca²+-sensitisation is considered important. Increasing evidence also implicates RhoA/ROK in PASMC proliferation, inflammatory cell recruitment and the regulation of cell motility, all of which are involved in the pulmonary vascular remodelling occurring in all forms of PH. ROK is therefore a potential therapeutic target in treating PH of various aetiologies. Here, we examine current concepts regarding the aetiology of PAH and also PH due to CH, focusing on the contribution that RhoA/ROK-mediated processes may make to their development and on ROK inhibitors as potential therapies.

Failure of Bay K 8644 to induce RhoA kinase-dependent calcium sensitization in rabbit blood vessels

BACKGROUND AND PURPOSE

RhoA kinase (ROCK) participates in K(+) depolarization (KCl)-induced Ca(2+) sensitization of contraction. Whether constitutive, depolarization- or Ca(2+)-activated ROCK plays the major role in this signalling system remains to be determined. Here, we determined whether Bay K 8644, a dihydropyridine that promotes Ca(2+) channel clusters to operate in a persistent Ca(2+) influx mode, could cause ROCK-dependent Ca(2+) sensitization.

EXPERIMENTAL APPROACH

Renal and femoral artery rings from New Zealand white rabbits were contracted with Bay K 8644. Tissues were frozen and processed to measure active RhoA and ROCK substrate (myosin phosphatase targeting subunit, MYPT1) and myosin light chain (MLC) phosphorylation, or loaded with fura-2 to measure intracellular free Ca(2+) ([Ca(2+)](i)). Effects of selective inhibitors of contraction were assessed in resting (basal) tissues and those contracted with Bay K 8644.

KEY RESULTS

Bay K 8644 produced strong increases in [Ca(2+)](i), MLC phosphorylation and tension, but not in MYPT1 phosphorylation. ROCK inhibition by H-1152 abolished basal MYPT1-pT853, diminished basal MLC phosphorylation and inhibited Bay K 8644-induced increases in MLC phosphorylation and tension. MLC kinase inhibition by wortmannin abolished Bay K 8644-induced contraction and increase in MLC phosphorylation but did not inhibit basal MYPT1-pT853. H-1152 and wortmannin had no effect on MYPT1-pT696, but 1 microM staurosporine inhibited basal MYPT1-pT853, MYPT1-pT696 and MLC phosphorylation.

CONCLUSIONS AND IMPLICATIONS

These data suggest that the constitutive activities of ROCK and a staurosporine-sensitive kinase regulate basal phosphorylation of MYPT1, which participates along with activation of MLC kinase in determining the strength of contraction induced by the Ca(2+) agonist, Bay K 8644.

Sarcoplasmic reticulum function in smooth muscle

The sarcoplasmic reticulum (SR) of smooth muscles presents many intriguing facets and questions concerning its roles, especially as these change with development, disease, and modulation of physiological activity. The SR's function was originally perceived to be synthetic and then that of a Ca store for the contractile proteins, acting as a Ca amplification mechanism as it does in striated muscles. Gradually, as investigators have struggled to find a convincing role for Ca-induced Ca release in many smooth muscles, a role in controlling excitability has emerged. This is the Ca spark/spontaneous transient outward current coupling mechanism which reduces excitability and limits contraction. Release of SR Ca occurs in response to inositol 1,4,5-trisphosphate, Ca, and nicotinic acid adenine dinucleotide phosphate, and depletion of SR Ca can initiate Ca entry, the mechanism of which is being investigated but seems to involve Stim and Orai as found in nonexcitable cells. The contribution of the elemental Ca signals from the SR, sparks and puffs, to global Ca signals, i.e., Ca waves and oscillations, is becoming clearer but is far from established. The dynamics of SR Ca release and uptake mechanisms are reviewed along with the control of luminal Ca. We review the growing list of the SR's functions that still includes Ca storage, contraction, and relaxation but has been expanded to encompass Ca homeostasis, generating local and global Ca signals, and contributing to cellular microdomains and signaling in other organelles, including mitochondria, lysosomes, and the nucleus. For an integrated approach, a review of aspects of the SR in health and disease and during development and aging are also included. While the sheer versatility of smooth muscle makes it foolish to have a "one model fits all" approach to this subject, we have tried to synthesize conclusions wherever possible.

Ureteral motility

The pyeloureteral function is to transport urine from the kidneys into the ureter toward the urinary bladder for storage until micturition. A set of mechanisms collaborates to achieve this purpose: the basic process regulating ureteral peristalsis is myogenic, initiated by active pacemaker cells located in the renal pelvis. Great emphasis has been given to hydrodynamic factors, such as urine flow rate in determining the size and pattern of urine boluses which, in turn, affect the mechanical aspects of peristaltic rhythm, rate, amplitude, and baseline pressure. Neurogenic contribution is thought to be limited to play a modulatory role in ureteral peristalsis. The myogenic theory of ureteral peristalsis can be traced back to Engelmann (1) who was able to localize the peristaltic pressure wave's origin in the renal pelvis and suggested that the ureteral contraction impulse passes from one ureteral cell to another, the whole ureter working as a functional syncitium. Recent studies of ureteral biomechanics, smooth muscle cell electrophysiology, membrane ionic currents, cytoskeletal components and pharmacophysiology much improved our understanding of the mechanism of how the urine bolus is propelled, how this process is disturbed in pathological states, and what could be done to improve it.

Reactive oxygen species and RhoA signaling in vascular smooth muscle: role in chronic hypoxia-induced pulmonary hypertension

Increases in myofilament Ca2+ sensitivity resulting from stimulation of RhoA and Rho kinase represent a primary mechanism of vasoconstriction and associated pulmonary hypertension resulting from chronic hypoxia (CH). This chapter summarizes recent advances in the understanding of RhoA/Rho kinase signaling mechanisms in pulmonary vascular smooth muscle (VSM) that increase the sensitivity of the contractile apparatus to Ca2+ and contribute to vasoconstriction in this setting. Such advances include the discovery of myogenic tone in small pulmonary arteries from CH rats that contributes to vasoconstriction through a mechanism inherent to the VSM, dependent on Rho kinase-induced Ca2+ sensitization but independent of L-type voltage-gated Ca2+ channels. Additional studies have revealed an important contribution of superoxide anion (O2-)-induced RhoA activation to both receptor-mediated and membrane depolarization-induced myofilament Ca2+ sensitization in hypertensive pulmonary arteries. Xanthine oxidase and NADPH oxidase isoforms are potential sources of O2- that mediate RhoA-dependent vasoconstriction and associated pulmonary hypertension.

Flavone Attenuates Vascular Contractions by Inhibiting RhoA/Rho Kinase Pathway

Our previous study demonstrated that flavone inhibits vascular contractions by decreasing the phosphorylation levelof the myosin phosphatase target subunit (MYPT1). In the present study, we hypothesized that flavone attenuates vascular contractions through the inhibition of the RhoA/Rho kinase pathway. Rat aortic rings were denuded of endothelium, mounted in organ baths, and contracted with either 30 nM U46619 (a thromboxane A2 analogue) or 8.0 mM NaF 30 min after pretreatment with either flavone (100 or 300 microM) or vehicle. We determined the phosphorylation level of the myosin light chain (MLC(20)), the myosin phophatase targeting subunit 1 (MYPT1) and the protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light chain phophatase of 17-kDa (CPI17) by means of Western blot analysis. Flavone inhibited, not only vascular contractions induced by these contractors, but also the levels of MLC(20) phosphorylation. Furthermore, flavone inhibited the activation of RhoA which had been induced by either U46619 or NaF. Incubation with flavone attenuated U46619-or NaF-induced phosphorylation of MYPT1(Thr855) and CPI17(Thr38), the downstream effectors of Rho-kinase. In regards to the Ca(2+)-free solution, flavone inhibited the phosphorylation of MYPT1(Thr855) and CPI17(Thr38), as well as vascular contractions induced by U46619. These results indicate that flavone attenuates vascular contractions, at least in part, through the inhibition of the RhoA/Rho-kinase pathway.

Losartan counteracts the hyper-reactivity to angiotensin II and ROCK1 over-activation in aortas isolated from streptozotocin-injected diabetic rats

Background

In streptozotocin-injected rats (STZ-rats), we previously demonstrated a role for angiotensin II (AT-II) in cardiac remodelling and insulin resistance partially counteracted by in vivo treatment with losartan, an AT-II receptor antagonist.

We now aimed to investigate the effect of treating diabetic STZ-rats with losartan on diabetes vascular response to vasoconstrictors.

Methods

Male Wistar rats were randomly divided in four groups, two of them were assigned to receive losartan in the drinking water (20 mg/kg/day) until the experiment ending (3 weeks afterward). After 1 week, two groups, one of which receiving losartan, were injected in the tail vein with citrate buffer (normoglycemic, N and normoglycemic, losartan-treated, NL). The remaining received a single injection of streptozotocin (50 mg/kg in citrate i.v.) thus becoming diabetic (D) and diabetic losartan-treated (DL). Plasma glycaemia and blood pressure were measured in all animals before the sacrifice (15 days after diabetes induction).

In aortic strips isolated from N, NL, D and DL rats we evaluated i) the isometric concentration-dependent contractile response to phenylephrine (Phe) and to AT-II; ii) the RhoA-kinase (ROCK1) activity and expression by enzyme-immunoassay and Western blot respectively.

Key results

The concentration-dependent contractile effect of Phe was similar in aortas from all groups, whereas at all concentrations tested, AT-II contraction efficacy was 2 and half and 1 and half times higher in D and DL respectively in comparison with N and NL. AT-II contracture was similarly reduced in all groups by AT-II receptor antagonists, irbesartan or irbesartan plus PD123319. HA-1077 (10 μM), an inhibitor of ROCK1 activity, reduced AT-II efficacy (Δmg/mg tissue w.w.) by -3.5 ± 1.0, -4.6 ± 1.9, -22.1 ± 2.2 and -11.4 ± 1.3 in N, NL, D and DL respectively). ROCK1 activity and expression were higher in D than in N/NL and DL aortas.

Conclusion and implications

Aortas isolated from STZ-rats present hyper-contracture to AT-II mainly dependent on the up-regulation of ROCK1 expression/activity. In vivo losartan treatment partially corrects AT-II hyper-contracture, limiting the increase in ROCK1 expression/activity. These data offer a new molecular mechanism supporting the rationale for using losartan in the prevention of diabetic vascular complications.

Ca2+ sensitization via phosphorylation of myosin phosphatase targeting subunit at threonine-855 by Rho kinase contributes to the arterial myogenic response

Ca(2+) sensitization has been postulated to contribute to the myogenic contraction of resistance arteries evoked by elevation of transmural pressure. However, the biochemical evidence of pressure-induced increases in phosphorylated myosin light chain phosphatase (MLCP) targeting subunit 1 (MYPT1) and/or 17 kDa protein kinase C (PKC)-potentiated protein phosphatase 1 inhibitor protein (CPI-17) required to sustain this view is not currently available. Here, we determined whether Ca(2+) sensitization pathways involving Rho kinase (ROK)- and PKC-dependent phosphorylation of MYPT1 and CPI-17, respectively, contribute to the myogenic response of rat middle cerebral arteries. ROK inhibitors (Y27632, 0.03-10 micromol l(-1); H1152, 0.001-0.3 micromol l(-1)) and PKC inhibitors (GF109203X, 3 micromol l(-1); Gö6976; 10 micromol l(-1)) suppressed myogenic vasoconstriction between 40 and 120 mmHg. An improved, highly sensitive 3-step Western blot method was developed for detection and quantification of MYPT1 and CPI-17 phosphorylation. Increasing pressure from 10 to 60 or 100 mmHg significantly increased phosphorylation of MYPT1 at threonine-855 (T855) and myosin light chain (LC(20)). Phosphorylation of MYPT1 at threonine-697 (T697) and CPI-17 were not affected by pressure. Pressure-evoked elevations in MYPT1-T855 and LC(20) phosphorylation were reduced by H1152, but MYPT1-T697 phosphorylation was unaffected. Inhibition of PKC with GF109203X did not affect MYPT1 or LC(20) phosphorylation at 100 mmHg. Our findings provide the first direct, biochemical evidence that a Ca(2+) sensitization pathway involving ROK-dependent phosphorylation of MYPT1 at T855 (but not T697) and subsequent augmentation of LC(20) phosphorylation contributes to myogenic control of arterial diameter in the cerebral vasculature. In contrast, suppression of the myogenic response by PKC inhibitors cannot be attributed to block of Ca(2+) sensitization mediated by CPI-17 or MYPT1 phosphorylation.

Y27632, a Rho-activated kinase inhibitor, normalizes dysregulation in alpha1-adrenergic receptor-induced contraction of Lyon hypertensive rat artery smooth muscle

RhoA-activated kinase (ROK) is involved in the disorders of smooth muscle contraction found in hypertension model animals and patients. We examined whether the alpha1-adrenergic receptor agonist-induced ROK signal is perturbed in resistance small mesentery artery (SMA) of Lyon genetically hypertensive (LH) rats, using a ROK antagonist, Y27632. Smooth muscle strips of SMA and aorta were isolated from LH and Lyon normotensive (LN) rats. After Ca(2+)-depletion and pre-treatment with phenylephrine (PE), smooth muscle contraction was induced by serial additions of CaCl(2). In LH SMA Ca(2+) permeated cells to a lesser extent as compared with LN SMA, while CaCl(2)-induced contraction of LH SMA was greater than that of LN SMA, indicating a higher ratio of force to Ca(2+) in LH SMA contraction (Ca(2+) sensitization). No hyper-contraction was observed in LH aorta tissues. Treatment of LH SMA with Y27632 restored both Ca(2+) permeability and Ca(2+)-force relationship to levels seen for LN SMA. In response to PE stimulation, phosphorylation of CPI-17, a phosphorylation-dependent myosin phosphatase inhibitor protein, and MYPT1 at Thr853, the inhibitory phosphorylation site of the myosin phosphatase regulatory subunit, was increased in LN SMA, but remained unchanged in LH SMA. These results suggest that the disorder in ROK-dependent Ca(2+) permeability and Ca(2+)-force relationship is responsible for LH SMA hyper-contraction. Unlike other hypertensive models, the ROK-induced hyper-contractility of LH SMA is independent of MYPT1 and CPI-17 phosphorylation, which suggests that ROK-mediated inhibition of myosin phosphatase does not affect SMA hyper-contractility in LH SMA cells.

Rho-kinase-mediated suppression of KDR current in cerebral arteries requires an intact actin cytoskeleton

This study examined the role of the actin cytoskeleton in Rho-kinase-mediated suppression of the delayed-rectifier K(+) (K(DR)) current in cerebral arteries. Myocytes from rat cerebral arteries were enzymatically isolated, and whole cell K(DR) currents were monitored using conventional patch-clamp electrophysiology. At +40 mV, the K(DR) current averaged 19.8 +/- 1.6 pA/pF (mean +/- SE) and was potently inhibited by UTP (3 x 10(-5) M). This suppression was observed to depend on Rho signaling and was abolished by the Rho-kinase inhibitors H-1152 (3 x 10(-7) M) and Y-27632 (3 x 10(-5) M). Rho-kinase was also found to concomitantly facilitate actin polymerization in response to UTP. We therefore examined whether actin dynamics played a role in the ability of Rho-kinase to suppress K(DR) current and found that actin disruption using either cytochalasin D (1 x 10(-5) M) or latrunculin A (1 x 10(-8) M) prevented current modulation. Consistent with our electrophysiological observations, both Rho-kinase inhibition and actin disruption significantly attenuated UTP-induced depolarization and constriction of cerebral arteries. We propose that UTP initiates Rho-kinase-mediated remodeling of the actin cytoskeleton and consequently suppresses the K(DR) current, thereby facilitating the depolarization and constriction of cerebral arteries.

Rho kinase inhibitors prevent endothelium-dependent contractions in the rat aorta

Rho kinase is involved in the pathogenesis of hypertension, which favors the occurrence of endothelium-dependent contractions. The present study was designed to determine the effects of two Rho kinase inhibitors, HA1077 [1-(5-isoquinolinesulfonyl)-homopiperazine (fasudil)] and Y27632 [(+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide dihydrochloride], on endothelium-dependent and -independent contractions. Isometric tension of 1-year-old spontaneously hypertensive rat and Wistar Kyoto aortae were measured. In the presence of N(omega)-nitro-L-arginine methyl ester, HA1077, and Y27632 reduced endothelium-dependent contractions caused by acetylcholine and the calcium ionophore 5-(methylamino)-2-[[2R,3R,6S,8S,9R,11R)-3,9,11-trimethyl-8-[(1S)-1-methyl-2-oxo-2-(1H-pyrrol-2-yl)-ethyl]-1,7-dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazolecarboxylic acid (A23187). The Rho kinase inhibitors did not significantly affect prostacyclin production measured as 6-keto prostaglandin F(1alpha). They nearly abolished endothelium-independent contractions to (5Z)-7-[(1R,4S,5S,6R)-6-[(1E,3S)-3-hydroxy-1-octenyl]-2-oxabicyclo-[2.2.1]hept-5-yl]-5-heptenoic acid (U46619), prostaglandin F(2alpha), and phenylephrine. Western blotting revealed a comparable expression of Rho kinase in the aortae of the two strains. The reduction by Rho kinase inhibitors of endothelium-dependent contractions is mainly because of their direct effect on the vascular smooth muscle cells.

Role of Ca2+ mobilization and Ca2+ sensitization in 8-iso-PGF 2 alpha-induced contraction in airway smooth muscle

BACKGROUND

Isoprostanes are prostaglandin (PG)-like compounds synthesized by oxidative stress, not by cyclooxygenase, and increase in bronchoalveolar lavage fluid of patients with asthma. The airway inflammation implicated in this disease may be amplified by oxidants. Although isoprostanes are useful biomarkers for oxidative stress, the action of these agents on airways has not been fully elucidated.

OBJECTIVE

This study was designed to determine the intracellular mechanisms underlying the effects of oxidative stress on airway smooth muscle, focused on Ca(2+) signalling pathways involved in the effect of 8-iso-PGF(2 alpha).

METHODS

Using simultaneous recording of isometric tension and F(340)/F(380) (an indicator of intracellular concentrations of Ca(2+), [Ca(2+)]i, we examined the correlation between tension and [Ca(2+)]i in response to 8-iso-PGF(2 alpha) in the fura-2 loaded tracheal smooth muscle.

RESULTS

Augmented tension and F(340)/F(380) by 8-iso-PGF(2 alpha) were attenuated by ICI-192605, an antagonist of thromboxane A(2) receptors (TP receptors). Moreover, D609, an antagonist of phosphatidylcholine-specific phospholipase C, markedly reduced both the tension and F(340)/F(380) induced by 8-iso-PGF(2 alpha), whereas U73122, an antagonist of phosphatidylinositol-specific phospholipase C, modestly inhibited them by 8-iso-PGF(2 alpha). SKF96365, a non-selective antagonist of Ca(2+) channels, markedly reduced both tension and F(340)/F(380) by 8-iso-PGF(2 alpha). However, diltiazem and verapamil, voltage-dependent Ca(2+) channel inhibitors, modestly attenuated tension although their reduction of F(340)/F(380) was not different from that by SKF96365. Y-27632, an inhibitor of Rho-kinase, significantly attenuated contraction induced by 8-iso-PGF(2 alpha) without reducing F(340)/F(380), whereas GF109203X and Go6983, protein kinase C inhibitors, did not markedly antagonize them although reducing F(340)/F(380) with a potency similar to Y-27632.

CONCLUSION

8-iso-PGF(2 alpha) causes airway smooth muscle contraction via activation of TP receptors. Ca(2+) mobilization by SKF96365- and D609-sensitive Ca(2+) influx and Ca(2+) sensitization by Rho-kinase contribute to the intracellular mechanisms underlying the action of 8-iso-PGF(2 alpha). Rho-kinase may be a therapeutic target for the physiologic abnormalities induced by oxidative stress in airways.

Role of protein kinase Czeta and calcium entry in KCl-induced vascular smooth muscle calcium sensitization and feedback control of cellular calcium levels

The degree of tonic force (F) maintenance induced in vascular smooth muscle upon K(+) depolarization with 110 mM KCl can be greatly reduced by inhibition of rhoA kinase (ROCK). We explored the possibility that a protein kinase C (PKC) isotype may also play a role in causing KCl-induced Ca(2+) sensitization. In isometric rings of rabbit artery, the PKC inhibitors, Go-6983 (3-[1-[3-(dimethylamino)propyl]-5-methoxy-1H-indol-3-yl]-4-(1H-indol-3-yl)-1H-pyrrole-2,5-dione), GF-109203X (2-[1-(3-dimethylaminopropyl)indol-3-yl]-3-(indol-3-yl) maleimide), and a cell-permeable (myristoylated) pseudosubstrate inhibitor of PKCzeta (PI(PKCzeta)) inhibited KCl-induced tonic F. A myristoylated pseudosubstrate inhibitor of PKCalpha/beta that inhibited phorbol dibutyrate-induced F slightly potentiated KCl-induced tonic F and attenuated 30 mM KCl-induced F. Although the ROCK inhibitor, H-1152 [(S)-(+)-2-methyl-1-[(4-methyl-5-isoquinolinyl)-sulfonyl]-hexahydro-1H-1,4-diazepine dihydrochloride], reduced basal phosphorylation of myosin light-chain phosphatase-targeting subunit at Thr853 (MYPT1-pT853), 3 and 10 muM GF-109203X inhibited only KCl-stimulated phosphorylation, not basal MYPT1-pT853. In fura-2-loaded tissues, GF-109203X and PI(PKCzeta) elevated basal [Ca(2+)](i) (calcium) and potentiated KCl-induced tonic increases in calcium while reducing KCl-induced tonic increases in F. Blockade by nifedipine of Ca(2+) entry through voltage-operated Ca(2+) channels reduced KCl-induced Ca(2+) sensitization and KCl-stimulated but not basal MYPT1-pT853. These data together support a model in which ROCK and PKCzeta are constitutively active and function in "resting" muscle to regulate the basal levels of MYPT1-pT853 and calcium, respectively. In this model, KCl-induced increases in calcium activate PKCzeta to feed forward and cause additional MYPT1-pT853 above that induced by constitutive ROCK, permitting Ca(2+) sensitization and strong F maintenance. Active PKCzeta also feeds back to attenuate the degree of KCl-induced increases in calcium.

Vasorelaxant and hypotensive effects of Allium cepa peel hydroalcoholic extract in rat

The aim of present study was to investigate the effect of onion (Allium cepa) peel hydroalcoholic extract (OPE) on rat hypertension induced by high-fructose diet and aorta contractility. The OPE was prepared by maceration method using 70% ethanol. The thoracic aorta from male adult rat (Wistar) was dissected and suspended in Krebs-Henseleit solution under 1 g resting tension. Tissue preparation was contracted by KCl (80 mM) or phenylephrine (Phe, 1 microM) and then the extract was applied cumulatively (0.0625-2 mg mL(-1)). Hypertension was induced in negative control and three groups of rats by adding fructose (10% WN/V) in drinking water for 6 weeks but control group received tap water. Hypertensive groups received saline or OPE at 200, 400 and 800 mg kg(-1) daily for last 3 weeks by gavage. Results showed that OPE reduces aorta contractions induced by KCl or Phe in a concentration-dependent manner (p < 0.001). Removing aorta endothelium did not attenuate the OPE activity. Inhibition of nitric oxide, cGMP and prostaglandin synthesis by L-NAME (100 microM), methylene blue (10 microM) and indomethacin (10 microM), respectively, did not attenuate OPE activity. Atropine abolished ACh-induced relaxation in Phe precontracted aorta but not the OPE-induced relaxation. Although the extract did not change heart rate but after 3 weeks reduced the hypertension induced by fructose (p < 0.001). Present results indicated that OPE reduces aortic contractions possibly via inhibition of calcium influx but without involving NO, cGMP, endothelium and prostaglandins. The OPE hypotensive effect could be due to extract quercetin content, antioxidant activity and inhibiting vascular smooth muscle cells Ca2+ influx.

PKD1 haploinsufficiency is associated with altered vascular reactivity and abnormal calcium signaling in the mouse aorta

Mutations in PKD1 are associated with autosomal dominant polycystic kidney disease (ADPKD), which leads to major cardiovascular complications. We used mice with a heterozygous deletion of Pkd1 (Pkd1+/-) and wild-type (Pkd1+/+) littermates to test whether Pkd1 haploinsufficiency is associated with a vascular phenotype in different age groups. Systolic blood pressure measured by the tail-cuff method was similar up to 20 weeks of age, but significantly higher in 30-week-old Pkd1+/- compared to Pkd1+/+. By contrast, similar telemetric recordings were obtained in unrestrained Pkd1+/- and Pkd1+/+ mice. The contractile responses evoked by KCl or phenylephrine were similar in young animals but increased in abdominal aortas of 30-week-old Pkd1+/- mice, and acetylcholine-evoked relaxation was depressed. Basal cytosolic calcium, KCl, and phenylephrine-evoked calcium signals were significantly lower in the Pkd1+/- aortas, whereas calcium release evoked by caffeine or thapsigargin was significantly larger. These changes were paralleled with a significant change in the mRNA expression of Pkd2, Trpc1, Orai1, and Serca2a in the aortas from Pkd1+/- vs. Pkd1+/+. These results are the first to indicate that haploinsufficiency in Pkd1 is associated with altered intracellular calcium homeostasis and increased vascular reactivity in the aorta with compensatory changes in transport proteins involved in the calcium signaling network.