Segmental differences in the roles of rho-kinase and protein kinase C in mediating vasoconstriction

Activation of Coronary Arteriolar PKCβ2 Impairs Endothelial NO-Mediated Vasodilation: Role of JNK/Rho Kinase Signaling and Xanthine Oxidase Activation

Protein kinase C (PKC) activation can evoke vasoconstriction and contribute to coronary disease. However, it is unclear whether PKC activation, without activating the contractile machinery, can lead to coronary arteriolar dysfunction. The vasoconstriction induced by the PKC activator phorbol 12,13-dibutyrate (PDBu) was examined in isolated porcine coronary arterioles. The PDBu-evoked vasoconstriction was sensitive to a broad-spectrum PKC inhibitor but not affected by inhibiting PKCβ2 or Rho kinase. After exposure of the vessels to a sub-vasomotor concentration of PDBu (1 nmol/L, 60 min), the endothelium-dependent nitric oxide (NO)-mediated dilations in response to serotonin and adenosine were compromised but the dilation induced by the NO donor sodium nitroprusside was unaltered. PDBu elevated superoxide production, which was blocked by the superoxide scavenger Tempol. The impaired NO-mediated vasodilations were reversed by Tempol or inhibition of PKCβ2, xanthine oxidase, c-Jun N-terminal kinase (JNK) and Rho kinase but were not affected by a hydrogen peroxide scavenger or inhibitors of NAD(P)H oxidase and p38 kinase. The PKCβ2 protein was detected in the arteriolar wall and co-localized with endothelial NO synthase. In conclusion, activation of PKCβ2 appears to compromise NO-mediated vasodilation via Rho kinase-mediated JNK signaling and superoxide production from xanthine oxidase, independent of the activation of the smooth muscle contractile machinery.

Resveratrol's Impact on Vascular Smooth Muscle Cells Hyporeactivity: The Role of Rho-Kinase Inhibition

Resveratrol (3,5,4′-trihydroxystilbene) is a chemical compound belonging to the group of polyphenols and flavonoids. The aim of the present study was to determine the influence of resveratrol application along with certain modulating factors, such as 8Br-cGMP-activator of cGMP-dependent protein kinases, HA-1077-Rho-kinase inhibitor, and Bay K8644-calcium channel agonist, on VMSCs constriction triggered by phenylephrine. Resveratrol at a dose of 10 mg/kg/24 h administered for 4 weeks reduced the reactivity of the arteries to the pressure action of catecholamines. Tests performed after four weeks of resveratrol administration showed that 8Br-cGMP at the concentrations of 0.01 mM/l and 0.1 mM/l intensifies this effect. Simultaneous resveratrol and Bay K8644 administration led to a significant decrease in contractility compared to the vessels collected from animals (Res−). This effect was dependent on the concentration of Bay K8644. Resveratrol seems to be counteractive against Bay K8644 by blocking L-type calcium channels. As the concentration of HA-1077 increased, there was a marked hyporeactivity of the vessels to the pressure effects of phenylephrine. The results indicate synergy between resveratrol and Rho-kinase inhibition.

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.

Smoothelin-like 1 deletion enhances myogenic reactivity of mesenteric arteries with alterations in PKC and myosin phosphatase signaling

The role of the smoothelin-like 1 (SMTNL1) protein in mediating vascular smooth muscle contractile responses to intraluminal pressure was examined in resistance vessels. Mesenteric arterioles from wild type (WT) and SMTNL1 global knock-out (KO) mice were examined with pressure myography. SMTNL1 deletion was associated with enhanced myogenic tone in vessels isolated from male, but not female, mice. Intraluminal pressures greater than 40 mmHg generated statistically significant differences in myogenic reactivity between WT and KO vessels. No overt morphological differences were recorded for vessels dissected from KO animals, but SMTNL1 deletion was associated with loss of myosin phosphatase-targeting protein MYPT1 and increase in the myosin phosphatase inhibitor protein CPI-17. Additionally, we observed altered contractile responses of isolated arteries from SMTNL1 KO mice to phenylephrine, KCl-dependent membrane depolarization and phorbol 12,13-dibutyrate (PDBu). Using pharmacological approaches, myogenic responses of both WT and KO vessels were equally affected by Rho-associated kinase (ROCK) inhibition; however, augmented protein kinase C (PKC) signaling was found to contribute to the increased myogenic reactivity of SMTNL1 KO vessels across the 60–120 mmHg pressure range. Based on these findings, we conclude that deletion of SMTNL1 contributes to enhancement of pressure-induced contractility of mesenteric resistance vessels by influencing the activity of myosin phosphatase.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

The role of Rho-kinase and calcium ions in constriction triggered by ET-1

Endothelin-1 (ET-1) is one of the key factors regulating tension of smooth muscles in blood vessels. It is believed that ET-1 plays an important role in pathogenesis of hypertension, and cardiovascular diseases; therefore, research in order to limit ET-1-mediated action is still in progress. The main objective of this paper was to evaluate the role of Rho-kinase in the ET-1-induced constriction of arteries. The analysis also included significance of intra- and extracellular pool of calcium ions in constriction triggered by ET-1. The studies were performed on perfused Wistar rat tail arteries. Concentration response curve (CRC) was determined for ET-1 in the presence of increased concentrations of Rho-kinase inhibitor (Y-27632) and IP3-receptor antagonist (2APB), both in reference to constriction triggered by solely ET-1. Afterwards, the influence of calcium ions present in the perfusion fluid was evaluated in terms of the effect triggered by 2APB and occurring in arteries constricted by ET-1. ET-1, in concentration dependent manner, leads to increase in perfusion pressure. Y-27632 and 2APB lead to shift of the concentration response curve for ET-1 to the right with simultaneously lowered maximum effect. There was no difference in reaction of the artery constricted by ET-1 and treated with 2APB in solution containing calcium and in calcium-free solution. Vasoconstrictive action of endothelin is not significantly dependent on the inflow of extracellular calcium, but it is proportional to inflow of Ca²⁺ related to activation of IP3 receptors and to Rho-kinase activity.

Involvement of transglutaminase 2 and voltage-gated potassium channels in cystamine vasodilatation in rat mesenteric small arteries

BACKGROUND AND PURPOSE

Vasodilatation may contribute to the neuroprotective and vascular anti-remodelling effect of the tissue transglutaminase 2 (TG2) inhibitor cystamine. Here, we hypothesized that inhibition of TG2 followed by blockade of smooth muscle calcium entry and/or inhibition of Rho kinase underlies cystamine vasodilatation.

EXPERIMENTAL APPROACH

We used rat mesenteric small arteries and RT-PCR, immunoblotting, and measurements of isometric wall tension, intracellular Ca(2+) ([Ca(2+)]i ), K(+) currents (patch clamp), and phosphorylation of myosin phosphatase targeting subunit 1 (MYPT1) and myosin regulatory light chain, in our experiments.

KEY RESULTS

RT-PCR and immunoblotting revealed expression of TG2 in mesenteric small arteries. Cystamine concentration-dependently inhibited responses to phenylephrine, 5-HT and U46619 and for extracellular potassium. Selective inhibitors of TG2, LDN 27129 and T101, also inhibited phenylephrine contraction. An inhibitor of PLC suppressed cystamine relaxation. Cystamine relaxed and reduced [Ca(2+)]i in phenylephrine-contracted arteries. In potassium-contracted arteries, cystamine induced less relaxation without changing [Ca(2+)]i , and these relaxations were blocked by mitochondrial complex inhibitors. Blockers of Kv 7 channels, XE991 and linopirdine, inhibited cystamine relaxation and increases in voltage-dependent smooth muscle currents. Cystamine and the Rho kinase inhibitor Y27632 reduced basal MYPT1-Thr(855) phosphorylation, but only Y27632 reduced phenylephrine-induced increases in MYPT1-Thr(855) and myosin regulatory light chain phosphorylation.

CONCLUSIONS AND IMPLICATIONS

Cystamine induced vasodilatation by inhibition of receptor-coupled TG2, leading to opening of Kv channels and reduction of intracellular calcium, and by activation of a pathway sensitive to inhibitors of the mitochondrial complexes I and III. Both pathways may contribute to the antihypertensive and neuroprotective effect of cystamine.

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.

A molecular signature in the pannexin1 intracellular loop confers channel activation by the α1 adrenoreceptor in smooth muscle cells

Both purinergic signaling through nucleotides such as ATP (adenosine 5'-triphosphate) and noradrenergic signaling through molecules such as norepinephrine regulate vascular tone and blood pressure. Pannexin1 (Panx1), which forms large-pore, ATP-releasing channels, is present in vascular smooth muscle cells in peripheral blood vessels and participates in noradrenergic responses. Using pharmacological approaches and mice conditionally lacking Panx1 in smooth muscle cells, we found that Panx1 contributed to vasoconstriction mediated by the α1 adrenoreceptor (α1AR), whereas vasoconstriction in response to serotonin or endothelin-1 was independent of Panx1. Analysis of the Panx1-deficient mice showed that Panx1 contributed to blood pressure regulation especially during the night cycle when sympathetic nervous activity is highest. Using mimetic peptides and site-directed mutagenesis, we identified a specific amino acid sequence in the Panx1 intracellular loop that is essential for activation by α1AR signaling. Collectively, these data describe a specific link between noradrenergic and purinergic signaling in blood pressure homeostasis.

Vascular O-GlcNAcylation augments reactivity to constrictor stimuli by prolonging phosphorylated levels of the myosin light chain

O-GlcNAcylation is a modification that alters the function of numerous proteins. We hypothesized that augmented O-GlcNAcylation levels enhance myosin light chain kinase (MLCK) and reduce myosin light chain phosphatase (MLCP) activity, leading to increased vascular contractile responsiveness. The vascular responses were measured by isometric force displacement. Thoracic aorta and vascular smooth muscle cells (VSMCs) from rats were incubated with vehicle or with PugNAc, which increases O-GlcNAcylation. In addition, we determined whether proteins that play an important role in the regulation of MLCK and MLCP activity are directly affected by O-GlcNAcylation. PugNAc enhanced phenylephrine (PE) responses in rat aortas (maximal effect, 14.2 ± 2 vs 7.9 ± 1 mN for vehicle, n=7). Treatment with an MLCP inhibitor (calyculin A) augmented vascular responses to PE (13.4 ± 2 mN) and abolished the differences in PE-response between the groups. The effect of PugNAc was not observed when vessels were preincubated with ML-9, an MLCK inhibitor (7.3 ± 2 vs 7.5 ± 2 mN for vehicle, n=5). Furthermore, our data showed that differences in the PE-induced contractile response between the groups were abolished by the activator of AMP-activated protein kinase (AICAR; 6.1 ± 2 vs 7.4 ± 2 mN for vehicle, n=5). PugNAc increased phosphorylation of myosin phosphatase target subunit 1 (MYPT-1) and protein kinase C-potentiated inhibitor protein of 17 kDa (CPI-17), which are involved in RhoA/Rho-kinase-mediated inhibition of myosin phosphatase activity. PugNAc incubation produced a time-dependent increase in vascular phosphorylation of myosin light chain and decreased phosphorylation levels of AMP-activated protein kinase, which decreased the affinity of MLCK for Ca(2+)/calmodulin. Our data suggest that proteins that play an important role in the regulation of MLCK and MLCP activity are directly affected by O-GlcNAcylation, favoring vascular contraction.

In vitro assessment of mouse fetal abdominal aortic vascular function

Fetal growth restriction (FGR) affects 3–8% of human pregnancies. Mouse models have provided important etiological data on FGR; they permit the assessment of treatment strategies on the physiological function of both mother and her developing offspring. Our study aimed to 1) develop a method to assess vascular function in fetal mice and 2) as a proof of principle ascertain whether a high dose of sildenafil citrate (SC; Viagra) administered to the pregnant dam affected fetal vascular reactivity. We developed a wire myography methodology for evaluation of fetal vascular function in vitro using the placenta-specific insulin-like growth factor II (Igf2) knockout mouse (P0; a model of FGR). Vascular function was determined in abdominal aortas isolated from P0 and wild-type (WT) fetuses at embryonic day (E) 18.5 of gestation. A subset of dams received SC 0.8 mg/ml via drinking water from E12.5; data were compared with water-only controls. Using wire myography, we found that fetal aortic rings exhibited significant agonist-induced contraction, and endothelium-dependent and endothelium-independent relaxation. Sex-specific alterations in reactivity were noted in both strains. Maternal treatment with SC significantly attenuated endothelium-dependent and endothelium-independent relaxation of fetal aortic rings. Mouse fetal abdominal aortas reproducibly respond to vasoactive agents. Study of these vessels in mouse genetic models of pregnancy complications may 1) help to delineate early signs of abnormal vascular reactivity and 2) inform whether treatments given to the mother during pregnancy may impact upon fetal vascular function.

Influence of pressure on adenosine triphosphate function as a sympathetic neurotransmitter in small mesenteric arteries from the spontaneously hypertensive rat

OBJECTIVES

Enhanced sympathetic neurotransmission contributes to hypertension in the spontaneously hypertensive rat (SHR). We recently reported a method for studying sympathetic neurotransmission in pressurized small arteries, demonstrating a major role of adenosine triphosphate (ATP) as a sympathetic neurotransmitter under these physiological conditions. We have now used this methodology to assess the role of ATP as a sympathetic neurotransmitter in small mesenteric arteries isolated from SHRs.

METHODS

Small arteries were mounted in a suction electrode, cannulated and pressurized to either 30 or 90 mmHg. Nerve-evoked alterations in membrane potential were assessed using sharp microelectrodes. Neurally evoked vasoconstrictor responses were measured in the absence and presence of the α1-adrenoceptor antagonist, tamsulosin (0.1 μmol/l), or the P2 purinoceptor antagonist suramin (0.1 mmol/l).

RESULTS

At 30 mmHg the P2X-receptor-mediated excitatory junctional potential (EJP) was larger in arteries from SHRs (7.9 ± 0.9 mV) than Wistar-Kyoto (WKY) rats (3.2 ± 0.4 mV, P < 0.05). Increasing pressure increased the amplitude of the EJP, which again, was larger in SHRs. At 90 mmHg, activation of the perivascular nerves produced a larger vasoconstriction in arteries isolated from SHRs compared with WKY rats. The vasoconstrictor response in SHRs was abolished by either suramin or tamsulosin.

CONCLUSION

These data provide electrophysiological evidence for enhanced purinergic function in the SHR and show that ATP is fundamentally important in contributing to the vasoconstriction produced after activation of the perivascular nerves in pressurized arteries from the SHR. This involves a synergistic interaction with noradrenaline to causes enhanced mesenteric arterial vasoconstriction, which may contribute to the hypertension in this model.

Role of nitric oxide and endothelin in endothelial maintenance of vasoconstrictor responses in aortas of diabetic female rats

BACKGROUND

Diabetes differentially affects the vascular system in males and females. Although various results have been reported, very few studies have focused on responses in females. In the present study, we investigated contractile responses to norepinephrine in aortas of alloxan-diabetic female rats and evaluated endothelial modulation of these responses.

METHODS

Concentration-response curves were constructed to norepinephrine in the absence or presence of N(G) -nitro-l-arginine methyl ester (l-NAME), indomethacin, losartan, tezosentan, and calphostin C; pre-pro-endothelin mRNA expression was evaluated; and norepinephrine-stimulated expression of phosphorylated (p-) Akt Ser(473) , p-endothelial nitric oxide synthase (eNOS) Ser(1177) , and p-eNOS Ser(633) was determined in endothelial cells incubated in the presence of low (5 mmol/L) or high (25 mmol/L) glucose concentrations.

RESULTS

Similar maximal responses (Rmax ) to norepinephrine were seen in control and diabetic endothelium-intact aortas; however, Rmax was reduced in diabetic endothelium-denuded aortas. Incubation of endothelium-intact aortas with 100 μmol/L l-NAME increased Rmax in the control group only. Inhibition of cyclo-oxygenase (10 μmol/L indomethacin) and blockade of angiotensin II receptors (10 μmol/L losartan) reduced Rmax in endothelium-intact aortas in both the control and diabetic groups. Blockade of endothelin receptors (0.1 μmol/L tezosentan) and inhibition of protein kinase C (PKC; 0.1 μmol/L calphostin C) reduced Rmax only in endothelium-intact aortas from diabetic rats. Pre-pro-endothelin mRNA expression was increased in aortas from diabetic female rats. Finally, p-Akt Ser(473) , p-eNOS Ser(1177) , and p-eNOS Ser(633) levels were enhanced after norepinephrine stimulation only in low glucose-treated endothelial cells.

CONCLUSIONS

In aortas of diabetic female rats, reductions in smooth muscle contractile responses to norepinephrine are counterbalanced by the endothelium via reduced eNOS activation and increased endothelin release and PKC activation.

Size-dependent heterogeneity of contractile Ca2+ sensitization in rat arterial smooth muscle

Each segment along arterial vessels adapts to different circumstances, including blood pressure and sympathetic innervation. PKC and Rho-associated kinase (ROCK) Ca(2+)-sensitizing pathways leading to myosin phosphatase inhibition are critically involved in α(1)-adrenoceptor-mediated vascular smooth muscle contraction in distinctive time-dependent manners. We tested whether the amplitude and time course of each pathway varies dynamically between arterial segments. Using pharmacological approaches, we determined the time-dependent roles of Ca(2+) release, Ca(2+) influx, PKC and ROCK in α(1)-agonist-induced contraction and phosphorylation of key proteins in denuded rat small mesenteric artery, midsized caudal artery and thoracic aorta. SR Ca(2+) release and voltage-dependent Ca(2+) influx were essential for the initial rising and late sustained phases, respectively, of phenylephrine-induced contraction, regardless of arterial size. In small mesenteric arteries, α(1A)-subtype-specific antagonists and inhibitors of PKC, but not ROCK, markedly reduced the initial and late phases of contraction in a non-additive manner and suppressed phosphorylation of myosin light chain (MLC) and CPI-17, but not myosin targeting subunit of myosin light chain phosphatase (MYPT1). In aorta, an α(1D)-specific antagonist reduced both the initial and late phases of contraction with a significant decrease in MLC but not CPI-17 or MYPT1 phosphorylation. ROCK inhibitors, but not PKC inhibitors, suppressed the sustained phase of contraction with a decrease in MLC and MYPT1 phosphorylation in the aorta. The effect of ROCK inhibitors was additive with the α(1D)-antagonist. The results for midsized arteries were intermediate. Thus, the PKC-CPI-17 Ca(2+)-sensitizing pathway, which is dependent on PKC subtype and a Ca(2+)-handling mechanism, and is downstream of α(1A) receptors, plays a major role in α(1)-agonist-induced contraction of small resistance arteries in the splanchnic vascular beds. The effect of PKC and ROCK increases and decreases, respectively, with decreasing arterial size.

Contractile responses of isolated equine digital arteries under hypoxic or hyperoxic conditions in vitro: role of reactive oxygen species and Rho kinase

The underlying pathophysiological triggers for equine acute laminitis are unknown, although digital vasoconstriction, ischaemia, hypoxia and reperfusion injury may be involved. The contractile responses of isolated equine digital arteries (EDAs), harvested from the hindlimbs of normal horses postmortem at an abattoir, were studied acutely (up to 3 h) under hyperoxic (95% oxygen, 5% CO2 ) and hypoxic (95% nitrogen, 5% CO2 ) conditions in organ baths. Phenylephrine (PHE; 10(-6) m), 5-hydroxytryptamine (5-HT; 10(-7) m) and high potassium (K(+) ; 118 mm) caused contraction in EDAs which was significantly (P<0.0001) enhanced under hypoxic conditions. In contrast, contraction stimulated by 9,11-dideoxy-9α,11α-epoxymethanoprostaglandin F2α (U44069; 3 × 10(-8) m) was not significantly enhanced by hypoxia (P=0.75). Hypoxia-enhanced contraction in response to K(+) was greater (P<0.03) in vessels with a functional endothelium than in vessels in which the endothelium was removed by rubbing. Fasudil (10(-6) to 10(-5) m), a Rho kinase inhibitor, and apocynin (10(-3) to 3 × 10(-3) m), an NADPH oxidase inhibitor, significantly (P ≤ 0.05) inhibited hypoxia-enhanced contraction in response to PHE and 5-HT. In conclusion, hypoxia-enhanced contraction occurred in EDAs. This appears to be partially mediated by reactive oxygen species produced by NAPDH oxidase, which activate Rho kinase to increase calcium sensitisation and enhance smooth muscle contraction.

A role for zinc in regulating hypoxia-induced contractile events in pulmonary endothelium

We previously reported that zinc thiolate signaling contributes to hypoxic contraction of small, nonmuscularized arteries of the lung. The present studies were designed to investigate mechanisms by which hypoxia-released zinc induces contraction in isolated pulmonary endothelial cells and to delineate the signaling pathways involved in zinc-mediated changes in the actin cytoskeleton. We used fluorescence-based imaging to show that hypoxia induced time-dependent increases in actin stress fibers that were reversed by the zinc chelator, N,N,N',N'-tetrakis-(2-pyridylmethyl)-ethylenediamine (TPEN). We further showed that hypoxia-induced phosphorylation of the contractile protein myosin light chain (MLC) and assembly of actin stress fibers were each TPEN sensitive. Hypoxia and zinc-induced inhibition of MLC phosphatase (MLCP) were independent of the regulatory subunit (MYPT1) of MLCP, and therefore hypoxia-released zinc likely inhibits MLCP at its catalytic (PP1) subunit. Inhibition of PKC by Ro-31-8220 and a dominant-negative construct of PKC-ε attenuated hypoxia-induced contraction of isolated pulmonary endothelial cells. Furthermore, zinc-induced phosphorylation of MLC (secondary to inhibition of MLCP) was PKC dependent, and hypoxia-released zinc promoted the phosphorylation of the PKC substrate, CPI-17. Collectively, these data suggest a link between hypoxia, elevations in labile zinc, and activation of PKC, which in turn acts through CPI-17 to inhibit MLCP activity and promote MLC phosphorylation, ultimately inducing stress fiber formation and endothelial cell contraction.

O-GlcNAcylation: a novel pathway contributing to the effects of endothelin in the vasculature

Glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc) or O-GlcNAcylation on serine and threonine residues of nuclear and cytoplasmic proteins is a posttranslational modification that alters the function of numerous proteins important in vascular function, including kinases, phosphatases, transcription factors, and cytoskeletal proteins. O-GlcNAcylation is an innovative way to think about vascular signaling events both in physiological conditions and in disease states. This posttranslational modification interferes with vascular processes, mainly vascular reactivity, in conditions where endothelin-1 (ET-1) levels are augmented (e.g. salt-sensitive hypertension, ischemia/reperfusion, and stroke). ET-1 plays a crucial role in the vascular function of most organ systems, both in physiological and pathophysiological conditions. Recognition of ET-1 by the ET(A) and ET(B) receptors activates intracellular signaling pathways and cascades that result in rapid and long-term alterations in vascular activity and function. Components of these ET-1-activated signaling pathways (e.g., mitogen-activated protein kinases, protein kinase C, RhoA/Rho kinase) are also targets for O-GlcNAcylation. Recent experimental evidence suggests that ET-1 directly activates O-GlcNAcylation, and this posttranslational modification mediates important vascular effects of the peptide. This review focuses on ET-1-activated signaling pathways that can be modified by O-GlcNAcylation. A brief description of the O-GlcNAcylation biology is presented, and its role on vascular function is addressed. ET-1-induced O-GlcNAcylation and its implications for vascular function are then discussed. Finally, the interplay between O-GlcNAcylation and O-phosphorylation is addressed.

The anti-platelet effects of apocynin in mice are not mediated by inhibition of NADPH oxidase activity

Apocynin, or a (myelo)peroxidase-derived product thereof, is a powerful inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Apocynin has also been shown to prevent aggregation of platelets in response to agonists such as collagen and thrombin. The aims of this study were to establish whether NADPH oxidase activity is required for aggregation of murine platelets to collagen and other agonists and whether the anti-aggregatory effects of apocynin are due to an inhibitory action against this enzyme. Washed platelets were isolated from male C57BL6 (wild-type), Nox2-deficient (Nox2(-/y )), and p47phox-deficient (p47phox(-/-)) mice for assessment of aggregation and NADPH oxidase subunit (Nox2, p47phox) expression. Collagen and U46619 elicited aggregation of murine platelets, and these responses were inhibited by apocynin at concentrations ≥100 μM. By contrast, aggregations to a direct protein kinase C activator, phorbol-12,13-dibutyrate, were insensitive to apocynin. Immunoblotting of platelet protein homogenates from wild-type mice with anti-Nox2 or p47phox antibodies revealed strong bands at 58 and 50 kDa, respectively. While expression of these immunoreactive bands was greatly diminished in platelets from Nox2(-/y ) and p47phox(-/-) mice, collagen still elicited aggregations that were similar to those observed in platelets from wild-types. Moreover, apocynin was an equally effective inhibitor of aggregation in platelets from all three mouse strains. In conclusion, these data suggest that NADPH oxidase-derived reactive oxygen species play no role in the aggregation response of washed murine platelets to collagen. Thus, our observation that apocynin is a powerful inhibitor of platelet aggregation raises further questions about the selectivity of this drug as an NADPH oxidase inhibitor.

Rho kinase activation and ROS production contributes to the cooling enhanced contraction in cutaneous equine digital veins

A decrease in environmental temperature can directly affect the contractility of cutaneous vasculature, mediated in part by α2-adrenoceptors. Most of the cellular mechanisms underlying the cooling-enhanced contractility to α2-adrenoceptor agonists have been reported in cutaneous arteries but little information is available on cutaneous veins. To investigate the cellular mechanisms associated with the cooling-enhanced contraction to UK-14304 (α2-adrenoceptor agonist), isolated equine digital veins (EDVs) were studied at 30°C and 22°C. The effects of inhibitors were studied on the contractile response to UK-14304 (0.1 μM). The cooling-enhanced responses were inhibited by Rho kinase inhibitors [maximum response to UK-14304 95.2 ± 8% of response to depolarizing Krebs solution (DKS) in control vessels cooled to 22°C, compared with 31.4 ± 6% in the presence of fasudil 1 μM and 75.8 ± 6% with Y-27632 0.1 μM] and the effects of these inhibitors were considerably less at 30°C (control response 56.4 ± 5% of DKS; 34.9 ± 6% with fasudil 1 μM and 50.6 ± 9% with Y-27632 0.1 μM). Furthermore, Western blotting showed that one of the downstream targets for Rho kinase activity, ezrin/radixin/moesin, was phosphorylated after cooling and reduced by fasudil (1 μM) only at 22°C. The activation of protein kinase C contributed to the contractile response, but predominantly at 30°C (maximum response 82.3 ± 9% of DKS for control; 57.7 ± 10% in the presence of chelerythrine 10 μM) with no significant effect at 22°C. The reduction of the response at 22°C by antioxidants, rotenone (14% reduction), and tempol (21% reduction) suggested the contribution of reactive oxygen species (ROS). No evidence was obtained to support the participation of tyrosine kinase. These data demonstrate that Rho kinase activation and the production of ROS contributes to the cooling-enhanced contraction in these cutaneous digital veins.

Raf-1 kinase regulates smooth muscle contraction in the rat mesenteric arteries

We investigated the potential role of Raf-1 kinase in mesenteric arterial contraction. Inhibitors of Raf-1 kinase, GW5074, L779450 and ZM 336372 reversed phenylephrine (PE)-induced mesenteric vascular contraction. Studies in vivo in rats showed that GW5074 inhibited PE-induced increase in mean arterial pressure in adult female Sprague-Dawley rats. Isometric tension studies in mesenteric arteries of rats showed that GW5074 did not change the KCl-evoked contraction but significantly inhibited the contractions to PE, 5-HT, U46619, endothelin 1, angiotensin II and phorbol 12, 13-dibutyrate (PDBu). In mesenteric vascular smooth muscle cells (VSMCs), PE stimulated increase in Raf-1 phosphorylation which was inhibited by GW5074. Measurement of [Ca(2+)](i) with Fura-2 showed that GW5074-mediated inhibition of PE-induced contraction was not associated with decreases in [Ca(2+)](i). VSMCs treated with PE exhibited higher levels of the contractile proteins, p-MYPT1 and p-MLC(20), which was inhibited by GW5074. Similarly, PDBu induced increases in phosphorylation of Raf-1, MLC(20) and MYPT1 and this was inhibited by GW5074. However, GW5074 did not have any significant effect on PE/PDBu-induced MEK/ERK activation. The results indicate that Raf-1 kinase plays an important role in the regulation of vascular contractility through regulation of calcium sensitization.

Peroxide generation by p47phox-Src activation of Nox2 has a key role in protein kinase C-induced arterial smooth muscle contraction

Protein kinase C (PKC) stimulation of NAD(P)H oxidases (Nox) is an important component of multiple vascular disease processes; however, the relationship between oxidase activation and the regulation of vascular smooth muscle contraction by PKC remains poorly understood. Therefore, we examined the signaling cascade of PKC-elicited Nox activation and the role of superoxide and hydrogen peroxide in mediating PKC-induced vascular contraction. Endothelium-denuded bovine coronary arteries showed a PKC-dependent basal production of lucigenin (5 muM)-detected Nox oxidase-derived superoxide, which was stimulated fourfold by PKC activation with 10 muM phorbol 12,13-dibutyrate (PDBu). PDBu appeared to increase superoxide generation by Nox2 through both p47(phox) and peroxide-dependent Src activation mechanisms based on the actions of inhibitors, properties of Src phosphorylation, and the loss of responses in aorta from mice deficient in Nox2 and p47(phox). The actions of inhibitors of contractile regulating mechanisms, scavengers of superoxide and peroxide, and responses in knockout mouse aortas suggest that a major component of the contraction elicited by PDBu appeared to be mediated through peroxide derived from Nox2 activation stimulating force generation through Rho kinase and calmodulin kinase-II mechanisms. Superoxide generated by PDBu also attenuated relaxation to nitroglycerin. Peroxide-derived from Nox2 activation by PKC appeared to be a major contributor to the thromboxane A(2) receptor agonist U46619 (100 nM)-elicited contraction of coronary arteries. Thus a p47(phox) and Src kinase activation of peroxide production by Nox2 appears to be an important contributor to vascular contractile mechanisms mediated through activation of PKC.

Mechanisms of augmented vasoconstriction induced by 5-hydroxytryptamine in aortic rings from spontaneously hypertensive rats

BACKGROUND AND PURPOSE

To test whether development of enhanced vasoconstriction to 5-hydroxytryptamine (5-HT; serotonin) in SHR was temporally related to hypertension, elevated vascular superoxide (O(2)(-)) levels, decreased NO bioavailability, or increased contractile effects of cyclooxygenase or rho-kinase and/or PKC.

EXPERIMENTAL APPROACH

We examined systolic blood pressure (SBP), vascular O(2)(-), and 5-HT-induced contractile responses of aortic segments from 4- and 8-week-old WKY and SHR.

KEY RESULTS

SBP was 35% higher in SHR than WKY at 4 weeks and 60% higher at 8 weeks. Contractile responses to 5-HT were similar in WKY and SHR at 4 weeks, but were markedly augmented in SHR at 8 weeks. The NO synthase inhibitor, L-NAME, enhanced contractile responses to 5-HT markedly in both strains at 4 weeks and in WKY at 8 weeks, but only very modestly in SHR at 8 weeks. These functional differences were associated with higher O(2)(-) levels in SHR versus WKY at 8 weeks, but not at 4 weeks. The rho-kinase inhibitor, Y-27632, and the PKC inhibitor, Ro 31-8220, each only modestly attenuated contractions in WKY and SHR in each age group, and their effects in each strain were more pronounced at 8 weeks. The cyclooxygenase inhibitor, indomethacin, had no effect on contractile responses.

CONCLUSIONS AND IMPLICATIONS

Development of augmented vascular contractile responses to 5-HT in SHR is preceded by hypertension. It is associated with increased vascular O(2)(-) levels and reduced modulatory effects of NO, and is unlikely to be due to enhanced activity of rho-kinase, PKC or cyclooxygenase.

Comparison of the involvement of protein kinase C in agonist-induced contractions in mouse aorta and corpus cavernosum

Protein kinase C (PKC) is involved in the regulation of vascular smooth muscle contraction. However, the role of PKC in erectile function is poorly understood. This study investigated whether PKC mediates agonist-induced contractions in mouse penile tissue (corpora cavernosa). We also compared the effects of PKC activators and inhibitors on contractile responses in mouse corpus cavernosum with those in mouse aorta. Aortic rings and corpus cavernosal strips from C57BL/6J mice were mounted in the organ bath for isometric tension recording. Our data showed that a PKC(alpha/beta) selective inhibitor, G(ö)6976 (10 microM), inhibited phenylephrine and 9,11-dideoxy-11alpha,9alpha-epoxymethanoprostaglandin F(2alpha) (U46619, a thromboxane mimetic)-induced contractions in mouse aorta, reducing the maximum contraction by 94% and 17%, respectively. A non-selective PKC inhibitor, chelerythrine (30 microM), also significantly reduced phenylephrine- and U46619-induced maximum contractions in mouse aorta. However, G(ö)6976 and chelerythrine had no significant effects on phenylephrine- and U46619-induced contractions in corpus cavernosum. Furthermore, a PKC activator, phorbol-12,13-dibutyrate (0.1 microM), significantly increased contractions in aorta (208+/-14% of KCl-induced maximum contraction) but failed to cause contractions in corpus cavernosum at 1 and 10 microM. Western blot analysis data suggested that protein expression of PKC was similar in aorta and corpus cavernosum. Taken together, our data indicate that PKC does not have a significant role in agonist-induced contractions in mouse corpus cavernosum, whereas it mediates the contractile response to agonists in the aorta.

Selectivity of ROCK inhibitors in the spontaneously tonic smooth muscle

The selectivity of different Rho kinase (ROCK) inhibitors in the spontaneously tonic smooth muscle has not been investigated. We examined this issue using Y-27632 [(R)-(+)-trans-N-(4-pyridyl)-4-(1-aminoethyl)-cyclohexanecarbox anecarboxamide, 2HCl], H-1152 [(S)-(+)-(2-methyl-5-isoquinolinyl) sulfonylhomopiperazine, 2HCl], HA-1077 [(5 isoquinolinesulfonyl) homopiperazine, 2HCl], and ROCK inhibitor II [N-(4-pyridyl)-N'-(2,4,6-trichlorophenyl)urea]. We compared these inhibitors in the spontaneously tonic smooth muscle of the internal anal sphincter (IAS). ROCK, protein kinase C (PKC), and myosin light chain kinase (MLCK) activities were determined in the IAS, before and after different ROCK inhibitors. Y-27632 and H-1152 were approximately 30-fold more potent in the IAS (IC(50): 4.4 x 10(-7) and 7.9 x 10(-8) M, respectively) vs. the phasic rectal smooth muscle (RSM) (IC(50): 1.3 x 10(-5) and 2.5 x 10(-6) M, respectively). HA-1077 and ROCK inhibitor II were equipotent in the IAS vs. RSM. In the IAS, H-1152 was the most potent whereas ROCK inhibitor II is the least. Y-27632 and H-1152 caused concentration-dependent decrease in the IAS tone that correlates directly with the decreases in ROCK activity, without significant effect in the PKC and MLCK activities. This specifically selective correlation between ROCK activity and decrease in the IAS tone was absent in the case of HA-1077 and ROCK inhibitor II, which also inhibited PKC and MLCK. We conclude that the IAS tone is critically dependent on ROCK activity, and H-1152 and Y-27632 are the most selective and potent ROCK inhibitors in the IAS.

Eucapnic intermittent hypoxia augments endothelin-1 vasoconstriction in rats: role of PKCdelta

We reported previously that simulating sleep apnea by exposing rats to eucapnic intermittent hypoxia (E-IH) causes endothelin-dependent hypertension and increases constrictor sensitivity to endothelin-1 (ET-1). In addition, augmented ET-1-induced constriction in small mesenteric arteries (sMA) is mediated by increased Ca(2+) sensitization independent of Rho-associated kinase. We hypothesized that exposing rats to E-IH augments ET-1-mediated vasoconstriction by increasing protein kinase C (PKC)-dependent Ca(2+) sensitization. In sMA, the nonselective PKC inhibitor GF-109203x (3 microM) significantly inhibited ET-1-stimulated constriction in E-IH arteries but did not affect ET-1-stimulated constriction in sham arteries. Phospholipase C inhibitor U-73122 (1 microM) also inhibited constriction by ET-1 in E-IH but not sham sMA. In contrast, the classical PKC (cPKC) inhibitor Gö-6976 (1 microM) had no effect on ET-1-mediated vasoconstriction in either group, but a PKCdelta-selective inhibitor (rottlerin, 3 microM) significantly decreased ET-1-mediated constriction in E-IH but not in sham sMA. ET-1 increased PKCdelta phosphorylation in E-IH but not sham sMA. In contrast, ET-1 constriction in thoracic aorta from both sham and E-IH rats was inhibited by Gö-6976 but not by rottlerin. These observations support our hypothesis that E-IH exposure significantly increases ET-1-mediated constriction of sMA through PKCdelta activation and modestly augments ET-1 contraction in thoracic aorta through activation of one or more cPKC isoforms. Therefore, upregulation of a PKC pathway may contribute to elevated ET-1-dependent vascular resistance in this model of hypertension.

ROK contribution to endothelin-mediated contraction in aorta and mesenteric arteries following intermittent hypoxia/hypercapnia in rats

We reported previously that intermittent hypoxia with CO(2) to maintain eucapnia (IH-C) elevates plasma endothelin-1 (ET-1) and arterial pressure. In small mesenteric arteries (sMA; inner diameter = 150 microm), IH-C augments ET-1 constrictor sensitivity but diminishes ET-1-induced increases in intracellular Ca(2+) concentration, suggesting IH-C exposure increases both ET-1 levels and ET-1-stimulated Ca(2+) sensitization. Because Rho-associated kinase (ROK) can mediate Ca(2+) sensitization, we hypothesized that augmented vasoconstrictor sensitivity to ET-1 in arteries from IH-C-exposed rats is dependent on ROK activation. In thoracic aortic rings, ET-1 contraction was not different between groups, but ROK inhibition (Y-27632, 3 and 10 microM) attenuated ET-1 contraction more in IH-C than in sham arteries (50 +/- 11 and 78 +/- 7% vs. 41 +/- 12 and 48 +/- 9% inhibition, respectively). Therefore, ROK appears to contribute more to ET-1 contraction in IH-C than in sham aorta. In sMA, ROK inhibitors did not affect ET-1-mediated constriction in sham arteries and only modestly inhibited it in IH-C arteries. In ionomycin-permeabilized sMA with intracellular Ca(2+) concentration held at basal levels, Y-27632 did not affect ET-1-mediated constriction in either IH-C or sham sMA and ET-1 did not stimulate ROK translocation. In contrast, inhibition of myosin light-chain kinase (ML-9, 100 microM) prevented ET-1-mediated constriction in sMA from both groups. Therefore, IH-C exposure increases ET-1 vasoconstrictor sensitivity in sMA but not in aorta. Furthermore, ET-1 constriction is myosin light-chain kinase dependent and mediated by Ca(2+) sensitization that is independent of ROK activation in sMA but not aorta. Thus ET-1-mediated signaling in aorta and sMA is altered by IH-C but is dependent on different second messenger systems in small vs. large arteries.

Vasoconstrictor effect of endothelin-1 on hypertensive pulmonary arterial smooth muscle involves Rho-kinase and protein kinase C

Although one of the common characteristics of pulmonary hypertension is abnormal sustained vasoconstriction, the signaling pathways that mediate this heightened pulmonary vascular response are still not well defined. Protein kinase C (PKC) and Rho-kinase are regulators of smooth muscle contraction induced by G protein-coupled receptor agonists including endothelin-1 (ET-1), which has been implicated as a signaling pathway in pulmonary hypertension. Toward this end, it was hypothesized that both Rho-kinase and PKC mediate the pulmonary vascular response to ET-1 in hypertensive pulmonary arterial smooth muscle, and therefore, the purpose of this study was to determine the role of PKC and Rho-kinase signaling in ET-1-induced vasoconstriction in both normotensive (Sprague-Dawley) and hypertensive (Fawn-Hooded) rat pulmonary arterial smooth muscle. Results indicate that ET-1 caused greater vasoconstriction in hypertensive pulmonary arteries compared with the normal vessels, and treatment with the PKC antagonists chelerythrine, rottlerin, and Gö 6983 inhibited the vasoconstrictor response to ET-1 in the hypertensive vessels. In addition, the specific Rho-kinase inhibitor Y-27632 significantly attenuated the effect of ET-1 in both normotensive and hypertensive phenotypes, with greater inhibition occurring in the hypertensive arteries. Furthermore, Western blot analysis revealed that ET-1 increased RhoA expression in both normotensive and hypertensive pulmonary arteries, with expression being greater in the hypertensive state. These results suggest that both PKC and Rho/Rho-kinase mediate the heightened pulmonary vascular response to ET-1 in hypertensive pulmonary arterial smooth muscle.

Kinase inhibitors for cardiovascular disease

Over the last decade, there has been substantial progress toward understanding the pathophysiology and treatment of cardiovascular diseases (CVDs). Elucidating cellular responses to the extracellular environment and signal transduction mechanisms have provided the opportunity to explore novel molecular therapeutic approaches for the treatment of CVDs. Neurohormonal stimulation has been implicated in these diseases; blockade of the renin-angiotensin and beta-adrenergic systems are examples of therapeutic effectiveness. There are multiple cell signaling cascades, some of which are beneficial or compensatory and others deleterious. The balance between these pathways, which in large part is dictated by the cellular environment, determines the outcome as a diseased or non-diseased state. Selective targeting of signaling pathways using protein kinase inhibitors, would have a potential advantage over receptor blockers. We review potential protein kinase targets and recent evidence supporting therapeutic interventional value in CVDs.