Regulatory mechanisms of calcium sensitization of contractile elements in smooth muscle

Erectile Dysfunction: Key Role of Cavernous Smooth Muscle Cells

Erectile dysfunction is increasingly affecting men, from the elderly to young adults, being a sexual disorder related to the inability to generate or maintain a penile erection. This disorder is related to psychosocial factors such as anxiety, depression, and low self-esteem, to organic factors such as the presence of preexisting conditions like hypertension, diabetes and dyslipidemia. The pathophysiology of the disease is related to changes in the neurotransmission of the autonomic or the non-cholinergic non-adrenergic nervous system, as well as the release of local mediators, such as thromboxane A₂ and endothelin, and hormonal action. These changes lead to impaired relaxation of cavernous smooth muscle, which reduces local blood flow and impairs penile erection. Currently, therapy is based on oral vasodilation, such as sildenafil, tadalafil, vardenafil and iodenafil, or by direct administration of these agents into the corpus cavernosum or by intraurethral route, such as alprostadil and papaverine. Despite this, studies that consolidate the understanding of its pathophysiological process contribute to the discovery of new more efficient drugs for the treatment of erectile dysfunction. In this sense, in the present work an extensive survey was carried out of the mechanisms already consolidated and the most recent ones related to the development of erectile dysfunction.

Citrus bergamia Risso Elevates Intracellular Ca (2+) in Human Vascular Endothelial Cells due to Release of Ca (2+) from Primary Intracellular Stores

The purpose of the present study is to examine the effects of essential oil of Citrus bergamia Risso (bergamot, BEO) on intracellular Ca²⁺ in human umbilical vein endothelial cells. Fura-2 fluorescence was used to examine changes in intracellular Ca²⁺ concentration [Ca²⁺]_i . In the presence of extracellular Ca²⁺, BEO increased [Ca²⁺]_i , which was partially inhibited by a nonselective Ca²⁺ channel blocker La³⁺. In Ca²⁺-free extracellular solutions, BEO increased [Ca²⁺]_i in a concentration-dependent manner, suggesting that BEO mobilizes intracellular Ca²⁺. BEO-induced [Ca²⁺]_i increase was partially inhibited by a Ca²⁺-induced Ca²⁺ release inhibitor dantrolene, a phospholipase C inhibitor U73122, and an inositol 1,4,5-triphosphate (IP₃)-gated Ca²⁺ channel blocker, 2-aminoethoxydiphenyl borane (2-APB). BEO also increased [Ca²⁺]_i in the presence of carbonyl cyanide m-chlorophenylhydrazone, an inhibitor of mitochondrial Ca²⁺ uptake. In addition, store-operated Ca²⁺ entry (SOC) was potentiated by BEO. These results suggest that BEO mobilizes Ca²⁺ from primary intracellular stores via Ca²⁺-induced and IP3-mediated Ca²⁺ release and affect promotion of Ca²⁺ influx, likely via an SOC mechanism.

Bergamot essential oil differentially modulates intracellular Ca2+ levels in vascular endothelial and smooth muscle cells: a new finding seen with fura-2

In this study, we compared the effect of the essential oil of Citrus bergamia Risso [bergamot, bergamot essential oil (BEO)] on the intracellular Ca levels in vascular endothelial (EA) and mouse vascular smooth muscle (MOVAS) cells, using the fura-2 fluorescence technique. BEO caused an initial transient increase in intracellular Ca concentration ([Ca]i) in EA cells, followed by a decrease, whereas it induced a sustained increase in [Ca]i in MOVAS cells. Linalyl acetate (LA) as a major component of BEO-induced [Ca]i mobilization was similar to BEO in EA cells. The increase of [Ca]i by LA was higher in EA cells than in MOVAS cells. [Ca]i rise induced by extracellular Ca application was significantly blocked by BEO or LA in EA cells but not in MOVAS cells, suggesting that BEO and LA block Ca influx in EA cells. The present results suggest that BEO and LA differentially modulate intracellular Ca levels in vascular endothelial and smooth muscle cells. In addition, blockade of Ca influx by BEO and LA in EA cells may explain the protective effects of BEO on endothelial dysfunction associated with cardiovascular disease.

Augmented PDBu-mediated contraction of bronchial smooth muscle of mice with antigen-induced airway hyperresponsiveness

To explore the role of protein kinase C (PKC) in the augmented bronchial smooth muscle (BSM) contraction observed in the antigen-induced airway hyperresponsive (AHR) mice, the effects of a PKC activator, phorbol 12,13-dibutylate (PDBu), on BSM contraction were compared between the AHR and control mice. Actively sensitized mice were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge the isometrical contractions of the BSMs were measured. The BSM contraction induced by acetylcholine, but not high K(+) depolarization, was significantly augmented in the AHR mice. In BSMs of control mice, PDBu caused a significant increase in tension when the tissues were precontracted with high K(+), although PDBu itself had no effect on basal tone. The PDBu-mediated contraction was markedly augmented in BSMs of the AHR mice. These findings suggest that an increase in the PKC-mediated signaling is involved in the augmented contraction of BSMs in the antigen-induced AHR mice.

Role of protein kinase Cbeta in rhythmic contractions of human pregnant myometrium

To assess the role of protein kinase Cbeta (PKCbeta) in human myometrial contractions during pregnancy, we evaluated the effect of a PKCbeta inhibitor (LY333531) on the pregnant and nonpregnant myometrial contractions and compared the level of PKCbeta in the pregnant myometrium with that in the nonpregnant myometrium. The effects of LY333531 on the myometrial contractions were examined by measuring contractile activity (frequency and amplitude). PKCbeta in human myometrium was assessed at mRNA level using real-time PCR method. The characteristics of contractile activity were different between the pregnant and the nonpregnant myometrium. The amplitude of rhythmic contractions in the preterm and term myometrium was increased 2- to 2.5-fold when compared with that in the nonpregnant myometrium, but the frequency of rhythmic contractions was decreased by about half. LY333531 (10(-6) M) reduced the increased amplitude in the preterm and term myometrium by about 50%, and the inhibitory effects of LY333531 in the pregnant myometrium were significantly greater than that in the nonpregnant myometrium (about 50 vs 25%). However, the frequency in the pregnant and nonpregnant myometrium was not influenced by LY333531. Real-time PCR revealed a significant, five- to sevenfold increase in the expression of PKCbeta mRNA in the preterm and term myometrium when compared with the nonpregnant myometrium. These findings suggest that the increased amplitude of human myometrial contractions during pregnancy is related to the increased level of PKCbeta. A PKCbeta inhibitor may reduce preterm uterine contractions and prevent preterm delivery.

Mechanism of abnormal intestinal motility in inflammatory bowel disease: how smooth muscle contraction is reduced?

Intestinal inflammation alters the contractile activity of intestinal smooth muscle. Motility disorders of the gastrointestinal tract are clinically important symptoms, because they are often associated with severe interstitial inflammation. In addition, the motility disorders secondarily induce abnormal growth of the intestinal flora, and the resulting disturbance of this flora aggravates the pathogenesis of mucosal inflammation. This in turn aggravates the intestinal dysmotility; i.e., it is an inflammatory spiral. Therefore, it is important to elucidate the mechanisms involved in the changes in motor function which occur in intestinal inflammation. Recent studies have revealed several molecular mechanisms responsible for the decreased motility which occurs in an inflamed gastrointestinal tract. In the present review, we discuss the functional failure of smooth muscle cells, including changes in the activity of muscarinic receptors, ion channels and the endogenous myosin phosphatase inhibitor CPI-17.

Involvement of CPI-17 downregulation in the dysmotility of the colon from dextran sodium sulphate-induced experimental colitis in a mouse model

The mechanism of gastrointestinal dysmotility in inflammatory bowel disease has not been clarified. In this study, we examined the mechanism involved in the inflamed distal colon isolated from a mouse model of dextran sodium sulphate-induced ulcerative colitis (DSS-treated mouse). Although substance P-induced contraction was not changed, carbachol-induced contraction was reduced in the DSS-treated mouse colon. Pre-incubation with the NO synthase inhibitor N(G)-monomethyl-L-arginine (L-NMMA) or the cyclooxygenase inhibitor indomethacin did not reverse the carbachol-induced contraction in the DSS-treated mouse colon. In semi-quantitative reverse transcription-polymerase chain reaction experiments and Western blot analysis, muscarinic M3 receptor expressions were not changed. The Ca2+ -sensitization of contractile elements induced by carbachol with GTP or GTPgammaS was reduced in the beta-escin-permeabilized DSS-treated mouse colon. Although the expression of proteins such as rhoA, ROCK1, ROCK2 or MYPT1 in smooth muscles was not changed, the expression of CPI-17, the functional protein involved in smooth muscle Ca2+ -sensitization, was significantly decreased in the DSS-treated mouse colon. These results suggest that the suppression of carbachol-induced contraction in mice with colitis is attributable at least partially to the increased activity of myosin phosphatase following the downregulation of CPI-17.

Hyperoxic conditions inhibit airway smooth muscle myosin phosphatase in rat pups

Exposure of rat pups to 100% oxygen is a model for studying neonatal lung injury. Airway reactivity is increased in this model, in part due to impaired airway smooth muscle (ASM) relaxation. We compared biochemical determinants of ASM contractility in rat pups exposed to 100% oxygen for 7 days vs. littermates raised in room air. The baseline quantities of ASM contractile proteins, extent of phosphorylation of the 20-kDa myosin regulatory light chain (LC20), and amount of the myosin-binding subunit of smooth muscle myosin phosphatase (MYPT) were all comparable between the two groups. Bethanechol-induced contraction increased the extent of phosphorylation of both LC20 and MYPT in the hyperoxic group (45% and 70% over control, respectively). Relaxation after electrical field stimulation demonstrated greater phosphorylation of both LC20 and MYPT in the hyperoxic group compared with controls (67% and 84%, respectively). To determine if hyperoxia induced changes in the isoforms of MYPT, isoform expression was also compared but differences were not found. To determine potential mechanisms whereby MYPT phosphorylation was increased by hyperoxia, separate tracheas were treated with the Rho kinase inhibitor Y-27632. This treatment completely eliminated differences in MYPT phosphorylation between the groups. Because phosphorylation of MYPT impairs the phosphatase activity of myosin phosphatase, these data suggest that hyperoxic conditioning during early postnatal life impairs relaxation through prolonging LC20 phosphorylation. This mechanism might contribute to increased ASM reactivity seen in bronchopulmonary dysplasia.

Linalyl acetate as a major ingredient of lavender essential oil relaxes the rabbit vascular smooth muscle through dephosphorylation of myosin light chain

In a preliminary experiment, we found that lavender essential oil relaxes vascular smooth muscle. Thus, the present experiments were designed to investigate the relaxation mechanism of linalyl acetate as the major ingredient of lavender essential oil in rabbit carotid artery specimens. Linalyl acetate produced sustained and progressive relaxation during the contraction caused by phenylephrine. The relaxation effect of linalyl acetate at a concentration near the EC50 was partially but significantly attenuated by nitroarginine as an inhibitor of nitric oxide synthase, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one as an inhibitor of guanylyl cyclase, or by the denudation of endothelial cells. In specimens without endothelium, the phenylephrine-induced contraction and phosphorylation of myosin light chain (MLC) were significantly attenuated after the pretreatment with linalyl acetate. The relaxation caused by linalyl acetate in the endothelium-denuded specimens was clearly inhibited by calyculin A as an inhibitor of MLC phosphatase, although not by ML-9 as an inhibitor of MLC kinase. Furthermore, suppression of the phenylephrine-induced contraction and MLC phosphorylation with linalyl acetate was canceled by the pretreatment with calyculin A. These results suggest that linalyl acetate relaxes the vascular smooth muscle through partially activation of nitric oxide/cyclic guanosine monophosphate pathway, and partially MLC dephosphorylation via activating MLC phosphatase.

Intestinal dysmotility in inflammatory bowel disease: mechanisms of the reduced activity of smooth muscle contraction

Inflammation suppresses intestinal motility, which secondarily induces abnormal growth of intestinal flora. Disturbance of this flora plays a role in the pathogenesis of mucosal inflammation, which in turn aggravates the intestinal dysmotility. Therefore, it is important to know the mechanism of alteration in motor function in the inflamed intestine. Recent studies have shown molecular mechanisms responsible for the motility disorder in the inflamed gut. These include an increase in the activity of myosin light-chain phosphatase and an alteration of ion channel activity in smooth muscle cells.

Differences in the gestational pattern of mRNA expression of the Rnd family in rat and human myometria

Uterine myometrial contractility remains a poorly characterized area of research in reproductive physiology. Rnd1, a novel member of the GTP-binding Rho protein family, inhibits Ca(2+)-sensitization by specifically interfering with a RhoA/Rho-activated kinases-dependent mechanism in smooth muscle. In addition to Rnd1, there are two other members, Rnd2 and Rnd3, in the Rnd family of Rho proteins. In the present comparative study of myometrial contractility in rats and humans, we found that all three Rnd mRNAs were expressed in nonpregnant rat myometrium and in nonpregnant human myometrial tissues. Although all three mRNA levels increased significantly after gestation in rat myometria, only Rnd1 expression was significantly greater after gestation in human samples. In the ovariectomized rat, administration of estrogen and/or progesterone increased the expression of all Rnd mRNAs. These results suggest that universal Rnd family up-regulation during pregnancy in rats may have an important role for negative-feedback control of uterine contraction during gestation by inhibiting RhoA-mediated increase in Ca(2+) sensitivity of contractile elements. Such increases in Rnd levels may be due to augmented levels of reproductive steroids in rats. Our data also point to gestational differences between rats and humans in Rnd isoform patterns.

Possible involvement of CPI-17 in augmented bronchial smooth muscle contraction in antigen-induced airway hyper-responsive rats

Airway hyper-responsiveness (AHR) associated with heightened airway resistance and inflammation is a characteristic feature of asthma. It has been demonstrated that contractile responsiveness and Ca(2+) sensitization to acetylcholine (ACh) in repeated antigen challenge-induced airway hyper-responsive bronchial preparation were significantly increased. The CPI-17 (PKC-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) is activated by protein kinase C and acts on a myosin light-chain phosphatase-specific target. The aim of the present study was to explore the role of CPI-17 in hyper-responsiveness of bronchial smooth muscle in antigen-induced AHR rats. In immunoblotting, the levels of expression of CPI-17 mRNA and protein were significantly increased in bronchus from rats that were repeatedly challenged with antigen. ACh-induced CPI-17 phosphorylation and translocation to membrane fraction were also significantly increased in bronchus from antigen-challenged rats. In conclusion, we suggest that augmented expression and activation of CPI-17 observed in the hyper-responsive bronchial smooth muscle might be responsible for the enhanced ACh-induced Ca(2+) sensitization of bronchial smooth muscle contraction associated with AHR.

Regulation of smooth muscle calcium sensitivity: KCl as a calcium-sensitizing stimulus

KCl has long been used as a convenient stimulus to bypass G protein-coupled receptors (GPCR) and activate smooth muscle by a highly reproducible and relatively “simple” mechanism involving activation of voltage-operated Ca2+channels that leads to increases in cytosolic free Ca2+([Ca2+]i), Ca2+-calmodulin-dependent myosin light chain (MLC) kinase activation, MLC phosphorylation and contraction. This KCl-induced stimulus-response coupling mechanism is a standard tool-set used in comparative studies to explore more complex mechanisms generated by activation of GPCRs. One area where this approach has been especially productive is in studies designed to understand Ca2+sensitization, the relationship between [Ca2+]iand force produced by GPCR agonists. Studies done in the late 1980s demonstrated that a unique relationship between stimulus-induced [Ca2+]iand force does not exist: for a given increase in [Ca2+]i, GPCR activation can produce greater force than KCl, and relaxant agents can produce the opposite effect to cause Ca2+desensitization. Such changes in Ca2+sensitivity are now known to involve multiple cell signaling strategies, including translocation of proteins from cytosol to plasma membrane, and activation of enzymes, including RhoA kinase and protein kinase C. However, recent studies show that KCl can also cause Ca2+sensitization involving translocation and activation of RhoA kinase. Rather than complicating the Ca2+sensitivity story, this surprising finding is already providing novel insights into mechanisms regulating Ca2+sensitivity of smooth muscle contraction. KCl as a “simple” stimulus promises to remain a standard tool for smooth muscle cell physiologists, whose focus is to understand mechanisms regulating Ca2+sensitivity.

Inhibition of Rho-Kinase by Hydroxyfasudil Prevents Vasopressin-Induced Myocardial Ischemia in Donryu Rats by Attenuating Coronary Vasoconstriction

BACKGROUND

Inhibition of rho-kinase has been shown to attenuate vasopressin (AVP)-induced myocardial ischemia measured as S-wave depression in Donryu rats. This has been attributed to a direct inhibitory effect on AVP-induced coronary vasoconstriction. However, since AVP also increased mean arterial blood pressure (MAP) which was attenuated by the rho-kinase inhibitors used, the prevention of myocardial ischemia could have been due to effects on afterload.

RESULTS

The purpose of this study was to determine if rho-kinase inhibition prevents S-wave depression independent of the effects on blood pressure. In anesthetized Donryu rats (200-340 g), infusion of AVP (0.1 IU/kg) resulted in a sustained increase in MAP (DeltaMAP=46+/-7 mm Hg) and a transient S-wave depression (-90+/-20 microV). Infusion of phenylephrine titrated to achieve a comparable pressor response (DeltaMAP=52+/-2 mm Hg) resulted in a significantly smaller S-wave depression (-30+/-20 microV). Pretreatment with the rho-kinase inhibitor, hydroxyfasudil (3 mg/kg), decreased MAP by -28+/-2 mm Hg and significantly attenuated AVP-induced S-wave depression (-10+/-10 microV) compared to AVP. When rats were pretreated with phenylephrine titrated to maintain MAP, hydroxyfasudil still significantly attenuated AVP-induced S-wave depression (-14+/-12 microV). Hydralazine (1 mg/kg), which lowered MAP by -36+/-5 mm Hg, had no significant effect on AVP-induced S-wave depression (-105+/-32 microV).

CONCLUSION

These data indicate that inhibition of rho-kinase with hydroxyfasudil attenuates AVP-induced myocardial ischemia independent of changes in MAP and are consistent with an inhibitory effect on coronary vasoconstriction.

Mechanism of human urotensin II-induced contraction in rat aorta

Urotensin II induced sustained contraction with an EC(50) value of 2.29 +/- 0.12 nM in rat aorta. Urotensin II (100 nM) transiently increased cytosolic Ca(2+) level ([Ca(2+)](i)), followed by a small sustained phase superimposed with rhythmic oscillatory change. In the presence of verapamil and La(3+), the [Ca(2+)](i) oscillation was completely inhibited, although a small transient increase in [Ca(2+)](i) remained. The urotensin II-induced contraction was also partially inhibited by verapamil and La(3+). Combined application of verapamil, La(3+), and thapsigargin completely inhibited the increase in [Ca(2+)](i) with only partial inhibition of the contraction elicited by urotensin II. Urotensin II increased myosin light chain (MLC) phosphorylation to a level greater than that induced by 72.7 mM KCl (high K(+)). Pretreatment with Go6983 (PKC inhibitor), U0126 (MEK inhibitor), or SB203580 (p38MARK inhibitor) partially inhibited the urotensin II-induced contraction with no effects on the high K(+)-induced contractions. Wortmannin (MLC kinase inhibitor) only partially inhibited urotensin II-induced contraction, although it completely inhibited the high K(+)-induced contraction. These results suggest that urotensin II-induced contraction is mediated by the Ca(2+)/calmodulin/MLC kinase system and modulated by the Ca(2+) sensitization mechanisms to increase MLC phosphorylation. In addition, activations of PKC, p38MAPK, and ERK1/2 modulate the contractility mediated by urotensin II in rat aorta.

Transduction of the N-Terminal Fragments of MYPT1 Enhances Myofilament Ca2+Sensitivity in an Intact Coronary Artery

OBJECTIVE

The region of the 110 kDa regulatory subunit (MYPT1) of smooth muscle myosin phosphatase involved in the regulation of contraction was determined under physiological conditions.

METHODS AND RESULTS

Using HIV Tat protein-mediated protein transduction, the N-terminal fragments of MYPT1 were introduced to the intact porcine coronary arterial strips. Pre-incubation with 3 micromol/L TAT-MYPT1(1-374), a construct containing the Tat peptide and the residues 1 to 374 of MYPT1, for 15 minutes augmented (2.4-fold) the subsequent contraction induced by adding 1.25 mmol/L of extracellular Ca2+ under 118 mmol/L K+ depolarization, with no augmentation of the [Ca2+]i elevation. The deletion of the Tat peptide, MYPT1(1-374), abolished the augmenting effect. TAT-MYPT1(1-296) demonstrated a weaker but significant augmentation (1.7-fold). However, TAT-MYPT1(1-171), TAT-MYPT1(39-374), TAT-MYPT1(39-296), and TAT-MYPT1(297-374) had no augmenting activity. The myosin light chain phosphorylation level as a function of extracellular Ca2+ concentrations was shifted to the left in the strips pretreated with TAT-MYPT1(1-374) compared with the control.

CONCLUSIONS

Region 1 to 296 was the minimal region involved in the enhancement of contraction, and region 297 to 374 played a supplemental role. These results suggested that the interaction mainly between catalytic subunit and MYPT1 play a critical role in the regulation of the endogenous myosin phosphatase in intact smooth muscle.

Sphingosine-1-phosphate stimulates contraction of human airway smooth muscle cells

The bioactive sphingolipid sphingosine-1-phosphate (S1P) that is increased in airways of asthmatic subjects markedly induced contraction of human airway smooth muscle (HASM) cells embedded in collagen matrices in a Gi-independent manner. Dihydro-S1P, which binds to S1P receptors, also stimulated contractility. S1P induced formation of stress fibers, contraction of individual HASM cells, and stimulated myosin light chain phosphorylation, which was inhibited by the Rho-associated kinase inhibitor Y-27632. S1P-stimulated HASM cell contractility was independent of the ERK1/2 and PKC signaling pathways, important regulators of airway smooth muscle contraction. However, removal of extracellular calcium completely blocked S1P-mediated contraction and Y-27632 reduced it. S1P also induced calcium mobilization that was not desensitized by repeated additions. Pretreatment with thapsigargin to deplete InsP3-sensitive calcium stores partially blocked increases in [Ca2+]i induced by S1P, yet did not inhibit S1P-stimulated contraction. In sharp contrast, the L-type calcium channel blocker verapamil markedly decreased S1P-induced HASM cell contraction, supporting a role for calcium influx from extracellular sources. Collectively, our results suggest that S1P may regulate HASM contractility, important in the pathobiology of asthma.

Up-regulation of Rnd1 during pregnancy serves as a negative-feedback control for Ca2+ sensitization of contractile elements in rat myometrium

We investigated the role of Rnd1, a member of the small GTP-binding Rho protein family, in the change in Ca(2+) sensitivity of contractile element in rat myometrium at estrus, gestation, and postpartum stages. In the permeabilized muscles, GTPgammaS or carbachol with GTP increased Ca(2+) sensitivity of contractile force in non-pregnant myometrium at the estrus stage, whereas these stimuli were ineffective in pregnant myometrium at day 21. After postpartum, the reduced Ca(2+) sensitization was recovered. Semi-quantitative RT-PCR analysis indicated that the expressions of RhoA, ROCKI, and ROCKII were not significantly different between non-pregnant and pregnant myometria. In contrast, the expression of Rnd1 was increased during the course of pregnancy, reaching a maximal at day 21, and rapidly declined after the delivery. On the other hand, Ca(2+) sensitization of contractile elements was decreased during the progress in gestation. These results suggest that Rnd1 may have an important role as a negative-feedback control of uterine contraction during gestation through the inhibition of RhoA-mediated increase in the Ca(2+) sensitivity of contractile elements.

Possible role of the protein kinase C/CPI-17 pathway in the augmented contraction of human myometrium after gestation

1. Activation of protein kinase C (PKC) by phorbol 12,13-dibutylate (PDBu, 1 microm) induced sustained contractions with no increase in [Ca2+]i in nonpregnant and pregnant human myometria. The contractile effects of PDBu in pregnant myometrium were much greater than those in nonpregnant myometrium, and the contractions in pregnant myometrium were accompanied by an increase in myosin light chain (MLC) phosphorylation at Ser19. 2. The contraction induced by PDBu in pregnant myometrium was inhibited by the inhibitors of conventional PKC isoforms, bisindolylmaleimides and indolocarbazole, such as Go6976, Go6983, and Go6850 (1 microM). LY333531 (1 microM), a specific inhibitor of PKC beta, also inhibited the PDBu-induced contraction in the pregnant myometrium. 3. In the pregnant myometrium permeabilized with alpha-toxin, PDBu increased the contractions induced at fixed Ca2+ concentration (0.3 microM) both in nonpregnant and pregnant myometria, indicating Ca2+ sensitization of contractile elements. 4. Western immunoblot analysis indicated that pregnant myometrium contained PKC isozymes such as conventional PKC (alpha, beta, gamma), novel PKC (delta, epsilon, theta), and atypical PKC (zeta but not iota and lambda). RT-PCR and real-time RT-PCR analysis indicated that, among the conventional PKC, the levels of mRNA of beta isoform in pregnant human myometrium were greater than those in nonpregnant myometrium. 5. CPI-17 is a substrate for PKC, and the phosphorylated CPI-17 is considered to inhibit myosin phosphatase. The levels of CPI-17 mRNA and protein expression were also greater in the pregnant myometrium. 6. These results suggest that the PKC-mediated contractile mechanism is augmented in human myometrium after gestation, and that this augmentation may be attributable to the increased activity of the beta PKC isoform and CPI-17.

Chronic treatment with interleukin-1beta attenuates contractions by decreasing the activities of CPI-17 and MYPT-1 in intestinal smooth muscle

Interleukin-1beta (IL-1beta) is a proinflammatory cytokine that plays a central role in inflammatory bowel disease (IBD). In order to elucidate the mechanism of motility disorders frequently observed in IBD, we investigated the long term effects of IL-1beta on rat ileal smooth muscle contractility by using an organ culture system. When ileal smooth muscle strips were cultured with IL-1beta (10 ng/ml), contractions elicited by high K+ and carbachol were inhibited in a time-dependent manner. IL-1beta more strongly inhibited the carbachol-induced contractions than high K+ with decreasing myosin light chain phosphorylation. In the alpha-toxin-permeabilized ileal muscle, carbachol with GTP or guanosine 5'-3-O-(thio)triphosphate increased the Ca2+ sensitivity of contractile elements, and this G protein-coupled Ca2+ sensitization was significantly reduced in the IL-1beta-treated ileum. Among the functional proteins involved in the smooth muscle Ca2+ sensitization, CPI-17 expression was significantly reduced after the culture with IL-1beta, whereas the expressions of RhoA, ROCK-I, ROCK-II, MYPT-1, myosin light chain kinase, and myosin phosphatase (PP1) were unchanged. The phosphorylation level of CPI-17 by carbachol was low in accordance with the decrease in CPI-17 expression due to IL-1beta treatment. In contrast, constitutively phosphorylated MYPT-1 was also decreased in the IL-1beta-treated muscles. These results suggest that long term treatment with IL-1beta decreases either CPI-17 expression or MYPT-1 phosphorylation, which may result in an increase in myosin phosphatase activity to reduce force generation. Based on these findings, we consider IL-1beta to be an important mediator of gastrointestinal motility disorders in IBD, and CPI-17 and MYPT-1 are key molecules in the decreased smooth muscle contractility due to IL-1beta.

Receptor-independent activation of Rho-kinase-mediated calcium sensitisation in smooth muscle

1. The aim of this work was to determine whether Rho-kinase-mediated calcium sensitisation contributes to contractions of the mouse anococcygeus smooth muscle and, if so, whether the process was activated by receptor-dependent or receptor-independent mechanisms. 2. The Rho-kinase inhibitor Y27632 produced concentration-dependent decreases in tone raised by either the muscarinic receptor agonist carbachol (CCh), or the sarco-endoplasmic reticulum calcium ATPase inhibitor thapsigargin (Tg) (EC(50) values against CCh and Tg of 8.4+/-3.3 (n=6) and 6.1+/-2.1 (n=7) micro M, respectively). Pretreatment of tissues with Y27632 also inhibited contractions produced by 65 mM external potassium (69+/-7% (n=4) inhibition using 10 micro M Y27632). Y27632 had no effect on contractions produced by the inhibitor of smooth muscle myosin light-chain phosphatase, calyculin-A. 3. In beta-escin-permeabilised preparations, both CCh and Tg produced significant increases in tone over-and-above that produced by a combination of calcium (1 micro M) and GTP (100 micro M). These responses to CCh and Tg were inhibited by Y27632 (10 micro M). 4. Western blot analysis of fractionated tissue samples probed for RhoA immunoreactivity, indicated that both CCh and Tg were able to induce translocation of RhoA from the cytosol to the membrane. 5. These findings suggest that Rho-kinase-mediated calcium sensitisation is activated by both receptor-dependent and receptor-independent mechanisms in the mouse anococcygeus.

Involvement of Rho-kinase in contraction of guinea-pig aorta induced by prostanoid EP3 receptor agonists

1. The mechanism of contraction of guinea-pig isolated aorta induced by the prostanoid EP(3) receptor agonist sulprostone (0.1-300 nM) has been investigated. In 60% of the experiments, the sulprostone log concentration-response curve (maximum=15-40% of 100 nM U-46619 response; low-responders) was unaffected by the removal of extracellular Ca(2+), blockade of L-type Ca(2+) channels with nifedipine and depletion of internal Ca(2+) stores. In the remaining preparations (35-65% of 100 nM U-46619 response; high-responders), contractions to higher sulprostone concentrations showed a nifedipine-sensitive component, which was enhanced by charybdotoxin. 2. In Ca(2+)-free Krebs solution, established contractions to 300 nM sulprostone were abolished by the Rho-kinase inhibitors H-1152, Y-27632 and HA-1077 (IC(50) values=190, 770 and 2030 nM). The PKA/Rho-kinase inhibitor H-89 (10 nM-10 micro M) caused enhancement progressing to inhibition. The selective PKC inhibitor Ro 32-0432 (3 micro M) had no effect, while staurosporine, recently shown to be a potent Rho-kinase inhibitor, abolished sulprostone responses (IC(50) approximately 47 nM), but its action was slow. The MAP kinase inhibitors SB 202190, SB 203580 and PD 80958 produced little inhibition. 3. In normal Krebs solution, H-1152 and Y-27632 abolished established contractions to 300 nM sulprostone and 1 micro M phenylephrine, and partially inhibited 10 micro M phenylephrine and 50 mM K(+) responses. 4. The results are discussed in relation to the reported potencies of the protein kinase inhibitors in enzyme assays. Activation of the Rho-kinase pathway appears to be a primary mechanism of contraction induced by EP(3) receptor agonists in guinea-pig aorta.

Inhibition of high K+-induced contraction by the ROCKs inhibitor Y-27632 in vascular smooth muscle: possible involvement of ROCKs in a signal transduction pathway

In the isolated rat aorta, a ROCKs (rhoA-dependent coiled coil serine/threonine kinases) inhibitor, Y-27632, inhibited the contractions induced not only by receptor agonists but also by high K(+) with the similar IC(50) values (0.8 - 4.9 microM). However, Y-27632 did not inhibit the increment of cytosolic Ca(2+) concentration ([Ca(2+)](i)) due to these stimulants. The Y-27632-induced inhibition of contraction was accompanied by an inhibition of myocin light chain (MLC) phosphorylation, although inhibition of contraction was stronger than that of MLC phosphorylation during the initial phase of contraction. Y-27632 had no effect on the myocin light chain kinase (MLCK) activity. This inhibitor also did not directly change the phosphatase activity. These results suggest that Y-27632 is a selective inhibitor of ROCKs with no direct inhibitory effect on [Ca(2+)](i), calmodulin, MLCK, or phosphatase. Y-27632 disrupted the actin filament network and decreased the filamentous actin, implying that the stronger inhibition by Y-27632 on early phase of contraction than MLC phosphorylation may be explained by this effect. These results suggest that the high K(+)-induced MLC phosphorylation and contraction are mediated not only by the classical Ca(2+)/calmodulin-dependent MLCK system but also by a novel MLC phosphorylation pathway involving ROCKs. One of the possibilities is that high K(+) activates ROCKs to inhibit myosin phosphatase resulting in an augmentation of MLC phosphorylation and contraction.

RhoA kinase and protein kinase C participate in regulation of rabbit stomach fundus smooth muscle contraction

1. The degree to which the RhoA kinase (ROK) blockers, Y-27632 (1 micro M) and HA-1077 (10 micro M), and the PKC blocker, GF-109203X (1 micro M), reduced force produced by carbachol, a muscarinic receptor agonist, and phenylephrine, an alpha-adrenoceptor agonist, was examined in rabbit stomach fundus smooth muscle. 2. When examining the effect on cumulative carbachol concentration-response curves (CRCs), ROK and PKC blockers shifted the potency EC50 to the right but did not reduce the maximum response. 3. In a single-dose carbachol protocol using moderate ( approximately EC50 and maximum carbachol concentrations, Y-27632 and HA-1077 reduced peak force, but GF-109203X had no effect. By contrast, all three agents inhibited the carbachol contractions of rabbit bladder (detrusor) smooth muscle. 4. Compared to carbachol, phenylephrine produced a weaker maximum response that was not inhibited by phentolamine, atropine nor capsaicin but was inhibited by Y-27632, HA-1077 and GF-109203X. 5. In detrusor, classical down-regulation occurred, but in fundus, up-regulation of responsiveness occurred. This up-regulation in fundus may have been a post-receptor event, because a KCl-induced contraction produced after a carbachol CRC was stronger than one produced before the carbachol stimulus. 6. In conclusion, these data suggest that ROK plays a critical role in the regulation of rabbit fundus smooth muscle contraction, which is distinct from chicken gizzard smooth muscle, where ROK is reported to exist but to not play a role in muscarinic receptor-induced contraction. Additional unique findings are that PKC participates in phenylephrine- but not carbachol-induced contraction in fundus, that carbachol does not activate identical subcellular signalling systems in fundus and detrusor, and that fundus, unlike detrusor, responds to carbachol stimulation with post-receptor up-regulation of contraction.

Effects of Rho-kinase inhibitor on vasopressin-induced chronic myocardial damage in rats

The aim of this study was to develop a new model of vasopressin-induced chronic myocardial damage based on sustained ST-segment depression in electrocardiogram (ECG) with progression of myocardial fibrosis in rats. Furthermore, using this model, we examined the prophylactic potential of fasudil, a Rho-kinase inhibitor, against myocardial damage induced by vasopressin. In 10-week old male Donryu rats, intravenous administration of arginine vasopressin (0.5 iu/kg) induced significant ST-segment depression. Two days and one week after the administration of vasopressin, ST-segment depression was -0.19 +/- 0.02 and -0.14 +/- 0.02 mV, respectively. Fasudil (10 and 30 mg/kg, p.o.) significantly attenuated the ST-segment depression induced by vasopressin. One week after the administration of vasopressin, the percent area of myocardial fibrosis in control animals (0.42 +/- 0.11%, p < 0.01) was significantly greater than that in normal animals (0.05 +/- 0.01%). Fasudil (10 and 30 mg/kg) significantly prevented the development of the fibrosis. We present a new model of chronic myocardial damage based on sustained ST-segment depression with progression of myocardial fibrosis in rats, and suggest that this model may be useful to investigate the treatment of chronic angina. Inhibition of Rho-kinase is efficacious in preventing the ECG change and development of fibrosis induced by vasopressin in this model.

Increased activity of calcium channels and Rho-associated kinase in the basilar artery during chronic hypertension in vivo

OBJECTIVES

Several factors mediating vascular responses appear to play an important role in the increased resistance of cerebral blood vessels during hypertension. The objective of this study was to elucidate the mechanisms by which hypertension increases the basal tone of the basilar artery in vivo.

METHODS

Using a cranial window, we examined effects of inhibitors of L-type voltage-dependent calcium channels (nicardipine) and Rho-associated kinase (Y-27632) on the baseline diameter of the basilar artery in spontaneously hypertensive rats (SHR) and compared to the responses in normotensive Wistar-Kyoto (WKY) rats.

RESULTS

Topical application of nicardipine (10(-8), 10(-7) and 10(-6) mol/l) produced dilatation of the basilar artery. Nicardipine-induced vasodilatation was enhanced in SHR compared to WKY rats. Nicardipine (10-6 mol/l) dilated the artery in WKY rats and SHR by 9 +/- 2 and 24 +/- 4%, respectively. Topical application of Y-27632 (10(-7), 10(-6) and 10(-5) mol/l) produced dilatation of the basilar artery in WKY rats in a concentration-related manner. The vasodilatation produced by Y-27632 was markedly enhanced in SHR compared to WKY rats. Y-27632 (10(-5) mol/l) dilated the artery in WKY rats and SHR by 14 +/- 2 and 45 +/- 6%, respectively. We also tested the effects of inhibitors of nitric oxide synthase (NG-nitro-l-arginine methyl ester, l-NAME), ATP-sensitive potassium channels (glibenclamide) and large-conductance calcium-activated potassium channels (tetraetyhlammonium, TEA). l-NAME and, to a lesser extent, glibenclamide produced similar constriction of the basilar artery in both strains. TEA did not affect the baseline diameter of the basilar artery in WKY rats and produced small but significant vasoconstriction in SHR.

CONCLUSIONS

These results suggest that the activity of L-type calcium channels and Rho-associated kinase is enhanced in the basilar artery during hypertensionin vivo. The enhanced contractility may contribute to the increased resistance of the basilar artery during chronic hypertension in vivo.

The nitrone spin trap PBN alters the cellular response to H(2)O(2): activation of the EGF receptor/ERK pathway

The nitrone spin trap PBN has been shown to protect neuronal cells from reactive oxygen species both in culture and in vivo. As an approach to understanding the molecular mechanisms by which PBN may function to protect cells, we examined whether PBN alters the cellular response to reactive oxygen species. H(2)O(2) stimulation of PC-12 cells results in weak activation of both the ERK and JNK signal transduction pathways. PBN pretreatment of PC-12 cells, followed by H(2)O(2) stimulation, results in strong and selective activation of the pro-survival ERK pathway. H(2)O(2) induction of ERK activity in PBN-pretreated cells was shown to be dependent on extracellular Ca(+2) influx. Further analysis of the ERK pathway showed that in PBN-pretreated cells, EGF receptor and the adapter protein SHC were phosphorylated in a Ca(+2)-dependent, ligand-independent manner following H(2)O(2) stimulation. Interestingly, H(2)O(2) stimulation of PBN-pretreated cells results in only 30% of the increase in intracellular Ca(+2) as compared to untreated cells following H(2)O(2) stimulation. These data suggest a model in which PBN attenuates H(2)O(2)-induced Ca(+2) entry, yet magnifies or alters Ca(+2) action, resulting in the activation of the EGF receptor/ERK pathway.

Antianginal effects of hydroxyfasudil, a Rho-kinase inhibitor, in a canine model of effort angina

1. The effects of Rho-kinase inhibitor, fasudil, and of a more specific Rho-kinase inhibitor, hydroxyfasudil, on pacing-induced myocardial ischaemia were determined in anaesthetized open-chest dogs. 2. The dogs were subjected to left anterior descending coronary artery (LAD) stenosis producing a sufficient ischaemia as measured by ST-segment depression on electrocardiograms only when the hearts were paced 60 beats min(-1) above the baseline. After a recovery (nonpacing) period, drugs or saline were infused intravenously over 30 min. The animals were again subjected to 5 min of pacing 25 min after the initiation of the treatment. 3. Hydroxyfasudil (0.1 and 0.3 mg kg(-1)) and fasudil (0.3 mg kg(-1)) suppressed the ST-segment depression. Hydroxyfasudil and fasudil also increased the regional blood flow of the LAD perfused endomyocardium region in the canine model of effort angina. 4. To determine the flow profile for hydroxyfasudil in dogs, blood flow in three vascular beds was measured. Hydroxyfasudil (0.3 mg kg(-1) for 30 min) significantly increased coronary blood flow and vertebral blood flow, without significantly changing the femoral blood flow. 5. Hydroxyfasudil had no inotropic or chronotropic effect on the isolated hearts of guinea-pigs. Hydroxyfasudil (2 mg kg(-1) for 20 min) did not affect the PR or QTc interval in anaesthetized dogs. 6. Inhibition of Rho-kinase appears to protect myocardium subjected to pacing-induced ischaemia through the increase in the regional myocardial blood flow. Hydroxyfasudil may be categorized as a novel type of anti-anginal drug, without any inotropic or chronotropic effects.

Purification of native myosin filaments from muscle

Analysis of the structure and function of native thick (myosin-containing) filaments of muscle has been hampered in the past by the difficulty of obtaining a pure preparation. We have developed a simple method for purifying native myosin filaments from muscle filament suspensions. The method involves severing thin (actin-containing) filaments into short segments using a Ca(2+)-insensitive fragment of gelsolin, followed by differential centrifugation to purify the thick filaments. By gel electrophoresis, the purified thick filaments show myosin heavy and light chains together with nonmyosin thick filament components. Contamination with actin is below 3.5%. Electron microscopy demonstrates intact thick filaments, with helical cross-bridge order preserved, and essentially complete removal of thin filaments. The method has been developed for striated muscles but can also be used in a modified form to remove contaminating thin filaments from native smooth muscle myofibrils. Such preparations should be useful for thick filament structural and biochemical studies.

Dependency of detrusor contractions on calcium sensitization and calcium entry through LOE-908-sensitive channels

1. The subcellular mechanisms regulating stimulus-contraction coupling in detrusor remain to be determined. We used Ca(2+)-free solutions, Ca(2+) channel blockers, cyclopiazonic acid (CPA), and RhoA kinase (ROK) inhibitors to test the hypothesis that Ca(2+) influx and Ca(2+) sensitization play primary roles. 2. In rabbit detrusor, peak bethanechol (BE)-induced force was inhibited 90% by incubation for 3 min in a Ca(2+)-free solution. By comparison, a 20 min incubation of rabbit femoral artery in a Ca(2+)-free solution reduced receptor-induced force by only 5%. 3. In detrusor, inhibition of sarcoplasmic reticular (SR) Ca(2+) release by 2APB, or depletion of SR Ca(2+) by CPA, inhibited BE-induced force by only 27%. The CPA-insensitive force was abolished by LaCl3. By comparison, 2APB inhibited receptor-induced force in rabbit femoral artery by 71%. 4. In the presence of the non-selective cation channel (NSCC) inhibitor, LOE-908, BE did not produce an increase in [Ca(2+)]i but did produce weak increases in myosin phosphorylation and force. 5. Inhibitors of ROK-induced Ca(2+) sensitization, HA-1077 and Y-27632, inhibited BE-induced force by approximately 50%, and in combination with LOE-908, nearly abolished force. 6. These data suggest that two principal muscarinic receptor-stimulated detrusor contractile mechanisms include NSCC activation, that elevates [Ca(2+)]i and ROK activation, that sensitizes cross bridges to Ca(2+).

Cross talk between cyclic nucleotides and polyphosphoinositide hydrolysis, protein kinases, and contraction in smooth muscle

This article provides an update of a minireview published in 1996 (Abdel-Latif AA. Proc Soc Exp Biol Med 211:163-177, 1996), the purpose of which was to examine in nonvascular smooth muscle the biochemical and functional cross talk between the sympathetic nervous system, which governs the formation of cAMP and muscle relaxation, and the parasympathetic nervous system, which governs the generation of IP3 and diacylglycerol, from the polyphosphoinositides, Ca2+ mobilization, and contraction. This review examines further evidence, both from nonvascular and vascular smooth muscle, for cross talk between the cyclic nucleotides, cAMP and cGMP via their respective protein kinases, and the Ca2+-dependent- and Ca2+-independent-signaling pathways involved in agonist-induced contraction. These include the IP3-Ca2+-CaM- myosin light chain kinase (MLCK) pathway and the Ca2+-independent pathways, including protein kinase C-, MAP kinase-, and Rho-kinase. In addition, MLC phosphorylation and contraction can also be increased by a decrease in myosin phosphatase activity. A summary of the cross talk between the cyclic nucleotides and these signaling pathways was presented. In smooth muscle, there are several targets for cyclic nucleotide inhibition and consequent relaxation, including the receptor, G proteins, phospholipase C-beta1-4 isoforms, IP3 receptor, Ca2+ mobilization, MLCK, MAP kinase, Rho-kinase, and myosin phosphatase. While significant progress has been made in the past four years on this cross talk, the precise mechanisms underlying the biochemical basis for the cyclic nucleotide inhibition of Ca2+ mobilization and consequently muscle contraction remain to be established. Although it is well established that second-messenger cross talk plays an important role in smooth muscle relaxation, the many sources which exist in smooth muscle for Ca2+ mobilization, coupled with the multiple signaling pathways involved in agonist-induced contraction, contribute appreciably to the difficulties found by many investigators in identifying the targets for cyclic nucleotide inhibition and consequent relaxation. Better methodology and more novel interdisciplinary approaches are required for elucidating the mechanism(s) of cAMP- and cGMP-inhibition of smooth muscle contraction.