Smooth muscle contraction and relaxation

Mechanisms underlying vasorelaxation induced in rat aorta by galetin 3,6-dimethyl ether, a flavonoid from Piptadenia stipulacea (Benth.) Ducke

In this study, we investigated the relaxant action of galetin 3,6-dimethyl ether (FGAL) on rat aorta. The flavonoid relaxed both PMA‑ and phenylephrine (Phe)-induced contractions (pD₂ = 5.36 ± 0.11 and 4.17 ± 0.10, respectively), suggesting the involvement of PKC and Phe pathways or α₁ adrenergic receptor blockade. FGAL inhibited and rightward shifted Phe-induced cumulative concentration‑response curves, indicating a noncompetitive antagonism of α₁ adrenergic receptors. The flavonoid was more potent in relaxing 30 mM KCl- than 80 mM KCl-induced contractions (pD₂ = 5.50 ± 0.22 and 4.37 ± 0.12). The vasorelaxant potency of FGAL on Phe-induced contraction was reduced in the presence of 10 mM TEA⁺. Furthermore, in the presence of apamin, glibenclamide, BaCl₂ or 4-AP, FGAL-induced relaxation was attenuated, indicating the participation of small conductance calcium-activated K⁺ channels (SK_Ca), ATP-sensitive K⁺ channels (K_ATP), inward rectifier K⁺ channels (K_ir) and voltage-dependent K⁺ channels (K_V), respectively. FGAL inhibited and rightward shifted CaCl₂-induced cumulative concentration-response curves in both depolarizing medium (high K⁺) and in the presence of verapamil and phenylephrine, suggesting inhibition of Ca²⁺ influx through voltage-gated calcium channels (Ca_V) and receptor operated channels (ROCs), respectively. Likewise, FGAL inhibited Phe-induced contractions in Ca²⁺-free medium, indicating inhibition of Ca²⁺ release from the sarcoplasmic reticulum (SR). FGAL potentiated the relaxant effect of aminophylline and sildenafil but not milrinone, suggesting the involvement of phosphodiesterase V (PDE V). Thus, the FGAL vasorelaxant mechanism involves noncompetitive antagonism of α₁ adrenergic receptors, the non-selective opening of K⁺ channels, inhibition of Ca²⁺ influx through Ca_V or ROCs and the inhibition of intracellular Ca²⁺ release. Additionally, there is the involvement of cyclic nucleotide pathway, particularly through PDE V inhibition.

A novel method for differentiation of human mesenchymal stem cells into smooth muscle-like cells on clinically deliverable thermally induced phase separation microspheres

Muscle degeneration is a prevalent disease, particularly in aging societies where it has a huge impact on quality of life and incurs colossal health costs. Suitable donor sources of smooth muscle cells are limited and minimally invasive therapeutic approaches are sought that will augment muscle volume by delivering cells to damaged or degenerated areas of muscle. For the first time, we report the use of highly porous microcarriers produced using thermally induced phase separation (TIPS) to expand and differentiate adipose-derived mesenchymal stem cells (AdMSCs) into smooth muscle-like cells in a format that requires minimal manipulation before clinical delivery. AdMSCs readily attached to the surface of TIPS microcarriers and proliferated while maintained in suspension culture for 12 days. Switching the incubation medium to a differentiation medium containing 2 ng/mL transforming growth factor beta-1 resulted in a significant increase in both the mRNA and protein expression of cell contractile apparatus components caldesmon, calponin, and myosin heavy chains, indicative of a smooth muscle cell-like phenotype. Growth of smooth muscle cells on the surface of the microcarriers caused no change to the integrity of the polymer microspheres making them suitable for a cell-delivery vehicle. Our results indicate that TIPS microspheres provide an ideal substrate for the expansion and differentiation of AdMSCs into smooth muscle-like cells as well as a microcarrier delivery vehicle for the attached cells ready for therapeutic applications.

The contractile strength of vascular smooth muscle myocytes is shape dependent

Vascular smooth muscle cells in muscular arteries are more elongated than those in elastic arteries. Previously, we reported changes in the contractility of engineered vascular smooth muscle tissue that appeared to be correlated with the shape of the constituent cells, supporting the commonly held belief that elongated muscle geometry may allow for the better contractile tone modulation required in response to changes in blood flow and pressure. To test this hypothesis more rigorously, we developed an in vitro model by engineering human vascular smooth muscle cells to take on the same shapes as those seen in elastic and muscular arteries and measured their contraction during stimulation with endothelin-1. We found that in the engineered cells, actin alignment and nuclear eccentricity increased as the shape of the cell elongated. Smooth muscle cells with elongated shapes exhibited lower contractile strength but greater percentage increase in contraction after endothelin-1 stimulation. We analysed the relationship between smooth muscle contractility and subcellular architecture and found that changes in contractility were correlated with actin alignment and nuclear shape. These results suggest that elongated smooth muscle cells facilitate muscular artery tone modulation by increasing its dynamic contractile range.

Relaxant effect of flavonoid naringenin on contractile activity of rat colonic smooth muscle

ETHNOPHARMACOLOGICAL RELEVANCE

Disturbed gastrointestinal (GI) motility can be associated with smooth muscle abnormalities and dysfunction. Exploring innovative approaches that can modulate the disturbed colonic motility are of great importance for clinical therapeutics. Naringenin, a flavonoid presented in many traditional Chinese herbal medicines, has been shown to have a relaxant effect on different smooth muscles. The aim of the present study was to investigate the effect of naringenin on regulation of GI motility.

MATERIAL AND METHODS

Mechanical recording was used to investigate the effect of naringenin on isolated rat colonic smooth muscle spontaneous contractions. Whole cell patch clamp, intracellular [Ca(2+)] concentration ([Ca(2+)]i) and membrane potential measurements were examined on primary cultures of colonic smooth muscle cells (SMCs). A neostigmine-stimulated rat model was utilized to investigate the effect of naringenin in vivo.

RESULTS

Naringenin induced a concentration-dependent inhibition (1-1000 μM) on rat colonic spontaneous contraction, which was reversible after wash out. The external Ca(2+) influx induced contraction and [Ca(2+)]i increase were inhibited by naringenin (100 μM). In rat colonic SMCs, naringenin-induced membrane potential hyperpolarization was sensitive to TEA and selective large-conductance calcium-activated K(+) (BKCa) channel inhibitor iberiotoxin. Under whole cell patch-clamp condition, naringenin stimulated an iberiotoxin-sensitive BKCa current, which was insensitive to changes in the [Ca(2+)]i concentration. Furthermore, naringenin significantly suppressed neostigmine-enhanced rat colon transit in vivo.

CONCLUSION

Our results for the first time demonstrated the relaxant effect of flavonoid naringenin on colon smooth muscle both in vitro and in vivo. The relaxant effect of naringenin was attributed to direct activation of BKCa channels, which subsequently hyperpolarized the colonic SMCs and decreased Ca(2+) influx through VDCC. Naringenin might be of therapeutic value in the treatment of GI motility disorders.

Metformin exaggerates phenylephrine-induced AMPK phosphorylation independent of CaMKKβ and attenuates contractile response in endothelium-denuded rat aorta

Metformin, a widely prescribed antidiabetic drug, has been shown to reduce the risk of cardiovascular disease, including hypertension. Its beneficial effect toward improved vasodilation results from its ability to activate AMPK and enhance nitric oxide formation in the endothelium. To date, metformin regulation of AMPK has not been fully studied in intact arterial smooth muscle, especially during contraction evoked by G protein-coupled receptor (GPCR) agonists. In the present study, ex vivo incubation of endothelium-denuded rat aortic rings with 3mM metformin for 2h resulted in significant accumulation of metformin (∼ 600 pmoles/mg tissue), as revealed by LC-MS/MS MRM analysis. However, metformin did not show significant increase in AMPK phosphorylation under these conditions. Exposure of aortic rings to a GPCR agonist (e.g., phenylephrine) resulted in enhanced AMPK phosphorylation by ∼ 2.5-fold. Importantly, in metformin-treated aortic rings, phenylephrine challenge showed an exaggerated increase in AMPK phosphorylation by ∼ 9.7-fold, which was associated with an increase in AMP/ATP ratio. Pretreatment with compound C (AMPK inhibitor) prevented AMPK phosphorylation induced by phenylephrine alone and also that induced by phenylephrine after metformin treatment. However, pretreatment with STO-609 (CaMKKβ inhibitor) diminished AMPK phosphorylation induced by phenylephrine alone but not that induced by phenylephrine after metformin treatment. Furthermore, attenuation of phenylephrine-induced contraction (observed after metformin treatment) was prevented by AMPK inhibition but not by CaMKKβ inhibition. Together, these findings suggest that, upon endothelial damage in the vessel wall, metformin uptake by the underlying vascular smooth muscle would accentuate AMPK phosphorylation by GPCR agonists independent of CaMKKβ to promote vasorelaxation.

Characteristics of evodiamine-exerted stimulatory effects on rat jejunal contractility

This study was designed to characterise the effects of evodiamine on intestinal contractility and reveal the correlated mechanisms. Evodiamine (2.5-80.0 μM) increased normal jejunal contractility and jejunal hypocontractility established under a variety of experimental conditions. Evodiamine-exerted stimulatory effects were blocked by the L-type Ca(2+) channel blocker nifedipine or abolished in the Ca(2+)-free assay condition. The stimulatory effects of evodiamine on jejunal contractility were partially blocked in the presence of neurotoxin tetrodotoxin or endogenous acetylcholine synthesis blocker hemicholinium-3 or muscarinic receptor antagonist atropine, respectively. Evodiamine-exerted stimulatory effects were blocked by c-kit receptor tyrosine kinase inhibitor imatinib. Evodiamine increased myosin phosphorylation in jejunal smooth muscle of constipation-prominent rats. These results showed that evodiamine-exerted stimulatory effects on jejunal segments are Ca(2+)-dependent, need the presence of interstitial cell of Cajal, requirement of cholinergic neuron and correlate with increased myosin phosphorylation, implicating the potential value of evodiamine in relieving hypo-motility disorders.

Cardiac, skeletal, and smooth muscle mitochondrial respiration: are all mitochondria created equal?

Unlike cardiac and skeletal muscle, little is known about vascular smooth muscle mitochondrial respiration. Therefore, the present study examined mitochondrial respiratory rates in smooth muscle of healthy human feed arteries and compared with that of healthy cardiac and skeletal muscles. Cardiac, skeletal, and smooth muscles were harvested from a total of 22 subjects (53 ± 6 yr), and mitochondrial respiration was assessed in permeabilized fibers. Complex I + II, state 3 respiration, an index of oxidative phosphorylation capacity, fell progressively from cardiac to skeletal to smooth muscles (54 ± 1, 39 ± 4, and 15 ± 1 pmol·s(-1)·mg(-1), P < 0.05, respectively). Citrate synthase (CS) activity, an index of mitochondrial density, also fell progressively from cardiac to skeletal to smooth muscles (222 ± 13, 115 ± 2, and 48 ± 2 μmol·g(-1)·min(-1), P < 0.05, respectively). Thus, when respiration rates were normalized by CS (respiration per mitochondrial content), oxidative phosphorylation capacity was no longer different between the three muscle types. Interestingly, complex I state 2 normalized for CS activity, an index of nonphosphorylating respiration per mitochondrial content, increased progressively from cardiac to skeletal to smooth muscles, such that the respiratory control ratio, state 3/state 2 respiration, fell progressively from cardiac to skeletal to smooth muscles (5.3 ± 0.7, 3.2 ± 0.4, and 1.6 ± 0.3 pmol·s(-1)·mg(-1), P < 0.05, respectively). Thus, although oxidative phosphorylation capacity per mitochondrial content in cardiac, skeletal, and smooth muscles suggest all mitochondria are created equal, the contrasting respiratory control ratio and nonphosphorylating respiration highlight the existence of intrinsic functional differences between these muscle mitochondria. This likely influences the efficiency of oxidative phosphorylation and could potentially alter ROS production.

Characteristics of nobiletin-induced effects on jejunal contractility

Nobiletin, a citrus polymethoxylated flavone, exhibits multiple biological properties including anti-inflammatory, anti-carcinogenic, and anti-insulin resistance effects. The present study found that nobiletin exerted significant stimulatory effects on the contractility of isolated rat jejunal segments in all 6 different low contractile states, and meanwhile significant inhibitory effects in all 6 different high contractile states, showing characteristics of bidirectional regulation (BR). Nobiletin-exerted BR on jejunal contractility was abolished in the presence of c-kit receptor tyrosine kinase inhibitor imatinib or Ca(2+) channel blocker verapamil. In the presence of neuroxin tetrodotoxin, nobiletin only exerted stimulatory effects on jejunal contractility in both low and high contractile states. Hemicholinium-3 and atropine partially blocked nobiletin-exerted stimulatory effects on jejunal contractility in low-Ca(2+)-induced low contractile state. Phentolamine or propranolol or l-NG-nitro-arginine significantly blocked nobiletin-exerted inhibitory effects on jejunal contractility in high-Ca(2+)-induced high contractile state respectively. The effects of nobiletin on myosin light chain kinase (MLCK) mRNA expression, MLCK protein content, and myosin light chain phosphorylation extent were also bidirectional. In summary, nobiletin-exerted BR depends on the contractile states of rat jejunal segments. Nobiletin-exerted BR requires the enteric nervous system, interstitial cell of Cajal, Ca(2+), and myosin phosphorylation-related mechanisms.

Gene-based association identifies SPATA13-AS1 as a pharmacogenomic predictor of inhaled short-acting beta-agonist response in multiple population groups

Inhaled short-acting beta-agonist (SABA) medication is commonly used in asthma patients to rapidly reverse airway obstruction and improve acute symptoms. We performed a genome wide association study of SABA medication response using gene-based association tests. A linear mixed model approach was first used for SNP associations, and results were later combined using GATES to generate gene-based associations. Our results identified SPATA13-AS1 as being significantly associated with SABA bronchodilator response in 328 healthy African Americans. In replication, this gene was associated with SABA response among 2 separate groups of African Americans with asthma (n=1,073, p=0.011 and n=1,968, p=0.014), 149 healthy African Americans (p=0.003), and 556 European Americans with asthma (p=0.041). SPATA13-AS1 was also associated with longitudinal SABA medication usage in 2 separate groups of African Americans with asthma (n=658, p=0.047 and n=1,968, p=0.025). Future studies are needed to delineate the precise mechanism by which SPATA13-AS1 may influence SABA response.

An active learning mammalian skeletal muscle lab demonstrating contractile and kinetic properties of fast- and slow-twitch muscle

The fact that humans possess fast- and slow-twitch muscle in the ratio of ∼50% has profound implications for designing exercise training strategies for power and endurance activities. With the growth of exercise and sport science courses, we have seen the need to develop an undergraduate student laboratory that demonstrates the basic properties of fast- and slow-twitch mammalian skeletal muscle. This laboratory illustrates the major differences in contractile properties and fatigue profiles exhibited by the two muscle types. Students compare and contrast twitch kinetics, fused tetanus characteristics, force-frequency relationships, and fatigue properties of fast- and slow-twitch muscles. Examples of results collected by students during class are used to illustrate the type of data collected and analysis performed. During the laboratory, students are encouraged to connect factual information from their skeletal muscle lectures to their laboratory findings. This enables student learning in an active fashion; in particular, the isolated muscle preparation demonstrates that much of what makes muscle fast or slow is myogenic and not the product of the nervous or circulatory systems. This has far-reaching implications for motor control and exercise behavior and therefore is a crucial element in exercise science, with its focus on power and endurance sport activities. To measure student satisfaction with this active learning technique, a questionnaire was administered after the laboratory; 96% of the comments were positive in their support of active versus passive learning strategies.

Effect of Australian propolis from stingless bees (Tetragonula carbonaria) on pre-contracted human and porcine isolated arteries

Bee propolis is a mixture of plant resins and bee secretions. While bioactivity of honeybee propolis has been reported previously, information is limited on propolis from Australian stingless bees (Tetragonula carbonaria). The aim of this study was to investigate possible vasomodulatory effects of propolis in KCl-precontracted porcine coronary arteries using an ex vivo tissue bath assay. Polar extracts of propolis produced a dose-dependent relaxant response (EC₅₀=44.7±7.0 μg/ml), which was unaffected by endothelial denudation, suggesting a direct effect on smooth muscle. Propolis markedly attenuated a contractile response to Ca²⁺ in vessels that were depolarised with 60 mM KCl, in Ca²⁺-free Krebs solution. Propolis (160 µg/ml) reduced vascular tone in KCl pre-contracted vessels to near-baseline levels over 90 min, and this effect was partially reversible with 6h washout. Some loss in membrane integrity, but no loss in mitochondrial function was detected after 90 min exposure of human cultured umbilical vein endothelial cells to 160 µg/ml propolis. We conclude that Australian stingless bee (T. carbonaria) propolis relaxes porcine coronary artery in an endothelial-independent manner that involves inhibition of voltage-gated Ca²⁺ channels. This effect is partially and slowly reversible upon washout. Further studies are required to determine the therapeutic potential of Australian stingless bee propolis for conditions in which vascular supply is compromised.

Na⁺/Ca²⁺ exchanger 1/2 double-heterozygote knockout mice display increased nitric oxide component and altered colonic motility

The Na⁺/Ca²⁺ exchanger (NCX) is a plasma membrane transporter involved in regulating intracellular Ca²⁺ concentrations. NCX is critical for Ca²⁺ regulation in cardiac muscle, vascular smooth muscle, and nerve fibers. To determine the role of NCX1 and NCX2 in gastrointestinal tissues, we examined electric field stimulation (EFS)-induced responses in the longitudinal smooth muscle of the distal colon in NCX1 and NCX2 double-heterozygote knockoutmice (Double HET). We found that the amplitudes of EFS-induced relaxation that persisted during EFS were greater in Double HET than in wild-type mice (WT). Under the non-adrenergic, non-cholinergic (NANC) condition, EFS-induced relaxation in Double HET was similar in amplitude to that of WT. In the experiments in which l-NNA was added under NANC conditions following the EFS, the magnitudes of EFS-induced relaxation were smaller in Double HET than those in WT. In addition, an NCX inhibitor, SN-6, enhanced EFS-induced relaxation but did not affect EFS-induced relaxation under NANC condition, as in Double HET. Moreover, the magnitudes of relaxation induced by NOR-1, which generates NO, were greater in Double HET compared with WT. Similarly, SN-6 potentiated the magnitudes of NOR-1-induced relaxation. In this study, we demonstrate that NCX regulate colonic motility by altering the sensitivity of the inhibitory component.

Transcriptional regulation and alternative splicing cooperate in muscle fiber-type specification in flies and mammals

Muscles coordinate body movements throughout the animal kingdom. Each skeletal muscle is built of large, multi-nucleated cells, called myofibers, which are classified into several functionally distinct types. The typical fiber-type composition of each muscle arises during development, and in mammals is extensively adjusted in response to postnatal exercise. Understanding how functionally distinct muscle fiber-types arise is important for unraveling the molecular basis of diseases from cardiomyopathies to muscular dystrophies. In this review, we focus on recent advances in Drosophila and mammals in understanding how muscle fiber-type specification is controlled by the regulation of transcription and alternative splicing. We illustrate the cooperation of general myogenic transcription factors with muscle fiber-type specific transcriptional regulators as a basic principle for fiber-type specification, which is conserved from flies to mammals. We also examine how regulated alternative splicing of sarcomeric proteins in both flies and mammals can directly instruct the physiological and biophysical differences between fiber-types. Thus, research in Drosophila can provide important mechanistic insight into muscle fiber specification, which is relevant to homologous processes in mammals and to the pathology of muscle diseases.

The effect of mechanical extension stimulation combined with epithelial cell sorting on outcomes of implanted tissue-engineered muscular urethras

Urethral defects are common and frequent disorders and are difficult to treat. Simple natural or synthetic materials do not provide a satisfactory curative solution for long urethral defects, and urethroplasty with large areas of autologous tissues is limited and might interfere with wound healing. In this study, adipose-derived stem cells were used. These cells can be derived from a wide range of sources, have extensive expansion capability, and were combined with oral mucosal epithelial cells to solve the problem of finding seeding cell sources for producing the tissue-engineered urethras. We also used the synthetic biodegradable polymer poly-glycolic acid (PGA) as a scaffold material to overcome issues such as potential pathogen infections derived from natural materials (such as de-vascular stents or animal-derived collagen) and differing diameters. Furthermore, we used a bioreactor to construct a tissue-engineered epithelial-muscular lumen with a double-layer structure (the epithelial lining and the muscle layer). Through these steps, we used an epithelial-muscular lumen built in vitro to repair defects in a canine urethral defect model (1 cm). Canine urethral reconstruction was successfully achieved based on image analysis and histological techniques at different time points. This study provides a basis for the clinical application of tissue engineering of an epithelial-muscular lumen.

Sphingosine-1-phosphate induced contraction of bladder smooth muscle

Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that contracts most smooth muscles. Although S1P has been shown to contract bladder smooth muscle, the mechanism(s) by which S1P initiates contraction has not been extensively investigated. The goal of this study was to determine if S1P-induced force generation and myosin light chain (MLC) phosphorylation are dependent on calcium sensitization pathways mediated by protein kinase C (PKC) and Rho kinase (ROCK) and which S1P receptor is important in this response. Bladder smooth muscle strips from rabbit and rat were mounted for isometric force recording and contracted in response to carbachol or S1P in the presence and absence of an inhibitor of PKC (3 µM Bisindolylmaleimide-1) or ROCK (1 µM H-1172). 10 µM S1P produced approximately 40% of the force generated in response to 110 mM KCl in rabbit bladder smooth muscle. S1P, up to 100 µM, did not produce a response in rat bladder smooth muscle, any response evoked was due to solvent (NaOH). S1P-dependent force development was associated with a concomitant increase in Ser(19), but not dual Thr(18)/Ser(19) MLC phosphorylation. Inhibition of PKC decreased force development, whereas inhibition of ROCK abolished S1P-induced force. An inhibitor of the S1P2 receptor, JTE-013, relaxed a S1P-induced contraction; whereas, an agonist with low affinity to the S1P2 receptor, dihydro-S1P, did not elicit a contraction. Our results suggest that S1P contracts rabbit, but not rat, bladder smooth muscle via the S1P2 receptor and is dependent on MLC phosphorylation and myofilament calcium sensitization primarily in response to ROCK activation.

Rho-kinase inhibitors offer a new approach in the treatment of glaucoma

INTRODUCTION

Primary open-angle glaucoma (POAG) is a leading cause for worldwide blindness and is characterized by progressive optic nerve damage. The etiology of POAG is unknown, but elevated intraocular pressure (IOP) and advanced age have been identified as risk factors. IOP reduction is the only known treatment for glaucoma. Recently, drugs that inhibit rho-associated protein kinase (ROCK) have been studied in animals and people for their ability to lower IOP and potentially treat POAG. ROCK inhibitors lower IOP through a trabecular mechanism and may represent a new therapeutic paradigm for the treatment of POAG.

AREAS COVERED

Exploring the place that ROCK inhibitors may occupy in our treatment of POAG requires a thorough understanding of pathophysiology and treatment. This article summarizes current research on the incidence, proposed etiologies and mechanisms of action for this drug class. ROCK inhibitor research is presented and considered in light of the current standard of pharmacologic care.

EXPERT OPINION

ROCK inhibitors alter the cell shape and extracellular matrix (ECM) of the trabecular meshwork. Preclinical studies demonstrate that these drugs have the potential to become a new therapy for glaucoma. However, ROCK inhibitors can affect multiple cell types, and their utility can be proven only after clinical studies in patients.

Vasoconstrictor effect of Africanized honeybee (Apis mellifera L.) venom on rat aorta

BACKGROUND

Apis mellifera stings are a problem for public health worldwide, particularly in Latin America due to the aggressiveness of its Africanized honeybees. Massive poisoning by A. mellifera venom (AmV) affects mainly the cardiovascular system, and several works have described its actions on heart muscle. Nevertheless, no work on the pharmacological action mechanisms of the AmV in isolated aorta has been reported. Thus, the present work aimed to investigate the actions of AmV and its main fractions, phospholipase A2 (PLA2) and melittin, on isolated aorta rings and a probable action mechanism.

RESULTS

AmV and the complex PLA2 + melittin (0.1-50 μg/mL) caused contraction in endothelium-containing aorta rings, but neither isolated PLA2 nor melittin were able to reproduce the effect. Endothelium removal did not change the maximum vasoconstrictor effect elicited by AmV. Ca2+-free medium, as well as treatment with phentolamine (5 μM), verapamil (10 μM), losartan (100 μM), and U-73122 (10 μM, a phospholipase C inhibitor), eliminated the AmV-induced contractile effects.

CONCLUSIONS

In conclusion, AmV caused contractile effect in aorta rings probably through the involvement of voltage-operated calcium channels, AT1 and α-adrenergic receptors via the downstream activation of phospholipase C. The protein complex, PLA2 + melittin, was also able to induce vasoconstriction, whereas the isolated proteins were not.

HEF-19-induced relaxation of colonic smooth muscles and the underlying mechanisms

AIM: To investigate the relaxant effect of chromane HEF-19 on colonic smooth muscles isolated from rabbits, and the underlying mechanisms.

METHODS: The relaxant effect and action mechanisms of HEF-19 were investigated using descending colon smooth muscle of the rabbits. Preparations 1 cm long were mounted in 15-mL tissue baths containing Tyrode’s solution, maintained at 37 ± 0.5 °C and aerated with a mixture of 5% CO₂ in oxygen (Carbogen). The tension and amplitude of the smooth muscle strips were recorded after adding HEF-19 (10^-6, 10^-5 and 10^-4 mol/L). After cumulative administration of four antispasmodic agents, including acetylcholine chloride (Ach) (10^-4 mol/L), histamine (10^-4 mol/L), high-K⁺ (60 mmol/L) and BaCl₂ (8.2 mmol/L), HEF-19 (3 × 10^-7-3 × 10^-4 mol/L) was added to investigate the relaxant effect of HEF-19. CaCl₂ (10^-4-2.5 × 10^-3 mol/L) was added cumulatively to the smooth muscle preparations pretreated with and without HEF-19 (1 × 10^-6 or 3 × 10^-6 mol/L) and verapamil (1 × 10^-7 mol/L) to study the mechanisms involved. Finally, phasic contraction was induced with ACh (15 × 10^-6 mol/L), and CaCl₂ (4 × 10^-3 mol/L) was added to the smooth muscle preparations pretreated with and without HEF-19 (3 × 10^-6 mol/L or 1 × 10^-5 mol/L) and verapamil (1 × 10^-7 mol/L) in calcium-free medium to further study the underlying mechanisms.

RESULTS: HEF-19 (1 × 10^-6, 1 × 10^-5 and 1 × 10^-4 mol/L) suppressed spontaneous contraction of rabbit colonic smooth muscles. HEF-19 (3 × 10^-7-3 × 10^-4 mol/L) relaxed in a concentration-dependent manner colonic smooth muscle preparations pre-contracted with BaCl₂, high-K⁺ solution, Ach or histamine with respective EC₅₀ values of 5.15 ± 0.05, 5.12 ± 0.08, 5.58 ± 0.16 and 5.25 ± 0.24, thus showing a spasmolytic activity. HEF-19 (1 × 10^-6 mol/L and 3 × 10^-6 mol/L) shifted the concentration-response curves of CaCl₂ to the right and depressed the maximum response to CaCl_2. The two components contracted by Ach were attenuated with HEF-19 (3 × 10^-6 mol/L or 10^-5 mol/L) in calcium-free medium.

CONCLUSION: HEF-19 inhibited rabbit colonic smooth muscle contraction, probably through inhibiting opening of voltage-dependent Ca²⁺ channels. HEF-19 reduced inflow and intracellular release of Ca²⁺ ions.

Importance of the interaction protein-protein of the CaM-PDE1A and CaM-MLCK complexes in the development of new anti-CaM drugs

Protein-protein interactions play central roles in physiological and pathological processes. The bases of the mechanisms of drug action are relevant to the discovery of new therapeutic targets. This work focuses on understanding the interactions in protein-protein-ligands complexes, using proteins calmodulin (CaM), human calcium/calmodulin-dependent 3',5'-cyclic nucleotide phosphodiesterase 1A active human (PDE1A), and myosin light chain kinase (MLCK) and ligands αII-spectrin peptide (αII-spec), and two inhibitors of CaM (chlorpromazine (CPZ) and malbrancheamide (MBC)). The interaction was monitored with a fluorescent biosensor of CaM (hCaM M124C-mBBr). The results showed changes in the affinity of CPZ and MBC depending on the CaM-protein complex under analysis. For the Ca(2+) -CaM, Ca(2+) -CaM-PDE1A, and Ca(2+) -CaM-MLCK complexes, CPZ apparent dissociation constants (Kds ) were 1.11, 0.28, and 0.55 μM, respectively; and for MBC Kds were 1.43, 1.10, and 0.61 μM, respectively. In competition experiments the addition of calmodulin binding peptide 1 (αII-spec) to Ca(2+) -hCaM M124C-mBBr quenched the fluorescence (Kd  = 2.55 ± 1.75 pM) and the later addition of MBC (up to 16 μM) did not affect the fluorescent signal. Instead, the additions of αII-spec to a preformed Ca(2+) -hCaM M124C-mBBr-MBC complex modified the fluorescent signal. However, MBC was able to displace the PDE1A and MLCK from its complex with Ca(2+) -CaM. In addition, docking studies were performed for all complexes with both ligands showing an excellent correlation with experimental data. These experiments may help to explain why in vivo many CaM drugs target prefer only a subset of the Ca(2+) -CaM regulated proteins and adds to the understanding of molecular interactions between protein complexes and small ligands.

Caffeine reduces myocardial blood flow during exercise

Caffeine consumption has been receiving increased interest from both the medical and lay press, especially given the increased amounts now available in energy products. Acute ingestion of caffeine usually increases cardiac work; however, caffeine impairs the expected proportional increase in myocardial blood flow to match this increased work of the heart, most notably during exercise. This appears to be mainly due to caffeine's effect on blocking adenosine-induced vasodilatation in the coronary arteries in normal healthy subjects. This review summarizes the available medical literature specifically relating to pure caffeine tablet ingestion and reduced exercise coronary blood flow, and suggests possible mechanisms. Further studies are needed to evaluate this effect for other common caffeine-delivery systems, including coffee, energy beverages, and energy gels, which are often used for exercise performance enhancement, especially in teenagers and young athletes.

Defective homocysteine metabolism: potential implications for skeletal muscle malfunction

Hyperhomocysteinemia (HHcy) is a systemic medical condition and has been attributed to multi-organ pathologies. Genetic, nutritional, hormonal, age and gender differences are involved in abnormal homocysteine (Hcy) metabolism that produces HHcy. Homocysteine is an intermediate for many key processes such as cellular methylation and cellular antioxidant potential and imbalances in Hcy production and/or catabolism impacts gene expression and cell signaling including GPCR signaling. Furthermore, HHcy might damage the vagus nerve and superior cervical ganglion and affects various GPCR functions; therefore it can impair both the parasympathetic and sympathetic regulation in the blood vessels of skeletal muscle and affect long-term muscle function. Understanding cellular targets of Hcy during HHcy in different contexts and its role either as a primary risk factor or as an aggravator of certain disease conditions would provide better interventions. In this review we have provided recent Hcy mediated mechanistic insights into different diseases and presented potential implications in the context of reduced muscle function and integrity. Overall, the impact of HHcy in various skeletal muscle malfunctions is underappreciated; future studies in this area will provide deeper insights and improve our understanding of the association between HHcy and diminished physical function.

Vascular Reactivity Concerning Orthosiphon stamineus Benth-Mediated Antihypertensive in Aortic Rings of Spontaneously Hypertensive Rats

Orthosiphon stamineus Benth has been traditionally used to treat hypertension. The study aimed to investigate the vascular reactivity of water extract (WOS) and water : methanolic (1 : 1) extract (WMOS) of Orthosiphon stamineus Benth and AT₁ receptors blocker in the mechanisms of antihypertensive mediated by α₁-adrenergic receptor and EDNO and PGI₂ releases in the SHR aortic rings. SHR (230–280 g) were divided into four groups: control, WOS, WMOS, and losartan. After being fed orally for 14 days, the aorta was harvested and subjected to PE (10⁻⁹ to 10⁻⁵ M) and ACh (10⁻⁹ to 10⁻⁵ M) with and without L-NAME (100 µM) and indomethacin (10 µM), respectively. WOS, WMOS, and losartan significantly reduced the contractile responses to PE intact suggesting the importance of endothelium in vasorelaxation. Losartan significantly enhanced the ACh-induced vasorelaxation. L-NAME significantly inhibited the ACh-induced relaxation in all groups. Indomethacin enhanced ACh-induced vasorelaxation in WMOS. Collectively, Orthosiphon stamineus leaves extract reduced vasoconstriction responses by the alteration of α₁-adrenergic and AT₁ receptors activities. The involvement of EDNO releases was clearly observed in this plant. In WOS, PGI₂ releases might not participate in the ACh-induced vasorelaxation. However, in WMOS, enhancement of vasorelaxation possibly due to continuous release of PGI₂.

Cocaine synergism with α agonists in rat aorta: computational analysis reveals an action beyond reuptake inhibition

BACKGROUND

Cocaine has long been known to increase blood pressure, but the degree and mechanism of vasoconstricting action remain poorly understood. Here we examine the interaction between cocaine and alpha-adrenoceptor agonists, with the action of reuptake inhibition minimized.

METHODS

Cocaine was administered to isolated rings of rat thoracic aorta, alone and in combination with three different adrenoceptor agonists: phenylephrine, methoxamine, and norepinephrine. Synergy analysis begins with the predicted additive effect of the combination of two agonists, based upon dose equivalence theory. This case where one agonist (cocaine) has no effect when administered alone requires only a t-test to demonstrate that a departure from additivity has occurred.

RESULTS

At doses where cocaine alone produced no vasoconstriction, it potentiated the vasoconstriction produced by all three alpha agonists, a clear indication of synergism between cocaine and these agents. Higher doses of cocaine in combination with alpha adrenoceptor agents gave an inverted-U shaped (hormetic) dose-effect curve, i.e., dose-related relaxation at higher doses. The hormetic dose-effect relation was analyzed using computational methodology based on dose equivalence to derive the unknown second component of action that causes relaxation.

CONCLUSIONS

Cocaine exhibits both vasoconstricting and vasorelaxant effects. This relaxing component, possibly related to activation of myosin light chain phosphatase, was quantified as a dose-effect curve. Most important is the synergism between cocaine and alpha-adrenoceptor stimulation which cannot be explained as an action due to reuptake inhibition, and has not been previously described.

The characteristics of genistin-induced inhibitory effects on intestinal motility

Genistin belongs to isoflavones. Based on the facts that genistin exerts inhibitory effects on the contractility of vascular smooth muscle,the present study was designed to characterize the effects of genistin on intestinal contractility and evaluate its potential clinical implication. Ex vivo [isolated jejunal segment (IJS) of rat], in vitro, and in vivo assays were used in the study. The results indicated that genistin (5-80 μmol/L) inhibited the contraction of IJS in a dose-dependent manner and inhibited the increased-contractility of IJS induced by acetylcholine (ACh), histamine, high Ca(2+), and erythromycin, respectively. The inhibitory effects of genistin were correlated with the stimulation of alpha adrenergic and beta adrenergic receptors since these inhibitory effects were significantly blocked in the presence of phentolamine and propranolol respectively. No further inhibitory effects of genistin were observed in the presence of verapamil or in Ca(2+)-free condition, indicating genistin-induced inhibitory effects are Ca(2+)-dependent. Genistin decreased myosin light chain kinase (MLCK) protein contents and MLCK mRNA expression in IJS, and inhibited both phosphorylation and Mg(2+)-ATPase activity of purified myosin, implicating that the decrease of MLCK contents and inhibition of MLCK activity are involved in the genistin-induced inhibitory effects. The study suggests the potential clinical implications of genistin in relieving intestinal hypercontractility.

The influence of ethanol intake on RhoA/Rho kinase signaling pathway in corpus cavernosum of OLETF rats

PURPOSE

To investigate the effect of the ethanol on corpus cavernosum of the type 2 diabetes mellitus (type 2 DM) rat, since previous studies have reported the positive effect of moderate drinking on type 2 DM and endothelial function.

METHODS

Otsuka Long Evans Tokushima Fatty (OLETF, n = 28) and Long Evans Tokushima Otsuka (LETO, n = 28) male rats were assigned to four groups: control (LETO, n = 14), control/ethanol (LETO with ethanol, n = 14), fatty (OLETF, n = 14) and fatty/ethanol (OLETF with ethanol, n = 14). The control/ethanol and fatty/ethanol groups were fed Lieber-DeCarli Regular EtOH. After 10 weeks, an intraperitoneal glucose tolerance test (IPGTT) was performed. RT-PCR and Western blot analyses of the RhoA/Rho kinase in the corpus cavernosum were performed. The expression of endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in the corpus cavernosum was evaluated by immunohistochemistry.

RESULTS

After a 10-week ethanol intake, the body weight and the IPGTT of the fatty/ethanol group were significantly lower compared with the fatty group (p < 0.05). A significantly increased mRNA and protein expression in the fatty group was observed compared with the control group by RT-PCR and Western blot analyses (p < 0.05): A significantly decreased expression was observed in the fatty/ethanol group compared with the fatty group (p < 0.05). The significantly increased expression of eNOS was observed in the fatty/ethanol group compared with the fatty group by immunohistochemistry.

CONCLUSIONS

Long-term ethanol intake may preserve the erectile function in type 2 DM through the down-regulation of the RhoA/Rho kinase pathway.

Prostate-apoptosis response-4 phosphorylation in vascular smooth muscle

The protein prostate-apoptosis response (Par)-4 has been implicated in the regulation of smooth muscle contraction, based largely on studies with the A7r5 cell line. A mechanism has been proposed whereby Par-4 binding to MYPT1 (the myosin-targeting subunit of myosin light chain phosphatase, MLCP) blocks access of zipper-interacting protein kinase (ZIPK) to Thr697 and Thr855 of MYPT1, whose phosphorylation is associated with MLCP inhibition. Phosphorylation of Par-4 at Thr155 disrupts its interaction with MYPT1, exposing the sites of phosphorylation in MYPT1 and leading to MLCP inhibition and contraction. We tested this "padlock" hypothesis in a well-characterized vascular smooth muscle system, the rat caudal artery. Par-4 was retained in Triton-skinned tissue, suggesting a tight association with the contractile machinery, and indeed Par-4 co-immunoprecipitated with MYPT1. Treatment of Triton-skinned tissue with the phosphatase inhibitor microcystin (MC) evoked phosphorylation of Par-4 at Thr155, but did not induce its dissociation from the contractile machinery. Furthermore, analysis of the time courses of MC-induced phosphorylation of MYPT1 and Par-4 revealed that MYPT1 phosphorylation at Thr697 or Thr855 preceded Par-4 phosphorylation. Par-4 phosphorylation was inhibited by the non-selective kinase inhibitor staurosporine, but not by inhibitors of ZIPK, Rho-associated kinase or protein kinase C. In addition, Par-4 phosphorylation did not occur upon addition of constitutively-active ZIPK to skinned tissue. We conclude that phosphorylation of Par-4 does not regulate contraction of this vascular smooth muscle tissue by inducing dissociation of Par-4 from MYPT1 to allow phosphorylation of MYPT1 and inhibition of MLCP.

Na(+) /Ca(2+) exchanger 2-heterozygote knockout mice display decreased acetylcholine release and altered colonic motility in vivo

BACKGROUND

The Na(+) /Ca(2+) exchanger (NCX) is a plasma membrane transporter involved in regulating intracellular Ca(2+) concentrations. NCX is critical for Ca(2+) regulation in cardiac muscle, vascular smooth muscle, and nerve fibers. However, little is known about the physiological role of NCX in the myenteric neurons and smooth muscles of the gastrointestinal tract.

METHODS

To determine the role of NCX1 and NCX2 in gastrointestinal tissues, we examined electric field stimulation (EFS)-induced responses in the longitudinal smooth muscle of the distal colon in NCX1- and NCX2-heterozygote knockout mice.

KEY RESULTS

We found that the amplitudes of EFS-induced relaxation that persisted during EFS were greater in NCX2 heterozygous mice (HET) than in wild-type mice (WT). Under the nonadrenergic, noncholinergic (NANC) condition, EFS-induced relaxation in NCX2 HET was similar in amplitude to that of WT. In addition, an NCX inhibitor, YM-244769 enhanced EFS-induced relaxation but did not affect EFS-induced relaxation under the NANC condition, as in NCX2 HET. Unlike NCX2 HET, NCX1 HET displayed no marked changes in colonic motility. These results indicate that cholinergic function in the colon is altered in NCX2 HET. The magnitude of acetylcholine (ACh)-induced contraction in NCX2 HET was similar to that in WT. In contrast, EFS-induced ACh release was reduced in NCX2 HET compared with that in WT.

CONCLUSIONS & INFERENCES

In this study, we demonstrate that NCX2 regulates colonic motility by altering ACh release onto the myenteric neurons of the distal colon.

O-GlcNAcylation: a novel post-translational mechanism to alter vascular cellular signaling in health and disease: focus on hypertension

O-Linked attachment of beta-N-acetyl-glucosamine (O-GlcNAc) on serine and threonine residues of nuclear and cytoplasmic proteins is a highly dynamic posttranslational modification that plays a key role in signal transduction pathways. Preliminary data show that O-GlcNAcylation may represent a key regulatory mechanism in the vasculature, modulating contractile and relaxant responses. Proteins with an important role in vascular function, such as endothelial nitric oxide synthase, sarcoplasmic reticulum Ca(2+)-ATPase, protein kinase C, mitogen-activated protein kinases, and proteins involved in cytoskeleton regulation and microtubule assembly are targets for O-GlcNAcylation, indicating that this posttranslational modification may play an important role in vascular reactivity. Here, we will focus on a few specific pathways that contribute to vascular function and cardiovascular disease-associated vascular dysfunction, and the implications of their modification by O-GlcNAc. New chemical tools have been developed to detect and study O-GlcNAcylation, including inhibitors of O-GlcNAc enzymes, chemoenzymatic tagging methods, and quantitative proteomics strategies; these will also be briefly addressed. An exciting challenge in the future will be to better understand the cellular dynamics of this posttranslational modification, as well as the signaling pathways and mechanisms by which O-GlcNAc is regulated on specific proteins in the vasculature in health and disease.

Involvements of calcium channel and potassium channel in Danshen and Gegen decoction induced vasodilation in porcine coronary LAD artery

Danshen (Salviae Miltiorrhizae Radix) and Gegen (Puerariae Lobatae Radix) have been widely used in treating cardiovascular diseases for thousands of years in China. The present study was carried out to evaluate the effects of a Danshen and Gegen decoction (DG) on the vascular reactivity of a porcine isolated coronary artery and the underlying mechanisms involved. Porcine coronary rings were precontracted with 15 nM U46619. The involvement of endothelium-dependent mechanisms was explored by removing the endothelium; the involvement of potassium channels was investigated by the pretreatment of the artery rings with various blockers, and the involvement of the calcium channels was investigated by incubating the artery rings with Ca²⁺-free buffer and priming them with high [K⁺] prior to adding CaCl₂ to elicit contraction. The involvement of Ca²⁺ sensitization was explored by evaluating the Rho-activity expression. The results revealed that DG elicited a concentration-dependent relaxation on a U46619-precontracted coronary artery ring. These relaxation responses were not altered by the pretreatment of inhibitors of endothelium-related dilator synthases, cGMP and cAMP pathway inhibitors, potassium channel (BK(Ca), SK(Ca), K(V) and K(ATP)) blockers and endothelium removal. The K(IR) channel blocker BaCl₂ only slightly attenuated the DG-induced relaxation. However, the Ca²⁺-induced artery contraction was inhibited by DG. Additionally, the expression of the phosphorylated myosin light chain was inhibited by DG whereas the activity of RhoA was not affected. Therefore, DG could be a useful cardioprotective agent for vasodilation in patients who have hypertension.

Cross-talk between Rho-associated kinase and cyclic nucleotide-dependent kinase signaling pathways in the regulation of smooth muscle myosin light chain phosphatase

Ca(2+) sensitization of smooth muscle contraction depends upon the activities of protein kinases, including Rho-associated kinase, that phosphorylate the myosin phosphatase targeting subunit (MYPT1) at Thr(697) and/or Thr(855) (rat sequence numbering) to inhibit phosphatase activity and increase contractile force. Both Thr residues are preceded by the sequence RRS, and it has been suggested that phosphorylation at Ser(696) prevents phosphorylation at Thr(697). However, the effects of Ser(854) and dual Ser(696)-Thr(697) and Ser(854)-Thr(855) phosphorylations on myosin phosphatase activity and contraction are unknown. We characterized a suite of MYPT1 proteins and phosphospecific antibodies for specificity toward monophosphorylation events (Ser(696), Thr(697), Ser(854), and Thr(855)), Ser phosphorylation events (Ser(696)/Ser(854)) and dual Ser/Thr phosphorylation events (Ser(696)-Thr(697) and Ser(854)-Thr(855)). Dual phosphorylation at Ser(696)-Thr(697) and Ser(854)-Thr(855) by cyclic nucleotide-dependent protein kinases had no effect on myosin phosphatase activity, whereas phosphorylation at Thr(697) and Thr(855) by Rho-associated kinase inhibited phosphatase activity and prevented phosphorylation by cAMP-dependent protein kinase at the neighboring Ser residues. Forskolin induced phosphorylation at Ser(696), Thr(697), Ser(854), and Thr(855) in rat caudal artery, whereas U46619 induced Thr(697) and Thr(855) phosphorylation and prevented the Ser phosphorylation induced by forskolin. Furthermore, pretreatment with forskolin prevented U46619-induced Thr phosphorylations. We conclude that cross-talk between cyclic nucleotide and RhoA signaling pathways dictates the phosphorylation status of the Ser(696)-Thr(697) and Ser(854)-Thr(855) inhibitory regions of MYPT1 in situ, thereby regulating the activity of myosin phosphatase and contraction.

Distribution of adenylyl cyclases in the rat ovary by immunofluorescence microscopy

In the mammalian ovary both gonadotropins and local cytokines, acting through G-protein coupled receptors, govern the physiology of the ovary in part by regulating the cyclic adenosine 3',5'-monophosphate via adenylyl cyclases. The nine transmembrane adenylyl cyclases and a soluble adenylyl cyclase are regulated by a diversity of ligands. In this study we have examined the rat ovaries, prior to and subsequent to gonadotropin treatment, for the presence of different transmembrane adenylyl cyclases by indirect immunofluorescence microscopy. Adenylyl cyclase I immunoreactivity was observed in the nuclei of oocytes in preantral and antral follicles along with some staining in granulosa cells. Equine chorionic gonadotropin injection increased adenylyl cyclase I staining in granulosa cells. Adenylyl cyclase I staining was also observed in luteal and endothelial cells. Adenylyl cyclase II was observed throughout the ovary, including granulosa cells and the ovarian surface epithelium. Adenylyl cyclase II staining was also found to increase in granulosa cells after equine chorionic gonadotropin injection. Adenylyl cyclase III was distributed primarily in theca and smooth muscle cells of arterioles, with faint staining in the oocytes of equine chorionic gonadotropin-injected ovaries. Adenylyl cyclase IV staining was present throughout the ovary, including the nuclei of oocytes. Adenylyl cyclase VIII staining in granulosa cells increased subsequent to equine chorionic gonadotropin injection and remained in luteal cells. Our study reveals the redundancy of adenylyl cyclases present in the rat ovary and, therefore, implies potential regulation of follicular and corpus luteum physiology by cyclic adenosine 3',5'-monophosphate generated through distinct adenylyl cyclases.

Salvia miltiorrhiza causes tonic contraction in rat ileum through Ca²⁺-calmodulin pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Danshen, root of Salvia miltiorrhiza (SM), has been traditionally used in Chinese medicine for the treatment of heart, abdomen, gurgling in the intestines, and relieving fullness. However, the effects of SM on intestine have rarely been done to date.

AIM OF THE STUDY

To investigate the contraction effect of SM on isolated rat ileum and its mechanisms involved.

MATERIALS AND METHODS

The isometric contractions of ileum segments were investigated in organ baths for spontaneous activity and response to ethanolic extracts of SM. To determine the contraction mechanism caused by SM extracts, atropine (a muscarinic receptor antagonist), tetrodotoxin (TTX, a sodium channel blocker), nifedipine (a calcium channel blocker), Ca(2+) free Krebs solution with EGTA, or trifluoperazine (TFP, a calmodulin blocker) was administered and its response to cumulative dosages of SM extracts were examined. The effect of SM extracts on Ca(2+) signaling in the intestinal epithelial cell-6 (IEC-6) was examined using fura-2 as a Ca(2+) indicator.

RESULTS

SM extracts caused dose-dependent tonic contraction on rat ileum in ex vivo organ bath studies. The contraction induced by SM extracts was not inhibited by atropine, TTX, nifedipine, or in Ca(2+) free solution. However, the ileal contractions induced by SM extracts were significantly inhibited by TFP in a dose-dependent manner. In IEC-6 cells, the SM extracts induced extracellular Ca(2+) entry and massive intracellular Ca(2+) release in Ca(2+)-contained medium, and induced intracellular Ca(2+) release in Ca(2+)-free medium.

CONCLUSION

These results demonstrate that SM extracts cause ileal contraction through the Ca(2+)-calmodulin pathway.

Tianma modulates blood vessel tonicity

Tianma is a traditional Chinese medicine (TCM) often used for the treatment of hypertension and heart diseases. To elucidate the function of tianma at the molecular level, we investigated the effect of tianma on vascular functions and aortic protein metabolism. We found that long-term treatment with tianma (~2.5g/kg/day for three months) in one-year-old rats could enhance acetylcholine (ACh)-induced vasorelaxation in endothelium-intact thoracic aortic rings against both KCl (80 mM)- and phenylephrine (PE)-induced contraction. By using the iTRAQ (isobaric tag for relative and absolute quantification) technique, we confirmed from the functional data at the proteome level that tianma treatment down-regulated the expressions of contractile proteins (e.g. Acta2) and other related structural proteins (e.g. desmin), and up-regulated the expressions of extracellular matrix (ECM) glycoproteins (e.g. Fbln5) and anti-thrombotic proteins (e.g. Anxa2) in aortic tissue. By inductive reasoning, tianma could perform its vasodilatory effect not only by inhibiting vascular smooth muscle contraction, but also by enhancing blood vessel elasticity and stabilizing the arterial structure. Thus, tianma might become a novel therapeutic herbal medicine for cardiovascular diseases by regulating the aortic proteome metabolism.

A three-dimensional chemo-mechanical continuum model for smooth muscle contraction

Based on two fields, namely the placement and the calcium concentration, a chemo-mechanically coupled three-dimensional model, describing the contractile behaviour of smooth muscles, is presented by means of a strain energy function. The strain energy function (Schmitz and Böl, 2011) is additively decomposed into a passive part, relating to elastin and collagen, and an active calcium-driven part related to the chemical contraction of the smooth muscle cells. For the description of the calcium phase the four state cross-bridge model of Hai and Murphy (Hai and Murphy, 1988) has been implemented into the finite element method. Beside three-dimensional illustrative boundary-value problems demonstrating the features of the presented modelling concept, simulations on an idealised artery document the applicability of the model to more realistic geometries.

Probing cellular traction forces with magnetic nanowires and microfabricated force sensor arrays

In this paper, the use of magnetic nanowires for the study of cellular response to force is demonstrated. High-aspect ratio Ni rods with diameter 300 nm and lengths up to 20 μm were bound to or internalized by pulmonary artery smooth muscle cells (SMCs) cultured on arrays of flexible micropost force sensors. Forces and torques were applied to the cells by driving the nanowires with AC magnetic fields in the frequency range 0.1-10 Hz, and the changes in cellular contractile forces were recorded with the microposts. These local stimulations yield global force reinforcement of the cells' traction forces, but this contractile reinforcement can be effectively suppressed upon addition of a calcium channel blocker, ruthenium red, suggesting the role of calcium channels in the mechanical response. The responsiveness of the SMCs to actuation depends on the frequency of the applied stimulation. These results show that the combination of magnetic nanoparticles and micropatterned, flexible substrates can provide new approaches to the study of cellular mechanotransduction.

Ent-7α-acetoxytrachyloban-18-oic acid and ent-7α-hydroxytrachyloban-18-oic acid from Xylopia langsdorfiana A. St-Hil. & Tul. modulate K(+) and Ca(2+) channels to reduce cytosolic calcium concentration on guinea pig ileum

In this study we investigated the mechanism underlying the spasmolytic action of ent-7α-acetoxytrachyloban-18-oic acid (trachylobane-360) and ent-7α-hydroxytrachyloban-18-oic acid (trachylobane-318), diterpenes obtained from Xylopia langsdorfiana, on guinea pig ileum. Both compounds inhibited histamine-induced cumulative contractions (slope=3.5±0.9 and 4.4±0.7) that suggests a noncompetitive antagonism to histaminergic receptors. CaCl(2)-induced contractions were nonparallelly and concentration-dependently reduced by both diterpenes, indicating blockade of calcium influx through voltage-dependent calcium channels (Ca(v)). The Ca(v) participation was confirmed since both trachylobanes equipotently relaxed ileum pre-contracted with S-(-)-Bay K8644 (EC(50)=3.5±0.7×10-(5) and 1.1±0.2×10-(5)M) and KCl (EC(50)=5.5±0.3×10-(5) and 1.4±0.2×10-(5)M). K(+) channels participation was confirmed since diterpene-induced relaxation curves were significantly shifted to right in the presence of 5mM tetraethylammonium (TEA(+)) (EC(50)=0.5±0.04×10-(4) and 2.0±0.5×10-(5)M). ATP-sensitive K(+) channel (K(ATP)), voltage activated K(+) channels (K(V)), small conductance calcium-activated K(+) channels (SK(Ca)) or big conductance calcium-activated K(+) channels (BK(Ca)) did not seem to participate of trachylobane-360 spasmolytic action. However trachylobane-318 modulated positively K(ATP), K(V) and SK(Ca) (EC(50)=1.1±0.3×10-(5), 0.7±0.2×10-(5) and 0.7±0.2×10-(5)M), but not BK(Ca). A fluorescence analysis technique confirmed the decrease of cytosolic calcium concentration ([Ca(2+)](c)) induced by both trachylobanes in ileal myocytes. In conclusion, trachylobane-360 and trachylobane-318 induced spasmolytic activity by K(+) channel positive modulation and Ca(2+) channel blockade, which results in [Ca(2+)](c) reduction at cellular level leading to smooth muscle relaxation.

Polymorphic markers associated with severe oxaliplatin-induced, chronic peripheral neuropathy in colon cancer patients

BACKGROUND

To identify potential genetic markers for severe oxaliplatin-induced chronic peripheral neuropathy (OXCPN), the authors performed a genome-wide association analysis of patients with colon cancer who received oxaliplatin-based chemotherapy.

METHODS

This was a prospective study in which DNA was purified in peripheral blood from patients with colon cancer who received oxaliplatin. The primary endpoint was the development of severe (grade 2 lasting for >7 days or grade 3) OXCPN. For the discovery set, genotyping was done for 96 patients who received adjuvant fluorouracil and oxaliplatin using the a genome-wide human single-nucleotide polymorphism (SNP) array. An association between polymorphisms and severe OXCPN was investigated. At the same time, 247 patients who received oxaliplatin-based, first-line chemotherapy for advanced disease were enrolled as a validation set.

RESULTS

Among the 32 genotyped candidate SNPs selected from the discovery set, 9 SNPs in 8 genes (tachykinin, precursor 1[TAC1]; forkhead box C1 [FOXC1]; integrin, alpha 1 [ITGA1]; acylphosphatase 2, muscle type [ACYP2]; deleted in lymphocytic leukemia, 7 [DLEU7]; B-cell translocation gene 4 [BTG4]; calcium/calmodulin-dependent protein kinase II inhibitor 1 [CAMK2N1]; and phenylalanyl-tRNA synthase 2 [FARS2]) had nominal replication (P < .05). The most significant association was observed at reference SNP number (rs)10486003 in TAC1 (P = 4.84 × 10(-7)) in combined data from 2 sets. Five SNPs (rs10486003, rs2338, rs830884, rs843748, and rs797519) were significant in a multiple regression analysis (P < .05). Overall prediction accuracy calculated by the regression model was 72.8% (95% confidence interval, 65.8%-79.9%) in the model development and 75.9% (95% confidence interval, 66.9%-84.9%) in the model evaluation.

CONCLUSIONS

The current results indicated that a genome-wide pharmacogenomic approach is useful for identifying novel polymorphism predictors of severe OXCPN that may be used in personalized chemotherapy.

Relaxant effects of Schisandra chinensis and its major lignans on agonists-induced contraction in guinea pig ileum

In this study, the herbal extracts of Schisandra chinensis were demonstrated to inhibit the contractions induced by acetylcholine (ACh) and serotonin (5-HT) in guinea pig ileum, and the 95% ethanol extract was more effective than the aqueous extract. Analysis with High Performance Liquid Chromatography (HPLC) indicated that schisandrin, schisandrol B, schisandrin A and schisandrin B were the major lignans of Schisandra chinensis, and the ethanol extract contained higher amount of these lignans than the aqueous extract. All four lignans inhibited the contractile responses to ACh, with EC(20) values ranging from 2.2±0.4μM (schisandrin A) to 13.2±4.7μM (schisandrin). The effectiveness of these compounds in relaxing the 5-HT-induced contraction was observed with a similar magnitude. Receptor binding assay indicated that Schisandra lignans did not show significant antagonistic effect on muscarinic M3 receptor. In Ca(2+)-free preparations primed with ACh or KCl, schisandrin A (50μM) attenuated the contractile responses to cumulative addition of CaCl(2) by 37%. In addition, schisandrin A also concentration-dependently inhibited ACh-induced contractions in Ca(2+)-free buffer. This study demonstrates that Schisandra chinensis exhibited relaxant effects on agonist-induced contraction in guinea pig ileum, with schisandrin, schisandrol B, schisandrin A and schisandrin B being the major active ingredients. The antispasmodic action of schisandrin A involved inhibitions on both Ca(2+) influx through L-type Ca(2+) channels and intracellular Ca(2+) mobilization, rather than specific antagonism of cholinergic muscarinic receptors.

Adiponectin opposes endothelin-1-mediated vasoconstriction in the perfused rat hindlimb

Recent studies have shown that adiponectin is able to increase nitric oxide (NO) production by the endothelium and relax preconstricted isolated aortic rings, suggesting that adiponectin may act as a vasodilator. Endothelin-1 (ET-1) is a potent vasoconstrictor, elevated levels of which are associated with obesity, type 2 diabetes, hypertension, and cardiovascular disease. We hypothesized that adiponectin has NO-dependent vascular actions opposing the vasoconstrictor actions of ET-1. We studied the vascular and metabolic effects of a physiological concentration of adiponectin (6.5 μg/ml) on hooded Wistar rats in the constant-flow pump-perfused rat hindlimb. Adiponectin alone had no observable vascular activity; however, adiponectin pretreatment and coinfusion inhibited the increase in perfusion pressure and associated metabolic stimulation caused by low-dose (1 nM) ET-1. Adiponectin was not able to oppose vasoconstriction when infusion was commenced after ET-1. This is in contrast to the NO donor sodium nitroprusside, which significantly reduced the pressure due to established ET-1 vasoconstriction, suggesting dissociation of the actions of adiponectin and NO. In addition, adiponectin had no effect on vasoconstriction caused by either high-dose (20 nM) ET-1 or low-dose (50 nM) norepinephrine. Our findings suggest that adiponectin has specific, apparently NO-independent, vascular activity to oppose the vasoconstrictor effects of ET-1. The hemodynamic actions of adiponectin may be an important aspect of its insulin-sensitizing ability by regulating access of insulin and glucose to myocytes. Imbalance in the relationship between adiponectin and ET-1 in obesity may contribute to the development of insulin resistance and cardiovascular disease.

Control of mammary myoepithelial cell contractile function by α3β1 integrin signalling

In the functionally differentiated mammary gland, basal myoepithelial cells contract to eject the milk produced by luminal epithelial cells from the body. We report that conditional deletion of a laminin receptor, α3β1 integrin, from myoepithelial cells leads to low rates of milk ejection due to a contractility defect but does not interfere with the integrity or functional differentiation of the mammary epithelium. In lactating mammary gland, in the absence of α3β1, focal adhesion kinase phosphorylation is impaired, the Rho/Rac balance is altered and myosin light-chain (MLC) phosphorylation is sustained. Cultured mammary myoepithelial cells depleted of α3β1 contract in response to oxytocin, but are unable to maintain the state of post-contractile relaxation. The expression of constitutively active Rac or its effector p21-activated kinase (PAK), or treatment with MLC kinase (MLCK) inhibitor, rescues the relaxation capacity of mutant cells, strongly suggesting that α3β1-mediated stimulation of the Rac/PAK pathway is required for the inhibition of MLCK activity, permitting completion of the myoepithelial cell contraction/relaxation cycle and successful lactation. This is the first study highlighting the impact of α3β1 integrin signalling on mammary gland function.

Vasorelaxant Effect of a Newly Synthesized Dihydropyridine Ethyl Ester (DHPEE) on Rat Thoracic Aorta: Dual Mechanism of Action

INTRODUCTION

DHPEE is a newly synthesized compound by merging the key structural elements in an angiotensin receptor blocker (Telmisartan) with key structural elements in 1,4- dihydropyridine calcium channel blocker (Nifedipine). In this study, we examined dual calcium channel blocking and AT1 antagonist activity for DHPEE.

METHODS

The functional inhibitory characteristics of DHPEE were studied in vitro in rat thoracic aorta preparations precontracted by phenylephrine (1μM) or KCl (80μM) or Ang II in normal or calcium-free solutions.

RESULTS

Concentration-dependent significant relaxation was observed in aortic rings precontracted with phenylephrine, KCl or Ang II. The tension increment produced by increasing external calcium was also reduced by DHPEE. DHPEE caused a marked decrease in the maximal contractile response of the vasoactive agents and shifted their concentration-response curves to the right.

CONCLUSION

DHPEE possesses dual characteristics and cause vasorelaxation by blocking the L-type calcium channels and blocking Ang II receptors (AT1) in rat aortic smooth muscle.

Metabolomic profiling of cellular responses to carvedilol enantiomers in vascular smooth muscle cells

Carvedilol is a non-selective β-blocker indicated in the treatment of hypertension and heart failure. Although the differential pharmacological effects of individual Carvedilol enantiomer is supported by preceding studies, the cellular response to each enantiomer is not well understood. Here we report the use of GC-MS metabolomic profiling to study the effects of Carvedilol enantiomers on vascular smooth muscle cells (A7r5) and to shed new light on molecular events underlying Carvedilol treatment. The metabolic analysis revealed alternations in the levels of 8 intracellular metabolites and 5 secreted metabolites in A7r5 cells incubated separately with S- and R-Carvedilol. Principal component analysis of the metabolite data demonstrated the characteristic metabolic signatures in S- and R-Carvedilol-treated cells. A panel of metabolites, including L-serine, L-threonine, 5-oxoproline, myristic acid, palmitic acid and inositol are closely correlated to the vascular smooth muscle contraction. Our findings reveal the differentiating metabolites for A7r5 cells incubated with individual enantiomer of Carvedilol, which opens new perspectives to employ metabolic profiling platform to study chiral drug-cell interactions and aid their incorporation into future improvement of β-blocker therapy.