Invited review: mechanisms of calcium handling in smooth muscles

Inositol 1,4,5-Trisphosphate Receptors Regulate Vascular Smooth Muscle Cell Proliferation and Neointima Formation in Mice

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation is involved in many types of arterial diseases, including neointima hyperplasia, in which Ca2+ has been recognized as a key player. However, the physiological role of Ca2+ release via inositol 1,4,5-trisphosphate receptors (IP3Rs) from endoplasmic reticulum in regulating VSMC proliferation has not been well determined.

METHODS AND RESULTS

Both in vitro cell culture models and in vivo mouse models were generated to investigate the role of IP3Rs in regulating VSMC proliferation. Expression of all 3 IP3R subtypes was increased in cultured VSMCs upon platelet-derived growth factor-BB and FBS stimulation as well as in the left carotid artery undergoing intimal thickening after vascular occlusion. Genetic ablation of all 3 IP3R subtypes abolished endoplasmic reticulum Ca2+ release in cultured VSMCs, significantly reduced cell proliferation induced by platelet-derived growth factor-BB and FBS stimulation, and also decreased cell migration of VSMCs. Furthermore, smooth muscle-specific deletion of all IP3R subtypes in adult mice dramatically attenuated neointima formation induced by left carotid artery ligation, accompanied by significant decreases in cell proliferation and matrix metalloproteinase-9 expression in injured vessels. Mechanistically, IP3R-mediated Ca2+ release may activate cAMP response element-binding protein, a key player in controlling VSMC proliferation, via Ca2+/calmodulin-dependent protein kinase II and Akt. Loss of IP3Rs suppressed cAMP response element-binding protein phosphorylation at Ser133 in both cultured VSMCs and injured vessels, whereas application of Ca2+ permeable ionophore, ionomycin, can reverse cAMP response element-binding protein phosphorylation in IP3R triple knockout VSMCs.

CONCLUSIONS

Our results demonstrated an essential role of IP3R-mediated Ca2+ release from endoplasmic reticulum in regulating cAMP response element-binding protein activation, VSMC proliferation, and neointima formation in mouse arteries.

Vasorelaxant mechanisms of the antidiabetic anagliptin in rabbit aorta: roles of Kv channels and SERCA pump

AIMS

The present study investigated the vasorelaxant mechanisms of an oral antidiabetic drug, anagliptin, using phenylephrine (Phe)-induced pre-contracted rabbit aortic rings.

METHODS

Arterial tone measurement was performed in rabbit thoracic aortic rings.

RESULTS

Anagliptin induced vasorelaxation in a dose-dependent manner. Pre-treatment with the classical voltagedependent K+ (Kv) channel inhibitors 4-aminopyridine and tetraethylammonium significantly decreased the vasorelaxant effect of anagliptin, whereas pre-treatment with the inwardly rectifying K+ (Kir) channel inhibitor Ba2+, the ATP-sensitive K+ (KATP) channel inhibitor glibenclamide, and the large-conductance Ca2+-activated K+ (BKCa) channel inhibitor paxilline did not attenuate the vasorelaxant effect. Furthermore, the vasorelaxant response of anagliptin was effectively inhibited by pre-treatment with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid. Neither cAMP/protein kinase A (PKA)-related signaling pathway inhibitors (adenylyl cyclase inhibitor SQ 22536 and PKA inhibitor KT 5720) nor cGMP/protein kinase G (PKG)-related signaling pathway inhibitors (guanylyl cyclase inhibitor ODQ and PKG inhibitor KT 5823) reduced the vasorelaxant effect of anagliptin. Similarly, the anagliptin-induced vasorelaxation was independent of the endothelium.

CONCLUSIONS

Based on these results, we suggest that anagliptin-induced vasorelaxation in rabbit aortic smooth muscle occurs by activating Kv channels and the SERCA pump, independent of other vascular K+ channels, cAMP/PKA- or cGMP/PKG-related signaling pathways, and the endothelium.

Anti-diarrheal effect of piperine possibly through the interaction with inflammation inducing enzymes: In vivo and in silico studies

Piperine is a natural alkaloid that possesses a variety of therapeutic properties, including anti-inflammatory, antioxidant, antibacterial, and anticarcinogenic activities. The present study aims to assess the medicinal benefits of piperine as an anti-diarrheal agent in a chick model by utilizing in vivo and in silico techniques. For this, castor oil was administered orally to 2-day-old chicks to cause diarrhea. Bismuth subsalicylate (10 mg/kg), loperamide (3 mg/kg), and nifedipine (2.5 mg/kg) were used as positive controls, while the vehicle was utilized as a negative control. Two different doses (25 and 50 mg/kg b.w.) of the test sample (piperine) were administered orally, and the highest dose was tested with standards to investigate the synergistic activity of the test sample. In our findings, piperine prolonged the latent period while reducing the number of diarrheal feces in the experimental chicks during the monitoring period (4 h). At higher doses, piperine appears to reduce diarrheal secretion while increasing latency in chicks. Throughout the combined pharmacotherapy, piperine outperformed bismuth subsalicylate and nifedipine in terms of anti-diarrheal effects with loperamide. In molecular docking, piperine exhibited higher binding affinities towards different inflammatory enzymes such as cyclooxygenase 1 (-7.9 kcal/mol), cyclooxygenase 2 (-8.4 kcal/mol), nitric oxide synthases (-8.9 kcal/mol), and L-type calcium channel (-8.8 kcal/mol), indicating better interaction of PP with these proteins. In conclusion, piperine showed a potent anti-diarrheal effect in castor oil-induced diarrheal chicks by suppressing the inflammation and calcium ion influx induced by castor oil.

Calcium Homeostasis, Transporters, and Blockers in Health and Diseases of the Cardiovascular System

Calcium is a highly positively charged ionic species. It regulates all cell types' functions and is an important second messenger that controls and triggers several mechanisms, including membrane stabilization, permeability, contraction, secretion, mitosis, intercellular communications, and in the activation of kinases and gene expression. Therefore, controlling calcium transport and its intracellular homeostasis in physiology leads to the healthy functioning of the biological system. However, abnormal extracellular and intracellular calcium homeostasis leads to cardiovascular, skeletal, immune, secretory diseases, and cancer. Therefore, the pharmacological control of calcium influx directly via calcium channels and exchangers and its outflow via calcium pumps and uptake by the ER/SR are crucial in treating calcium transport remodeling in pathology. Here, we mainly focused on selective calcium transporters and blockers in the cardiovascular system.

Post-injury Inhibition of Endothelin-1 Dependent Renal Vasoregulation Mitigates Rhabdomyolysis-Induced Acute Kidney Injury

In patients with rhabdomyolysis, the overwhelming release of myoglobin into the circulation is the primary cause of kidney injury. Myoglobin causes direct kidney injury as well as severe renal vasoconstriction. An increase in renal vascular resistance (RVR) results in renal blood flow (RBF) and glomerular filtration rate (GFR) reduction, tubular injury, and acute kidney injury (AKI). The mechanisms that underlie rhabdomyolysis-induced AKI are not fully understood but may involve the local production of vasoactive mediators in the kidney. Studies have shown that myoglobin stimulates endothelin-1 (ET-1) production in glomerular mesangial cells. Circulating ET-1 is also increased in rats subjected to glycerol-induced rhabdomyolysis. However, the upstream mechanisms of ET-1 production and downstream effectors of ET-1 actions in rhabdomyolysis-induced AKI remain unclear. Vasoactive ET-1 is generated by ET converting enzyme 1 (ECE-1)-induced proteolytic processing of inactive big ET to biologically active peptides. The downstream ion channel effectors of ET-1-induced vasoregulation include the transient receptor potential cation channel, subfamily C member 3 (TRPC3). This study demonstrates that glycerol-induced rhabdomyolysis in Wistar rats promotes ECE-1-dependent ET-1 production, RVR increase, GFR decrease, and AKI. Rhabdomyolysis-induced increases in RVR and AKI in the rats were attenuated by post-injury pharmacological inhibition of ECE-1, ET receptors, and TRPC3 channels. CRISPR/Cas9-mediated knockout of TRPC3 channels attenuated ET-1-induced renal vascular reactivity and rhabdomyolysis-induced AKI. These findings suggest that ECE-1-driven ET-1 production and downstream activation of TRPC3-dependent renal vasoconstriction contribute to rhabdomyolysis-induced AKI. Hence, post-injury inhibition of ET-1-mediated renal vasoregulation may provide therapeutic targets for rhabdomyolysis-induced AKI.

The inhibitory effect of escitalopram on mouse detrusor contractility: The role of L-type calcium channels

Selective serotonin reuptake inhibitors (SSRIs) are associated with urinary problems attributed to their central effects. ESC is a preferred SSRI and several case reports described that ESC is related to urinary retention. However, the direct effect of ESC on detrusor contractility is still not completely elucidated. Thus, we investigated the effect of ESC on detrusor contractility and mechanism(s) of its action in isolated mouse detrusor strips. Molecular docking and measurement of intracellular calcium were performed to determine the possible calcium channel blocking effect of ESC. The contractile responses to carbachol (CCh), KCl and electrical field stimulation of detrusor strips were significantly abolished by ESC (10 or 100 μM). ESC relaxed KCl-precontracted detrusor strips concentration-dependently, which was not affected by tetraethylammonium, glibenclamide, 4-aminopyridine, propranolol, L-NAME or methylene blue. ESC (10 or 100 μM) reduced both the CaCl₂- and CCh-induced contractions under calcium-free conditions, indicating the role of calcium-involved mechanisms in ESC-mediated relaxation. Furthermore, ESC significantly decreased Bay K8644-induced contraction and the cytosolic calcium level in fura-2-loaded A7r5 cells. Molecular docking study also revealed the potential of ESC to bind L-type calcium (Ca_v1) channels. Our results demonstrate that ESC inhibits detrusor contractility via blocking Ca_v1 channels, which provides evidence for the direct effect of ESC on detrusor contractility and its mechanism.

Airway smooth muscle function in asthma

Known to have affected around 340 million people across the world in 2018, asthma is a prevalent chronic inflammatory disease of the airways. The symptoms such as wheezing, dyspnea, chest tightness, and cough reflect episodes of reversible airway obstruction. Asthma is a heterogeneous disease that varies in clinical presentation, severity, and pathobiology, but consistently features airway hyperresponsiveness (AHR)—excessive airway narrowing due to an exaggerated response of the airways to various stimuli. Airway smooth muscle (ASM) is the major effector of exaggerated airway narrowing and AHR and many factors may contribute to its altered function in asthma. These include genetic predispositions, early life exposure to viruses, pollutants and allergens that lead to chronic exposure to inflammatory cells and mediators, altered innervation, airway structural cell remodeling, and airway mechanical stress. Early studies aiming to address the dysfunctional nature of ASM in the etiology and pathogenesis of asthma have been inconclusive due to the methodological limitations in assessing the intrapulmonary airways, the site of asthma. The study of the trachealis, although convenient, has been misleading as it has shown no alterations in asthma and it is not as exposed to inflammatory cells as intrapulmonary ASM. Furthermore, the cartilage rings offer protection against stress and strain of repeated contractions. More recent strategies that allow for the isolation of viable intrapulmonary ASM tissue reveal significant mechanical differences between asthmatic and non-asthmatic tissues. This review will thus summarize the latest techniques used to study ASM mechanics within its environment and in isolation, identify the potential causes of the discrepancy between the ASM of the extra- and intrapulmonary airways, and address future directions that may lead to an improved understanding of ASM hypercontractility in asthma.

The Role of Junctophilin Proteins in Cellular Function

Junctophilins (JPHs) comprise a family of structural proteins that connect the plasma membrane to intracellular organelles such as the endo/sarcoplasmic reticulum. Tethering of these membrane structures results in the formation of highly organized subcellular junctions that play important signaling roles in all excitable cell types. There are four JPH isoforms, expressed primarily in muscle and neuronal cell types. Each JPH protein consists of 6 'membrane occupation and recognition nexus' (MORN) motifs, a joining region connecting these to another set of 2 MORN motifs, a putative alpha-helical region, a divergent region exhibiting low homology between JPH isoforms, and a carboxy-terminal transmembrane region anchoring into the ER/SR membrane. JPH isoforms play essential roles in developing and maintaining subcellular membrane junctions. Conversely, inherited mutations in JPH2 cause hypertrophic or dilated cardiomyopathy, while trinucleotide expansions in the JPH3 gene cause Huntington Disease-Like 2. Loss of JPH1 protein levels can cause skeletal myopathy, while loss of cardiac JPH2 levels causes heart failure and atrial fibrillation, among other disease. This review will provide a comprehensive overview of the JPH gene family, phylogeny, and evolutionary analysis of JPH genes and other MORN domain proteins. JPH biogenesis, membrane tethering, and binding partners will be discussed, as well as functional roles of JPH isoforms in excitable cells. Finally, potential roles of JPH isoform deficits in human disease pathogenesis will be reviewed.

Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters

Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Ca_v1.2 and Ca_v1.3 channels to obligatory dimeric assembly and gating of voltage-gated Na_v1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP₃Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.

Mechanisms underlying the vasodilatory effects of canagliflozin in the rabbit thoracic aorta: Involvement of the SERCA pump and Kv channels

AIMS

Canagliflozin is an anti-diabetic agent and sodium glucose co-transporter-2 inhibitor. Despite numerous clinical trials demonstrating its beneficial effects on blood pressure, the cellular mechanisms underlying the effects of canagliflozin on vascular reactivity have yet to be clarified. We investigated the vasodilatory effect of canagliflozin on aortic rings isolated from rabbits.

MAIN METHODS

We used rabbit thoracic aortic rings and its arterial tone was tested by using wire myography system.

KEY FINDINGS

Canagliflozin caused concentration-dependent vasodilation in aortic rings pre-constricted with phenylephrine or high K⁺. However, the degree of canagliflozin-induced vasodilation of the aortic rings pre-constricted with high K⁺ was less than that of rings pre-constricted with phenylephrine. Application of 4-aminopyridine, a voltage-dependent K⁺ (Kv) channel inhibitor, reduced canagliflozin-induced vasodilation. However, pre-incubation of an inwardly rectifying K⁺ channel inhibitor, a large-conductance Ca²⁺-activated K⁺ channel inhibitor, and an ATP-sensitive K⁺ inhibitor did not modulate the vasodilatory effects of canagliflozin. Indeed, canagliflozin increased Kv currents in aortic smooth muscle cells. Pre-treatment with thapsigargin or cyclopiazonic acid, a sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors, reduced the vasodilatory effects of canagliflozin. Conversely, pre-treatment with a Ca²⁺ channel inhibitor, adenylyl cyclase/PKA inhibitors, and guanylyl cyclase/PKG inhibitors did not modulate the vasodilatory effects of canagliflozin. Endothelium removal, and pre-treatment with the nitric oxide synthase inhibitor L-NAME, and small- and intermediate-conductance Ca²⁺-activated K⁺ channel inhibitor apamin and TRAM-34, did not diminish the vasodilatory effects of canagliflozin.

SIGNIFICANCE

Our results indicate that canagliflozin induces vasodilation, which is dependent on the robust SERCA activity and Kv channel activation.

Physiological and transcriptomic changes of zebrafish (Danio rerio) embryos-larvae in response to 2-MIB exposure

2-Methylisoborneol (2-MIB), a natural odorous substance, is widely distributed in water environment, but there is a paucity of information concerning its systemic toxicity. Herein, we investigated the effects of 2-MIB exposure on developmental parameters, locomotive behavior, oxidative stress, apoptosis and transcriptome of zebrafish. Zebrafish embryos exposed to different concentrations (0, 0.5, 5 and 42.8 μg/L) of 2-MIB showed no changes in mortality, hatchability, and malformation rate, but the body length of zebrafish larvae was significantly increased in a dose-dependent manner, and accompanied by the changes of growth hormone/insulin-like growth factor (GH/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis genes. Moreover, the swimming activity of zebrafish larvae increased, which may be due to the increase of acetylcholinesterase (AChE) activity. Meanwhile, 2-MIB caused oxidative stress and apoptosis in zebrafish larvae by altering the NF-E2-related factor 2 (Nrf2) and mitochondrial signaling pathways, respectively. Transcriptome sequencing assay showed that the phototransduction signaling pathway was significantly enriched, and most of the genes in this pathway exhibited enhanced expression after exposure to 2-MIB. These findings provide an important reference for risk assessment and early warning to 2-MIB exposure.

Molecular mechanism of apelin-13 regulation of colonic motility in rats

Apelin is a novel neuropeptide identified as the endogenous ligand for the apelin receptor. Apelin and its receptor are widely distributed in the gastrointestinal tract. Studies have reported that apelin-13 is involved in modulating gastrointestinal motility; however, the evidence is insufficient and the relevant mechanism is still not fully clear. Consequently, our study designed to explore the effect induced by exogenous apelin-13, to analyze the mechanism of action in isolated rat colons and colonic smooth muscle cells. The spontaneous contractions of colonic smooth muscle strips from rat were measured in an organ bath system. L-type calcium currents and large conductance Ca2+-activated K+ (BKCa) currents in rat colonic smooth muscle cells were investigated using the electrophysiological patch-clamp technique. Apelin-13 decreased the spontaneous contractile activity of colonic smooth muscle strips in a dose-dependent manner, and the inhibitory effect was not abolished by tetrodotoxin. The electrophysiological recordings revealed that apelin-13 reduced the crest currents of L-type calcium in a concentration-dependent manner in colonic smooth muscle cells at the test potential of 0 mV. Moreover, apelin-13 moved the current-voltage (I-V) curves of L-type calcium channels upward, but did not change their contour. Furthermore, the characteristics of L-type calcium channels with steady-state activation and steady-state inactivation were not significantly changed. Similarly, application of apelin-13 also significantly decreased BKCa currents in a concentration-dependent manner. In conclusion, apelin-13 inhibited the spontaneous contractile activity of isolated rat colons via the suppression of L-type calcium channels and BKCa channels in colonic smooth muscle cells.

Junctophilins: Key Membrane Tethers in Muscles and Neurons

Contacts between the endoplasmic reticulum (ER) and plasma membrane (PM) contain specialized tethering proteins that bind both ER and PM membranes. In excitable cells, ER–PM contacts play an important role in calcium signaling and transferring lipids. Junctophilins are a conserved family of ER–PM tethering proteins. They are predominantly expressed in muscles and neurons and known to simultaneously bind both ER- and PM-localized ion channels. Since their discovery two decades ago, functional studies using junctophilin-deficient animals have provided a deep understanding of their roles in muscles and neurons, including excitation-contraction coupling, store-operated calcium entry (SOCE), and afterhyperpolarization (AHP). In this review, we highlight key findings from mouse, fly, and worm that support evolutionary conservation of junctophilins.

The inhibitory effect of trimetazidine on detrusor contractility - a potential repositioning of trimetazidine for the treatment of overactive bladder

OBJECTIVES

This study aimed to identify the effect of trimetazidine (TMZ), an antianginal drug, on detrusor smooth muscle (DSM) contractility and its possible mechanisms of action.

METHODS

We performed in-vitro contractility studies on isolated mouse DSM strips and investigated the effect of TMZ on Ca2+ levels in fura-2-loaded A7r5 cells.

KEY FINDINGS

TMZ (300 or 1000 µM) inhibited carbachol (CCh)- and KCl-induced contractions and produced a concentration-dependent (10-1000 µM) relaxation in KCl-precontracted DSM strips. TMZ-induced relaxation was markedly decreased by BaCl2, an inward-rectifying K+ channel blocker, but was not altered by preincubation with tetraethylammonium, glibenclamide, 4-aminopyridine, propranolol, L-NAME or methylene blue. TMZ (300 or 1000 µM) reduced both the CaCl2-induced contraction of depolarized DSM strips under Ca2+-free conditions and the CCh-induced contraction of DSM strips preincubated with nifedipine in Ca2+-containing Krebs solution. Furthermore, TMZ (1000 µM) significantly decreased the Ca2+ levels in fura-2-loaded A7r5 cells.

CONCLUSIONS

TMZ decreased DSM contractility and caused a concentration-dependent relaxation of the tissue possibly through its actions on Ca2+ transients and K+ channels. Our results provide preclinical evidence that TMZ would be a potential candidate to treat disorders related to the overactivity of the bladder.

Transgelin-2: A Double-Edged Sword in Immunity and Cancer Metastasis

Transgelin-2, a small actin-binding protein, is the only transgelin family member expressed in immune cells. In T and B lymphocytes, transgelin-2 is constitutively expressed, but in antigen-presenting cells, it is significantly upregulated upon lipopolysaccharide stimulation. Transgelin-2 acts as a molecular staple to stabilize the actin cytoskeleton, and it competes with cofilin to bind filamentous (F)-actin. This action may enable immune synapse stabilization during T-cell interaction with cognate antigen-presenting cells. Furthermore, transgelin-2 blocks Arp2/3 complex-nucleated actin branching, which is presumably related to small filopodia formation, enhanced phagocytic function, and antigen presentation. Overall, transgelin-2 is an essential part of the molecular armament required for host defense against neoplasms and infectious diseases. However, transgelin-2 acts as a double-edged sword, as its expression is also essential for a wide range of tumor development, including drug resistance and metastasis. Thus, targeting transgelin-2 can also have a therapeutic advantage for cancer treatment; selectively suppressing transgelin-2 expression may prevent multidrug resistance in cancer chemotherapy. Here, we review newly discovered molecular characteristics of transgelin-2 and discuss clinical applications for cancer and immunotherapy.

Effect of Evodiamine on Rat Colonic Hypermotility Induced by Water Avoidance Stress and the Underlying Mechanism

Background and Aim

EVO is a natural alkaloid that reportedly has potential value in regulating gastrointestinal motility, but this conclusion remains controversial, and the molecular mechanism is unclear. In this study, we aimed to explore the effect of short-chain fatty acids on rat colonic hypermotility induced by water avoidance stress and the underlying mechanism.

Methods

We constructed a hypermotile rat model by chronic water avoidance stress, and Western blot was used to detect the protein level of nNOS in colon tissue. The organ bath and multichannel physiological signal acquisition systems were used to examine the spontaneous contractions of smooth muscle strips. The whole-cell patch-clamp technique was used to investigate L-type voltage-dependent calcium and BK_Ca channel currents in colonic smooth muscle cells.

Results

EVO inhibited the spontaneous contractions of colonic smooth muscle strips in a dose-dependent manner. Moreover, EVO decreased the fecal output induced by chronic water avoidance stress. TTX did not block the inhibitory effect of EVO on spontaneous colon contractions, while L-NNA, a selective nNOS synthase inhibitor, did partially abolish this inhibitory effect. The protein expression of nNOS in the colon tissues of rats administered EVO was significantly increased compared to that in control rats. EVO reversibly inhibited the L-type calcium channel current without changing the steady-state activation or inactivation in colonic smooth muscle cells. EVO significantly inhibited the BK_Ca current but did not change the shape of the I-V curves.

Conclusion

EVO inhibits gastrointestinal motility by inhibiting L-type calcium and BK_Ca channels in colonic smooth muscle cells and indirectly interacting with nNOS.

An Indole Alkaloid Extracted from Evodia rutaecarpa Inhibits Colonic Motility of Rats In Vitro

Evodiamine (Evo) is an indole alkaloid extracted from the traditional Chinese medicinal herb Evodia rutaecarpa. Evo may regulate gastrointestinal motility, but the evidence is insufficient, and the mechanisms remain unknown. The aim of this study was to investigate the effect of Evo on colonic motility of rats and the underlying mechanisms in vitro. Rat colonic muscle was exposed to Evo (10 and 100 μM) followed by immunohistochemistry of cholecystokinin receptor 1 (CCK1R). Muscle contractions were studied in an organ bath system to determine whether CCK1R, nitric oxide (NO), and enteric neurons are involved in the relaxant effect of Evo. Whole-cell patch-clamp was used to detect L-type calcium currents (I_Ca,L) in isolated colonic smooth muscle cells (SMCs). CCK1R was observed in SMCs, intermuscular neurons, and mucosa of rat colon. Evo could inhibit spontaneous muscle contractions; NO synthase, inhibitor L-NAME CCK1R antagonist, could partly block this effect, while the enteric neurons may not play a major role. Evo inhibited the peak I_Ca,L in colonic SMCs at a membrane potential of 0 mV. The current-voltage (I–V) relationship of L-type calcium channels was modified by Evo, while the peak of the I–V curve remained at 0 mV. Furthermore, Evo inhibited the activation of L-type calcium channels and decreased the peak I_Ca,L. The relaxant effect of Evo on colonic muscle is associated with the inhibition of L-type calcium channels. The enteric neurons, NO, and CCK1R may be partly related to the inhibitory effect of Evo on colonic motility. This study provides the first evidence that evodiamine can regulate colonic motility in rats by mediating calcium homeostasis in smooth muscle cells. These data form a theoretical basis for the clinical application of evodiamine for treatment of gastrointestinal motility diseases.

Estrogen receptors differentially regulate intracellular calcium handling in human nonasthmatic and asthmatic airway smooth muscle cells

Asthma is defined as chronic inflammation of the airways and is characterized by airway remodeling, hyperresponsiveness, and acute bronchoconstriction of airway smooth muscle (ASM) cells. Clinical findings suggest a higher incidence and severity of asthma in adult women, indicating a concrete role of sex steroids in modulating the airway tone. Estrogen, a major female sex steroid mediates its role through estrogen receptors (ER) ERα and ERβ, which are shown to be expressed in human ASM, and their expression is upregulated in lung inflammation and asthma. Previous studies suggested rapid, nongenomic signaling of estrogen via ERs reduces intracellular calcium ([Ca²⁺]_i), thereby promoting relaxation of ASM. However, long-term ER activation on [Ca²⁺]_i regulation in human ASM during inflammation or in asthma is still not known. In Fura-2-loaded nonasthmatic and asthmatic human ASM cells, we found that prolonged (24 h) exposure to ERα agonist (PPT) increased [Ca²⁺]_i response to histamine, whereas ERβ activation (WAY) led to decreased [Ca²⁺] compared with vehicle. This was further confirmed by ER overexpression and knockdown studies using various bronchoconstrictor agents. Interestingly, ERβ activation was more effective than 17β-estradiol in reducing [Ca²⁺]_i responses in the presence of TNF-α or IL-13, while no observable changes were noticed with PPT in the presence of either cytokine. The [Ca²⁺]_i-reducing effects of ERβ were mediated partially via L-type calcium channel inhibition and increased Ca²⁺ sequestration by sarcoplasmic reticulum_. Overall, these data highlight the differential signaling of ERα and ERβ in ASM during inflammation. Specific ERβ activation reduces [Ca²⁺]_i in the inflamed ASM cells and is likely to play a crucial role in regulating ASM contractility, thereby relaxing airways.

Inositol 1,4,5-Trisphosphate Receptors in Endothelial Cells Play an Essential Role in Vasodilation and Blood Pressure Regulation

Background Endothelial NO synthase plays a central role in regulating vasodilation and blood pressure. Intracellular Ca2+ mobilization is a critical modulator of endothelial NO synthase function, and increased cytosolic Ca2+ concentration in endothelial cells is able to induce endothelial NO synthase phosphorylation. Ca2+ release mediated by 3 subtypes of inositol 1,4,5-trisphosphate receptors ( IP 3Rs) from the endoplasmic reticulum and subsequent Ca2+ entry after endoplasmic reticulum Ca2+ store depletion has been proposed to be the major pathway to mobilize Ca2+ in endothelial cells. However, the physiological role of IP 3Rs in regulating blood pressure remains largely unclear. Methods and Results To investigate the role of endothelial IP 3Rs in blood pressure regulation, we first generated an inducible endothelial cell-specific IP 3R1 knockout mouse model and found that deletion of IP 3R1 in adult endothelial cells did not affect vasodilation and blood pressure. Considering all 3 subtypes of IP 3Rs are expressed in mouse endothelial cells, we further generated inducible endothelial cell-specific IP 3R triple knockout mice and found that deletion of all 3 IP 3R subtypes decreased plasma NO concentration and increased basal blood pressure. Furthermore, IP 3R deficiency reduced acetylcholine-induced vasodilation and endothelial NO synthase phosphorylation at Ser1177. Conclusions Our results reveal that IP 3R-mediated Ca2+ release in vascular endothelial cells plays an important role in regulating vasodilation and physiological blood pressure.

Effects of exendin-4 on colonic motility in rats and its underlying mechanism

BACKGROUND

Glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) agonists modulate gastrointestinal motility; however, the effects of GLP-1R agonists on colonic motility are still controversial, and the molecular mechanism is unclear. Exendin-4 shares 53% homology with GLP-1 and is a full agonist of GLP-1R. In this study, our aims were to explore the role and mechanism of exendin-4 in isolated rat colonic tissues and cells.

METHODS

An organ bath system was used to examine the spontaneous contractions of smooth muscle strips. The whole-cell patch-clamp technique was used to investigate the currents of L-type voltage-dependent calcium channels and large conductance Ca²⁺ -activated K⁺ (BK_Ca ) channels in smooth muscle cells.

KEY RESULTS

Exendin-4 decreased both the amplitude and frequency of spontaneous contractions of smooth muscle strips in a concentration-dependent manner. The inhibitory effect was completely blocked by exendin-4(9-39), a GLP-1R antagonist. Moreover, this effect was partially abolished by tetrodotoxin (TTX), a blocker of neuronal voltage-dependent Na⁺ channels, Nω-Nitro-l-arginine (L-NNA), a nitric oxide synthase (NOS) inhibitor, apamin, an inhibitor of small-conductance Ca²⁺ -activated K⁺ (SK) channels. Whole-cell patch-clamp recordings revealed that exendin-4 inhibited the peak current of L-type calcium channels in colonic smooth muscle cells, but did not change the shape of the current-voltage (I-V) curves. The steady-state activation and steady-state inactivation of L-type calcium channels were not affected. Likewise, BK_Ca currents were significantly inhibited by exendin-4.

CONCLUSIONS

Exendin-4 indirectly inhibits colonic muscle activity via a nitrergic and a purinergic neural pathway through NO and ATP release and inhibits L-type voltage-dependent calcium channels and BK_Ca channels in smooth muscle cells.

Effects of Fengliao-Changweikang in Diarrhea-predominant Irritable Bowel Syndrome Rats and Its Mechanism Involving Colonic Motility

Background/Aims

This study was designed to investigate the effect of Fengliao-Changweikang (FLCWK) in diarrhea-predominant irritable bowel syndrome (IBS-D) rats and explore its underlying mechanisms.

Methods

IBS-D model rats were induced by neonatal maternal separation (NMS) combined with restraint stress (RS). In in vivo experiments, the model rats were randomly divided into 5 groups: NMS + RS, FLCWK (low dose, middle dose, and high dose), and pinaverium bromide. The normal control (no handling) rats were classified as the NH group. The therapeutic effect of FLCWK was evaluated by fecal characteristics, electromyographic response and abdominal withdrawal reflex scores. In in vitro experiments, the model rats were randomly divided into 2 groups: NMS + RS, FLCWK (middle dose), and no handling rats were used as the NH group. The differences in basic tension and ACh-induced tension of isolated colonic longitudinal smooth muscle strips (CLSMs) among the 3 groups were observed. In addition, different inhibitors (nifedipine, TMB-8, L-NAME, methylene blue, and 4-AP) were pretreated to explore the underlying mechanisms.

Results

In in vivo experiments, fecal characteristics, electromyographic response, and abdominal withdrawal reflex scores significantly improved in the FLCWK group, compared with the NMS + RS group. In in vitro experiments, the basic tension and ACh-induced tension of CLSMs in IBS-D rats were significantly inhibited by FLCWK. After pre-treatment with different inhibitors, the ACh-induced tension of CLSMs in each group showed no significant difference.

Conclusions

FLCWK manifested curative effect in IBS-D rats by inhibiting colonic contraction. The underlying mechanisms may be related to regulatory pathway of nitric oxide/cGMP/Ca²⁺ and specific potassium channels.

Possible antagonistic effects of the TRPC4 channel blocker ML204 on M2 and M3 muscarinic receptors in mouse ileal and detrusor smooth muscles and atrial myocardium

ML204, a potent transient receptor potential canonical 4 (TRPC4) channel blocker, is often used to elucidate the involvement of TRPC4 channels in receptor-operated signaling processes in visceral smooth muscles. In the present study, we investigated the possible antagonistic actions of ML204 on M₂ and M₃ muscarinic receptors, which mediate contractions in mouse ileal and detrusor smooth muscles. In ileal and detrusor smooth muscle preparations, ML204 (3 or 10 µM) significantly inhibited electrical field stimulation (EFS)-evoked cholinergic contractions. However, it did not significantly inhibit high K⁺-induced and EFS-evoked non-cholinergic contractions in the ileal preparations. When the muscarinic agonist, carbachol was cumulatively applied, ML204 (1, 3 and 10 µM) caused a rightward parallel shift of the concentration-response curves of carbachol. Additionally, ML204 (1, 3 and 10 µM) inhibited carbachol-induced negative chronotropic response in atrial preparations, which is mediated by M₂ muscarinic receptors. Furthermore, ML204 significantly inhibited the contractions evoked by carbachol-induced intracellular Ca²⁺ release, which is mediated by M₃ muscarinic receptors. These results suggested that ML204 might exhibit antagonistic actions on M₂ and M₃ muscarinic receptors; in addition, the inhibitory effects of ML204 against EFS-induced cholinergic contractions might be attributed to this receptor antagonism rather than inhibition of TRPC4 channel activity. Therefore, these effects should be considered when ML204 is used as a TRPC4 channel blocker.

Adenosine A1 receptor-operated calcium entry in renal afferent arterioles is dependent on postnatal maturation of TRPC3 channels

Adenosine, a regulator of cardiovascular development and renal function, constricts renal afferent arterioles by inducing intracellular Ca²⁺ concentration ([Ca²⁺]_i) elevation in smooth muscle cells (SMCs) via activation of its cognate A₁ receptors (A₁Rs). Mechanisms that underlie A₁R-dependent [Ca²⁺]_i elevation in renal vascular SMCs are not fully resolved. Whether A₁R expression and function in preglomerular microvessels are dependent on postnatal kidney maturation is also unclear. In this study, we show that selective activation of A₁Rs by 2-chloro-N⁶-cyclopentyladenosine (CCPA) does not stimulate store-operated Ca²⁺ entry in afferent arterioles isolated from neonatal pigs. However, CCPA-induced [Ca²⁺]_i elevation is dependent on phospholipase C and transient receptor potential cation channel, subfamily C, member 3 (TRPC3). Basal [Ca²⁺]_i was unchanged in afferent arterioles isolated from newborn (0-day-old) pigs compared with their 20-day-old counterparts. By contrast, CCPA treatment resulted in significantly larger [Ca²⁺]_i in afferent arterioles from 20-day-old pigs. A₁R protein expression levels in the kidneys and afferent arterioles were unaltered in 0- vs. 20-day-old pigs. However, the TRPC3 channel protein expression level was ~92 and 78% higher in 20-day-old pig kidneys and afferent arterioles, respectively. These data suggest that activation of A₁Rs elicits receptor-operated Ca²⁺ entry in porcine afferent arterioles, the level of which is dependent on postnatal maturation of TRPC3 channels. We propose that TRPC3 channels may contribute to the physiology and pathophysiology of A₁Rs.

Importance of Altered Levels of SERCA, IP3R, and RyR in Vascular Smooth Muscle Cell

Calcium cycling between the sarcoplasmic reticulum (SR) and the cytosol via the sarco-/endoplasmic reticulum Ca-ATPase (SERCA) pump, inositol-1,4,5-triphosphate receptor (IP₃R), and Ryanodine receptor (RyR), plays a major role in agonist-induced intracellular calcium ([Ca²⁺]_cyt) dynamics in vascular smooth muscle cells (VSMC). Levels of these calcium handling proteins in SR get altered under disease conditions. We have developed a mathematical model to understand the significance of altered levels of SERCA, IP₃R, and RyR on the intracellular calcium dynamics of VSMC and to understand how variation in protein levels that arise due to diabetes contribute to different VSMC behavior and thus vascular disease. SR is modeled as a single continuous entity with homogeneous intra-SR calcium. Model results show that agonist-induced intracellular calcium dynamics can be modified by changing the levels of SERCA, IP₃R, and/or RyR. Lowering SERCA level will enable intracellular calcium oscillations at low agonist concentrations whereas lowered levels of IP₃R and RyR need higher agonist concentration for intracellular calcium oscillations. This research suggests that reduced SERCA level is the main factor responsible for the reduced intracellular calcium transients and contractility in VSMCs.

A controlled study to investigate anti-diarrhoeal effect of the stem-bark fractions of Terminalia avicennioides in laboratory animal models

Due to the shortcomings associated with modern synthetic antidiarrhoeal drugs, it is important to find newer, safer and cheaper antidiarrhoeal agents from natural sources. The study was conducted to evaluate the anti-diarrhoeal activity of the fractions of the stem-bark of Terminalia avicennioides in laboratory animal models. The effect of different concentrations (1.0 × 10⁻³, 2.0 × 10⁻³, 4.0 × 10⁻³ and 8.0 × 10⁻³ mg/mL) of the aqueous methanol (AMF), ethyl acetate (EAF) and hexane (HXF) fractions of T. avicennioides were tested against spontaneous and acetylcholine-induced contractions of rabbit jejunum as well as on histamine-induced contraction of guinea pig ileum. Similarly, the effects of the AMF on gastro-intestinal transit time, castor oil-induced diarrhoea and castor oil-induced enteropooling were evaluated. The AMF, EAF and HXF at concentrations of 1.0 × 10⁻³, 2.0 × 10⁻³, 4.0 × 10⁻³ and 8.0 × 10⁻³ mg/mL attenuated the contractile effects of both the spontaneous and acetylcholine-induced contractions of rabbit jejunum and that of histamine-induced contraction of guinea pig ileum in a concentration-dependent manner. The AMF at doses of 200, 300 and 500 mg/kg produced significant (p < 0.05) reductions in gastrointestinal transit time of charcoal and incidence of castor oil-induced diarrhoea in mice relative to the untreated control. Similarly, at doses of 300 and 500 mg/kg, AMF significantly (p < 0.05) reduced the weight and volume of intestinal fluid in the treated mice when compared to the untreated animals. The results of this study showed that the stem-bark of T. avicennioides possesses spasmolytic effect and could be a potential antidiarrhoeal agent. However, detailed pharmacological trials are required to justify the clinical use of the plant for treating diarrhoea.

The sources of calcium for noradrenaline-induced contraction in the human thoracic internal artery

The aim of the present study was to examine the contribution of intracellular and extracellular calcium sources in contraction caused by noradrenaline (NA) of the human internal thoracic artery (ITA) in vitro. Distal segments of ITA were obtained from 20 patients (aged 38-73, at the time of routine coronary artery surgical revascularization (CABG)). Contractile responses to 10^-6 mol/L NA in the physiological salt solution and in Ca²⁺-free solution without and after incubation with 10^-6 mol/L thapsigargin (TSG) were recorded under isometric conditions. Responses of ITA rings to 1 μM NA without incubation with TSG accounted (% of reaction to 80 mM KCl) 224.70 ± 14.06% in PSS solution, 141.30 ± 8.66% in Ca²⁺-free solution, and 80.03 ± 1.71% after PSS restoration and were statistically significantly different (p < 0.0001, one-way ANOVA). Responses of ITA rings to 1 μM NA with 1 μM TSG accounted (% of reaction to 80 mM KCl) 114.50 ± 2.79% in Ca²⁺-free solution and 36.70 ± 2.38% after PSS restoration. Responses in Ca²⁺-free solution and after PSS restoration without and with TSG were statistically significantly different (p = 0.0257 and p < 0.0001, respectively-t test). ITA contraction is caused by calcium derived not only from the SR and the extracellular matrix. The delivery of calcium to the space surrounding tissue does not immediately deliver calcium to the myofilaments.

Regulation of Gastrointestinal Smooth Muscle Function by Interstitial Cells

Interstitial cells of mesenchymal origin form gap junctions with smooth muscle cells in visceral smooth muscles and provide important regulatory functions. In gastrointestinal (GI) muscles, there are two distinct classes of interstitial cells, c-Kit(+) interstitial cells of Cajal and PDGFRα(+) cells, that regulate motility patterns. Loss of these cells may contribute to symptoms in GI motility disorders.

Chemical composition, vasorelaxant, antioxidant and antiplatelet effects of essential oil of Artemisia campestris L. from Oriental Morocco

BACKGROUND

Artemisia campestris L. (Asteraceae) is a medicinal herb traditionally used to treat hypertension and many other diseases. Hence, this study is aimed to analyze the essential oil of A. campestris L (AcEO) and to investigate the antiplatelet, antioxidant effects and the mechanisms of its vasorelaxant effect.

METHODS

The chemical composition of AcEO was elucidated using GC/MS analysis. Then, the antioxidant effect was tested on DPPH radical scavenging and on the prevention of β-carotene bleaching. The antiplatelet effect was performed on the presence of the platelet agonists: thrombin and ADP. The mechanism of action of the vasorelaxant effect was studied by using the cellular blockers specified to explore the involvement of NO/GC pathway and in the presence of calcium channels blockers and potassium channels blockers.

RESULTS

AcEO is predominated by the volatiles: spathulenol, ß-eudesmol and p-cymene. The maximal antioxidant effect was obtained with the dose 2 mg/ml of AcEO. The dose 1 mg/ml of AcEO showed a maximum antiplatelet effect of, respectively 49.73% ±9.54 and 48.20% ±8.49 on thrombin and ADP. The vasorelaxation seems not to be mediated via NOS/GC pathway neither via the potassium channels. However, pretreatment with calcium channels blockers attenuated this effect, suggesting that the vasorelaxation is mediated via inhibition of L-type Ca2+ channels and the activation of SERCA pumps of reticulum plasma.

CONCLUSION

This study confirms the antioxidant, antiplatelet and vasorelaxant effects of A.campestris L essential oil. However, the antihypertensive use of this oil should be further confirmed by the chemical fractionation and subsequent bio-guided assays.

Positive correlation of vanilloid receptor subtype1 and prostaglandin E2 expression with pain in leiomyomas

Cutaneous leiomyomas are benign smooth muscle tumors that are occasionally painful. The mechanism of pain related to leiomyoma is not fully understood. To investigate the possible involvement of algoneic factors in pain from cutaneous leiomyomas. We present a case of cutaneous leiomyoma with severe, diffused pain in a large area and collected 10 more specimens of cutaneous leiomyoma with or without pain in patient histories. We immunohistochemiacally examined the expression of algoneic factors: serotonin, histamin, Substance P, PGE2, BDKRB2, VR1 and CGRP. We compared the pain area and expression of algoneic factors to reveal possible correlations. We describe here a patient with a cutaneous leiomyoma 1-cm in diameter, which caused severe pain diffused throughout an area of 20-cm around the tumor. The pain completely resolved after surgical excision of the leiomyoma. We observed that the leiomyoma cells expressed CGRP, PGE2 and VR1 in this case. We found a positive correlation between VR1 and PGE2 expression in the leiomyoma cells and areas with pain around the tumors among 11 specimens in total. VR1 and PGE2 might be key algogenic substances in painful leiomyoma.

IP3 receptors regulate vascular smooth muscle contractility and hypertension

Inositol 1, 4, 5-trisphosphate receptor-mediated (IP₃R-mediated) calcium (Ca²⁺) release has been proposed to play an important role in regulating vascular smooth muscle cell (VSMC) contraction for decades. However, whether and how IP₃R regulates blood pressure in vivo remains unclear. To address these questions, we have generated a smooth muscle-specific IP₃R triple-knockout (smTKO) mouse model using a tamoxifen-inducible system. In this study, the role of IP₃R-mediated Ca²⁺ release in adult VSMCs on aortic vascular contractility and blood pressure was assessed following tamoxifen induction. We demonstrated that deletion of IP₃Rs significantly reduced aortic contractile responses to vasoconstrictors, including phenylephrine, U46619, serotonin, and endothelin 1. Deletion of IP₃Rs also dramatically reduced the phosphorylation of MLC20 and MYPT1 induced by U46619. Furthermore, although the basal blood pressure of smTKO mice remained similar to that of wild-type controls, the increase in systolic blood pressure upon chronic infusion of angiotensin II was significantly attenuated in smTKO mice. Taken together, our results demonstrate an important role for IP₃R-mediated Ca²⁺ release in VSMCs in regulating vascular contractility and hypertension.

Pharmacological profile of N-(2,6-dichlorophenyl)-2-(4-methyl-1-piperidinyl)acetamide, a novel analogue of lidocaine

AIM

N-(2,6-Dichlorophenyl)-2-(4-methyl-1-piperidinyl)acetamide (LIA), a lidocaine analogue, has potential applications in treating neuropathic pain. The aim of this work was to characterize the pharmacological activity of LIA related with central nervous system and cardiovascular activity.

METHODS

Anesthetic effect was tested in guinea pigs and mice. Ambulatory activity, anti-anxiety effect, sodium pentobarbital (PB)-induced hypnosis and pentylenetetrazol (PTZ)-induced seizures test were evaluated in mice to determine the possible central nervous system activity. The cardiovascular activities in vivo and ex vivo were analyzed in rats.

KEY FINDINGS

LIA (2%) presents, similar to lidocaine (2%), anesthetic activity on the corneal reflex, infiltration anesthesia and tail immersion test. LIA (1-100mg/kg, i.p.), similar to lidocaine (1-100mg/kg, i.p.), presents a dose-dependent sedative-hypnotic effect in mice. Both compounds did not produce anti-anxiety activity in mice. LIA did not prevent PTZ-induced seizures. However, LIA itself did not produce seizures at high doses in mice, as lidocaine does. LIA is a vasorelaxant compound for smooth muscle cells and presents hypotensive effect in vivo without increments to the heart rate significantly.

SIGNIFICANCE

High doses of lidocaine produce seizures and vasoconstriction. In this study, we found that LIA shares a similar pharmacological profile as lidocaine's but without the primary adverse effects of seizures and vasoconstriction.

Activation of PKA and Epac proteins by cyclic AMP depletes intracellular calcium stores and reduces calcium availability for vasoconstriction

AIMS

We investigated the implication of PKA and Epac proteins in the endothelium-independent vasorelaxant effects of cyclic AMP (cAMP).

MAIN METHODS

Cytosolic Ca(2+) concentration ([Ca(2+)]c) was measured by fura-2 imaging in rat aortic smooth muscle cells (RASMC). Contraction-relaxation experiments were performed in rat aortic rings deprived of endothelium.

KEY FINDINGS

In extracellular Ca(2+)-free solution, cAMP-elevating agents induced an increase in [Ca(2+)]c in RASMC that was reproduced by PKA and Epac activation and reduced after depletion of intracellular Ca(2+) reservoirs. Arginine-vasopressin (AVP)-evoked increase of [Ca(2+)]c and store-operated Ca(2+) entry (SOCE) were inhibited by cAMP-elevating agents, PKA or Epac activation in these cells. In aortic rings, the contractions induced by phenylephrine in absence of extracellular Ca(2+) were inhibited by cAMP-elevating agents, PKA or Epac activation. In these conditions, reintroduction of Ca(2+) induced a contraction that was inhibited by cAMP-elevating agents, an effect reduced by PKA inhibition and reproduced by PKA or Epac activators.

SIGNIFICANCE

Our results suggest that increased cAMP depletes intracellular, thapsigargin-sensitive Ca(2+) stores through activation of PKA and Epac in RASMC, thus reducing the amount of Ca(2+) released by IP3-generating agonists during the contraction of rat aorta. cAMP rise also inhibits the contraction induced by depletion of intracellular Ca(2+), an effect mediated by reduction of SOCE after PKA or Epac activation. Both effects participate in the cAMP-induced endothelium-independent vasorelaxation.

Calcium Sensitization Mechanisms in Gastrointestinal Smooth Muscles

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

Role of NO-cGMP pathway in ovine cervical relaxation induced by Erythroxylum caatingae Plowman

Erythroxylum caatingae Plowman has a myorelaxing effect on smooth muscle tissue. We investigated the effect of the crude ethanolic extract of E. caatingae Plowman (Ec-EtOH) on the contractility of the ovine cervix. In an isometric system, circular strips were subjected to 90mM potassium (K(+)) or 30μM carbamylcholine (CCh)-induced contraction. We then exposed the tissue to cumulative concentrations of Ec-EtOH (1-729 μg/ml). In other bath solutions, the tissues were exposed to l-NG-nitroarginine methyl ester (l-NAME; 100μM), l-NAME (100μM)+l-arginine (300μM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, ODQ; 5μM), 4-aminopyridine (4-AP; 3mM), tetraethylammonium (TEA; 0.3mM), glybenclamide (1μM), atosiban (10μM) or verapamil (3μM), followed by the addition of Ec-EtOH (1-729 μg/ml). We also evaluated the effect of cervical Ec-EtOH infusion (2mg) on cervical contractility in vivo. Ec-EtOH decreased cervical contractility induced by K(+) or CCh, and 729 μg/ml Ec-EtOH decreased 85.4±5.1% the amplitude of basal contractility in vitro, with an EC50 of 17.9±3.7 μg/ml. This effect of Ec-EtOH was prevented by l-NAME or ODQ. l-arginine impaired the blunting effect of l-NAME on cervical relaxation caused by Ec-EtOH. However, the potassium channel blockers 4-AP, TEA, and glybenclamide did not modify this myorelaxation triggered by Ec-EtOH. Ec-EtOH also decreased acetylcholine-induced contractions in tissue preincubated with verapamil. In addition, Ec-EtOH decreased ovine cervical contractions in vivo. Thus, Ec-EtOH had a relaxant effect on ovine cervical contractions. This may involve the nitric oxide signal, mediated by cGMP cellular transduction, and be related to intracellular calcium sequestration.

Mechanism of bombesin-induced tonic contraction of the porcine lower esophageal sphincter

Gastroesophageal reflux disease (GERD) is a disorder that is related to an incompetent lower esophageal sphincter (LES). Previous studies showed that bombesin could increase LES pressure in humans and opossums. The aim of the present study was to characterize the effects of bombesin on porcine LES contraction. We used the selective agonists, neuromedin B (NMB), gastrin-releasing peptide (GRP), and [D-Tyr⁶,Apa-4Cl¹¹,Phe¹³,Nle¹⁴]bombesin-(6-14) (DTACPN-BN), as well as receptor antagonists of bombesin receptor subtype 2 (BB₂), and 3 (BB₃) for ex vivo contraction studies. Atropine, nifedipine, tetrodotoxin, and ω-conotoxin GVIA were used to explore the agonist-induced LES contraction mechanism. Reverse transcription polymerase chain reaction and immunohistochemistry were applied to detect bombesin receptor expression. Our results indicate that GRP and DTACPN-BN, but not NMB, induced tonic contractions of the porcine LES in a dose-dependent manner, and the contractions were inhibited with selective BB₂ and BB₃ antagonists. The GRP-induced contraction is mainly caused by L-type Ca²⁺ channel-mediated Ca²⁺ influx. However, DTACPN-BN-induced contractions are associated with neuronal conduction. RT-PCR and immunohistochemistry revealed that BB₂ and BB₃ were expressed in the porcine LES. Bombesin-induced tonic contraction of the LES is mediated through BB₂ and BB₃. Bombesin, BB_2, and BB₃ agonists might have the potential to treat GERD.

Salvia miltiorrhiza Induces Tonic Contraction of the Lower Esophageal Sphincter in Rats via Activation of Extracellular Ca2+ Influx

Up to 40% of patients with gastroesophageal reflux disease (GERD) suffer from proton pump inhibitor refractory GERD but clinically the medications to strengthen the lower esophageal sphincter (LES) to avoid irritating reflux are few in number. This study aimed to examine whether Salvia miltiorrhiza (SM) extracts induce tonic contraction of rat LES ex vivo and elucidate the underlying mechanisms. To investigate the mechanism underlying the SM extract-induced contractile effects, rats were pretreated with atropine (a muscarinic receptor antagonist), tetrodotoxin (a sodium channel blocker), nifedipine (a calcium channel blocker), and Ca²⁺-free Krebs-Henseleit solution with ethylene glycol tetraacetic acid (EGTA), followed by administration of cumulative dosages of SM extracts. SM extracts induced dose-related tonic contraction of the LES, which was unaffected by tetrodotoxin, atropine, or nifedipine. However, the SM extract-induced LES contraction was significantly inhibited by Ca²⁺-free Krebs-Henseleit solution with EGTA. Next, SM extracts significantly induce extracellular Ca²⁺ entry into primary LES cells in addition to intracellular Ca²⁺ release and in a dose-response manner. Confocal fluorescence microscopy showed that the SM extracts consistently induced significant extracellular Ca²⁺influx into primary LES cells in a time-dependent manner. In conclusion, SM extracts could induce tonic contraction of LES mainly through the extracellular Ca²⁺ influx pathway.

Hydrogen sulfide regulates the colonic motility by inhibiting both L-type calcium channels and BKCa channels in smooth muscle cells of rat colon

Objective

To examine the hypothesis that hydrogen sulfide (H₂S) regulates the colonic motility by modulating both L-type voltage-dependent calcium channels and large conductance Ca²⁺-activated K⁺ (BK_Ca) channels.

Methods

Immunohistochemistry was performed on rat colonic samples to investigate the localization of the H₂S-producing enzymes cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE). The contractions of proximal colonic smooth muscle were studied in an organ bath system. The whole-cell patch-clamp technique was used to record both L-type calcium currents (I_Ca,L) and BK_Ca currents in colonic smooth muscle cells (SMCs) isolated from male Wistar rats.

Results

Immunohistochemistry revealed the presence of CBS and CSE in mucosa, smooth muscle cells and myenteric neurons. The H₂S donor NaHS inhibited spontaneous contractions of the longitudinal muscle and circular muscle strips in a dose-dependent manner, and the inhibitory effects were not blocked by tetrodotoxin. NaHS inhibited the peak I_Ca,L in colonic SMCs at a membrane potential of 0 mV. The current-voltage (I-V) relationship of L-type calcium channels was modified by NaHS, and the peak of the I-V curve was shifted to the right. NaHS (200μΜ) evoked a significant rightward shift of the steady-state activation curve and inhibited the inactivation of L-type calcium channels. Furthermore, NaHS reversibly decreased the peak I_Ca,L in a dose-dependent manner. Likewise, BK_Ca channels were significantly inhibited by NaHS, and the addition of NaHS caused a time- and dose-dependent reduction in the BK_Ca current.

Conclusion

The relaxant effect of H₂S on colonic muscle strips may be associated with the direct inhibition of H₂S on L-type calcium channels. H₂S may be involved in the regulation of calcium homeostasis in colonic SMCs of rat colon.

Poly(ethylene glycol)-cholesterol inhibits L-type Ca2+ channel currents and augments voltage-dependent inactivation in A7r5 cells

Cholesterol distributes at a high density in the membrane lipid raft and modulates ion channel currents. Poly(ethylene glycol) cholesteryl ether (PEG-cholesterol) is a nonionic amphipathic lipid consisting of lipophilic cholesterol and covalently bound hydrophilic PEG. PEG-cholesterol is used to formulate lipoplexes to transfect cultured cells, and liposomes for encapsulated drug delivery. PEG-cholesterol is dissolved in the external leaflet of the lipid bilayer, and expands it to flatten the caveolae and widen the gap between the two leaflets. We studied the effect of PEG-cholesterol on whole cell L-type Ca²⁺ channel currents (I_Ca,L) recorded from cultured A7r5 arterial smooth muscle cells. The pretreatment of cells with PEG-cholesterol decreased the density of I_Ca,L and augmented the voltage-dependent inactivation with acceleration of time course of inactivation and negative shift of steady-state inactivation curve. Methyl-β-cyclodextrin (MβCD) is a cholesterol-binding oligosaccharide. The enrichment of cholesterol by the MβCD:cholesterol complex (cholesterol (MβCD)) caused inhibition of I_Ca,L but did not augment voltage-dependent inactivation. Incubation with MβCD increased I_Ca,L, slowed the time course of inactivation and shifted the inactivation curve to a positive direction. Additional pretreatment by a high concentration of MβCD of the cells initially pretreated with PEG-cholesterol, increased I_Ca,L to a greater level than the control, and removed the augmented voltage-dependent inactivation. Due to the enhancement of the voltage-dependent inactivation, PEG-cholesterol inhibited window I_Ca,L more strongly as compared with cholesterol (MβCD). Poly(ethylene glycol) conferred to cholesterol the efficacy to induce sustained augmentation of voltage-dependent inactivation of I_Ca,L.

Optical induction of muscle contraction at the tissue scale through intrinsic cellular amplifiers

The smooth muscle cell is the principal component responsible for involuntary control of visceral organs, including vascular tonicity, secretion, and sphincter regulation. It is known that the neurotransmitters released from nerve endings increase the intracellular Ca(2+) level in smooth muscle cells followed by muscle contraction. We herein report that femtosecond laser pulses focused on the diffraction-limited volume can induce intracellular Ca(2+) increases in the irradiated smooth muscle cell without neurotransmitters, and locally increased intracellular Ca(2+) levels are amplified by calcium-induced calcium-releasing mechanisms through the ryanodine receptor, a Ca(2+) channel of the endoplasmic reticulum. The laser-induced Ca(2+) increases propagate to adjacent cells through gap junctions. Thus, ultrashort-pulsed lasers can induce smooth muscle contraction by controlling Ca(2+), even with optical stimulation of the diffraction-limited volume. This optical method, which leads to reversible and reproducible muscle contraction, can be used in research into muscle dynamics, neuromuscular disease treatment, and nanorobot control.

Altered vascular smooth muscle function in the ApoE knockout mouse during the progression of atherosclerosis

Objectives

Relaxation of vascular smooth muscle (VSM) requires re-uptake of cytosolic Ca²⁺ into the sarcoplasmic reticulum (SR) via the Sarco/Endoplasmic Reticulum Ca²⁺ ATPase (SERCA), or extrusion via the Plasma Membrane Ca²⁺ ATPase (PMCA) or sodium Ca²⁺ exchanger (NCX). Peroxynitrite, a reactive species formed in vascular inflammatory diseases, upregulates SERCA activity to induce relaxation but, chronically, can contribute to atherogenesis and altered vascular function by escalating endoplasmic reticulum stress. Our objectives were to determine if peroxynitrite-induced relaxation and Ca²⁺ handling processes within vascular smooth muscle cells were altered as atherosclerosis develops.

Methods

Aortae from control and ApoE^−/− mice were studied histologically, functionally and for protein expression levels of SERCA and PMCA. Ca²⁺ responses were assessed in dissociated aortic smooth muscle cells in the presence and absence of extracellular Ca²⁺.

Results

Relaxation to peroxynitrite was concentration-dependent and endothelium-independent. The abilities of the SERCA blocker thapsigargin and the PMCA inhibitor carboxyeosin to block this relaxation were altered during fat feeding and plaque progression. SERCA levels were progressively reduced, while PMCA expression was upregulated. In ApoE^−/− VSM cells, increases in cytosolic Ca²⁺ [Ca²⁺]_c in response to SERCA blockade were reduced, while SERCA-independent Ca²⁺ clearance was faster compared to control.

Conclusion

As atherosclerosis develops in the ApoE^−/− mouse, expression and function of Ca²⁺ handling proteins are altered. Up-regulation of Ca²⁺ removal via PMCA may offer a potential compensatory mechanism to help normalise the dysfunctional relaxation observed during disease progression.

•

Expression and function of SERCA and PMCA are temporally altered in ApoE^−/− VSM.

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TG-induced increases in [Ca²⁺]_c were reduced in ApoE^−/− aortic SM cells.

•

Ca²⁺ extrusion is upregulated in isolated ApoE^−/− aortic SM cells.

Pressor and renal regional hemodynamic effects of urotensin II in neonatal pigs

Renal expression of the peptide hormone urotensin II (UII) and its receptor (UTR) are dependent on kidney maturation and anatomical regions. However, renal regional hemodynamic effects of UII in neonates are unclear. Here, we investigated regional hemodynamic responses to acute intrarenal arterial administration of UII in newborn pigs. Western immunoblotting and immunofluorescence confirmed UTR expression and membrane localization in newborn pig renal afferent arterioles and afferent arteriolar smooth muscle cells respectively. Intrarenal arterial bolus injections of human UII (hUII; 1-100  ng/kg) resulted in a dose-dependent decrease in total renal blood flow (RBF) and an increase in mean arterial pressure (MAP) and renal vascular resistance (RVR) in newborn pigs. Moreover, hUII dose dependently reduced cortical blood flow (CBF) but increased medullary blood flow (MBF) in the piglets. hUII-induced MAP elevation and hemodynamic changes were inhibited by urantide, a UTR antagonist, but not losartan, a type 1 angiotensin II receptor antagonist. U-73122, a phospholipase C (PLC) inhibitor, and 2-aminoethoxydiphenyl borate, an inositol 1,4,5 trisphosphate (IP₃) receptor antagonist, attenuated hUII-induced MAP and RVR elevations, RBF and CBF reductions, but not MBF increase. These findings indicate that intrarenal arterial administration of hUII elevates blood pressure and induces region-selective renal hemodynamic changes in newborn pigs. Our data also suggest that the PLC/IP₃ signaling pathway contributes to hUII-induced alterations in MAP, RBF, RVR, and CBF but not MBF in newborn pigs.

Effects of ginger and its constituents on airway smooth muscle relaxation and calcium regulation

The prevalence of asthma has increased in recent years, and is characterized by airway hyperresponsiveness and inflammation. Many patients report using alternative therapies to self-treat asthma symptoms as adjuncts to short-acting and long-acting β-agonists and inhaled corticosteroids (ICS). As many as 40% of patients with asthma use herbal therapies to manage asthma symptoms, often without proven efficacy or known mechanisms of action. Therefore, investigations of both the therapeutic and possible detrimental effects of isolated components of herbal treatments on the airway are important. We hypothesized that ginger and its active components induce bronchodilation by modulating intracellular calcium ([Ca(2+)](i)) in airway smooth muscle (ASM). In isolated human ASM, ginger caused significant and rapid relaxation. Four purified constituents of ginger were subsequently tested for ASM relaxant properties in both guinea pig and human tracheas: [6]-gingerol, [8]-gingerol, and [6]-shogaol induced rapid relaxation of precontracted ASM (100-300 μM), whereas [10]-gingerol failed to induce relaxation. In human ASM cells, exposure to [6]-gingerol, [8]-gingerol, and [6]-shogaol, but not [10]-gingerol (100 μM), blunted subsequent Ca(2+) responses to bradykinin (10 μM) and S-(-)-Bay K 8644 (10 μM). In A/J mice, the nebulization of [8]-gingerol (100 μM), 15 minutes before methacholine challenge, significantly attenuated airway resistance, compared with vehicle. Taken together, these novel data show that ginger and its isolated active components, [6]-gingerol, [8]-gingerol, and [6]-shogaol, relax ASM, and [8]-gingerol attenuates airway hyperresponsiveness, in part by altering [Ca(2+)](i) regulation. These purified compounds may provide a therapeutic option alone or in combination with accepted therapeutics, including β(2)-agonists, in airway diseases such as asthma.

Cross talk between plasma membrane Na(+)/Ca (2+) exchanger-1 and TRPC/Orai-containing channels: key players in arterial hypertension

Arterial smooth muscle (ASM) Na(+)/Ca(2+) exchanger type 1 (NCX1) and TRPC/Orai-containing receptor/store-operated cation channels (ROC/SOC) are clustered with α2 Na(+) pumps in plasma membrane microdomains adjacent to the underlying junctional sarcoplasmic reticulum. This arrangement enables these transport proteins to function as integrated units to help regulate local Na(+) metabolism, Ca(2+) signaling, and arterial tone. They thus influence vascular resistance and blood pressure (BP). For instance, upregulation of NCX1 and TRPC6 has been implicated in the pathogenesis of high BP in several models of essential hypertension. The models include ouabain-induced hypertensive rats, Milan hypertensive rats, and Dahl salt-sensitive hypertensive rats, all of which exhibit elevated plasma ouabain levels. We suggest that these molecular mechanisms are key contributors to the increased vascular resistance ("whole body autoregulation") that elevates BP in essential hypertension. Enhanced expression and function of ASM NCX1 and TRPC/Orai1-containing channels in hypertension implies that these proteins are potential targets for pharmacological intervention.

Regulation of gastrointestinal motility--insights from smooth muscle biology

Gastrointestinal motility results from coordinated contractions of the tunica muscularis, the muscular layers of the alimentary canal. Throughout most of the gastrointestinal tract, smooth muscles are organized into two layers of circularly or longitudinally oriented muscle bundles. Smooth muscle cells form electrical and mechanical junctions between cells that facilitate coordination of contractions. Excitation-contraction coupling occurs by Ca(2+) entry via ion channels in the plasma membrane, leading to a rise in intracellular Ca(2+). Ca(2+) binding to calmodulin activates myosin light chain kinase; subsequent phosphorylation of myosin initiates cross-bridge cycling. Myosin phosphatase dephosphorylates myosin to relax muscles, and a process known as Ca(2+) sensitization regulates the activity of the phosphatase. Gastrointestinal smooth muscles are 'autonomous' and generate spontaneous electrical activity (slow waves) that does not depend upon input from nerves. Intrinsic pacemaker activity comes from interstitial cells of Cajal, which are electrically coupled to smooth muscle cells. Patterns of contractile activity in gastrointestinal muscles are determined by inputs from enteric motor neurons that innervate smooth muscle cells and interstitial cells. Here we provide an overview of the cells and mechanisms that generate smooth muscle contractile behaviour and gastrointestinal motility.

Effects of ginger and its constituents on airway smooth muscle relaxation and calcium regulation

The prevalence of asthma has increased in recent years, and is characterized by airway hyperresponsiveness and inflammation. Many patients report using alternative therapies to self-treat asthma symptoms as adjuncts to short-acting and long-acting β-agonists and inhaled corticosteroids (ICS). As many as 40% of patients with asthma use herbal therapies to manage asthma symptoms, often without proven efficacy or known mechanisms of action. Therefore, investigations of both the therapeutic and possible detrimental effects of isolated components of herbal treatments on the airway are important. We hypothesized that ginger and its active components induce bronchodilation by modulating intracellular calcium ([Ca(2+)](i)) in airway smooth muscle (ASM). In isolated human ASM, ginger caused significant and rapid relaxation. Four purified constituents of ginger were subsequently tested for ASM relaxant properties in both guinea pig and human tracheas: [6]-gingerol, [8]-gingerol, and [6]-shogaol induced rapid relaxation of precontracted ASM (100-300 μM), whereas [10]-gingerol failed to induce relaxation. In human ASM cells, exposure to [6]-gingerol, [8]-gingerol, and [6]-shogaol, but not [10]-gingerol (100 μM), blunted subsequent Ca(2+) responses to bradykinin (10 μM) and S-(-)-Bay K 8644 (10 μM). In A/J mice, the nebulization of [8]-gingerol (100 μM), 15 minutes before methacholine challenge, significantly attenuated airway resistance, compared with vehicle. Taken together, these novel data show that ginger and its isolated active components, [6]-gingerol, [8]-gingerol, and [6]-shogaol, relax ASM, and [8]-gingerol attenuates airway hyperresponsiveness, in part by altering [Ca(2+)](i) regulation. These purified compounds may provide a therapeutic option alone or in combination with accepted therapeutics, including β(2)-agonists, in airway diseases such as asthma.

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.

Cyclic AMP relaxation of rat aortic smooth muscle is mediated in part by decrease of depletion of intracellular Ca(2+) stores and inhibition of capacitative calcium entry

Despite a large number of studies, the mechanism by which 3',5'-cyclic monophosphate (cAMP) induces vasorelaxation is not fully understood. The comparison between results obtained in different vessels or species has often been the source of conflicting reports. In order to shed more light onto this mechanism, we studied the effects of forskolin in phenylephrine-pre-contracted endothelium-denuded rat aorta and measured cAMP levels in rat aortic myocytes by enzyme-immunoassay. Nanomolar forskolin relaxed phenylephrine-induced contractions. This effect was mimicked by dibutyryl-cAMP and was potentiated by rolipram or a p38-mitogen-activated protein kinase (p38-MAPK) inhibitor (SB-203580). Nifedipine and verapamil partially relaxed phenylephrine-induced contractions, while further application of cAMP-elevating agents fully relaxed these contractions. In Ca(2+)-free extracellular solution, forskolin reduced phenylephrine-induced transient contractions and reduced the Ca(2+)-induced contraction after depletion of intracellular stores. Nanomolar concentrations of forskolin increased basal cAMP levels only in the presence of rolipram or phenylephrine, which did not modify intracellular levels of cAMP by themselves. In conclusion, relaxation by cAMP is mediated in part by decrease of depletion of intracellular Ca(2+) stores and inhibition of capacitative calcium entry. This study provides the first evidence that inhibition of PDE4 or p38-MAPK potentiates the vasodilator effect of cAMP-elevating agents in rat aortic myocytes.