High K+-induced contraction requires depolarization-induced Ca2+ release from internal stores in rat gut smooth muscle

Age-dependent effects of the β3 adrenoceptor agonist CL316,243 on human and rat detrusor muscle strips

Motility of detrusor smooth muscle includes adrenergic relaxation and cholinergic contraction. Since the latter may be deregulated in overactive bladder (OAB) pathophysiology, anticholinergics are the standard therapy but occasionally less tolerated due to side effects such as dry mouth and constipation. β3 adrenoceptor agonists also alleviate OAB symptoms by relaxing the detrusor muscle. Their age dependence, however, is far from understood. To address this issue, we induced contractions with KCl (60 mM) and carbachol (from 10 nM to 100 μM) in the presence of the β3 adrenoceptor agonist CL316,243 (from 0.1 to 10 μM) in both human and rat muscle strips. Our results confirmed that both contractions were attenuated by β3 adrenoceptor activation in both species, but with differing age dependence. In humans, specimens from mid-life subjects showed a significantly more pronounced effect of CL316,243 in attenuating carbachol-induced contractions than those from aged subjects (Cohen's d of maximal attenuation: 1.82 in mid-life versus 0.13 in aged) without altering EC50. Conversely, attenuation of KCl responses by CL316,243 increased during ageing (Spearman correlation coefficient = -0.584, P<0.01). In rats, both KCl- and carbachol-induced contractions were significantly more attenuated by CL316,243 in samples from adolescent as compared to aged samples. Immunohistochemistry in human detrusor sections proved β3 adrenoreceptor abundance to remain unaltered during ageing. In conclusion, our findings suggest differential age-dependent changes in human β3 adrenoceptor-dependent attenuation of detrusor contraction in terms of electromechanical versus pharmacomechanical coupling; they may help understand the differential responsiveness of OAB patients to β3 agents.

Effects of Microbeam Irradiation on Rodent Esophageal Smooth Muscle Contraction

BACKGROUND

High-dose-rate radiotherapy has shown promising results with respect to normal tissue preservation. We developed an ex vivo model to study the physiological effects of experimental radiotherapy in the rodent esophageal smooth muscle.

METHODS

We assessed the physiological parameters of the esophageal function in ex vivo preparations of the proximal, middle, and distal segments in the organ bath. High-dose-rate synchrotron irradiation was conducted using both the microbeam irradiation (MBI) technique with peak doses greater than 200 Gy and broadbeam irradiation (BBI) with doses ranging between 3.5-4 Gy.

RESULTS

Neither MBI nor BBI affected the function of the contractile apparatus. While peak latency and maximal force change were not affected in the BBI group, and no changes were seen in the proximal esophagus segments after MBI, a significant increase in peak latency and a decrease in maximal force change was observed in the middle and distal esophageal segments.

CONCLUSION

No severe changes in physiological parameters of esophageal contraction were determined after high-dose-rate radiotherapy in our model, but our results indicate a delayed esophageal function. From the clinical perspective, the observed increase in peak latency and decreased maximal force change may indicate delayed esophageal transit.

Influence of lauric acid on the relaxation of corpus cavernosum in streptozotocin-induced diabetic male Wistar rats

Background

Diabetes mellitus is a global health challenge and has been recognised as a risk factor for erectile dysfunction. Dissatisfaction with standard medications has been reported by some patients, hence therapeutic plants are being considered as a viable alternative therapy, with their active components being investigated to create a standard regimen. Lauric acid is the most abundant constituent of coconut oil and is proposed to be responsible for its therapeutic properties. The corpus cavernosum plays an important role in erectile function with its relaxation favouring erection. This study thus sought to investigate the possible relaxant action and mechanism of lauric acid on the corpus cavernosum of diabetic male Wistar rats. Diabetes was induced by intraperitoneal injection of streptozotocin after which graded doses of lauric acid were administered orally to three groups of diabetic rats, once daily for 4 weeks. At the end of the experiment, the corpus cavernosal tissues of the rat penis were extracted. Following phenylephrine or potassium chloride (KCl)—induced contraction, relaxation response to acetylcholine and sodium nitroprusside was used to evaluate endothelium-dependent and nitric oxide-mediated relaxation, respectively.

Results

Relaxation response to acetylcholine, following pre-contraction with phenylephrine, was significantly decreased in the cavernosal tissues of diabetic untreated rats and was not significantly improved in lauric acid treated diabetic groups. Relaxation response to acetylcholine, following pre-contraction with KCl, was significantly decreased in the diabetic untreated group but was significantly improved in lauric acid treated diabetic groups at the lowest dose. Decreased relaxation response to sodium nitroprusside, following pre-contraction with phenylephrine in tissues of diabetic untreated rats, was significantly improved in lauric acid-treated diabetic groups at lower doses. Decreased relaxation response to sodium nitroprusside, following pre-contraction with KCl, was significantly improved in lauric acid-treated diabetic groups at all doses.

Conclusion

Lauric acid improved relaxation of corpus cavernosum muscle in diabetic male rats by enhancing nitric oxide-mediated relaxing action of sodium nitroprusside and possibly inhibiting KCl-induced contraction.

Antispasmodic Effect of Asperidine B, a Pyrrolidine Derivative, through Inhibition of L-Type Ca2+ Channel in Rat Ileal Smooth Muscle

Antispasmodic agents are used for modulating gastrointestinal motility. Several compounds isolated from terrestrial plants have antispasmodic properties. This study aimed to explore the inhibitory effect of the pyrrolidine derivative, asperidine B, isolated from the soil-derived fungus Aspergillus sclerotiorum PSU-RSPG178, on spasmodic activity. Isolated rat ileum was set up in an organ bath. The contractile responses of asperidine B (0.3 to 30 µM) on potassium chloride and acetylcholine-induced contractions were recorded. To investigate its antispasmodic mechanism, CaCl2, acetylcholine, Nω-nitro-l-arginine methyl ester (l-NAME), nifedipine, methylene blue and tetraethylammonium chloride (TEA) were tested in the absence or in the presence of asperidine B. Cumulative concentrations of asperidine B reduced the ileal contraction by ~37%. The calcium chloride and acetylcholine-induced ileal contraction was suppressed by asperidine B. The effects of asperidine B combined with nifedipine, atropine or TEA were similar to those treated with nifedipine, atropine or TEA, respectively. In contrast, in the presence of l-NAME and methylene blue, the antispasmodic effect of asperidine B was unaltered. These results suggest that the antispasmodic property of asperidine B is probably due to the blockage of the L-type Ca2+ channel and is associated with K+ channels and muscarinic receptor, possibly by affecting non-selective cation channels and/or releasing intracellular calcium.

Vasorelaxant property of Plectranthus vettiveroides root essential oil and its possible mechanism

ETHNOPHARMACOLOGICAL RELEVANCE

Plectranthus vettiveroides (Jacob) N.P. Singh & B.D. Sharma is a traditional medicinal plant used in Siddha System of Medicine and its aromatic root is used to reduce the elevated blood pressure.

AIM

The aim of the present study was to study vasorelaxant property of the root essential oil nanoemulsion (EON) of P. vettiveroides.

METHODS

The EON was formulated to enhance the solubility and bioavailability and characterized. The preliminary screening was performed by treating the EON with aortic rings pre-contracted with phenylephrine (1 μM) and potassium chloride (80 mM). The role of K⁺ channels in EON induced vasorelaxation was investigated by pre-incubating the aortic rings with different K⁺ channel inhibitors namely, glibenclamide (a non-specific ATP sensitive K⁺ channel blocker, 10 μM), TEA (a Ca2⁺ activated non-selective K⁺ channel blocker, 10-2 M), 4-AP (a voltage-activated K⁺ channel blocker, 10-3 M) and barium chloride (inward rectifier K⁺ channel blocker, 1 mM). The involvement of extracellular Ca2+ was performed by adding cumulative dose of extracellular calcium in the presence and absence of EON and the concentration-response curve (CRC) obtained is compared. Similarly, the role of nitric oxide synthase, muscarinic and prostacyclin receptors on EON induced vasorelaxation were evaluated by pre-incubating the aortic rings with their inhibitors and the CRC obtained in the presence and absence of inhibitor were compared.

RESULTS

The GC-MS and GC-FID analyses of the root essential oil revealed the presence of 62 volatile compounds. The EON exhibited significant vasorelaxant effect through nitric oxide-mediated pathway, G-protein coupled muscarinic (M3) receptor pathway, involvement of K+ channels (KATP, KIR, KCa), and blocking of the calcium influx by receptor-operated calcium channel.

CONCLUSION

It is concluded that the root essential oil of P. vettiveroides is possessing marked vasorelaxant property. The multiple mechanisms of action of the essential oil of P. vettiveroides make it a potential source of antihypertensive drug.

Analysis of KATP Channels Opening Probability of Hippocampus Cells Treated with Kainic Acid

Background

Kainic acid (KA)-induced seizures may be a valuable tool in the assessment of anti-epileptic drug efficacy in complex partial seizures. This study investigated the effects of KA on ATP-sensitive K⁺ (K_ATP) channels opening probability (NPo), which plays a crucial role in neuronal activities.

Methods

For the optimisation and validation protocol, β-cells were plated onto 35 mm plastic petri dishes and maintained in RPMI-1640 media supplemented with 10 mM glucose, 10% FCS and 25 mM of N-2-hydroxyethylpiperazine-N-ethanesulfonic acid (HEPES). The treatment effects of 10 mM glucose and 30 μM fluoxetine on K_ATP channels NPo of β-cells were assessed via cell-attached patch-clamp recordings. For hippocampus cell experiments, hippocampi were harvested from day 17 of maternal Lister-hooded rat foetus, and then transferred to a Ca²⁺ and Mg²⁺-free HEPES-buffered Hank's salt solution (HHSS). The dissociated cells were cultured and plated onto a 25 mm round cover glasses coated with poly-d-lysine (0.1 mg/mL) in a petri dish. The K_ATP channels NPo of hippocampus cells when perfused with 1 mM and 10 mM of KA were determined.

Results

NPo of β-cells showed significant decreasing patterns (P < 0.001) when treated with 10 mM glucose 0.048 (0.027) as well as 30 μM fluoxetine 0.190 (0.141) as compared to basal counterpart. In hippocampus cell experiment, a significant increase (P < 0.001) in mean NPo 2.148 (0.175) of neurons when applied with 1 mM of KA as compared to basal was observed.

Conclusion

The two concentrations of KA used in the study exerted contrasting effects toward the mean of NPo. It is hypothesised that KA at lower concentration (1 mM) opens more K_ATP channels, leading to hyperpolarisation of the neurons, which may prevent neuronal hyper excitability. No effect was shown in 10 mM KA treatment, suggesting that only lower than 10 mM KA produced significant changes in K_ATP channels. This implies further validation of KA concentration to be used in the future.

Dandelion extract relaxes mouse airway smooth muscle by blocking VDLCC and NSCC channels

BACKGROUND

Asthma is one of the main intractable diseases recognized by the international medical community. The current widely used bronchodilators for asthma-β2-adrenal receptor agonists-have limited therapeutic effects, necessitating the development of novel antiasthma drugs with increased efficacy and fewer adverse effects. In this study, we investigated the relaxant effects and underlying mechanism of an ethyl acetate extract from dandelion (EAED) on mouse airway smooth muscle.

METHODS

The effects of EAED on agonist-induced precontraction in mouse airway smooth muscle were evaluated with force measurement. Mouse lung slices were used to study the effects of EAED on bronchial smooth muscle. The intracellular Ca2+ concentration was measured using a calcium imaging system. L-type voltage-dependent calcium channel (VDLCC) and non-selective cationic channel (NSCC) currents were measured by patch-clamp. The lung functions of healthy and asthmatic mouse groups were assessed via the forced oscillation technique.

RESULTS

EAED inhibits acetylcholine-induced sustained contractions of whole airway smooth muscle by inhibiting VDLCCs, NSCCs, and some unknown channels, reduces the agonist-induced increase in the cytosolic free Ca2+ concentration in airway smooth muscle cells, blocks VDLCC and NSCC currents, and relieves the respiratory resistance of healthy and asthmatic mice.

CONCLUSIONS

EAED may have potential beneficial effects on mitigating asthma attacks.

Assessment of Polygonum odoratum Lour. Leaf Extract on Rat's Ileum Contraction and the Mechanisms Involved

Vietnamese coriander (Polygonum odoratum Lour.) is a plant native to northern Thailand. The biological activities of P. odoratum Lour. extract (POE) include antibacterial, antiviral, and expectorant. However, the effect of POE on intestinal smooth muscle motility is unclear. The aim of this study was to evaluate the relaxant effects of POE on isolated rat ileum. Propranolol (1 μM), calcium chloride (1-20 mM), and Nω-nitro-l-arginine methylester (l-NAME, 100 μM) were used to investigate the mechanisms of action. The results showed that POE (0.01-5 mg/mL) reduced KCl-induced contraction. In addition, POE (1 mg/mL) reduced the contraction by propranolol and l-NAME and attenuated CaCl₂-induced contractions. Our results indicate that the relaxation effect of POE on ileum contractions seems to involve nitric oxide and β-adrenergic pathways, and blockade of calcium influx. These findings provide a pharmacological basis for the traditional use of POE to treat gastrointestinal disorders such as irritable bowel syndrome or diarrhea.

The Spasmolytic Effect of Astragalus Sarcocolla on the Intestinal Smooth Muscles of Rabbit In Vitro: Potassium Channel Opening

Introduction

Astragalus species have been widely used in Chinese herbal medicine to treat gastrointestinal and inflammatory disorders. This study was conducted to evaluate the efficacy of Astragalus sarcocolla (ASE) and to rationalize its medicinal use as an antispasmodic drug for the treatment of spasmodic gastrointestinal and inflammatory disorders associated with increased intestinal motility.

Methods

The ethanolic extract of ASE was studied to examine its antispasmodic effect on the isolated rabbit ileum preparations, and the contractions were recorded on PowerLab (ADInstruments, Sydney, Australia).

Results

ASE was able to inhibit spontaneous ileum contractions. It also completely inhibited K⁺ (25 mM)-induced contractions but was unable to inhibit high K⁺ (80 mM)-induced sustained contractions. Pretreatment of the tissue with glibenclamide, a potassium channel blocker, caused a rightward shift of the dose-response curve when stimulated with K⁺ (25 mM) in the presence of an increasing concentration of the extract. Verapamil at very low doses inhibited both the 25 mM and 80 mM K⁺-induced contractions.

Conclusion

The results of our study demonstrated the spasmolytic activity of ASE with the potential mechanism of activation of K⁺ATP, which provides a strong basis for its medicinal use in motility and inflammatory disorders of the intestine.

Involvement of inhibitor kappa B kinase 2 (IKK2) in the regulation of vascular tone

Inhibitor kappa B kinase 2 (IKK2) plays an essential role in the activation of nuclear factor kappa B (NF-kB). Recently, it has been suggested that IKK2 acts as a myosin light chain kinase (MLCK) and contributes to vasoconstriction in mouse aorta. However, the underlying mechanisms are still unknown. Therefore, we investigated whether IKK2 acts as a MLCK or regulates the activity of myosin light chain phosphatase (MLCP). Pressure myograph was used to measure vascular tone in rat mesenteric arteries. Immunofluorescence staining was performed to identify phosphorylation levels of MLC (ser19), MYPT1 (thr853 and thr696) and CPI-17 (thr38). SC-514 (IKK2 inhibitor, 50 μM) induced relaxation in the mesenteric arteries pre-contracted with 70 mM high K⁺ solution or U-46619 (thromboxane analog, 5 μM). The relaxation induced by SC-514 was increased in the arteries pre-contracted with U-46619 compared to arteries pre-contracted with 70 mM high K⁺ solution. U-46619-induced contraction was decreased by treatment of SC-514 in the presence of MLCK inhibitor, ML-7 (10 μM). In the absence of intracellular Ca²⁺, U-46619 still induced contraction, which was decreased by treatment of SC-514. Furthermore, phosphorylation levels of MLC (ser19) and MYPT1 (thr853) were decreased by treatment of SC-514. IKK2 is involved in the vascular contraction through regulation of MLCP activity by phosphorylating MYPT1 at thr853 in rat mesenteric arteries. These findings suggest IKK2 could be a new pharmacological target for specific therapies of various vascular diseases.

Antispasmodic Effect of Blackcurrant (Ribes nigrum L.) Juice and Its Potential Use as Functional Food in Gastrointestinal Disorders

OBJECTIVE

The purpose of this study was to investigate the relaxative effects of blackcurrant juice on the gastrointestinal smooth muscle in vitro.

MATERIALS AND METHODS

Berries of the blackcurrant cultivar Ometa were used for the preparation of the juice used. The spasmolytic activity of blackcurrant juice was tested on rat ileum isolated from male Wistar rats by monitoring its influence on spontaneous contractions, as well as contractions induced by potassium chloride (KCl), barium chloride (BaCl2), calcium chloride (CaCl2), and acetylcholine (Ach). The results are expressed as the mean ± standard deviation obtained in 6 measurements and statistical significance was determined by the Student t test, with p < 0.05 taken as significant.

RESULTS

The blackcurrant cultivar Ometa significantly reduced the frequency and the amplitude of spontaneous contractions (57.94 ± 3.44%) and Ach-induced contractions (42.74 ± 5.36%; p < 0.05) of the isolated rat ileum. Cumulative concentrations (0.01-3 mg/mL) of the Ometa juice also reduced contractions of the isolated rat ileum stimulated by KCl (51.46 ± 6.87%), CaCl2 (57.54 ± 6.47%), and BaCl2 (58.54 ± 10.55%). The inhibitory effects of the juice were proportional to the applied concentration.

CONCLUSION

The antispasmodic effect of Ometa cultivar shows that common gastrointestinal disorders could be treated by the functional food.

Extracellular acidosis selectively inhibits pharmacomechanical coupling induced by carbachol in strips of rat gastric fundus

NEW FINDINGS

What is the central question of this study? Acute acidosis that results from short-term exercise is involved in delayed gastric emptying in rats and the lower responsiveness of gastric fundus strips to carbachol. Does extracellular acidosis decrease responsiveness to carbachol in tissues of sedentary rats? How? What is the main finding and its importance? Extracellular acidosis inhibits cholinergic signalling in the rat gastric fundus by selectively influencing the G_q/11 protein signalling pathway. Acute acidosis that results from short-term exercise delays gastric emptying in rats and decreases the responsiveness to carbachol in gastric fundus strips. The regulation of cytosolic Ca²⁺ concentrations appears to be a mechanism of action of acidosis. The present study investigated the way in which acidosis interferes with gastric smooth muscle contractions. Rat gastric fundus isolated strips at pH 6.0 presented a lower magnitude of carbachol-induced contractions compared with preparations at pH 7.4. This lower magnitude was absent in carbachol-stimulated duodenum and KCl-stimulated gastric fundus strips. In Ca²⁺ -free conditions, repeated contractions that were induced by carbachol progressively decreased, with no influence of extracellular pH. In fundus strips, CaCl₂ -induced contractions were lower at pH 6.0 than at pH 7.4 but only when stimulated in the combined presence of carbachol and verapamil. In contrast, verapamil-sensitive contractions that were induced by CaCl₂ in the presence of KCl did not change with pH acidification. In Ca²⁺ store-depleted preparations that were treated with thapsigargin, the contractions that were induced by extracellular Ca²⁺ restoration were smaller at pH 6.0 than at pH 7.4, but relaxation that was induced by SKF-96365 (an inhibitor of store-operated Ca²⁺ entry) was unaltered by extracellular acidification. At pH 6.0, the phospholipase C inhibitor U-73122 relaxed carbachol-induced contractions less than at pH 7.4, and this phenomenon was absent in tissue that was treated with the RhoA kinase blocker Y-27632. Thus, extracellular acidosis inhibited pharmacomechanical coupling in gastric fundus by selectively inhibiting the G_q/11 protein signalling pathway, whereas electromechanical coupling remained functionally preserved.

The Role of Visceral Hypersensitivity in Irritable Bowel Syndrome: Pharmacological Targets and Novel Treatments

Irritable bowel syndrome (IBS) is the most common disorder referred to gastroenterologists and is characterized by altered bowel habits, abdominal pain, and bloating. Visceral hypersensitivity (VH) is a multifactorial process that may occur within the peripheral or central nervous systems and plays a principal role in the etiology of IBS symptoms. The pharmacological studies on selective drugs based on targeting specific ligands can provide novel therapies for modulation of persistent visceral hyperalgesia. The current paper reviews the cellular and molecular mechanisms underlying therapeutic targeting for providing future drugs to protect or treat visceroperception and pain sensitization in IBS patients. There are a wide range of mediators and receptors participating in visceral pain perception amongst which substances targeting afferent receptors are attractive sources of novel drugs. Novel therapeutic targets for the management of VH include compounds which alter gut-brain pathways and local neuroimmune pathways. Molecular mediators and receptors participating in pain perception and visceroperception include histamine-1 receptors, serotonin (5-hydrodytryptamine) receptors, transient receptor potential vanilloid type I, tachykinins ligands, opioid receptors, voltage-gated channels, tyrosine receptor kinase receptors, protease-activated receptors, adrenergic system ligands, cannabinoid receptors, sex hormones, and glutamate receptors which are discussed in the current review. Moreover, several plant-derived natural compounds with potential to alleviate VH in IBS have been highlighted. VH has an important role in the pathology and severity of complications in IBS. Therefore, managing VH can remarkably modulate the symptoms of IBS. More preclinical and clinical investigations are needed to provide efficacious and targeted medicines for the management of VH.

P2Y receptor-mediated transient relaxation of rat longitudinal ileum preparations involves phospholipase C activation, intracellular Ca(2+) release and SK channel activation

AIM

Purinergic signaling plays a major role in the enteric nervous system, where it governs gut motility through a number of P2X and P2Y receptors. The aim of this study was to investigate the P2Y receptor-mediated motility in rat longitudinal ileum preparations.

METHODS

Ileum smooth muscle strips were prepared from rats, and fixed in an organ bath. Isometric contraction and relaxation responses of the muscle strips were measured with force transducers. Drugs were applied by adding of stock solutions to the organ bath to yield the individual final concentrations.

RESULTS

Application of the non-hydrolyzable P2 receptor agonists α,β-Me-ATP or 2-Me-S-ADP (10, 100 μmol/L) dose-dependently elicited a transient relaxation response followed by a sustained contraction. The relaxation response was largely blocked by SK channel blockers apamin (500 nmol/L) and UCL1684 (10 μmol/L), PLC inhibitor U73122 (100 μmol/L), IP3 receptor blocker 2-APB (100 μmol/L) or sarcoendoplasmic Ca(2+) ATPase inhibitor thapsigargin (1 μmol/L), but not affected by atropine, NO synthase blocker L-NAME or tetrodotoxin. Furthermore, α,β-Me-ATP-induced relaxation was suppressed by P2Y1 receptor antagonist MRS2179 (50 μmol/L) or P2Y13 receptor antagonist MRS2211 (100 μmol/L), and was abolished by co-application of the two antagonists, whereas 2-Me-S-ADP-induced relaxation was abolished by P2Y6 receptor antagonist MRS2578 (50 μmol/L). In addition, P2Y1 receptor antagonist MRS2500 (1 μmol/L) not only abolished α,β-Me-ATP-induced relaxation, but also suppressed 2-Me-S-ADP-induced relaxation.

CONCLUSION

P2Y receptor agonist-induced transient relaxation of rat ileum smooth muscle strips is mediated predominantly by P2Y1 receptor, but also by P2Y6 and P2Y13 receptors, and involves PLC, IP3, Ca(2+) release and SK channel activation, but is independent of acetylcholine and NO release.

Cortex phellodendri Extract Relaxes Airway Smooth Muscle

Cortex phellodendri is used to reduce fever and remove dampness and toxin. Berberine is an active ingredient of C. phellodendri. Berberine from Argemone ochroleuca can relax airway smooth muscle (ASM); however, whether the nonberberine component of C. phellodendri has similar relaxant action was unclear. An n-butyl alcohol extract of C. phellodendri (NBAECP, nonberberine component) was prepared, which completely inhibits high K⁺- and acetylcholine- (ACH-) induced precontraction of airway smooth muscle in tracheal rings and lung slices from control and asthmatic mice, respectively. The contraction induced by high K⁺ was also blocked by nifedipine, a selective blocker of L-type Ca²⁺ channels. The ACH-induced contraction was partially inhibited by nifedipine and pyrazole 3, an inhibitor of TRPC3 and STIM/Orai channels. Taken together, our data demonstrate that NBAECP can relax ASM by inhibiting L-type Ca²⁺ channels and TRPC3 and/or STIM/Orai channels, suggesting that NBAECP could be developed to a new drug for relieving bronchospasm.

Age-related decrease of adenosine-mediated relaxation in rat detrusor is a result of A2B receptor downregulation

OBJECTIVES

To analyze the effect of adenosine on detrusor smooth muscle contraction and to assess age-related changes of adenosine function.

METHODS

Sustained contractions were induced in young (10-30 days) and old (>60 days) rat detrusor muscle strips by application of 30 mmol/L K(+) and adenosine (0.1-400 µmol/L), which was either applied before raising the K(+) concentration or added to the precontracted muscle strip. Quantitative polymerase chain reaction analyses were used to study adenosine receptor expression in rat and human detrusor specimens.

RESULTS

Pretreatment with adenosine dose-dependently reduced subsequent K(+) -induced contraction in detrusor muscle strips from young rats (half-maximal effect = 40 µmol/L). The residual depolarization-induced contraction strength in young tissue was significantly smaller than in tissue from old animals, showing a greater potency of adenosine in young detrusor samples. Likewise, the relaxing effect of adenosine on precontracted detrusor muscle was also significantly more pronounced in young compared with older detrusor. Quantitative polymerase chain reaction showed an age-related downregulation of the adenosine A2B receptor in rat detrusor tissues, which could be confirmed in human detrusor samples. Furthermore, relaxation of both K(+) -induced as well as carbachol-induced contraction by the specific A2B receptor agonist BAY 60-6583 was significantly more pronounced in young than in old rats.

CONCLUSIONS

Adenosine powerfully counteracts contraction of detrusor smooth muscle, which is lost in the aging bladder. This is paralleled by an age-dependent transcriptional downregulation of the low-affinity A2B receptor. Hence, this might be pathophysiologically relevant in conditions of raised adenosine concentrations, such as hyperactive bladder contractility.

Relaxant action of plumula nelumbinis extract on mouse airway smooth muscle

The traditional herb Plumula Nelumbinis is widely used in the world because it has many biological activities, such as anti-inflammation, antioxidant, antihypertension, and butyrylcholinesterase inhibition. However, the action of Plumula Nelumbinis on airway smooth muscle (ASM) relaxation has not been investigated. A chloroform extract of Plumula Nelumbinis (CEPN) was prepared, which completely inhibited precontraction induced by high K⁺ in a concentration-dependent manner in mouse tracheal rings, but it had no effect on resting tension. CEPN also blocked voltage-dependent L-type Ca²⁺ channel- (VDCC-) mediated currents. In addition, ACh-induced precontraction was also completely blocked by CEPN and partially inhibited by nifedipine or pyrazole 3. Besides, CEPN partially reduced ACh-activated nonselective cation channel (NSCC) currents. Taken together, our data demonstrate that CEPN blocked VDCC and NSCC to inhibit Ca²⁺ influx, resulting in relaxation of precontracted ASM. This finding indicates that CEPN would be a candidate of new potent bronchodilators.

Age-dependent contribution of Rho kinase in carbachol-induced contraction of human detrusor smooth muscle in vitro

AIM

Activation of muscarinic receptors on the detrusor smooth muscle is followed by contraction, which involves both myosin light chain kinase (MLCK) and Rho kinase (ROCK). The aim of this study was to determine the relative contributions of MLCK and ROCK to carbachol-induced contraction of human detrusor smooth muscle in vitro.

METHODS

Detrusor smooth muscle strips were prepared from the macroscopically unaffected bladder wall of patients underwent cystectomy. The strips were fixed in an organ bath, and carbachol or KCl-induced isometric contractions were measured by force transducers.

RESULTS

Addition of carbachol (0.4-4 μmol/L) into the bath induced concentration-dependent contractions of detrusor specimens, which was completely abolished by atropine (1 μmol/L). Pre-incubation of detrusor specimens with either the MLCK inhibitor ML-9 or the ROCK inhibitors HA1100 and Y-27632 (each at 10 μmol/L) significantly blocked carbachol-induced contractions as compared to the time-control experiments. Moreover, MLCK and ROCK inhibition were equally effective in reducing carbachol-induced contractions. The residual carbachol-induced contractions in the presence of both MLCK and ROCK inhibitors were significantly smaller than the contractions obtained when only one enzyme (either MLCK or ROCK) was inhibited, suggesting an additive effect of the two kinases. Interestingly, ROCK-mediated carbachol-induced contractions were positively correlated to the age of patients (r=o.52, P<0.05).

CONCLUSION

Both MLCK and ROCK contribute to carbachol-induced contractions of human detrusor smooth muscle. ROCK inhibitors may be a new pharmacological approach to modulate human bladder hyperactivity.

Main ion channels and receptors associated with visceral hypersensitivity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a very frequent functional gastrointestinal disorder characterized by recurrent abdominal pain or discomfort and alteration of bowel habits. The IBS physiopathology is extremely complex. Visceral hypersensitivity plays an important role in the pathogenesis of abdominal pain in both in vitro and in vivo models of this functional disorder. In order to obtain a general view of the participation of the main ion channels and receptors regarding the visceral hypersensitivity in the IBS and to describe their chemical structure, a literature review was carried out. A bibliographical research in the following electronic databases: Pubmed and Virtual Library in Health (BVS) was fulfilled by using the search terms "ion channels" "or" "receptors" "and" "visceral hypersensitivity" "or" "visceral nociception" "and" "irritable bowel syndrome". Original and review articles were considered for data acquisition. The activation of the ATP ion-gated channels, voltage-gated sodium (Na_v) and calcium (Ca_v) channels, as well as the activation of protease-activated receptors (PAR2), transient receptor potential vanilloide-1, serotonin, cannabinoids and cholecystokinin are involved in the genesis of visceral hypersensitivity in IBS. The involvement of ion channels and receptors concerning visceral hypersensitivity is noteworthy in IBS models.

Inositol trisphosphate receptors in smooth muscle cells

Inositol 1,4,5-trisphosphate receptors (IP(3)Rs) are a family of tetrameric intracellular calcium (Ca(2+)) release channels that are located on the sarcoplasmic reticulum (SR) membrane of virtually all mammalian cell types, including smooth muscle cells (SMC). Here, we have reviewed literature investigating IP(3)R expression, cellular localization, tissue distribution, activity regulation, communication with ion channels and organelles, generation of Ca(2+) signals, modulation of physiological functions, and alterations in pathologies in SMCs. Three IP(3)R isoforms have been identified, with relative expression and cellular localization of each contributing to signaling differences in diverse SMC types. Several endogenous ligands, kinases, proteins, and other modulators control SMC IP(3)R channel activity. SMC IP(3)Rs communicate with nearby ryanodine-sensitive Ca(2+) channels and mitochondria to influence SR Ca(2+) release and reactive oxygen species generation. IP(3)R-mediated Ca(2+) release can stimulate plasma membrane-localized channels, including transient receptor potential (TRP) channels and store-operated Ca(2+) channels. SMC IP(3)Rs also signal to other proteins via SR Ca(2+) release-independent mechanisms through physical coupling to TRP channels and local communication with large-conductance Ca(2+)-activated potassium channels. IP(3)R-mediated Ca(2+) release generates a wide variety of intracellular Ca(2+) signals, which vary with respect to frequency, amplitude, spatial, and temporal properties. IP(3)R signaling controls multiple SMC functions, including contraction, gene expression, migration, and proliferation. IP(3)R expression and cellular signaling are altered in several SMC diseases, notably asthma, atherosclerosis, diabetes, and hypertension. In summary, IP(3)R-mediated pathways control diverse SMC physiological functions, with pathological alterations in IP(3)R signaling contributing to disease.

Increased colonic motility in a rat model of irritable bowel syndrome is associated with up-regulation of L-type calcium channels in colonic smooth muscle cells

OBJECTIVE

This paper aimed to investigate the relationship between up-regulation of L-type calcium channels and altered motility disorder in a rat model of irritable bowel syndrome (IBS).

METHODS

Male Sprague-Dawley rats were subjected to neonatal maternal separation (NMS) from postnatal day 2-14 or normal handling (NH), and used when weighted 250-300 g. Colonic smooth muscle contractions was studied in an organ bath system. L-type Ca(2+) channel alpha(1c) subunit expression in smooth muscles from rat colon were studied by immunofluorescence and Western blotting analysis. The intracellular calcium concentration ([Ca(2+)](i)) of enzymatically isolated single colonic smooth muscle cell was studied with laser confocal fluorescent microscopy.

RESULTS

The fecal pellets during 1 h water avoidance stress (WAS) were significantly increased; the amplitude of spontaneous contractions and contractions induced by Bay K 8644 (10 nM-1 microM), KCl (10-60 mM) and ACh (100 nM-10 microM) were significantly increased in NMS rats, when comparing with that of NH rats. [Ca(2+)]i induced by Bay K 8644 (1 microM), KCl (40 mM), and ACh (10 microM) significantly increased in muscle cells of NMS rats than NH rats. Further, alpha(1c) protein expression was significantly up-regulated in colonic smooth muscle of NMS rats than NH rats.

CONCLUSION

These results suggest that NMS lead to up-regulation of L-type Ca(2+) channels expression in the colon, which contributes to the colonic motility disorder. Our findings provide direct evidence to help understanding the underlying mechanism of chronic stress-induced colonic motility disorder in IBS.