Contraction In Rats Research Articles

Changes in the Function and Expression of T-Type and N-Type Calcium Channels in the Rat Bladder after Bladder Outlet Obstruction

We evaluated possible changes in the function and expression of T-type and N-type Ca(2+) channels in the bladder of rats with bladder outlet obstruction. Female Sprague Dawley® rats were divided into a group with bladder outlet obstruction created by partial urethral ligation and a sham operated group. Six weeks postoperatively we determined the mRNA expression of T-type and N-type Ca(2+) channels in the bladder, dorsal root ganglion and spinal cord. We also cystometrically investigated expression by intravenous administration of the T-Ca blocker RQ-00311610 or the N-type Ca(2+) channel blocker ω-conotoxin GVIA. We then performed in vitro functional studies of detrusor strips using these blockers. mRNA expression of T-type Ca(2+) channels in the bladder detrusor and mucosa layers, and the spinal cord dorsal horn, and N-type Ca(2+) channels in the whole bladder and detrusor layer, and the spinal cord dorsal horn was greater in the obstructed group than the sham operated group. In obstructed rats bladder capacity and voided volume increased after RQ-00311610 administration but the number of nonvoiding contractions decreased after ω-conotoxin GVIA administration. Detrusor strips from obstructed rats showed weaker contractile responses to electrical field stimulation, particularly in regard to the purinergic component. ω-Conotoxin GVIA suppressed electrical field stimulation induced contractions only in the detrusor of obstructed rats, especially the cholinergic component. Blocking T-type Ca(2+) channels increased bladder capacity while N-type Ca(2+) channel blockade inhibited nonvoiding contractions in rats with bladder outlet obstruction. Decreased bladder efferent neurotransmission occurred after bladder outlet obstruction, predominantly in its purinergic component and detrusor contractions via cholinergic neurotransmission were activated in a compensatory manner, probably via N-type Ca(2+) channel up-regulation.

Functional bombesin receptors in urinary tract of rats and human but not of pigs and mice, an in vitro study

AimsBombesin receptors (BB receptors) and/or bombesin related peptides are expressed in the lower urinary tract, though their function and distribution in different species is largely unknown. This study examines whether BB receptor agonists can contract bladder smooth muscle in rats, mice, pigs and humans. MethodsBladder strips were placed in tissue baths for in vitro contractility. Neuronally evoked contractions were elicited using electric field stimulation (EFS). Effects of the BB receptor agonists, neuromedin B (NMB; BB1 receptor agonist) and gastrin-releasing peptide (GRP; BB2 receptor agonist) on baseline tone and EFS-induced contractions were monitored. ResultsIn rat and human bladder strips, NMB and GRP (10−11–10−6M) increased EFS-induced contractions in a concentration dependent manner. In these species, NMB and GRP also increased baseline tension. In mouse and pig bladder strips, NMB and GRP (10−8–3×10−6M) had no effects on either parameter. ConclusionsThese data suggest that bombesin receptors BB receptor 1 and/or BB receptor 2 increase bladder contractions in rat and human. The site of action of these receptors may be pre- and/or post-synaptic, increasing release of transmitters or enhancing smooth muscle excitability, respectively. Thus, BB1 receptor and/or BB2 receptor may offer therapeutic targets for voiding dysfunction associated with impaired bladder contractility; however, species differences must be considered when studying these receptors.Part of this work was published in an abstract form at the SFN meeting New Orleans, 2012.

Effects of Chronic Tenotomy on the Post-Tetanic Responses of Fast and Slow Muscles in Rats

The effects of tenotomy present for two weeks on the post-tetanic responses of isolated fast (extensor digitorum longus) and slow (soleus) muscles were studied by isometric recording of muscle contraction in rats. After tetanic stimulation with bursts of 100 impulses at a frequency of 20 impulses/sec, the force of single fast muscle contractions exceeded the pretetanic level by 20‐25% (p < 0.05) in both intact and tenotomized muscles. In similar conditions, the slow muscle soleus showed a decrease in the amplitudes of single contractions, i.e., post-tetanic depression. Post-tetanic depression was not seen after tenotomy. Caffeine (4 mM) increased the force of single and tetanic contractions in control and tenotomized fast muscles, though no corresponding increase in post-tetanic responses were seen. In slow muscles, caffeine had no effect on the nature of post-tetanic responses. Dantrolene (10 μM) decreased the force of single and tetanic contractions but did not prevent the appearance of post-tetanic potentiation in fast muscles and depression in intact slow muscles. The fact that the phenomenon of post-tetanic potentiation disappeared after denervation of fast muscles within two weeks while it was present after tenotomy for as long as 40 days after surgery provides grounds for suggesting the existence of a potentiating factor which reaches muscles by axonal transport and increases single contractions.

Effect of leonurine hydrochloride on endothelin and the endothelin receptor-mediated signal pathway in medically-induced incomplete abortion in rats

ObjectiveEndothelin (ET) is involved in uterine contractions. Our previous study showed that leonurine hydrochloride (LH) inhibits abnormal bleeding caused by incomplete abortion through an increase in uterine contractions in rats. The present study was conducted to show that LH treatment regulates the ET-mediated signal pathway in abortion in rats. Study designEarly pregnancies in rats had incomplete abortions induced using mifepristone in combination with misoprostol. After the abortions, the rats were treated with LH orally for 7 days and surgery was performed. The sinistro-uterus was dissected for measurement of ET and nitric oxide (NO); the dextro-uterus was stored at −80°C for ET receptor (ETA and ETB) analysis. Myometrial cells from the dextro-uterus were cultured for measurement of phospholipase C (PLC) activity, intra-cellular Ca2+ concentration ([Ca2+]i), and protein kinase C (PKC) activity. ResultsIn in vivo experiments, LH treatment elevated the ET level and ET/NO ratio in rats with induced abortions and up-regulated ETA mRNA expression (P<0.01 vs. the model group), but there was no change in ETB mRNA. LH significantly increased the [Ca2+]i, PLC activity, and relative production of PKC protein in myometrial cells. ConclusionLH increased uterine contractions in rats with incomplete abortions by modulating the ET receptor-mediated signal pathway.

24 EFFECTS OF MIRABEGRON, A β3-ADRENOCEPTOR AGONIST, ON THE PRIMARY BLADDER AFFERENT ACTIVITY SYNCHRONIZED WITH RHYTHMIC BLADDER CONTRACTIONS IN RATS IN COMPARISON WITH THOSE OF OXYBUTYNIN

You have accessJournal of UrologyUrodynamics/Incontinence/Female Urology: Basic Research (1)1 Apr 201324 EFFECTS OF MIRABEGRON, A β3-ADRENOCEPTOR AGONIST, ON THE PRIMARY BLADDER AFFERENT ACTIVITY SYNCHRONIZED WITH RHYTHMIC BLADDER CONTRACTIONS IN RATS IN COMPARISON WITH THOSE OF OXYBUTYNIN Naoki Aizawa, Yukio Homma, and Yasuhiko Igawa Naoki AizawaNaoki Aizawa Tokyo, Japan More articles by this author , Yukio HommaYukio Homma Tokyo, Japan More articles by this author , and Yasuhiko IgawaYasuhiko Igawa Tokyo, Japan More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2013.02.1399AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES β3-adrenoceptor (β3-AR) agonists can inhibit the single unit mechanosensitve bladder afferent activities (SAAs) in response to bladder distension. These SAAs, however, might be enhanced also by bladder contractions. Therefore, we measured SAAs during rhythmic bladder contractions (RBCs) in an isovolumetric condition, and examined whether mirabegron, a β3-AR agonist, can affect the SAAs in such condition in rats, and compared with the effect of oxybutynin, an antimuscarinic agent. METHODS Twenty-five female SD rats were used. Under urethane anesthesia, SAAs were dissected from the left L6 dorsal roots and identified by electrical stimulation of the left pelvic nerve and by bladder distension. Nerves were classified as an Aδ- or C-fiber by conduction velocity (2.5 m/second). To produce the RBCs, right L6 dorsal roots were kept intact and the urethral meatus was clamped. When RBCs were reproducibly induced by intravesical saline-instillation, the instillation was stopped and the bladder was kept under an isovolumetric condition. Then, vehicle and 1 mg/kg of mirabegron or oxybutynin were administrated intravenously. RESULTS After mirabegron-treatment, the amplitude and duration of RBCs significantly decreased. Similar effects were observed also after oxybutynin-treatment. The interval of RBCs increased and the basal pressure decreased significantly only after mirabegron-treatment. Forty-one single afferent fibers (Aδ-fibers: n=19, C-fibers: n=22) were isolated. SAAs of both Aδ- and C-fibers were enhanced in a fashion synchronized with RBCs. After mirabegron-treatment, the peak of FR (firing rate) of SAAs synchronized with RBCs significantly decreased in Aδ-fibers, but not C-fibers (figure). After oxybutynin-treatment, the peak of FR of both fiber-SAAs significantly decreased, but the change was not significant when the value was normalized by the change in the amplitude of RBCs. CONCLUSIONS The present results indicate that the stimulation of β3-AR by mirabegron can inhibit mechanosensitive primary bladder afferent activities synchronized with RBCs, mainly of Aδ-fibers. However, these effects were not observed with oxybutynin. © 2013 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 189Issue 4SApril 2013Page: e9-e10 Advertisement Copyright & Permissions© 2013 by American Urological Association Education and Research, Inc.MetricsAuthor Information Naoki Aizawa Tokyo, Japan More articles by this author Yukio Homma Tokyo, Japan More articles by this author Yasuhiko Igawa Tokyo, Japan More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

440 Effects of the combination of β3-adrenoceptor agonists and antimuscarinics on EFS-induced contractions of rat isolated urinary bladder

440 Effects of the combination of β3-adrenoceptor agonists and antimuscarinics on EFS-induced contractions of rat isolated urinary bladder

A role for M2 and M3 muscarinic receptors in the contraction of rat and human small airways

Large airway bronchoconstriction acts mainly through cholinergic pathways via muscarinic M3 receptors with some contribution from M2 receptors. By contrast, the mechanisms of small airway contraction are largely unknown. This study used precision cut lung slices to examine the role of muscarinic M2 and M3 receptors in the contractile response of rat and human small airways.In rat small airways, the M3 preferential antagonist, 4-DAMP, inhibited carbachol-mediated contraction (1×10−6M) more than that of the M2 selective antagonist, AF-DX116 (pIC50 values: 8.85±0.18 and 6.31±0.19, n=6–8 respectively). Tiotropium, inhibited the contractile response to carbachol with (pIC50: 9.86±0.07, n=6), but could not distinguish between M2 and M3 mediated effects. Similar experiments using human small airways with tiotropium and AF-DX116, gave a pIC50 of 10.35±0.05 and a pKB of 6.37±0.13, n=5 respectively. Therefore, M3 receptors play a key role in muscarinic contraction of small airways in both rats and humans but the effect of M2 receptors cannot be excluded.To investigate the role of M2 receptors, carbachol-induced contraction of small airways was performed in the presence and absence of a β2-agonist in order to elevate intracellular cAMP levels prior to contraction. Isoproterenol-induced relaxation was significantly increased by AF-DX116 (P<0.001) in rat small airways and by AF-DX116 (P<0.01), gallamine (P<0.05) and pertussis toxin (P<0.05) in human small airways.Taken together, these data suggest that cholinergic antagonism of muscarinic receptors in human and rat small airways inhibits airway contraction via direct inhibition of contraction through M3 receptors, and by M2 receptor mediated inhibition of relaxation.

Naftopidil inhibits 5-hydroxytryptamine-induced bladder contraction in rats

Naftopidil is an α1D and α1A subtype-selective α1-adrenoceptor antagonist that has been used to treat lower urinary tract symptoms of benign prostatic hyperplasia. In this study, we investigated the effects of naftopidil on 5-hydroxytryptamine (5-HT)-induced rat bladder contraction (10−8–10−4M). Naftopidil (0.3, 1, and 3μM) inhibited 5-HT-induced bladder contraction in a concentration-dependent manner. On the other hand, other α1-adrenoceptor antagonists, tamsulosin, silodosin or prazosin, did not inhibit 5-HT-induced bladder contraction. The 5-HT-induced bladder contraction was inhibited by both ketanserin and 4-(4-fluoronaphthalen-1-yl)-6-propan-2-ylpyrimidin-2-amine (RS127445), serotonin 5-HT2A and 5-HT2B receptor antagonists, respectively. In addition, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and α-methyl-5-HT, 5-HT2A and 5-HT2 receptor agonists, respectively, induced bladder contraction. The 5-HT-induced bladder contraction was not inhibited by N-[2-[4-(2-methoxyphenyl)piperazin-1-yl]ethyl]-N-pyridin-2-yl-cyclohexanecarboxamide (WAY-100635), [1-[2[(methylsulfonyl)amino]ethyl]-4-piperidinyl]methyl-1-methyl-1H-indole-3-carboxylate (GR113808) or (R)-3-[2-[2-(4-methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulphonyl]phenol (SB269970), 5-HT1A, 5-HT4 and 5-HT7 receptor antagonists, respectively. Naftopidil inhibited both the 5-HT2A and 5-HT2 receptor agonists-induced bladder contractions. Naftopidil binds to the human 5-HT2A and 5-HT2B receptors with pKi values of 6.55 and 7.82, respectively. These results suggest that naftopidil inhibits 5-HT-induced bladder contraction via blockade of the 5-HT2A and 5-HT2B receptors in rats. Furthermore, 5-HT-induced bladder contraction was enhanced in bladder strips obtained from bladder outlet obstructed rats, with this contraction inhibited by naftopidil. The beneficial effects of naftopidil on storage symptoms such as urinary frequency and nocturia in patients with benign prostatic hyperplasia may be due, in part, to the blockade of the 5-HT2A and 5-HT2B receptors in the bladder.

Meranzin hydrate exhibits anti-depressive and prokinetic-like effects through regulation of the shared alpha 2-adrenoceptor in the brain–gut axis of rats in the forced swimming test

BackgroundIn recent years, the brain–gut axis theory has received increasing attention in studies of depression. However, most studies separately address potential antidepressant and prokinetic treatments. Investigations of drugs that could potentially treat comorbid depression and gastrointestinal (GI) dysfunction via a common mechanism of action have not yet been performed in detail. AimTo find a common mechanism of action of our patented drug, meranzin hydrate (MH), in the antidepressant and prokinetic treatment. MethodsThe forced swimming test (FST) model of depression, plasma ghrelin measurement, and in vivo and in vitro measurements of GI motility were used. Results1. Administration of MH (9 mg/kg) decreased the immobility time during the FST after acute treatment; this effect was inhibited by the alpha 2-adrenoceptor antagonist, yohimbine, but not by the alpha 1-adrenoceptor antagonist, prazosin. 2. After chronic treatment, the immobility time of rats during the FST was decreased significantly by MH (2.25 mg/kg). 3. MH (9 mg/kg) increased plasma ghrelin levels in rats subjected to the FST; this increase was enhanced by the ghrelin receptor agonist, GHRP-6. 4. MH (9 mg/kg) also promoted gastric emptying and intestinal transit in rats with or without FST. 5. In vitro, MH (10 μM) increased jejunal contractions in rats subjected to the FST; this effect was inhibited by yohimbine. Furthermore, the inhibitory effect of yohimbine was partly reversed by the ghrelin receptor agonist, GHRP-6. ConclusionOur study revealed that MH from natural resources exhibits antidepressive and prokinetic-like effects through the regulation of the common mediator, the alpha 2-adrenoceptor.

Neurochemical mechanism of the gastrointestinal interdigestive migrating motor complex in rats with acute inflammatory stomach ache.

The normal gastrointestinal interdigestive migrating motor complex cycle was interrupted, and paroxysmal contraction appeared after formaldehyde-induced stomach ache. Activities of nitric oxide synthase, acetylcholinesterase and vasoactive intestinal peptide neurons were significantly reduced, whereas activities of calcitonin gene-related peptide neurons were significantly increased in the pyloric sphincter muscular layer, myenteric nerve plexus and submucous nerve plexus. Electroacupuncture at Zusanli (ST36) suppressed paroxysmal contraction in rats with formaldehyde-induced stomach ache, and neurons in the enteric nervous system were normal. These results indicated that nitrergic neurons, cholinergic neurons, vasoactive intestinal peptide neurons and calcitonin gene-related peptide neurons in the enteric nervous system may be involved in changes to the gastrointestinal interdigestive migrating motor complex following stomach ache, and that electroacupuncture can regulate this process.

Mitochondrial ROS and muscle glucose uptake during exercise in transgenic mice

much research has examined the factors regulating skeletal muscle glucose uptake during exercise. Part of the impetus for this work has been to describe and understand the effects of regular physical activity (i.e., exercise training) on muscle glucose uptake and energy substrate partitioning,

Linalool-rich rosewood oil evoked a vago-vagal bradycardic and depressor effect in normotensive rats

Cardiovascular effects of the linalool-rich essential oil of Aniba rosaeodora (EOAR or rosewood) in normotensive rats were investigated. Male Wistar rats were anesthetized and two catheters were implanted for blood pressure recording and drug injection. In anesthetized rats, intravenous (i.v.) EOAR elicited dose-dependent hypotensive and bradycardiac effects which were characterized in two periods (phases 1 and 2). The first rapid component (phase 1) evoked by EOAR was abolished by bilateral vagotomy, perineural treatment of both cervical vagus nerves with capsaicin and was absent after left ventricle injection. However, i.v. pretreatment with capsazepine, ondansetron or HC030031 did not alter phase 1 of the cardiovascular responses to EOAR. In conscious rats, EOAR evoked rapid hypotensive and bradycardiac (phase 1) effects that were abolished by i.v. methylatropine. EOAR induces a vago-vagal bradycardiac and depressor reflex (phase 1) that apparently results from the stimulation of vagal pulmonary rather than cardiac C-fiber afferents and does appear to involve activation of neither the 5HT3 receptors nor the two chemosensory ion channels TRPV1 and TRPA1 receptors. The phase 2 hypotensive response to EOAR seems to result from a direct vasodilatory effect since EOAR relaxed phenylephrine-induced contractions in rat isolated aortic rings.

Involvement of P2Y receptors in myocardial contractile activity of rats during postnatal ontogeny

We studied the effect of uridine 5'-triphosphate in concentrations of 10(-10)-10(-6) M on myocardial contractile activity in 7-100-day-old rats. Analysis of isometric contraction of myocardial strips showed that uridine 5'-triphosphate reduced the strength of myocardial contraction in rats of all age groups. In 21- and 100-day-old rat pups, exogenous uridine 5'-triphosphate produced a stronger inhibitory effect than in 7-day-old animals. The negative inotropic effect of UTP was abolished under conditions of P2Y(4) purinoceptor blockade with reagent blue-2. These data indicate that the effect of UTP on the myocardium is realized via P2Y(4) purinoceptors.

IL-6, TNF-α, and iNOS is associated with decreased colonic contraction in rats with multiple organ dysfunction syndrome

BackgroundGastrointestinal stasis is frequently accompanied by multiple organ dysfunction syndrome (MODS), which may lead to gastrointestinal smooth muscle dysfunction. The aim of this study is to investigate whether MODS initiates an inflammatory response and produces IL-6, TNF-α, and iNOS cytokines, as well as to determine whether these cytokines give rise to gastrointestinal smooth muscle dysfunction. Materials and methodsSixty Wistar rats were divided equally into a negative control group, a positive control group, and a MODS group. The number of stool spots, the contractility of muscle strips in the colon, and morphologic changes to the colon smooth muscle were recorded. The mRNA and protein expressions of IL-6, TNF-α, and iNOS in the colon were detected by semiquantitative reverse transcription polymerase chain reaction and immunohistochemistry respectively. In addition, the NO level was observed. ResultsFor the MODS group, the colon stool numbers, maximal contractive stress, and spontaneous frequency of muscle strips were, respectively, 0.77 ± 0.52 pill/h, 301g/cm3, and 11.52 ± 0.38 contractions/min (P < 0.05); for the negative control group, 1.54 ± 0.64 pills/h, 645 g/cm3, and 19.2 ± 0.71 contractions/min, respectively (P < 0.05); and for the positive control group, 0.94 ± 0.21 pills/h, 415 g/cm3, and 14.1 ± 0.52 contractions/min, respectively (P < 0.05). In the MODS group, there was a marked up-regulation of expression of IL-6, TNF-α, and iNOS and the contractility of the smooth muscle strips had a negative correlation with the expression of IL-6, TNF-α, and iNOS. ConclusionWe speculate that reduced colon motility in the MODS rats may be related to the increase in iNOS, IL-6, and TNF-α in the colon muscularis.

Selective inhibitory action of Biginelli-type dihydropyrimidines on depolarization-induced arterial smooth muscle contraction

Dihydropyridine calcium channel blockers have some disadvantages such as light sensitivity and relatively short plasma half-lives. Stability of dihydropyrimidines analogues could be of advantage, yet they remain less well characterized. We aimed to test four newly synthesized Biginelli-type dihydropyrimidines for their calcium channel blocking activity on rat isolated aorta. Dihydropyrimidines (compounds A-D) were prepared by the Biginelli-like three-component condensation of benzaldehydes with urea/thiourea and dimethyl or diethyl acetone-1,3-dicarboxylate, and their physicochemical properties and effects on depolarization-induced and noradrenaline-induced contractions of rat isolated aorta were evaluated. Dihydropyrimidines A and C blocked KCl-induced contraction only weakly (-log(IC50)=5.03 and 3.73, respectively), while dihydropyrimidine D (-log(IC50)=7.03) was almost as potent as nifedipine (-log(IC50)=8.14). Washout experiments revealed that dihydropyrimidine D may bind strongly to the L-type calcium channel or remains bound to membrane. All tested dihydropyrimidines only marginally inhibited noradrenaline-induced contractions of rat isolated aorta (20% reduction of noradrenaline E(max) ), indicating a more selective action on L-type calcium channel than nifedipine with 75% inhibition of noradrenaline E(max) at 10(-4) m nifedipine). Compounds A and, particularly, D are potent calcium channel blockers in vitro, with a better selectivity in inhibiting depolarization-induced arterial smooth muscle contraction than nifedipine.

Effect of Chemical Stimulation of the Medial Frontal Lobe on the Micturition Reflex in Rats

We assessed the influence of the medial frontal lobe on micturition after chemical stimulation. We also examined the relation between the medial frontal lobe and the rostral pontine reticular formation, which has a strong inhibitory effect on micturition. A total of 35 female rats underwent continuous cystometry. Bladder activity changes were examined after physiological saline, glutamate, the glutamate receptor antagonist MK-801, noradrenaline or the adrenergic α-1 receptor antagonist naftopidil was injected in the medial frontal lobe. When glutamate was injected in the medial frontal lobe, MK-801 was also injected in the rostral pontine reticular formation. Glutamate injection in the medial frontal lobe prolonged the interval between bladder contractions while injection of the glutamate antagonist MK-801 shortened the interval. Glutamate injection in the medial frontal lobe just after MK-801 injection in the ipsilateral rostral pontine reticular formation also prolonged the interval between bladder contractions. However, after prior injection of MK-801 in the bilateral rostral pontine reticular formation glutamate injection in the medial frontal lobe did not influence cystometric parameters. Noradrenaline injection in the medial frontal lobe shortened the interval between bladder contractions while injection of its antagonist naftopidil prolonged the interval. Medial frontal lobe neurons excited by glutamate inhibited the micturition reflex via activation of the rostral pontine reticular formation by glutamatergic projection while medial frontal lobe neurons excited by noradrenaline facilitated the micturition reflex. Thus, the medial frontal lobe may be an important integration center for the initiation of micturition and urine storage mechanisms.

Postnatal changes in vagal control of esophageal muscle contractions in rats

AimsReplacement of smooth muscles by striated muscles occurs in the esophagus during the early postnatal period. The aim of this study was to clarify postnatal changes in vagal control of esophageal muscle contractions in rats. Main methodsAn isolated segment of the neonatal rat esophagus was placed in an organ bath and the contractile responses were recorded using a force transducer. Key findingsElectrical stimulation of the vagus trunk evoked a biphasic contractile response in the neonatal esophageal segment. The first and second components of the contractions were inhibited by α-bungarotoxin and atropine, respectively. Ganglion blockers, hexamethonium and mecamylamine, did not affect vagally mediated contractions. The first component gradually enlarged with age in days, whereas the second component declined during the first week after birth. Application of d-tubocurarine or acetylcholine caused an apparent contraction in the esophageal striated muscle at postnatal day 0, but responses to these drugs were not observed at 1week after birth. The neonatal esophagus expressed the γ-subunit of nicotinic acetylcholine receptors. In contrast, the ε-subunit was dominantly expressed in the adult esophagus. SignificanceThe vagus nerves directly innervate both the esophageal striated muscles and smooth muscles in the early neonatal period. During the process of muscle rearrangement, the property of the striated muscles is altered substantially. The specific features of striated muscles in the neonatal rat esophagus might compensate for immature formation of neuromuscular junctions. Unsuccessful conversion of the striated muscle property during postnatal muscle rearrangement would be related to disorders of esophageal motility.

Effects of magnolol on vascular contraction in rat aortic rings

1. Magnolol (5,5'-diallyl-2,2'-dihydroxybiphenyl) is a major phenolic compound purified from Magnolia officinalis. The aim of the present study was to elucidate the effects of magnolol on vascular contractions. 2. Rat aortic rings were mounted in organ baths. Magnolol was added cumulatively (0.3-30 μmol/L) to elicit relaxation in endothelium-intact and -denuded rat aortic rings precontracted with U46619 (30 nmol/L, 20 min), NaF (8.0 mmol/L, 40 min), phenylephrine (1.0 or 0.1 μmol/L, 15 min) or phorbol-12,13-dibutyrate (PDBu, 0.3 or 0.1 μmol/L, 40 min). In separate experiments, cumulative concentrationresponse curves were obtained for NaF (2.0-12 mmol/L), U46619 (1.0 nmol/L1.0 μmol/L) or PDBu (1.0 nmol/L1.0 μmol/L) after pretreatment with either magnolol or vehicle for 30 min in endothelium-denuded aortic rings. After completion of the functional study, we measured the amount of guanosine triphosphate (GTP) RhoA by using a G-LISA RhoA Activation Assay, as well as the phosphorylation of 20 kDa myosin light chain (MLC₂₀), myosin phosphatase-targeting subunit 1 (MYPT1) and protein kinase C-potentiated inhibitory protein for heterotrimeric myosin light-chain phosphatase of 17 kDa (CPI-17) by immunobloting. 3. Magnolol (0.3-30 μmol/L) reduced vascular tension induced by the thromboxane A₂ agonist U46619 (30 nmol/L), sodium fluoride (NaF) (8.0 mmol/L) and the α₁ -adrenoceptor agonist phenylephrine (1.0 or 0.1 μmol/L) in both endothelium-intact and -denuded rings. The magnitude of the relaxation effects of magnolol on the contraction induced by each of the drugs were similar. The magnitude of the effect of magnolol in endothelium-intact and -denuded rings were similar. 4. Pretreatment of rat aortic rings with 1.0, 3.0 or 10 μmol/L magnolol for 30 min dose-dependently inhibited the maximum response on the concentration-response curves to NaF and U46619, but not to phorbol-12,13-dibutyrate (PDBu). 5. Magnolol (3.0 or 10 μmol/L) decreased RhoA activation, as well as the phosphorylation of MLC₂₀ , MYPT1(Thr855) and CPI-17(Thr38) induced by either 8.0 mmol/L NaF or 30 nmol/L U46619. In contrast, magnolol did not affect PDBu (0.1 μmol/L)-induced phosphorylation of CPI-17(Thr38) . 6. In conclusion, magnolol reduces vascular contraction by inhibiting the RhoA/Rho kinase pathway in endothelium-denuded rat aorta.

Kinetics of muscle deoxygenation and microvascular Po2 during contractions in rat: comparison of optical spectroscopy and phosphorescence-quenching techniques

The overarching presumption with near-infrared spectroscopy measurement of muscle deoxygenation is that the signal reflects predominantly the intramuscular microcirculatory compartment rather than intramyocyte myoglobin (Mb). To test this hypothesis, we compared the kinetics profile of muscle deoxygenation using visible light spectroscopy (suitable for the superficial fiber layers) with that for microvascular O(2) partial pressure (i.e., Pmv(O(2)), phosphorescence quenching) within the same muscle region (0.5∼1 mm depth) during transitions from rest to electrically stimulated contractions in the gastrocnemius of male Wistar rats (n = 14). Both responses could be modeled by a time delay (TD), followed by a close-to-exponential change to the new steady level. However, the TD for the muscle deoxygenation profile was significantly longer compared with that for the phosphorescence-quenching Pmv(O(2)) [8.6 ± 1.4 and 2.7 ± 0.6 s (means ± SE) for the deoxygenation and Pmv(O(2)), respectively; P < 0.05]. The time constants (τ) of the responses were not different (8.8 ± 4.7 and 11.2 ± 1.8 s for the deoxygenation and Pmv(O(2)), respectively). These disparate (TD) responses suggest that the deoxygenation characteristics of Mb extend the TD, thereby increasing the duration (number of contractions) before the onset of muscle deoxygenation. However, this effect was insufficient to increase the mean response time. Somewhat differently, the muscle deoxygenation response measured using near-infrared spectroscopy in the deeper regions (∼5 mm depth) (∼50% type I Mb-rich, highly oxidative fibers) was slower (τ = 42.3 ± 6.6 s; P < 0.05) than the corresponding value for superficial muscle measured using visible light spectroscopy or Pmv(O(2)) and can be explained on the basis of known fiber-type differences in Pmv(O(2)) kinetics. These data suggest that, within the superficial and also deeper muscle regions, the τ of the deoxygenation signal may represent a useful index of local O(2) extraction kinetics during exercise transients.

Plasticity of non-adrenergic non-cholinergic bladder contractions in rats after chronic spinal cord injury

The purpose of this study was to examine the pharmacologic plasticity of cholinergic, non-adrenergic non-cholinergic (NANC), and purinergic contractions in neurogenic bladder strips from spinal cord injured (SCI) rats. Bladder strips were harvested from female rats three to four weeks after T9–T10 spinal cord transection. The strips were electrically stimulated using two experimental protocols to compare the contribution of muscarinic and NANC/purinergic contractions in the presence and the absence of carbachol or muscarine. The endpoints of the study were: (1) percent NANC contraction that was unmasked by the muscarinic antagonist 4-DAMP, and (2) P2X purinergic contraction that was evoked by α,β-methylene ATP. NANC contraction accounted for 78.5% of the neurally evoked contraction in SCI bladders. When SCI bladder strips were treated with carbachol (10μM) prior to 4-DAMP (500nM), the percent NANC contraction decreased dramatically to only 13.1% of the neurally evoked contraction (P=0.041). This was accompanied by a substantial decrease in α,β-methylene ATP evoked P2X contraction, and desensitization of purinergic receptors (the ratio of subsequent over initial P2X contraction decreased from 97.2% to 42.1%, P=0.0017). Sequential activation of the cholinergic receptors with carbachol (or with muscarine in neurally intact bladders) and unmasking of the NANC response with 4-DAMP switched the neurally evoked bladder contraction from predominantly NANC to predominantly cholinergic. We conclude that activation of muscarinic receptors (with carbachol or muscarine) blocks NANC and purinergic contractions in neurally intact or in SCI rat bladders. The carbachol-induced inhibition of the NANC contraction is expressed more in SCI bladders compared to neurally intact bladders. Along with receptor plasticity, this change in bladder function may involve P2X-independent mechanisms.