GLT-1 overexpression attenuates bladder nociception and local/cross-organ sensitization of bladder nociception

Glutamatergic pathways mediate transmission of pain. Strategies to reduce glutamatergic neurotransmission may have beneficial effects to mitigate nociception. Recent work revealed that overexpression of the astrocytic glutamate transporter (GLT-1) by transgenic or pharmacologic approaches produced a diminished visceral nociceptive response to colonic distension. The purpose of this study was to determine the effect of GLT-1 overexpression on the visceromotor response to bladder distension. Increased glutamate uptake activity produced by 1-wk ceftriaxone (CTX) treatment attenuated 60-64% the visceromotor response to graded bladder distension compared with vehicle-treated mice. One-hour pretreatment with selective GLT-1 antagonist dihydrokainate reversed the blunted visceromotor response to bladder distension produced by 1-wk CTX, suggesting that GLT-1 overexpression mediated the analgesic effect of CTX. Moreover, sensitization of the visceromotor response to bladder distension produced by local bladder irritation (acrolein) was also attenuated by 1-wk CTX treatment. A model of cross-organ sensitization of bladder visceromotor response to distension was next studied to determine whether increased expression of GLT-1 can mitigate colon to bladder sensitization. Intracolonic trinitrobenzene sulfonic acid (TNBS) administered 1 h before eliciting the visceromotor response to graded bladder distension produced a 75-138% increase in visceromotor response compared with animals receiving intracolonic vehicle. In marked contrast, animals treated with 1-wk CTX + intracolonic TNBS showed no enhanced visceromotor response compared with the 1-wk vehicle + intracolonic vehicle group. The study suggests that GLT-1 overexpression attenuates the visceromotor response to bladder distension and both local irritant-induced and cross-organ-sensitized visceromotor response to bladder distension.     

Effect of partial and complete blockade of vanilloid (TRPV1-6) and ankyrin (TRPA1) transient receptor potential ion channels on urinary bladder motor activity in an experimental hyperosmolar overactive bladder rat model

The study investigated the mechanisms through which the hyperosmolarity might induce detrusor overactivity (DO). We compared the bladder activity in response to partial and complete blockade of TRPV1-6 and TRPA1 receptors. Experiments were performed on 42 rats. DO was induced by using hyperosmolar saline. All animals were randomly divided into six groups. The measurements represent the average of five bladder micturition cycles. Hyperosmolar saline induced DO. The complete blockade of TRPV1-6 and TRPA1 prevented DO. The partial blockade of TRPV1 didn't prevented DO. In the voiding phase periodical bladder contractions complexes occurred leading to slow urine flow due to bladder distension. Ruthenium red and capsaicin resulted in complete disorganisation of detrusor muscle contractility impairing urine voiding and leading to constantly lasting urine retention in healthy rats. Conclusions: hyperosmolar-induced DO is mediated by TRPV and TRPA1 channels; the hyperosmolar stimuli of urinary bladder might be transmitted mostly via ruthenium red sensitivity pathway.     

Ca2+ mobilization and activation of extracellular acidification by carbachol in acutely dispersed cells from guinea pig detrusor: Fura 2 fluorometry and microphysiometry using the cytosensor

The study aim was to develop a simple in vitro model for pharmacophysiological investigation of urinary bladder smooth muscles. Smooth muscle cells from guinea pig detrusor were dissociated, and the suspended cells were stimulated with carbachol (CCh), an acetylcholine receptor agonist. Cytosolic Ca2+ levels were determined using Fura 2 fluorescence and extracellular acidification rates were monitored by the Cytosensor microphysiometer. CCh dose-dependently increased cytosolic Ca2+ levels and extracellular acidification rates, with EC50 values of approximately 1 microM. Both the acetylcholine muscarinic receptor antagonist atropine and the M3 muscarinic receptor-preferring antagonist 4-diphenylacetoxy-N-methylpiperidine (4-DAMP) inhibited the effects of CCh, three orders of magnitude more potently than the selective M2 muscarinic receptor antagonist, methoctramine. These data indicate the dominant role of M3 receptors in guinea-pig bladder but fail to show clear evidence of any functional role for M2 receptors. Since this finding agrees with a number of other studies using in vivo and in vitro models (1), cell suspensions such as these may prove to be simple tools for the pharmacological study of urinary bladder smooth muscle tissue.     

Local disruption of the celiac ganglion inhibits substance P release and ameliorates caerulein-induced pancreatitis in rats

Primary sensory neurons of the C and Adelta subtypes express the vanilloid capsaicin receptor TRPV1 and contain proinflammatory peptides such as substance P (SP) that mediate neurogenic inflammation. Pancreatic injury stimulates these neurons causing the release of SP in the pancreas resulting in pancreatic edema and neutrophil infiltration that contributes to pancreatitis. Axons of primary sensory neurons innervating the pancreas course through the celiac ganglion. We hypothesized that disruption of the celiac ganglion by surgical excision or inhibition of C and Adelta fibers through blockade of TRPV1 would reduce the severity of experimental pancreatitis by inhibiting neurogenic inflammation. Resiniferatoxin (RTX) is a specific TRPV1 agonist that, in high doses, selectively destroys C and Adelta fibers. Sprague-Dawley rats underwent surgical ganglionectomy or application of 10 microg RTX (vs. vehicle alone) to the celiac ganglion. One week later, pancreatitis was induced by six hourly intraperitoneal injections of caerulein (50 microg/kg). The severity of pancreatitis was assessed by serum amylase, pancreatic edema, and pancreatic myeloperoxidase (MPO) activity. SP receptor (neurokinin-1 receptor, NK-1R) internalization in acinar cells, used as an index of endogenous SP release, was assessed by immunocytochemical quantification of NK-1R endocytosis. Caerulein administration caused significant increases in pancreatic edema, serum amylase, MPO activity, and NK-1R internalization. RTX treatment and ganglionectomy significantly reduced pancreatic edema by 46% (P < 0.001) and NK-1R internalization by 80% and 51% (P < 0.001 and P < 0.05, respectively). RTX administration also significantly reduced MPO activity by 47% (P < 0.05). Neither treatment affected serum amylase, consistent with a direct effect of caerulein. These results demonstrate that disruption of or local application of RTX to the celiac ganglion inhibits SP release in the pancreas and reduces the severity of acute secretagogue-induced pancreatitis. It is possible that selectively disrupting TRPV1-bearing neurons could be used to reduce pancreatitis severity.     

Uterine motor alterations and estrous cycle disturbances associated with colonic inflammation in the rat

The impact of colitis on uterine contractility and estrous cycle was investigated after intracolonic administration of 2,4,6-trinitrobenzenesulfonic acid (TNBS) in rats. Colitis severity was assessed by macroscopic damage scoring (MDS) 4 days after TNBS, and myeloperoxidase (MPO) activity was measured in both colon and uterus of control and colitic rats. Estrous cycle stages were determined by vaginal smears and histology, and uterine contractility was assessed in vitro on longitudinal and circular strips. In control rats, uterine MPO activity varied markedly during the cycle and peaked around estrus. In rats with moderate colitis [MDS < 5, 3.1 +/- 0.2 (mean +/- SE)], uterine MPO decreased by 61% compared with estrus control, without disruption of the cycle. Frequency of spontaneous contractions was reduced by 32% in circular muscle. Contractile responses to KCl and carbachol were not affected, whereas maximal response to oxytocin decreased by 47% in the longitudinal muscle. In rats with severe colitis (MDS > 5, 6.0 +/- 0.2), uterine MPO was reduced by 96% and estrous cycle was disrupted. Spontaneous contractility was impaired in circular strips, and a 39% decrease in the contraction frequency occurred in the longitudinal strips. Circular strips did not contract to KCl or carbachol; however, longitudinal strips had maximal responses to KCl, carbachol, and oxytocin reduced by 36%, 27%, and 46%, respectively. Estrogen replacement protected the uterine responses to carbachol in colitic rats, whereas oxytocin responses remained depressed. These data indicate that colonic inflammation can influence both spontaneous and evoked uterine contractility, in relation to estrous cycle disturbances, impaired estradiol production, and functional alterations of myometrial cells.     

Transient receptor potential vanilloid subtype 1 mediates microglial cell death in vivo and in vitro via Ca2+-mediated mitochondrial damage and cytochrome c release

The present study examined the expression of transient receptor potential vanilloid subtype 1 (TRPV1) in microglia, and its association with microglial cell death. In vitro cell cultures, RT-PCR, Western blot analysis, and immunocytochemical staining experiments revealed that rat microglia and a human microglia cell line (HMO6) showed TRPV1 expression. Furthermore, exposure of these cells to TRPV1 agonists, capsaicin (CAP) and resiniferatoxin (RTX), triggered cell death. This effect was ameliorated by the TRPV1 antagonists, capsazepine and iodo-resiniferatoxin (I-RTX), suggesting that TRPV1 is directly involved. Further examinations revealed that TRPV1-induced toxicity was accompanied by increases in intracellular Ca(2+), and mitochondrial damage; these effects were inhibited by capsazepine, I-RTX, and the intracellular Ca(2+) chelator BAPTA-AM. Treatment of cells with CAP or RTX led to increased mitochondrial cytochrome c release and enhanced immunoreactivity to cleaved caspase-3. In contrast, the caspase-3 inhibitor z-DEVD-fmk protected microglia from CAP- or RTX-induced toxicity. In vivo, we also found that intranigral injection of CAP or 12-hydroperoxyeicosatetraenoic acid, an endogenous agonist of TRPV1, into the rat brain produced microglial damage via TRPV1 in the substantia nigra, as visualized by immunocytochemistry. To our knowledge, this study is the first to demonstrate that microglia express TRPV1, and that activation of this receptor may contribute to microglial damage via Ca(2+) signaling and mitochondrial disruption.     

Aging impairs neurogenic contraction in guinea pig urinary bladder: role of oxidative stress and melatonin

The incidence of urinary bladder disturbances increases with age, and free radical accumulation has been proposed as a causal factor. Here we investigated the association between changes in bladder neuromuscular function and oxidative stress in aging and the possible benefits of melatonin treatment. Neuromuscular function was assessed by electrical field stimulation (EFS) of isolated guinea pig detrusor strips from adult and aged female guinea pigs. A group of adult and aged animals were treated with 2.5 mg x kg(-1) x day(-1) melatonin for 28 days. Neurotransmitter blockers were used to dissect pharmacologically the EFS-elicited contractile response. EFS induced a neurogenic and frequency-dependent contraction that was impaired by aging. This impairment is in part related to a decrease in detrusor myogenic contractility. Age also decreased the sensitivity of the contraction to pharmacological blockade of purinergic and sensitive fibers but increased the effect of blockade of nitrergic and adrenergic nerves. The density of cholinergic and nitrergic nerves remained unaltered, but aging modified afferent fibers. These changes were associated with an increased level of markers for oxidative stress. Melatonin treatment normalized oxidative levels and counteracted the aging-associated changes in bladder neuromuscular function. In conclusion, these results show that aging modifies neurogenic contraction and the functional profile of the urinary bladder plexus and simultaneously increases the oxidative damage to the organ. Melatonin reduces oxidative stress and improves the age-induced changes in bladder neuromuscular function, which could be of importance in reducing the impact of age-related bladder disorders.     

Dietary Resistant Starch Alters the Characteristics of Colonic Mucosa and Exerts a Protective Effect on Trinitrobenzene Sulfonic Acid-induced Colitis in Rats

The protective effect of a dietary high-amylose cornstarch (HAS) against trinitrobenzene sulfonic acid (TNBS)-induced colitis was examined in rats. Rats were fed a HAS-free basal diet or, a 15% or 30% HAS supplemented diet for 10 d, and then received intracolonic TNBS to induce colitis and fed the respective diets for a further 8 d. HAS ingestion significantly protected colonic injuries as evidenced by lower colonic myeloperoxidase activity. Rats fed the HAS diet showed greater cecal short-chain fatty acid (SCFA) production than those fed the basal diet. Further, just before TNBS administration, HAS ingestion dose-dependently increased fecal and cecal mucin contents, and protein and nucleic acid contents in the colonic mucosa. HAS ingestion also reduced colonic permeability. The protective effect of HAS ingestion on TNBS-induced colitis is perhaps exerted through alterations in colonic mucosa, possibly due to cecal SCFA production.     

Dietary resistant starch alters the characteristics of colonic mucosa and exerts a protective effect on trinitrobenzene sulfonic acid-induced colitis in rats

The protective effect of a dietary high-amylose cornstarch (HAS) against trinitrobenzene sulfonic acid (TNBS)-induced colitis was examined in rats. Rats were fed a HAS-free basal diet or, a 15% or 30% HAS supplemented diet for 10 d, and then received intracolonic TNBS to induce colitis and fed the respective diets for a further 8 d. HAS ingestion significantly protected colonic injuries as evidenced by lower colonic myeloperoxidase activity. Rats fed the HAS diet showed greater cecal short-chain fatty acid (SCFA) production than those fed the basal diet. Further, just before TNBS administration, HAS ingestion dose-dependently increased fecal and cecal mucin contents, and protein and nucleic acid contents in the colonic mucosa. HAS ingestion also reduced colonic permeability. The protective effect of HAS ingestion on TNBS-induced colitis is perhaps exerted through alterations in colonic mucosa, possibly due to cecal SCFA production.     

Resiniferatoxin binds to the capsaicin receptor (TRPV1) near the extracellular side of the S4 transmembrane domain

The capsaicin receptor (TRPV1) is a nonselective cation channel that is activated in nociceptors by several painful stimuli, and hence TRPV1 antagonists could represent a novel class of analgesic compounds. Resiniferatoxin (RTX), a potent agonist of TRPV1, and iodoresiniferatoxin (I-RTX), a potent antagonist of TRPV1, both bind with higher affinity to the rat TRPV1 (rTRPV1) than the human (hTRPV1) isoform. To identify the structural features responsible for this difference in affinity, [(3)H]RTX binding to chimeras between hTRPV1 and rTRPV1 was characterized. The "sensor" region within the transmembrane domain (S1-S4) was found to determine [(3)H]RTX binding affinity. All 16 different residues in this region were systematically substituted in hTRPV1 with rTRPV1 residues. A single mutation in the S4 membrane domain of hTRPV1, L547M, caused a 30-fold increase in [(3)H]RTX affinity whereas the inverse mutation in rTRPV1, M547L, caused a 30-fold decrease in affinity for [(3)H]RTX, and several other agonists and antagonists were similarly affected by these mutations. TRPV1 channels with mutations at position 547 were expressed in oocytes, and the relative response to RTX followed a pattern similar to that seen with [(3)H]RTX binding. These data suggest a model where Met-547 in the S4 domain of TRPV1 forms a binding pocket with Tyr-511 in the S3 domain. This model places RTX near the sensor domain thought to move during the gating process and should help to guide further work designed to understand the gating mechanisms of TRPV1 channels based on comparisons between the agonist RTX and the related competitive antagonist I-RTX.     

Estrous Cycle Dependent Fluctuations of Regulatory Neuropeptides in the Lower Urinary Tract of Female Rats upon Colon-Bladder Cross-Sensitization

Co-morbidity of bladder, bowel, and non-specific pelvic pain symptoms is highly prevalent in women. Little evidence is present on modulation of pelvic pain syndromes by sex hormones, therefore, the objective of this study was to clarify the effects of hormonal fluctuations within the estrous cycle on regulatory neuropeptides in female rats using a model of neurogenic bladder dysfunction. The estrous cycle in female rats (Sprague-Dawley, 230–250 g) was assessed by vaginal smears and weight of uterine horns. Neurogenic bladder dysfunction was induced by a single inflammatory insult to the distal colon. Protein expression of calcitonin gene related peptide (CGRP), substance P (SP), nerve growth factor (NGF), and brain derived neurotrophic factor (BDNF) in the pelvic organs, sensory ganglia and lumbosacral spinal cord was compared in rats in proestrus (high estrogen) vs diestrus (low estrogen). Under normal physiological conditions, concentration of SP and CGRP was similar in the distal colon and urinary bladder during all phases of the estrous cycle, however, acute colitis induced a significant up-regulation of CGRP content in the colon (by 63%) and urinary bladder (by 54%, p≤0.05 to control) of rats in proestrus. These changes were accompanied by a significant diminution of CGRP content in L6-S2 DRG after colonic treatment, likely associated with its release in the periphery. In rats with high estrogen at the time of testing (proestrus), experimental colitis caused a significant up-regulation of BDNF colonic content from 26.1±8.5 pg/ml to 83.4±32.5 pg/ml (N = 7, p≤0.05 to control) and also induced similar effects on BDNF in the urinary bladder which was also up-regulated by 5-fold in rats in proestrus (p≤0.05 to respective control). Our results demonstrate estrous cycle dependent fluctuations of regulatory neuropeptides in the lower urinary tract upon colon-bladder cross-sensitization, which may contribute to pain fluctuations in female patients with neurogenic bladder pain.     

Beneficial effect of trimebutine and N-monodesmethyl trimebutine on trinitrobenzene sulfonic acid-induced colitis in rats

The use of local anesthetics, such as lidocaine, has been proposed in the treatment of distal ulcerative colitis. Trimebutine maleate (TMB) displays a local anesthetic activity higher than that of lidocaine in rabbit corneal reflex. TMB and nor-TMB its main metabolite in human show similar affinity to that of bupivacaine toward sodium channel labeled by [3H]batrachotoxin and block sodium currents in sensory neurons from rat dorsal root ganglia. The aim of this study was to evaluate the effects of TMB and nor-TMB in comparison to lidocaine and bupivacaine in a rat model of acute colonic inflammation induced by trinitrobenzene sulfonic acid (TNBS). A single intracolonic instillation of TNBS (50 mg/kg dissolved in ethanol 30%) led to early plasma extravasation then macroscopic damage (hyperemia and necrosis), increased colonic weight and tissular MPO, a marker of neutrophilic infiltration. Local administration of TMB at dose of 3 to 60 mg/kg, 30 min before, 24 and 48 h after colitis induction, significantly reduced the severity of colitis. Nor-TMB (1, 3, 10, 30 mg/kg) as well as lidocaine (1, 3, 10 mg/kg) dose-dependently reduced colitis while bupivacaine at 10 mg/kg did not affect it significantly. In contrast systemic administration of TMB, nor-TMB and lidocaine at 10 mg/kg had no significant effect. Furthermore, local administration of TMB (30 mg/kg) and lidocaine (10 mg/kg) significantly reduced plasmatic extravasation. In conclusion, intracolonic treatment with TMB and nor-TMB improved acute experimental TNBS-induced colitis in rat and these effects could be explained by their local anesthetic activity.     

Molecular determinants of vanilloid sensitivity in TRPV1

Vanilloid receptor 1 (TRPV1), a membrane-associated cation channel, is activated by the pungent vanilloid from chili peppers, capsaicin, and the ultra potent vanilloid from Euphorbia resinifera, resiniferatoxin (RTX), as well as by physical stimuli (heat and protons) and proposed endogenous ligands (anandamide, N-arachidonyldopamine, N-oleoyldopamine, and products of lipoxygenase). Only limited information is available in TRPV1 on the residues that contribute to vanilloid activation. Interestingly, rabbits have been suggested to be insensitive to capsaicin and have been shown to lack detectable [(3)H]RTX binding in membranes prepared from their dorsal root ganglia. We have cloned rabbit TRPV1 (oTRPV1) and report that it exhibits high homology to rat and human TRPV1. Like its mammalian orthologs, oTRPV1 is selectively expressed in sensory neurons and is sensitive to protons and heat activation but is 100-fold less sensitive to vanilloid activation than either rat or human. Here we identify key residues (Met(547) and Thr(550)) in transmembrane regions 3 and 4 (TM3/4) of rat and human TRPV1 that confer vanilloid sensitivity, [(3)H]RTX binding and competitive antagonist binding to rabbit TRPV1. We also show that these residues differentially affect ligand recognition as well as the assays of functional response versus ligand binding. Furthermore, these residues account for the reported pharmacological differences of RTX, PPAHV (phorbol 12-phenyl-acetate 13-acetate 20-homovanillate) and capsazepine between human and rat TRPV1. Based on our data we propose a model of the TM3/4 region of TRPV1 bound to capsaicin or RTX that may aid in the development of potent TRPV1 antagonists with utility in the treatment of sensory disorders.     

A comparative study of the preventative effects exerted by three probiotics, Bifidobacterium lactis, Lactobacillus casei and Lactobacillus acidophilus, in the TNBS model of rat colitis

AIMS: The intestinal anti-inflammatory effects of three probiotics with immunomodulatory properties, Lactobacillus casei, Lactobacillus acidophilus and Bifidobacterium lactis, were evaluated and compared in the trinitrobenzenesulphonic acid (TNBS) model of rat colitis. METHODS AND RESULTS: Colitis was induced in rats by intracolonic administration of 10 mg of TNBS dissolved in 0.25 ml of 50% ethanol. Each probiotic was administered orally (5x10(8) CFU suspended in 0.5 ml of skimmed milk) for 3 weeks, starting 2 weeks before the administration of TNBS. Colonic damage was evaluated histologically and biochemically 1 week after TNBS instillation. The results obtained revealed that all probiotics assayed showed intestinal anti-inflammatory effects, macroscopically evidenced by a significant reduction in the colonic weight/length ratio. Only B. lactis showed a lower incidence of diarrhoea in comparison with untreated rats. Biochemically, all probiotics restored colonic glutathione levels, depleted as a consequence of the oxidative stress of the inflammatory process. Bifidobacterium lactis treatment reduced colonic tumour necrosis factor (TNF)-alpha production, and inducible nitric oxide synthase (iNOS) and cyclo-oxygenase-2 (COX-2) expression; L. acidophilus administration reduced colonic leukotriene B4 production and iNOS expression and L. casei intake was associated with a decrease in colonic COX-2 expression. CONCLUSION: The three probiotics assayed have shown intestinal anti-inflammatory activity in the TNBS model of rat colitis, although each probiotic shows its own anti-inflammatory profile. SIGNIFICANCE AND IMPACT OF THE STUDY: These probiotics could be considered as potential adjuvants in the treatment of inflammatory bowel disease, although more studies are required in order to demonstrate their efficacy in humans.     

Blebbistain, a myosin II inhibitor, as a novel strategy to regulate detrusor contractility in a rat model of partial bladder outlet obstruction

Partial bladder outlet obstruction (PBOO), a common urologic pathology mostly caused by benign prostatic hyperplasia, can coexist in 40-45% of patients with overactive bladder (OAB) and is associated with detrusor overactivity (DO). PBOO that induces DO results in alteration in bladder myosin II type and isoform composition. Blebbistatin (BLEB) is a myosin II inhibitor we recently demonstrated potently relaxed normal detrusor smooth muscle (SM) and reports suggest varied BLEB efficacy for different SM myosin (SMM) isoforms and/or SMM vs nonmuscle myosin (NMM). We hypothesize BLEB inhibition of myosin II as a novel contraction protein targeted strategy to regulate DO. Using a surgically-induced male rat PBOO model, organ bath contractility, competitive and Real-Time-RT-PCR were performed. It was found that obstructed-bladder weight significantly increased 2.74-fold while in vitro contractility of detrusor to various stimuli was impaired ～50% along with decreased shortening velocity. Obstruction also altered detrusor spontaneous activities with significantly increased amplitude but depressed frequency. PBOO switched bladder from a phasic-type to a more tonic-type SM. Expression of 5' myosin heavy chain (MHC) alternatively spliced isoform SM-A (associated with tonic-type SM) increased 3-fold while 3' MHC SM1 and essential light chain isoform MLC(17b) also exhibited increased relative expression. Total SMMHC expression was decreased by 25% while the expression of NMM IIB (SMemb) was greatly increased by 4.5-fold. BLEB was found to completely relax detrusor strips from both sham-operated and PBOO rats pre-contracted with KCl, carbachol or electrical field stimulation although sensitivity was slightly decreased (20%) only at lower doses for PBOO. Thus we provide the first thorough characterization of the response of rat bladder myosin to PBOO and demonstrate complete BLEB-induced PBOO bladder SM relaxation. Furthermore, the present study provides valuable evidence that BLEB may be a novel type of potential therapeutic agent for regulation of myogenic and nerve-evoked DO in OAB.     

Frequency encoding of cholinergic- and purinergic-mediated signaling to mouse urinary bladder smooth muscle: modulation by BK channels

In the urinary bladder, contractions of the detrusor muscle and urine voiding are induced by the neurotransmitters ACh and ATP, released from parasympathetic nerves. Activation of K(+) channels, in particular the large-conductance Ca(2+)-activated K(+) (BK) channels, opposes increases in excitability and contractility of urinary bladder smooth muscle (UBSM). We have shown that deleting the gene mSlo1 in mice (Slo(-/-)), encoding the BK channel, leads to enhanced nerve-mediated and neurotransmitter-dependent contractility of UBSM (38). Here, we examine the location of the BK channel in urinary bladder strips from mouse. Immunohistochemical analysis revealed that the channel is expressed in UBSM but not in nerves that innervate the smooth muscle. The relationship between electrical field stimulation and force generation of the cholinergic and purinergic pathways was examined by applying blockers of the respective receptors in UBSM strips from wild-type and from Slo(-/-) (knockout) mice. In wild-type strips, the stimulation frequency required to obtain a half-maximal force was significantly lower for the purinergic (7.2 +/- 0.3 Hz) than the cholinergic pathway (19.1 +/- 1.5 Hz), whereas the maximum force was similar. Blocking BK channels with iberiotoxin or ablation of the Slo gene increased cholinergic- and purinergic-mediated force at low frequencies, i.e., significantly decreased the frequency for a half-maximal force. Our results indicate that the BK channel has a very significant role in reducing both cholinergic- and purinergic-induced contractility and suggest that alterations in BK channel expression or function could contribute to pathologies such as overactive detrusor.     

Central effects of selective NK1 and NK3 tachykinin receptor agonists on two models of experimentally-induced colitis in rats

Peripheral tachykinins (TKs) are believed to play a role in the pathogenesis of inflammatory bowel diseases (IBD). In this study we investigated changes induced by central administration of two natural TK receptor agonists, NK(1) (PG-SPI) and NK(3) (PG-KII), on trinitrobenzene sulphonic acid (TNBS)- and dextran sodium sulphate (DSS)-induced experimental colitis in rats. Colitis was induced by instilling a single intracolonic dose of TNBS 50 mgkg(-1) (0.5 ml in 50% ethanol) or by oral administration of 5% DSS for 7 days. Each group of rats was intracerebroventricularly injected daily with PG-SPI and PG-KII (0.5, 5, and 50 microgkg(-1)). On day 3, TNBS-treated animals were killed and the severity of gut inflammation was evaluated by measuring myeloperoxidase (MPO) activity, interleukin-1beta (IL-1beta) production and by scoring macroscopic and histologic colonic damage. DSS-treated animals were checked daily for the length of survival and for stool consistency and faecal blood. In the TNBS group, PG-SPI and PG-KII increased scores for the severity of colonic damage, stimulated the production of IL-1beta and increased granulocyte infiltration into the colon (MPO activity). In the DSS group, PG-SPI and PG-KII decreased the percentage of surviving animals, and increased the number of rats that developed loose stools and blood in the faeces and the MPO activity. These results indicate that centrally injected NK(1) and NK(3) tachykinin receptor agonists play a proinflammatory role in experimentally-induced colitis in rats.     

SKA-31-induced activation of small-conductance calcium-activated potassium channels decreased modulation of detrusor smooth muscle function in a rat model of obesity

Journal of Bioenergetics and Biomembranes - Increased excitability and contractility of detrusor smooth muscle (DSM) cells are associated with overactive bladder (OAB), which is often induced by...