Presence of constitutive endothelial nitric oxide synthase immunoreactivity in urothelial cells of hamster proximal urethra

Molecular profiling of sponge deflation reveals an ancient relaxant-inflammatory response

A hallmark of animals is the coordination of whole-body movement. Neurons and muscles are central to this, yet coordinated movements also exist in sponges that lack these cell types. Sponges are sessile animals with a complex canal system for filter-feeding. They undergo whole-body movements resembling "contractions" that lead to canal closure and water expulsion. Here, we combine 3D optical coherence microscopy, pharmacology, and functional proteomics to elucidate anatomy, molecular physiology, and control of these movements. We find them driven by the relaxation of actomyosin stress fibers in epithelial canal cells, which leads to whole-body deflation via collapse of the incurrent and expansion of the excurrent system, controlled by an Akt/NO/PKG/A pathway. A concomitant increase in reactive oxygen species and secretion of proteinases and cytokines indicate an inflammation-like state reminiscent of vascular endothelial cells experiencing oscillatory shear stress. This suggests an ancient relaxant-inflammatory response of perturbed fluid-carrying systems in animals.

Urothelial mucosal signaling and the overactive bladder-ICI-RS 2013

There is abundant evidence that the lower urinary tract (LUT) mucosal layer is involved both in mechanosensory functions that regulate bladder contractile activity and in urethral sensation. Changes to the mucosa can be associated with a number of bladder pathologies. For example, alterations of the urothelium and underlying lamina propria at both the molecular and structural levels have been reported in both patients and animals associated with disorders such as bladder pain syndrome and diabetic cystopathy. In contrast to the urinary bladder, much less is known about the urothelium/lamina propria of the bladder neck/proximal urethra. There are important gender differences in the outflow region both anatomically and with respect to innervation, hormonal sensitivity, and location of the external urethral sphincter. There is reasonable evidence to support the view that the mucosal signaling pathway in the proximal urethra is important for normal voiding, but it has also been speculated that the proximal urethra can initiate bladder overactivity. When dysfunctional, the proximal urethra may be an interesting target, for example, botulinum toxin injections aiming at eliminating both urgency and incontinence due to detrusor overactivity.

Modulation of bladder function by luminal adenosine turnover and A1 receptor activation

The bladder uroepithelium transmits information to the underlying nervous and musculature systems, is under constant cyclical strain, expresses all four adenosine receptors (A(1), A(2A), A(2B), and A(3)), and is a site of adenosine production. Although adenosine has a well-described protective effect in several organs, there is a lack of information about adenosine turnover in the uroepithelium or whether altering luminal adenosine concentrations impacts bladder function or overactivity. We observed that the concentration of extracellular adenosine at the mucosal surface of the uroepithelium was regulated by ecto-adenosine deaminase and by equilibrative nucleoside transporters, whereas adenosine kinase and equilibrative nucleoside transporters modulated serosal levels. We further observed that enriching endogenous adenosine by blocking its routes of metabolism or direct activation of mucosal A(1) receptors with 2-chloro-N(6)-cyclopentyladenosine (CCPA), a selective agonist, stimulated bladder activity by lowering the threshold pressure for voiding. Finally, CCPA did not quell bladder hyperactivity in animals with acute cyclophosphamide-induced cystitis but instead exacerbated their irritated bladder phenotype. In conclusion, we find that adenosine levels at both surfaces of the uroepithelium are modulated by turnover, that blocking these pathways or stimulating A(1) receptors directly at the luminal surface promotes bladder contractions, and that adenosine further stimulates voiding in animals with cyclophosphamide-induced cystitis.

Purine- and pyrimidine-induced responses and P2Y receptor characterization in the hamster proximal urethra

1. Purine and pyrimidine compounds were investigated on hamster proximal urethral circular smooth muscle preparations. In situ hybridization studies were carried out to localize P2Y(1), P2Y(2), P2Y(4) and P2Y(6) mRNA. Protein expression was studied using Western blotting analysis with antibodies against P2Y(1) and P2Y(2) receptors. 2. The hamster urethra relaxed with an agonist potency order of: 2-MeSADP>beta,gamma-meATP=ATP=adenosine=ADP>2-MeSATP>alpha,beta-meATP>TTP>CTP=UTP>GTP=UDP. The high potency of 2-MeSADP is suggestive of an action via P2Y(1) receptors. Although the order is not characteristic for any known single P2Y receptor subtype, it may represent a combination of P2Y receptor subtypes. 4. The selective P2Y(1) receptor antagonist MRS2179 inhibited ATP-, 2-MeSADP-, 2-MeSATP-, beta,gamma-meATP-, and to a lesser degree alpha,beta-meATP-induced responses. 3. Adenosine, but not ATP, was inhibited by the adenosine receptor antagonist 8-phenyltheophylline, indicating that ATP was not acting via adenosine following enzymatic breakdown. 5. Western blotting analysis showed the expression of both P2Y(1) and P2Y(2) receptors, confirming the results obtained with in situ hybridization that showed the expression of both P2Y(1) and P2Y(2), but not P2Y(4) or P2Y(6) mRNA, in smooth muscle layers of the hamster proximal urethra. 6. It is proposed that the relaxant response of the urethra to ATP may be evoked through the activation of the combination of receptors for P2Y(1) and to a lesser extent P2Y(2) receptors, which may mediate a trophic effect in addition. A P2Y subtype responsive to alpha,beta-meATP and P1 receptors may contribute to urethral smooth muscle relaxation.

Nitric Oxide Production Within Rat Urothelial Cells

PURPOSE

Recent studies have suggested that nitric oxide (NO) synthase (NOS) may be localized in the urothelium of the proximal part of the mammalian ureter. We investigated endogenous NO production in the proximal half of the rat ureter, localized its cellular source, characterized the NOS isoforms involved and assessed the impact of NO on ureteral motility.

MATERIALS AND METHODS

Direct detection of NO production was performed on primary cultures of living rat ureteral cells with the fluorescent indicator diaminofluorescein. Cultures were incubated with the NO precursor L-arginine or the NOS inhibitors L-NAME (N-nitro-L-arginine-methyl ester) and 1400W. NOS expression was determined by immunofluorescence and Western blot analysis. The functional effects of NO donors were assessed on isolated ureters.

RESULTS

Significant basal NO production was demonstrated by the high fluorescence level detected in diaminofluorescein treated cell cultures. NO production was strictly limited to urothelial cells since no fluorescence was seen in smooth muscle cells. Pretreatment with L-NAME or 1400W resulted in a significant decrease in fluorescence. Constitutive and inducible NOS isoforms were detected in urothelial cultured cells and in lysates of the urothelial layer. NO donors inhibited in a concentration dependent manner the agonist induced contractile activity of isolated ureters.

CONCLUSIONS

These results suggest that NO production stems from the urothelium and the NO pathway inhibits contractile activity in the proximal half of the rat ureter. Hence, the nitrergic pathway may be an important target for drugs producing relaxation of the mammalian ureter.

Overactive bladder--pharmacological aspects

The micturition reflex can be initiated by contraction or distension of detrusor smooth muscle cells, or by signals from the urothelium. It has been shown that bladder distension causes release of ATP from the urothelium, and that ATP can activate P2X3 receptors on suburothelial afferent nerve terminals to evoke a neural discharge. However, most probably the activation of afferent fibres during bladder filling involves not only ATP, but a cascade of inhibitory and stimulatory transmitters/mediators. These mechanisms may be targets for future drugs. Both in the normal and functionally disturbed bladder, muscarinic receptor stimulation produces the main part of detrusor contraction, but evidence is accumulating that in disease states, such as neurogenic bladders, outflow obstruction, idiopathic detrusor instability, interstitial cystitis, and also in the ageing bladder, a non-cholinergic activation via purinergic receptors may occur. If this component of activation is responsible not only for part of the bladder contractions, but also for the symptoms of the overactive bladder, it should be considered an important target for therapeutic interventions. Drags blocking different P2X receptor subtypes, or counteracting bladder contraction via other mechanisms, e.g. beta3-adrenoceptor stimulation, may be developed for treatment of the overactive bladder.

Sphincterotomy and the treatment of detrusor-sphincter dyssynergia: current status, future prospects

STUDY DESIGN

Literature review of current treatment options for detrusor-sphincter dyssynergia (DSD) in spinal cord injury.

OBJECTIVES

To review the outcomes and complications associated with external sphincterotomy and to summarise the results and complications of alternative treatment options for detrusor-sphincter dyssynergia in spinal cord injury. In addition, we propose a potential alternative future drug treatment for external sphincter dyssynergia based upon recent research on the neuropharmacology of the external urethral sphincter.

SETTING

The National Spinal Injuries Centre, Stoke Mandeville Hospital, Aylesbury, UK.

METHODS

Medline search from 1966 to 2002 using the words 'external sphincterotomy', 'detrusor-sphincter dyssynergia' and 'neurogenic bladder combined with surgery'.

RESULTS

While external sphincterotomy is an effective treatment for DSD, a significant number of men following this procedure continue to have high intrarenal pressures, recurrent urinary infection or troublesome autonomic dysreflexia and a worryingly high proportion demonstrate persistently raised leak point pressures, putting them at subsequent risk of renal damage. Alternative treatments for external sphincter dyssynergia include urethral stents and balloon dilatation, both of which are effective. However, over the long term stents can undergo encrustation and there remains a definite risk of stent migration necessitating stent removal or replacement. Balloon dilatation of the external sphincter is associated with a risk of subsequent stricture formation. Intraurethral Botulinum A toxin seems to be effective though there have been no large randomised studies comparing it against placebo. However, it is not a durable treatment option and it has not found a common place in the treatment of DSD. There is now a considerable amount of experimental data from both animal and human studies to suggest that nitric oxide (NO) is an important physiological inhibitory neurotransmitter in the urethral sphincter, mediating relaxation of the external urethral sphincter. The potential role of sphincter NO augmentation for treatment of DSD is discussed.

CONCLUSION

External sphincterotomy remains the mainstay of treatment for urodynamically significant detrusor-sphincter dyssynergia, but in recent years a number of effective, alternative treatment options have become available. While at present there is no effective systemic drug treatment, recent research into external sphincter neuropharmacology suggests that systemic or topical augmentation of external sphincter NO may provide an effective method for lowering sphincter pressure.

Beta-adrenoceptor agonists stimulate endothelial nitric oxide synthase in rat urinary bladder urothelial cells

We have investigated the intracellular signaling mechanisms underlying the release of nitric oxide (NO) evoked by beta-adrenoceptor (AR) agonists in urinary bladder strips and cultured bladder urothelial cells from adult rats. Reverse transcription-PCR revealed that inducible NO synthase and endothelial NOS but not neuronal NOS genes were expressed in urothelial cells. NO release from both urothelial cells and bladder strips was decreased (37-42%) in the absence of extracellular Ca2+ (100 microm EGTA) and was ablated after incubation with BAPTA-AM (5 microm) or caffeine (10 mm), indicating that the NO production is mediated in part by intracellular calcium stores. NO release was reduced (18-24%) by nifedipine (10 microm) and potentiated (29-32%) by incubation with the Ca2+ channel opener BAYK8644 (1-10 microm). In addition, beta-AR-evoked NO release (isoproterenol; dobutamine; terbutaline; 10(-9) to 10(-5) m) was blocked by the NOS inhibitors N(G)-nitro-L-arginine methyl ester (30 microm) or N(G)-monomethyl-L-arginine (50 microm), by beta-adrenoceptor antagonists (propranol, beta1/beta2; atenolol, beta1; ICI 118551; beta2; 100 microm), or by the calmodulin antagonist trifluoperazine (50 microm). Incubating cells with the nonhydrolyzable GTP analog GTPgammaS (1 microm) or the membrane-permeant cAMP analog dibutyryl-cAMP (10-100 microm) directly evoked NO release. Forskolin (10 microm) or the phosphodiesterase IBMX (50 microm) enhanced (39-42%) agonist-evoked NO release. These results indicate that beta-adrenoceptor stimulation activates the adenylate cyclase pathway in bladder epithelial cells and initiates an increase in intracellular Ca2+ that triggers NO production and release. These findings are considered in light of recent reports that urothelial cells may exhibit a number of "neuron-like" properties, including the expression of receptors/ion channels similar to those found in sensory neurons.