Insulin receptor signaling engages bladder urothelial defenses that limit urinary tract infection

Urinary tract infections (UTIs) commonly afflict people with diabetes. To better understand the mechanisms that predispose diabetics to UTIs, we employ diabetic mouse models and altered insulin signaling to show that insulin receptor (IR) shapes UTI defenses. Our findings are validated in human biosamples. We report that diabetic mice have suppressed IR expression and are more susceptible to UTIs caused by uropathogenic Escherichia coli (UPEC). Systemic IR inhibition increases UPEC susceptibility, while IR activation reduces UTIs. Localized IR deletion in bladder urothelium promotes UTI by increasing barrier permeability and suppressing antimicrobial peptides. Mechanistically, IR deletion reduces nuclear factor κB (NF-κB)-dependent programming that co-regulates urothelial tight junction integrity and antimicrobial peptides. Exfoliated urothelial cells or urine samples from diabetic youths show suppressed expression of IR, barrier genes, and antimicrobial peptides. These observations demonstrate that urothelial insulin signaling has a role in UTI prevention and link IR to urothelial barrier maintenance and antimicrobial peptide expression.

Purine nucleoside phosphorylase inhibition is an effective approach for the treatment of chemical hemorrhagic cystitis

Hemorrhagic cystitis may be induced by infection, radiation therapy, or medications or may be idiopathic. Along with hemorrhagic features, symptoms include urinary urgency and frequency, dysuria (painful urination), and visceral pain. Cystitis-induced visceral pain is one of the most challenging types of pain to treat, and an effective treatment would address a major unmet medical need. We assessed the efficacy of a purine nucleoside phosphorylase inhibitor, 8-aminoguanine (8-AG), for the treatment of hemorrhagic/ulcerative cystitis. Lower urinary tract (LUT) function and structure were assessed in adult Sprague-Dawley rats, treated chronically with cyclophosphamide (CYP; sacrificed day 8) and randomized to daily oral treatment with 8-AG (begun 14 days prior to CYP induction) or its vehicle. CYP-treated rats exhibited multiple abnormalities, including increased urinary frequency and neural mechanosensitivity, reduced bladder levels of inosine, urothelial inflammation/damage, and activation of spinal cord microglia, which is associated with pain hypersensitivity. 8-AG treatment of CYP-treated rats normalized all observed histological, structural, biochemical, and physiological abnormalities. In cystitis 8-AG improved function and reduced both pain and inflammation likely by increasing inosine, a tissue-protective purine metabolite. These findings demonstrate that 8-AG has translational potential for reducing pain and preventing bladder damage in cystitis-associated LUT dysfunctions.

Hypoxanthine Induces Signs of Bladder Aging with Voiding dysfunction and Lower Urinary Tract Remodeling

BACKGROUND

Lower urinary tract syndrome (LUTS) is a group of urinary tract symptoms and signs which can include urinary incontinence. Advancing age is a major risk factors for LUTS; however the underlying biochemical mechanisms of age-related LUTS remain unknown. HX (hypoxanthine) is a purine metabolite associated with generation of tissue damaging reactive oxygen species (ROS). This study tested the hypothesis that exposure of the adult bladder to HX-ROS over time damages key LUT elements, mimicking qualitatively some of the changes observed with aging.

METHODS

Adult 3-month-old female Fischer 344 (F344) rats were treated with vehicle or HX (10 mg/kg/day; 3 weeks) administered in drinking water. Targeted purine metabolomics and molecular approaches were used to assess purine metabolites and biomarkers for oxidative stress and cellular damage. Biomechanical approaches assessed LUT structure and measurements of LUT function (using custom-metabolic cages and cystometry) were also employed.

RESULTS

HX exposure increased biomarkers indicative of oxidative stress, pathophysiological ROS production and depletion of cellular energy with declines in NAD + levels. Moreover, HX treatment caused bladder remodeling and decreased the intercontraction interval and leak point pressure (surrogate measure to assess stress urinary incontinence).

CONCLUSIONS

These studies provide evidence that in adult rats chronic exposure to HX causes changes in voiding behavior and in bladder structure resembling alterations observed with aging. These results suggest that increased levels of uro-damaging HX were associated with ROS/oxidative stress-associated cellular damage which may be central to age-associated development of LUTS, opening up potential opportunities for geroscience-guided interventions.

Effects of vasopressin receptor agonists on detrusor smooth muscle tone in young and aged bladders: Implications for nocturia treatment

PURPOSE

The main goal of this study was to determine the effects of arginine vasopressin (AVP) and desmopressin on bladder contractility and to examine whether the effects of these vasopressin receptor (VR) agonists differ in young versus aged animals. These aims were addressed using urinary bladders from young (3 months) and aged (24 month) female Fischer 344 rats that were isolated and dissected into strips for isometric tension recordings. Bladder strips were exposed to AVP and desmopressin through the perfusate, and tension changes recorded.

RESULTS

In young rat bladders, AVP, an agonist at both vasopressin-1 receptors (V₁Rs) and vasopressin-2 receptor (V₂Rs), concentration-dependently caused contraction of bladder strips with a sensitivity that was greater in young versus aged bladder strips. Removal of the mucosa did not alter the sensitivity of young bladder strips to AVP yet enhanced the AVP sensitivity of aged bladder strips. The differential sensitivity to AVP between young denuded and aged denuded bladder strips was similar. In contrast to AVP, desmopressin (V₂R selective agonist) relaxed bladder strips. This response was reduced by removal of the mucosa in young, but not aged, bladder strips.

CONCLUSION

These findings support a direct role for VRs in regulating detrusor tone with V₁Rs causing contraction and V₂Rs relaxation. In aged bladders, the contractile response to V₁R activation is attenuated due to release of a mucosal factor that attenuates V₁R-induced contractions. Also in aged bladders, the relaxation response to V₂R activation is attenuated by lack of release of a mucosal factor that contributes to V₂R-induced relaxation. Thus age-associated changes in the bladder mucosa impair the effects of VRs on bladder tone. Because the V₂R signaling system is impaired in the older bladder, administering an exogenous V₂R agonist (e.g., desmopressin) could counteract this defect. Thus, desmopressin could potentially increase nighttime bladder capacity through detrusor relaxation in concert with decreased urine production, reducing nocturnal voiding frequency.

Targeting neurotrophin and nitric oxide signaling to treat spinal cord injury and associated neurogenic bladder overactivity

Purpose or the research

Nearly 300,000 people are affected by spinal cord injury (SCI) with approximately 18,000 new cases annually, according to the National SCI Statistics Center. SCI affects physical mobility and impairs the function of multiple internal organs to cause lower urinary tract (LUT) dysfunctions manifesting as detrusor sphincter dyssynergia (DSD) and neurogenic detrusor overactivity (NDO) with detrimental consequences to the quality of life and increased morbidity. Multiple lines of evidence now support time dependent evolution of the complex SCI pathology which requires a multipronged treatment approach of immediate, specialized care after spinal cord trauma bookended by physical rehabilitation to improve the clinical outcomes. Instead of one size fits all treatment approach, we propose adaptive drug treatment to counter the time dependent evolution of SCI pathology, with three small molecule drugs with distinctive sites of action for the recovery of multiple functions.

Principal results

Our findings demonstrate the improvement in the recovery of hindlimb mobility and bladder function of spinal cord contused mice following administration of small molecules targeting neurotrophin receptors, LM11A-31 and LM22B-10. While LM11A-31 reduced the cell death in the spinal cord, LM22B-10 promoted cell survival and axonal growth. Moreover, the soluble guanylate cyclase (sGC) activator, cinaciguat, enhanced the revascularization of the SCI injury site to promote vessel formation, dilation, and increased perfusion.

Major conclusions

Our adaptive three drug cocktail targets different stages of SCI and LUTD pathology: neuroprotective effect of LM11A-31 retards the cell death that occurs in the early stages of SCI; and LM22B-10 and cinaciguat promote neural remodeling and reperfusion at later stages to repair spinal cord scarring, DSD and NDO. LM11A-31 and cinaciguat have passed phase I and IIa clinical trials and possess significant potential for accelerated clinical testing in SCI/LUTD patients.

Role of hyperpolarization-activated cyclic nucleotide-gated channels in aging bladder phenotype

OBJECTIVE

To assess the functional role of Hyperpolarization-activated cyclic nucleotide-gated gated channel (HCN) subtypes in the aging bladder phenotype characterized by diminished bladder volume sensation (BVS) with or without the detrusor instability (DI).

METHODS

Expression of HCN subtypes was examined by quantitative RT-PCR and Western blot in aged male Fisher 344 rats (n = 15) and young rats (n = 15). Nocturnal urination and awake cystometry (CMG) were assessed in presence and absence of a steady state HCN channel blockade achieved with daily oral gavage of vehicle or Ivabradine (HCN blocker) 6 mg/kg for 7 days.

RESULTS

The association of BVS with the age-related downregulation (~30%) of cAMP sensitive HCN1, HCN2 subtypes, and (~50%) upregulation of cAMP insensitive HCN3 subtype is evinced by the doubling in the mean urine volume of nocturnal voids (0.82 ± 0.22 mL vs 0.41 ± 0.12 mL; n = 10; p < 0.05) predicting an age-related rise in the micturition volume threshold (p < 0.0001) in CMG, which is raised further by Ivabradine treatment (p < 0.0005). Ivabradine also doubled non-voiding contractions (NVC) and maximum voiding pressure (MVP) in young and aged rats, respectively (p < 0.0001) to abolish the age-related, innate two -fold elevation in NVC not accompanied with MVP rise in untreated aged rats (p < 0.005).

CONCLUSION

The age-related HCN downregulation is mechanistically linked to the exhibition of aging bladder phenotype with the manifestation of DI following steady state blockade of HCN channels in Ivabradine treated young rats. The amplification of MVP in aged rats mediated by FDA approved Ivabradine hints at potential repurposing opportunity in detrusor underactivity.

Virtual measurements of paracellular permeability and chronic inflammation via color coded pixel-wise T1 mapping

To assess whether quantitative T₁ relaxometry can measure permeability, chronic inflammation and mural thickening of mouse bladder wall. Adult female C57BL6 mice unexposed to radiation (controls) or 40 wk postirradiation of 10 Gy were scanned at 9.4 T before and after instillation (0.1 mL) of aqueous, novel contrast mixture (NCM) containing 4 mM gadobutrol and 5 mM ferumoxytol. Rapid acquisition with refocused echo (RARE) sequence was used with variable repetition times (TR). Pixel-wise maps of T₁ relaxation times for the segmented bladder wall layers were generated from voxel-wise, nonlinear least square data fitting of TR-dependent signal intensity acquired with TR array of 0.4-10 s followed by the histology of harvested bladder. Significant differences between precontrast and postcontrast T₁ (ΔT₁) were noted in urothelium and lamina propria of both groups but only in detrusor of irradiated group (P < 0.001; 2-way ANOVA). Nearly twofold higher gadobutrol permeability (550 ± 73 vs. 294 ± 160 μM; P < 0.01) derived as per 1/ΔT₁ = r1. [C] in urothelium of irradiated group. Inflammation and bladder wall thickening (0.75 ± 0. vs. 0.44 ± 0.08 mm; P < 0.001) predicted by MRI was subsequently confirmed by histology and altered expression of CD45 and zonula occludens-1 (ZO-1) relative to controls. NCM enhanced MRI relies on the retention of large molecular weight ferumoxytol in lumen for negative contrast, while permeation of the non-ionic, small molecular weight gadobutrol through ZO-1 generates positive contrast in bladder wall for virtual measurement of paracellular permeability and assessment of chronic inflammation in thin and distensible bladder wall, which is also defined by its variable shape and location within pelvis.

Excitatory effect of acotiamide on rat and human bladder: Implications for underactive bladder treatment

OBJECTIVE

To evaluate whether approved gastroprokinetic agent, acotiamide exerts a direct excitatory effect on bladder to help explain the reported meaningful reduction of post-void residual urine volume (PVR) in detrusor underactivity (DU) patients after thrice daily oral intake of acotiamide 100 mg for 2 weeks.

METHODS

Effect of acotiamide [1-16 μM] was assessed on nerve-mediated contractions evoked by electrical field stimulation (EFS) for 5 s with 5 ms pulse trains of 10 V in longitudinal, mucosa intact rat and human bladder strips to construct frequency response curve (1-32 Hz) and repeat 10 Hz stimulation at 60s interval. Effect of acotiamide 2 μM on spontaneous and carbachol evoked contractions was also assessed.

RESULTS

Acotiamide 2 μM significantly enhanced the Atropine and Tetrodotoxin (TTX)-sensitive EFS evoked contractions of rat and human bladder at 8-32 Hz (Two-way ANOVA followed Sidak's multiple comparison; *p < 0.01) and on repeat 10 Hz stimulation (Paired Student's t-test; *p < 0.05), while producing a modest effect on the spontaneous contractions and a negligible effect on the carbachol evoked contractions.

CONCLUSIONS

Enhancement of TTX-sensitive evoked contractions of rat and human bladder by acotiamide is consistent with the enhancement of excitatory neuro-effector transmission mainly through prejunctional mechanisms. Findings highlight immense therapeutic potential of antimuscarinics with low M3 receptor affinity like acotiamide in Underactive bladder (UAB)/DU treatment.

Role of proNGF/p75 signaling in bladder dysfunction after spinal cord injury

Loss of bladder control is a challenging outcome facing patients with spinal cord injury (SCI). We report that systemic blocking of pro-nerve growth factor (proNGF) signaling through p75 with a CNS-penetrating small-molecule p75 inhibitor resulted in significant improvement in bladder function after SCI in rodents. The usual hyperreflexia was attenuated with normal bladder pressure, and automatic micturition was acquired weeks earlier than in the controls. The improvement was associated with increased excitatory input to the spinal cord, in particular onto the tyrosine hydroxylase-positive fibers in the dorsal commissure. The drug also had an effect on the bladder itself, as the urothelial hyperplasia and detrusor hypertrophy that accompany SCI were largely prevented. Urothelial cell loss that precedes hyperplasia was dependent on p75 in response to urinary proNGF that is detected after SCI in rodents and humans. Surprisingly, death of urothelial cells and the ensuing hyperplastic response were beneficial to functional recovery. Deleting p75 from the urothelium prevented urothelial death, but resulted in reduction in overall voiding efficiency after SCI. These results unveil a dual role of proNGF/p75 signaling in bladder function under pathological conditions with a CNS effect overriding the peripheral one.

Fgfr2 is integral for bladder mesenchyme patterning and function

While urothelial signals, including sonic hedgehog (Shh), drive bladder mesenchyme differentiation, it is unclear which pathways within the mesenchyme are critical for its development. Studies have shown that fibroblast growth factor receptor 2 (Fgfr2) is necessary for kidney and ureter mesenchymal development. Our objective was to determine the role of Fgfr2 in bladder mesenchyme. We used Tbx18cre mice to delete Fgfr2 in bladder mesenchyme (Fgfr2^BM-/-). We performed three-dimensional reconstructions, quantitative real-time PCR, in situ hybridization, immunolabeling, ELISAs, immunoblotting, void stain on paper, ex vivo bladder sheet assays, and in vivo decerebrated cystometry. Compared with controls, embryonic (E) day 16.5 (E16.5) Fgfr2^BM-/- bladders have thin muscle layers with reduced α-smooth muscle actin levels and thickened lamina propria with increased collagen expression that intrudes into muscle. From postnatal (P) day 1 (P1) to P30, Fgfr2^BM-/- bladders demonstrate progressive muscle loss and increased collagen expression. Postnatal Fgfr2^BM-/- bladder sheets exhibit decreased contractility and increased passive stretch tension compared with controls. In vivo cystometry revealed high baseline and threshold pressures and shortened intercontractile intervals in Fgfr2^BM-/- bladders compared with controls. Mechanistically, while Shh expression appears normal, mRNA and protein readouts of hedgehog activity are increased in E16.5 Fgfr2^BM-/- bladders compared with controls. Moreover, E16.5Fgfr2^BM-/- bladders exhibit higher levels of Cdo and Boc, hedgehog coreceptors that enhance sensitivity to Shh, than controls. Fgfr2 is critical for bladder mesenchyme patterning by virtue of its role in modulation of hedgehog signaling.

The potential role of unregulated autonomous bladder micromotions in urinary storage and voiding dysfunction; overactive bladder and detrusor underactivity

The isolated bladder shows autonomous micromotions, which increase with bladder distension, generate sensory nerve activity, and are altered in models of urinary dysfunction. Intravesical pressure resulting from autonomous activity putatively reflects three key variables; the extent of micromotion initiation, distances over which micromotions propagate, and overall bladder tone. In vivo, these variables are subordinate to the efferent drive of the central nervous system. In the micturition cycle storage phase, efferent inhibition keeps autonomous activity generally at a low level, where it may signal 'state of fullness', whilst maintaining compliance. In the voiding phase, mass efferent excitation elicits generalised contraction (global motility initiation). In lower urinary tract dysfunction, efferent control of the bladder can be impaired, for example due to peripheral 'patchy' denervation. In this case, loss of efferent inhibition may enable unregulated micromotility, and afferent stimulation, predisposing to urinary urgency. If denervation is relatively slight, the detrimental impact on voiding may be low, as the adjacent innervated areas may be able to initiate micromotility synchronous with the efferent nerve drive, so that even denervated areas can contribute to the voiding contraction. This would become increasingly inefficient the more severe the denervation, such that ability of triggered micromotility to propagate sufficiently to engage the denervated areas in voiding declines, so the voiding contraction increasingly develops the characteristics of underactivity. In summary, reduced peripheral coverage by the dual efferent innervation (inhibitory and excitatory) impairs regulation of micromotility initiation and propagation, potentially allowing emergence of overactive bladder and, with progression, detrusor underactivity.

Fgfr2 is integral for bladder mesenchyme patterning and function

While urothelial signals, including sonic hedgehog (Shh), drive bladder mesenchyme differentiation, it is unclear which pathways within the mesenchyme are critical for its development. Studies have shown that fibroblast growth factor receptor (Fgfr)2 is necessary for kidney and ureter mesenchymal development. The objective of the present study was to determine the role of Fgfr2 in the bladder mesenchyme. We used Tbx18cre mice to delete Fgfr2 in the bladder mesenchyme (Fgfr2(BM-/-)). We performed three-dimensional reconstructions, quantitative real-time PCR, in situ hybridization, immunolabeling, ELISAs, immunoblot analysis, void stain on paper, ex vivo bladder sheet assays, and in vivo decerebrated cystometry. Compared with control bladders, embryonic day 16.5 (E16.5) Fgfr2(BM-/-) bladders had thin muscle layers with less α-smooth muscle actin and thickened lamina propria with increased collagen type Ia and IIIa that intruded into the muscle. The reciprocal changes in mutant layer thicknesses appeared partly due to a cell fate switch. From postnatal days 1 to 30, Fgfr2(BM-/-) bladders demonstrated progressive muscle loss and increased collagen expression. Postnatal Fgfr2(BM-/-) bladder sheets exhibited decreased agonist-mediated contractility and increased passive stretch tension versus control bladder sheets. Cystometry revealed high baseline and threshold pressures and shortened intercontractile intervals in Fgfr2(BM-/-) versus control bladders. Mechanistically, whereas Shh expression appeared normal, mRNA and protein readouts of hedgehog activity were increased in E16.5 Fgfr2(BM-/-) versus control bladders. Moreover, E16.5 Fgfr2(BM-/-) bladders exhibited higher levels of Cdo and Boc, hedgehog coreceptors that enhance sensitivity to Shh, compared with control bladders. In conclusion, loss of Fgfr2 in the bladder mesenchyme leads to abnormal bladder morphology and decreased compliance and contractility.

Do we understand any more about bladder interstitial cells?-ICI-RS 2013

AIMS

To present a brief review on discussions from "Do we understand any more about lower urinary tract interstitial cells?" session at the 2013 International Consultation on Incontinence-Research Society (ICI-RS) meeting in Bristol, UK.

METHODS

Discussion focused on bladder interstitial cell (IC) subtypes, their localization and characterization, and communication between themselves, the urothelium, and detrusor smooth muscle. The role of ICs in bladder pathologies and new methods for studying ICs were also addressed.

RESULTS

ICs have been studied extensively in the lower urinary tract and have been characterized based on comparisons with ICs of Cajal in the gastro-intestinal tract. In fetal bladders it is believed that ICs drive intrinsic contractions to expel urine through the urachus. These contractions diminish postpartum as bladder innervation develops. Voiding in human neonates occurs when filling triggers a spinal cord reflex that contracts the detrusor; in rodents, maternal stimulation of the perineum triggers voiding. Following spinal cord injury, intrinsic contractions, and spinal micturition reflexes develop, similar to those seen during neonatal development. These enhanced contractions may stimulate nociceptive and mechanosensitive afferents contributing to neurogenic detrusor overactivity and incontinence. The IC-mediated activity is believed to be initiated in the lamina propria by responding to urothelial factors. These IC may act syncytially through gap junction coupling and modulate detrusor activity through unknown mechanisms.

CONCLUSION

There has been a great deal of information discovered regarding bladder ICs, however, many of their (patho)physiological functions and mechanisms are still unclear and necessitates further research. Neurourol. Urodynam. 33:573-576, 2014. © 2014 Wiley Periodicals, Inc.

Sophisticated models and methods for studying neurogenic bladder dysfunction

AIM

To describe how the use of new and established animal models and methods can generate vital and far reaching experimental data in the study of mechanism underlying neurogenic bladder overactivity.

METHODS

Bladder and colonic irradiated mice and those with upper and lower motor neuron lesions were used to study neurogenic bladder overactivity. Methods included cystometry, tension measurements, afferent nerve recordings and optical mapping of action potentials and intracellular Ca(2+) transients. Recordings were made in a number of innovative preparations including in-line cultured cells, bladder-urethra sheets and cross-sections, spinal cord slices and the cerebral cortex.

RESULTS

The animal models and methods used allow for the study of peripheral and central mechanisms of neurogenic overactivity. While colonic irradiation results in solely neurogenic dysfunction, spinal cord lesions also induce non-neural changes resulting in increased spontaneous detrusor contractions that can directly stimulate afferent nerves. Imaging of cultured bladder interstitial cells reveals spontaneous firing that could contribute to detrusor overactivity, while optical imaging of the spinal cord and brain could identify changes in central pathways that underlie lower urinary tract dysfunction.

CONCLUSIONS

The animal models and methods described allow for the study of neurogenic overactivity at the peripheral, spinal and cortical levels. This may lead to greater understanding of sensory and motor mechanisms involved in incontinence, the contributions of interstitial cells and spontaneous detrusor contractions, and the involvement of the cortex.

Researching bladder afferents-determining the effects of β(3) -adrenergic receptor agonists and botulinum toxin type-A

A substantial portion of the current research on lower urinary tract dysfunction is focused on afferent mechanisms. The main goals are to define and modulate the signaling pathways by which afferent information is generated, enhanced and conveyed to the central nervous system. Alterations in bladder afferent mechanisms are a potential source of voiding dysfunction and an emerging source for drug targets. Established drug therapies such as muscarinic receptor antagonists, and two emerging therapies, β(3) -adrenergic receptor agonists and botulinum toxin type-A, may act partly through afferent mechanisms. This review focuses on these two new principles and new and established methods for determining their sites of action. It also provides brief information on the innervation of the bladder, afferent receptors and transmitters and how these may communicate with the urothelium, interstitial cells and detrusor smooth muscle to regulate micturition. Peripheral and central mechanisms of afferent sensitization and myogenic mechanisms that lead to detrusor overactivity, overactive bladder symptoms and urgency sensations are also covered. This work is the result from 'Think Tank' presentations, and the lengthy discussions that followed, at the 2010 International Consultation on Incontinence Research Society meeting in Bristol, UK.

Targeted delivery of radioprotective agents to mitochondria

Adverse effects of ionizing radiation are mediated through reactive oxygen and nitrogen species. Mitochondria are the principal source of these species in the cell and play an important role in irradiation-induced apoptosis. The use of free radical scavengers and nitric oxide synthase inhibitors has proven to protect normal tissues and, in some cases, to sensitize tumor tissues to radiation damage. Dual molecules that combine radical-scavenging and NOS-inhibitory functions may be particularly effective. Drugging strategies that target mitochondria can enhance the effectiveness of such agents, in comparison to systemic administration, and circumvent side effects.

Mitochondrial targeting of radioprotectants using peptidyl conjugates

Ionizing radiation activates a mitochondrial nitric oxide synthase, leading to inhibition of the respiratory chain, generation of excess superoxide, peroxynitrite production and nitrosative damage. We have measured the radioprotective effects of a nitric oxide synthase antagonist (AMT) versus a free radical scavenger (4-amino-TEMPO) using electrochemical detection of nitric oxide and peroxynitrite. To enhance their efficacy, we have conjugated these compounds to peptides and peptide isosteres--derived from the antibiotic gramicidin S--that target the mitochondria. The targeting ability of these peptidyl conjugates was measured using quantitative mass spectrometry.

Origin of spontaneous activity in neonatal and adult rat bladders and its enhancement by stretch and muscarinic agonists

This study examined the origin of spontaneous activity in neonatal and adult rat bladders and the effect of stretch and muscarinic agonists and antagonists on spontaneous activity. Rats were anesthetized and their bladders were excised, cannulated, and loaded with voltage- and Ca(2+)-sensitive dyes. Intracellular Ca(2+) and membrane potential transients were mapped using photodiode arrays in whole bladders, bladder sheets, or cross-section preparations at 37 degrees C. Intravesical pressure was recorded from whole bladders. In neonatal bladders and sheets, spontaneous Ca(2+) and electrical signals arose at a site near the dome and spread in a coordinated manner throughout the bladder with different dome-to-neck conduction velocities (Ca(2+): 3.7 +/- 0.4 mm/s; membrane potential: 46.2 +/- 3.1 mm/s). In whole bladders, optical signals were associated with spontaneous contractions (10-20 cmH(2)O). By contrast, in adult bladders spontaneous Ca(2+) and electrical activity was uncoordinated, originating at multiple sites and was associated with smaller (2-5 cmH(2)O) contractions. Spontaneous contractions and optical signals were insensitive to tetrodotoxin (2 muM) but were blocked by nifedipine (10 muM). Stretch or low carbachol concentrations (50 nM) applied to neonatal whole bladders enhanced the amplitude (to 20-35 cmH(2)O) of spontaneous activity, which was blocked by atropine. Bladder cross sections revealed that Ca(2+) and membrane potential transients produced by stretch or carbachol began near the urothelial-suburothelial interface and then spread to the detrusor. In conclusion, spontaneous activity in neonatal bladders, unlike activity in adult bladders, is highly organized, originating in the urothelium-suburothelium near the dome. Activity is enhanced by stretch or carbachol and this enhancement is blocked by atropine. It is hypothesized that acetylcholine is released from the urothelium during bladder filling to enhance spontaneous activity.