Pharmacological techniques for the in vitro study of the urinary bladder

Loss of resilience contributes to detrusor underactivity in advanced age

Volume hyposensitivity resulting from impaired sympathetic detrusor relaxation during bladder filling contributes to detrusor underactivity (DU) associated with aging. Detrusor tension regulation provides an adaptive sensory input of bladder volume to the brainstem and is challenged by physiological stressors superimposed upon biological aging. We recently showed that HCN channels have a stabilizing role in detrusor sympathetic relaxation. While mature mice maintain homeostasis in the face of stressors, old mice are not always capable. In old mice, there is a dichotomous phenotype, in which resilient mice adapt and maintain homeostasis, while non-resilient mice fail to maintain physiologic homeostasis. In this DU model, we used cystometry as a stressor to categorize mice as old-responders (old-R, develop a filling/voiding cycle) or old-non-responders (old-NR, fail to develop a filling/voiding cycle; fluctuating high pressures and continuous leaking), while also assessing functional and molecular differences. Lamotrigine (HCN activator)-induced bladder relaxation is diminished in old-NR mice following HCN-blockade. Relaxation responses to NS 1619 were reduced in old-NR mice, with the effect lost following HCN-blockade. However, RNA-sequencing revealed no differences in HCN gene expression and electrophysiology studies showed similar percentage of detrusor myocytes expressing HCN (I_h) current between old-R and old-NR mice. Our murine model of DU further defines a role for HCN, with failure of adaptive recalibration of HCN participation and intensity of HCN-mediated stabilization, while genomic studies show upregulated myofibroblast and fibrosis pathways and downregulated neurotransmitter-degradation pathways in old-NR mice. Thus, the DU phenotype is multifactorial and represents the accumulation of age-associated loss in homeostatic mechanisms.

Neurogenic Lower Urinary Tract Dysfunction in Spinal Dysraphism: Morphological and Molecular Evidence in Children

Spinal dysraphism, most commonly myelomeningocele, is the typical cause of a neurogenic lower urinary tract dysfunction (NLUTD) in childhood. The structural changes in the bladder wall in spinal dysraphism already occur in the fetal period and affect all bladder wall compartments. The progressive decrease in smooth muscle and the gradual increase in fibrosis in the detrusor, the impairment of the barrier function of the urothelium, and the global decrease in nerve density, lead to severe functional impairment characterized by reduced compliance and increased elastic modulus. Children present a particular challenge, as their diseases and capabilities evolve with age. An increased understanding of the signaling pathways involved in lower urinary tract development and function could also fill an important knowledge gap at the interface between basic science and clinical implications, leading to new opportunities for prenatal screening, diagnosis, and therapy. In this review, we aim to summarize the evidence on structural, functional, and molecular changes in the NLUTD bladder in children with spinal dysraphism and discuss possible strategies for improved management and for the development of new therapeutic approaches for affected children.

The hyperpolarization-activated, cyclic nucleotide-gated channel resides on myocytes in mouse bladders and contributes to adrenergic-induced detrusor relaxation

Control of urinary continence is predicated on sensory signaling about bladder volume. Bladder sensory nerve activity is dependent on tension, implicating autonomic control over detrusor myocyte activity during bladder filling. Hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels are known contributors to bladder control, but their mechanism of action is not well understood. The lack of a definitive identification of cell type(s) expressing HCN in the bladder presents a significant knowledge gap. We recently reported a complete transcriptomic atlas of the C57BL/6 mouse bladder showing the dominant HCN paralog in mouse bladder, Hcn1, is limited to a subpopulation of detrusor smooth myocytes (DSMs). Here, we report details of these findings, along with results of patch-clamp experiments, immunohistochemistry, and functional myobath/tension experiments in bladder strips. With the use of a transgenic mouse expressing fluorescence-tagged α-smooth muscle actin, our data confirmed location and function of DSM HCN channels. Despite previous associations of HCN with postulated bladder interstitial cells, neither evidence of specific interstitial cell types nor an association of nonmyocytes with HCN was discovered. We confirm that HCN activation participates in reducing sustained (tonic) detrusor tension via cAMP, with no effect on intermittent (phasic) detrusor activity. In contrast, blockade of HCN increases phasic activity induced by a protein kinase A (PKA) blocker or a large-conductance Ca²⁺-activated K⁺ (BK) channel opener. Our findings, therefore, suggest a central role for detrusor myocyte HCN in regulating and constraining detrusor myocyte activity during bladder filling.

Cuprizone-mediated demyelination reversibly degrades voiding behavior in mice while sparing brainstem reflex

Multiple sclerosis (MS) is a chronic, progressively debilitating demyelinating disease of the central nervous system (CNS). Nearly 80% of MS patients experience lower urinary tract dysfunction early in their diagnosis. This significantly affects the quality of life, and in latter stages of disease is a leading cause of hospitalization. Previously, animal models have shown that inflammatory demyelination in the CNS causes profound bladder dysfunction, but the confounding influence of systemic inflammation limits the potential interpretation of the contribution of CNS demyelination to bladder dysfunction. Since the micturition circuit has myelinated neuronal connections in the cortex, brainstem, and spinal cord, we examined alterations in bladder function in the cuprizone model characterized by demyelinating lesions in the cortex and corpus callosum that are independent of T-cell-mediated autoimmunity. Herein, we report that a 4-week dietary cuprizone treatment in C57Bl/6J mice induced alterations in voiding behavior with increased micturition frequency and reduced volume voided, similar to human MS bladder dysfunction. Subsequently, recovery from cuprizone treatment restored normal bladder function. Demyelination and remyelination were confirmed by Luxol Fast Blue staining of the corpus callosum. Additionally, we also determined that an 8-week cuprizone treatment, resulting in chronic demyelination lacking spontaneous remyelination potential, is associated with an exacerbated voiding phenotype. Interestingly, while cuprizone-induced CNS demyelination severely affected conscious (cortical) urinary behavior, the brainstem and spinal cord reflex remained unchanged, as confirmed by urethane-anesthetized cystometry. This is the first study to show that cortical demyelination independent of inflammation can negatively impact urinary function.

The anxiolytic sertraline reduces the impact of psychological stress on bladder function in mice

AIMS

To determine if treatment with the selective serotonin reuptake inhibitor (SSRI) sertraline reduces the bladder dysfunction caused by water avoidance stress in mice.

MAIN METHODS

Adult female mice were randomly allocated to (1) Unstressed, (2) Stressed or (3) Stress + Sertraline experimental groups. Stressed mice were subjected to water avoidance for 1 h/day for 10 days and received sertraline or vehicle in drinking water, starting 10-days prior to the first stress exposure. Age matched control/unstressed mice were house under normal conditions without stress exposure. Voiding behaviour was assessed throughout the experimental protocol. After the final stress exposure, a blood sample was taken to measure plasma corticosterone levels and bladders were removed, catheterised and intravesical pressure responses recorded during distension and in response to pharmacological agents.

KEY FINDINGS

Plasma corticosterone levels in sertraline-treated animals were equivalent to unstressed controls and significantly decreased compared to the stressed group. Voiding frequency was significantly increased in the stressed group, and treatment with sertraline significantly decreased voiding frequency, however, this remained elevated compared to unstressed control animals. Bladders from stressed mice displayed enhanced maximal contractile response to the muscarinic agonist carbachol and greater release of ACh in the serosal fluid, which was reduced to control levels by sertraline treatment. Spontaneous phasic contractions were not altered by stress but were significantly reduced in bladders from sertraline treated animals, relative to controls.

SIGNIFICANCE

These results indicate that management of voiding dysfunction caused by psychological stress may be aided by the addition of an SSRI such as sertraline.

Diabetes-induced alterations in urothelium function: Enhanced ATP release and nerve-evoked contractions in the streptozotocin rat bladder

Up to 80% of patients with diabetes mellitus develop lower urinary tract complications, most commonly diabetic bladder dysfunction (DBD). The aim of this study was to investigate the impact of diabetes on the function of the inner bladder lining (urothelium). Bladder compliance and intraluminal release of urothelial mediators, adenosine triphosphate (ATP) and acetylcholine (ACh) in response to distension were investigated in whole bladders isolated from 2- and 12-week streptozotocin (STZ)-diabetic rats. Intact and urothelium-denuded bladder strips were used to assess the influence of the urothelium on bladder contractility. Intraluminal ATP release was significantly enhanced at 2 weeks of diabetes, although not at 12 weeks. In contrast, intraluminal ACh release was unaltered by diabetes. Bladder compliance was also significantly enhanced at both 2 and 12 weeks of diabetes, with greatly reduced intravesical pressures in response to distension. Nerve-evoked contractions of bladder strips were significantly greater at 2 weeks of diabetes. When the urothelium was absent, nerve-evoked contractions were reduced, but contractions remained significantly elevated at lower frequencies of stimulation (<5 Hz) in diabetics. Interestingly, although relaxations of bladder strips to isoprenaline were unaltered by diabetes, removal of the urothelium unmasked significantly enhanced relaxations in strips from 2- and 12-week diabetic animals. In conclusion, diabetes alters urothelial function. Enhanced urothelial ATP release may be involved in the hypercontractility observed at early time points of diabetes. These alterations are time-dependent and may contribute to the mechanisms at play during the development of diabetic bladder dysfunction.

Hyperpolarization-Activated Cyclic Nucleotide-Gated Non-selective (HCN) Ion Channels Regulate Human and Murine Urinary Bladder Contractility

Purpose: Hyperpolarization-activated cyclic nucleotide gated non-selective (HCN) channels have been demonstrated in the urinary bladder in various species. Since they play a major role in governing rhythmic activity in pacemaker cells like in the sinoatrial node, we explored the role of these channels in human and murine detrusor smooth muscle.

Methods: In an organ bath, human and murine detrusor smooth muscle specimens were challenged with the HCN channel blocker ZD7288. In human tissue derived from macroscopically tumor-free cancer resections, the urothelium was removed. In addition, HCN1-deficient mice were used to identify the contribution of this particular isoform. Expression of HCN channels in the urinary bladder was analyzed using histological and ultrastructural analyses as well as quantitative reverse transcriptase polymerase chain reaction (RT-PCR).

Results: We found that the HCN channel blocker ZD7288 (50 μM) both induced tonic contractions and increased phasic contraction amplitudes in human and murine detrusor specimens. While these responses were not sensitive to tetrodotoxin, they were significantly reduced by the gap junction inhibitor 18β-glycyrrhetic acid suggesting that HCN channels are located within the gap junction-interconnected smooth muscle cell network rather than on efferent nerve fibers. Immunohistochemistry suggested HCN channel expression on smooth muscle tissue, and immunoelectron microscopy confirmed the scattered presence of HCN2 on smooth muscle cell membranes. HCN channels seem to be down-regulated with aging, which is paralleled by an increasing effect of ZD7288 in aging detrusor tissue. Importantly, the anticonvulsant and HCN channel activator lamotrigine relaxed the detrusor which could be reversed by ZD7288.

Conclusion: These findings demonstrate that HCN channels are functionally present and localized on smooth muscle cells of the urinary bladder. Given the age-dependent decline of these channels in humans, activation of HCN channels by compounds such as lamotrigine opens up the opportunity to combat detrusor hyperactivity in the elderly by drugs already approved for epilepsy.

Development of an in vitro model to measure bioactivity of botulinum neurotoxin A in rat bladder muscle strips

Background

Botulinum toxin A (BoNT-A) is a new treatment modality in various causes of bladder dysfunction; like neurogenic detrusor overactivity and overactive bladder. The best technique of administrating BoNT-A in patients is unknown. A validated in vitro model could be used to investigate newer intravesical administration techniques of BoNT-A. In this study, we describe the development and validation of in vitro model to measure inhibitory effects of BoNT-A on bladder strip contractions.

Methods

Rat bladder strips were mounted in organ baths filled with Krebs’ solution. The strips were stimulated chemically (80 mM potassium chloride, 1 μM carbachol) and electrically (Electrical Field Stimulation (EFS) 100 shocks, 50 V, 20 Hz, every 3 minutes). The viability of the strips was measured by carbachol stimulation at the beginning and at the end of the experiments. The strips were incubated in various concentrations of BoNT-A (0.03, 0.2, 0.3 nM). Controls were incubated in Krebs’ solution only. The inhibition of strip contraction induced by EFS was measured. These measurements were statistically analyzed with a log-logistic model representing diffusion.

Results

All strips remained viable during the experiments. Inhibition of strip contraction was observed after incubation with 0.3 nM BoNT-A. The measurements fitted to a log-logistic model describing diffusion of BoNT-A in the bladder strip. The parameters of the log-logistic model representing diffusion were significant for 0.3 nM BoNT-A. Incubation with 0.2 nM BoNT-A showed insignificant results for 2 out of 3 runs. Incubation with 0.03 nM BoNT-A did not result in significant inhibition of strip contractions.

Conclusions

An in vitro model was developed and validated in which the inhibitory effect of low concentrations of BoNT-A on bladder strip contractions can be measured.

Exercise improves bladder function in diabetic mice

AIMS

We determined the effect of exercise on bladder dysfunction and voiding frequency in db/db mice.

MATERIALS AND METHODS

Diabetic db/db female mice (BKS.Cg-Dock7m +/+ Leprdb/J strain) and their age-matched wild-type controls (WT) were equally divided into sedentary and exercise groups. Mice were exercised for 1 hr everyday for 8 weeks (speed of 5.2 m/min). We performed a voiding pattern test, cystometric analysis and reactivity of isolated bladder strips in WT and db/db mice, both sedentary and exercised.

RESULTS

Diabetes increased the frequency of voiding, bladder capacity, and residual volume. Exercise decreased voiding frequency in db/db mice; voiding frequency was 5.8 ± 0.5 (db/db exercise) versus 10.8 ± 1.1 (db/db control, P < 0.001). In cystometric analysis, the bladder capacity of db/db sedentary mice was 0.27 ± 0.05 ml and was 0.14 ± 0.02 ml in the db/db exercise group (P < 0.05), whereas the residual volume was 0.2 ± 0.03 ml in db/db sedentary mice and 0.06 ± 0.02 ml in db/db Ex mice. Isolated strips of bladder muscle from sedentary db/db mice were more responsive to carbachol than strips from db/db exercise mice. Exercise did not improve the urodynamic properties of WT mice, both sedentary and exercised.

CONCLUSIONS

Exercise improves bladder function in diabetic mice by reducing voiding frequency and improving urodynamic parameters.

Exploring the mechanisms of intravesical electrical stimulation in the in vitro rat whole bladder after treatment with atropine, α,β-methylATP and tetrodotoxin

AIMS

In a previous study, we showed that the working mechanism of intravesical electrical stimulation (IVES) is probably mainly nerve mediated. But even after bladder decentralization, IVES can induce detrusor contraction. This study explores the effect of IVES in decentralized bladders and the importance of receptors in the bladder wall for a response on IVES.

METHODS

IVES (10 Hz square wave pulses, 20 msec pulse duration, 6 mA) was used in the bladder of 16 female Sprague-Dawley rats. After repeating IVES after consecutive bilateral bladder nerves section (L6-roots, pelvic nerves, and major pelvic ganglion (MPG)), the bladders were mounted in a tissue bath. IVES was performed in the control (n=16), after administration of tetrodotoxin (TTX) (n=6), after atropine and atropine with α,β-methylATP (n=6), and after α,β-methylATP and α,β-methylATP with atropine (n=4). The IVES-induced pressure rise (ΔP) was recorded.

RESULTS

Maximum ΔP (maxΔP) after transection of the MPG was significantly lower than after pelvic nerves transection. Treatment with TTX and with α,β-methylATP plus atropine abolished ΔP. Atropine alone gave an insignificant decrease of maxΔP. Treatment with α,β-methylATP alone reduced maxΔP significantly.

CONCLUSIONS

IVES can evoke contractions in a decentralized bladder. IVES-induced contractions are not a result of direct muscle stimulation, but are nerve mediated, involving intramural innervation and several parts of the bladder innervation. IVES-evoked contraction can be divided in a, contraction duration determining, cholinergic part and a, contraction strength determining, purinergic part. The peripheral innervation could play a role in IVES treatment in patients with interrupted central reflex pathway.

Bladder and urethral function in pelvic organ prolapsed lysyl oxidase like-1 knockout mice

OBJECTIVES

To examine bladder and urethral function in pelvic organ prolapsed lysyl oxidase like-1 (LOXL1) knockout mice.

MATERIALS AND METHODS

Female parous Loxl1 (-/-) mice in the stable phase of prolapse, and age-matched wild type (WT) mice (six each) had conscious cystometry, leak-point pressure (LPP) testing, and contractile responses assessed of their bladder muscle strips to KCl, electrical-field stimulation, ATP, and carbachol.

RESULTS

Loxl1 (-/-) mice voided more frequently and had lower mean (sem) bladder capacity, at 0.10 (0.01) vs 0.20 (0.01) mL, and voiding pressure, at 25.0 (1.90) vs 36.6 (4.04) cmH(2)O, respectively, during cystometry than had WT mice. The LPP was not significantly different between WT and Loxl1 (-/-) mice, at 7.05 (0.81) vs 5.22 (1.23) cmH(2)O, respectively. There were no significant differences between bladder strips from Loxl1 (-/-) mice and WT mice in their responsiveness to various stimuli.

CONCLUSIONS

Loxl1 (-/-) knockout mice had lower urinary tract dysfunction, most likely due to urethral dysfunction. Loxl1 (-/-) knockout mice can be used as an animal model for pelvic floor disorders. Further studies are needed to characterize the morphological and molecular alterations of the bladder and urethra.

Relaxation of human detrusor muscle by selective beta-2 and beta-3 agonists and endogenous catecholamines

OBJECTIVES

The goal of this study was to identify potent relaxant agents of the human detrusor muscle. Therefore, the relaxant effects of different selective beta (beta)-adrenoceptor agonists were examined. Also, the relaxant effects of the endogenous catecholamines were investigated to functionally characterize the beta-adrenoceptor subtype mainly responsible for adrenergic-mediated relaxation in the detrusor muscle of humans.

METHODS

Experiments were performed on muscle strips of human detrusor suspended in a tissue bath. The tissue originated from patients who had undergone total cystectomy. The selective beta3-agonists BRL 37344, ZD 7114, and CGP 12177, the selective beta2-agonists terbutaline and clenbuterol, and the nonselective beta-agonist isoprenaline were investigated. Concentration-relaxation curves of the catecholamines were performed to determine the rank order of potency.

RESULTS

The maximal relaxation induced by BRL 37344, ZD 7114, and CGP 12177 was 36%, 39%, and 37%, respectively. The corresponding pD2 values were 6.73, 4.82, and 6.09, respectively. Terbutaline and clenbuterol induced a maximal relaxation of 48% and 27%, and their pD2 value was 4.97 and 5.34, respectively. Isoprenaline, adrenaline, and noradrenaline induced a maximal relaxation of 72%, 58%, and 79%, respectively. The corresponding pD2 values were 6.18, 6.16, and 6.09, respectively. Because their differences were not significant, no rank order of potency was determined.

CONCLUSIONS

Beta-adrenergic agonists are potent relaxant agents of the human detrusor muscle in vitro. Both beta2 and beta3-adrenoceptors contribute to adrenergic-mediated relaxation. Our results point to a slightly greater role for the beta3-receptor in human detrusor muscle.

Effects of cold storage on the function and morphology of isolated urinary bladder in rat

AIMS

We investigated the effects of 24- and 48-hr storage at 4 degrees C in Krebs solution on the function and morphology of isolated, rat urinary bladders.

METHODS

Strips of bladder were obtained from eight male Sprague-Dawley rats. Six strips were harvested from each bladder and randomized to storage for 24 or 48 hr at 4 degrees C in Krebs solution or examination immediately after harvest. Contractile responses of the strips to potassium chloride (KCl), electric field stimulation (EFS), adenosine 5'-triphosphate (ATP) and carbamylcholine (CCh) were assessed. Histological examination of the bladder strips was performed. The pO(2), pCO(2), and pH of the solution in each storage container were measured at each storage time point.

RESULTS

Cold storage induced a significant decrease in the amplitude of contraction in response to KCl and EFS after 24 or 48 hr of storage compared with control. The response of the bladder strips to ATP and CCh was significantly reduced after 48-hr storage compared with control, but not 24-hr storage. The pO(2) and pCO(2) decreased after cold storage. The pH increased after 24 hr of storage and remained stable between 24 and 48 hr of storage. Histological evaluation of the strips showed tissue swelling after 24 and 48 hr of storage.

CONCLUSIONS

These results suggest that the morphology and function of bladder strips stored for 24 to 48 hr at 4 degrees C in Krebs solution undergo significant changes. Further studies are needed to assess the allowable time for storage of bladder tissue.

Relaxant effects of beta-adrenergic agonists on porcine and human detrusor muscle

AIM

Relaxant effects of different beta-adrenoceptor agonists on porcine and human detrusor were examined. Thus, the beta-adrenoceptor subtype mainly responsible for relaxation in the detrusor muscle of pigs was characterized. Additionally, different effects of several beta-agonists in both species were shown.

METHODS

Experiments were performed on muscle strips of porcine and human detrusor suspended in a tissue bath. The relaxant effects of the non-selective beta-agonist isoprenaline, the selective beta2-agonists procaterol, salbutamol and the selective beta3-agonists BRL 37344, CL 316 243 and CGP 12177 on potassium-induced contraction were investigated. The inhibitory effect of different substances on the maximum contraction and the rank order of potency for endogenous catecholamines was determined in pigs. Furthermore, concentration-relaxation curves were performed for pigs and humans.

RESULTS

Pigs: In the pre-treatment experiments isoprenaline and procaterol showed similar effects. The concentration-response experiments showed that the maximum relaxation induced by procaterol and salbutamol was more than 90%, not significantly different from isoprenaline, whereas the maximum relaxations of CL 316 243, BRL 37344 and CGP 12177 amounted to 68, 70 or 30%, respectively. Rank order of potencies was isoprenaline > or = adrenaline > noradrenaline. Humans: Isoprenaline, procaterol, salbutamol and CL 316 243 showed a maximum relaxation of 80, 41, 24 and 35% and pD2 values of 6.24, 5.65, 5.48 and 5.55, respectively.

CONCLUSION

Beta2-receptors play a main functional role in mediating relaxation of porcine detrusor. Selective beta2- and beta3-agonists similarly relax the human detrusor. Effects were smaller compared with the pig.

Alterations in neurogenically mediated contractile responses of urinary bladder in rats with diabetes

Diabetic bladder dysfunction (DBD) is among the most common and bothersome complications of diabetes mellitus. Autonomic neuropathy has been counted as the cause of DBD. In the present study, we compared the alterations in the neurogenically mediated contractile responses of urinary bladder in rats with streptozocin-induced diabetes, 5% sucrose-induced diuresis, and age-matched controls. Male Sprague-Dawley rats were divided into three groups: 9-wk diabetic rats, diuretic rats, and age-matched controls. Micturition and morphometric characteristics were evaluated using metabolic cage and gross examination of the bladder. Bladder detrusor muscle strips were exposed to either periodic electrical field stimulation (EFS) or to EFS in the presence of atropine, alpha,beta-methylene adrenasine 5'-triphosphate, or tetrodotoxin. The proportions of cholinergic, purinergic, and residual nonadrenergic-noncholinergic (NANC) components of contractile response were compared among the three groups of animals. Diabetes caused a significant reduction of body weight compared with diuresis and controls, although the bladders of diabetic and diuretic rats weighed more than the controls. Both diabetes and diuresis caused significant increase in fluid intake, urine output, and bladder size. Diabetes and diuresis caused similarly increased response to EFS and reduced response to cholinergic component compared with controls. However, the purinergic response was significantly smaller in diuretic bladder strips compared with controls but not in diabetic rats. A residual NANC of unknown origin increased significantly but differently in diabetics and diuretics compared with controls. In conclusion, neurogenically mediated bladder contraction is altered in the diabetic rat. Diabetic-related changes do not parallel diuretic-induced changes, indicating that the pathogenesis of DBD needs further exploration.