Age-dependent contribution of Rho kinase in carbachol-induced contraction of human detrusor smooth muscle in vitro

Age-dependent effects of the β3 adrenoceptor agonist CL316,243 on human and rat detrusor muscle strips

Motility of detrusor smooth muscle includes adrenergic relaxation and cholinergic contraction. Since the latter may be deregulated in overactive bladder (OAB) pathophysiology, anticholinergics are the standard therapy but occasionally less tolerated due to side effects such as dry mouth and constipation. β3 adrenoceptor agonists also alleviate OAB symptoms by relaxing the detrusor muscle. Their age dependence, however, is far from understood. To address this issue, we induced contractions with KCl (60 mM) and carbachol (from 10 nM to 100 μM) in the presence of the β3 adrenoceptor agonist CL316,243 (from 0.1 to 10 μM) in both human and rat muscle strips. Our results confirmed that both contractions were attenuated by β3 adrenoceptor activation in both species, but with differing age dependence. In humans, specimens from mid-life subjects showed a significantly more pronounced effect of CL316,243 in attenuating carbachol-induced contractions than those from aged subjects (Cohen's d of maximal attenuation: 1.82 in mid-life versus 0.13 in aged) without altering EC50. Conversely, attenuation of KCl responses by CL316,243 increased during ageing (Spearman correlation coefficient = -0.584, P<0.01). In rats, both KCl- and carbachol-induced contractions were significantly more attenuated by CL316,243 in samples from adolescent as compared to aged samples. Immunohistochemistry in human detrusor sections proved β3 adrenoreceptor abundance to remain unaltered during ageing. In conclusion, our findings suggest differential age-dependent changes in human β3 adrenoceptor-dependent attenuation of detrusor contraction in terms of electromechanical versus pharmacomechanical coupling; they may help understand the differential responsiveness of OAB patients to β3 agents.

Intracellular signaling pathways of muscarinic acetylcholine receptor-mediated detrusor muscle contractions

Acetylcholine plays an essential role in the regulation of detrusor muscle contractions, and antimuscarinics are widely used in the management of overactive bladder syndrome. However, several adverse effects limit their application and patients' compliance. Thus, this study aimed to further analyze the signal transduction of M2 and M3 receptors in the murine urinary bladder to eventually find more specific therapeutic targets. Experiments were performed on adult male wild-type, M2, M3, M2/M3, or Gαq/11 knockout (KO), and pertussis toxin (PTX)-treated mice. Contraction force and RhoA activity were measured in the urinary bladder smooth muscle (UBSM). Our results indicate that carbamoylcholine (CCh)-induced contractions were associated with increased activity of RhoA and were reduced in the presence of the Rho-associated kinase (ROCK) inhibitor Y-27632 in UBSM. CCh-evoked contractile responses and RhoA activation were markedly reduced in detrusor strips lacking either M2 or M3 receptors and abolished in M2/M3 KO mice. Inhibition of Gαi-coupled signaling by PTX treatment shifted the concentration-response curve of CCh to the right and diminished RhoA activation. CCh-induced contractile responses were markedly decreased in Gαq/11 KO mice; however, RhoA activation was unaffected. In conclusion, cholinergic detrusor contraction and RhoA activation are mediated by both M2 and M3 receptors. Furthermore, whereas both Gαi and Gαq/11 proteins mediate UBSM contraction, the activation at the RhoA-ROCK pathway appears to be linked specifically to Gαi. These findings may aid the identification of more specific therapeutic targets for bladder dysfunctions.NEW & NOTEWORTHY Muscarinic acetylcholine receptors are of utmost importance in physiological regulation of micturition and also in the development of voiding disorders. We demonstrate that the RhoA-Rho-associated kinase (ROCK) pathway plays a crucial role in contractions induced by cholinergic stimulation in detrusor muscle. Activation of RhoA is mediated by both M2 and M3 receptors as well as by Gi but not Gq/11 proteins. The Gi-RhoA-ROCK pathway may provide a novel therapeutic target for overactive voiding disorders.

Ageing influences detrusor contractions to prostaglandin, angiotensin, histamine and 5-HT (serotonin), independent to the Rho kinase and extracellular calcium pathways

Ageing is associated with deteriorating urinary bladder function and an increasing prevalence of disorders such as underactive bladder. There are suggestions that G protein-coupled receptor (GPCR) second messenger pathways are altered during ageing, rather than the receptor proteins themselves. The aim of this study was to identify age-related variations in GPCR activation systems in urinary bladder smooth muscle (detrusor). Isolated porcine detrusor strips were mounted in organ baths and contractile responses induced by receptor agonists were assessed and compared between juvenile (6 months) and adult (2 years) animals. The effects of drugs disrupting intracellular calcium signalling were also studied. Adult tissue was far more sensitive to stimulation by 5-hydroxytryptamine (42% greater increase than juvenile), prostaglandin-E2 (26% greater increase), and angiotensin-II (39% greater increase), however less sensitive to histamine. Although nifedipine and Y-27632 impacted the contraction to all agonists, there were no significant differences between juvenile and adult detrusor. Impairment of IP3-mediated calcium release by 2-aminoethyl diphenylborinate had no effect on any contractile activity, except for neurokinin-A which inhibited both juvenile and adult detrusor, and prostaglandin-E2 which inhibited juvenile. Carbachol, histamine, 5-hydroxytryptamine, and angiotensin-II were not affected by the application of 2-aminoethyl diphenylborinate. In conclusion, the contractile responses to all the GPCR agonists involved extracellular calcium influx and calcium sensitisation, but for prostaglandin-E2 the dependence on calcium from intracellular sources was greater in the younger animals.

Current and Emerging Pharmacological Targets and Treatments of Urinary Incontinence and Related Disorders

Overactive bladder syndrome with and without urinary incontinence and related conditions, signs, and disorders such as detrusor overactivity, neurogenic lower urinary tract dysfunction, underactive bladder, stress urinary incontinence, and nocturia are common in the general population and have a major impact on the quality of life of the affected patients and their partners. Based on the deliberations of the subcommittee on pharmacological treatments of the 7th International Consultation on Incontinence, we present a comprehensive review of established drug targets in the treatment of overactive bladder syndrome and the aforementioned related conditions and the approved drugs used in its treatment. Investigational drug targets and compounds are also reviewed. We conclude that, despite a range of available medical treatment options, a considerable medical need continues to exist. This is largely because the existing treatments are symptomatic and have limited efficacy and/or tolerability, which leads to poor long-term adherence. SIGNIFICANCE STATEMENT: Urinary incontinence and related disorders are prevalent in the general population. While many treatments have been approved, few patients stay on long-term treatment despite none of them being curative. This paper provides a comprehensive discussion of existing and emerging treatment options for various types of incontinence and related disorders.

Effects of Microbeam Irradiation on Rodent Esophageal Smooth Muscle Contraction

BACKGROUND

High-dose-rate radiotherapy has shown promising results with respect to normal tissue preservation. We developed an ex vivo model to study the physiological effects of experimental radiotherapy in the rodent esophageal smooth muscle.

METHODS

We assessed the physiological parameters of the esophageal function in ex vivo preparations of the proximal, middle, and distal segments in the organ bath. High-dose-rate synchrotron irradiation was conducted using both the microbeam irradiation (MBI) technique with peak doses greater than 200 Gy and broadbeam irradiation (BBI) with doses ranging between 3.5-4 Gy.

RESULTS

Neither MBI nor BBI affected the function of the contractile apparatus. While peak latency and maximal force change were not affected in the BBI group, and no changes were seen in the proximal esophagus segments after MBI, a significant increase in peak latency and a decrease in maximal force change was observed in the middle and distal esophageal segments.

CONCLUSION

No severe changes in physiological parameters of esophageal contraction were determined after high-dose-rate radiotherapy in our model, but our results indicate a delayed esophageal function. From the clinical perspective, the observed increase in peak latency and decreased maximal force change may indicate delayed esophageal transit.

Signaling Pathways Mediating Bradykinin-Induced Contraction in Murine and Human Detrusor Muscle

Bradykinin (BK) has been proposed to modulate urinary bladder functions and implicated in the pathophysiology of detrusor overactivity. The present study aims to elucidate the signaling pathways of BK-induced detrusor muscle contraction, with the goal of better understanding the molecular regulation of micturition and identifying potential novel therapeutic targets of its disorders. Experiments have been carried out on bladders isolated from wild-type or genetically modified [smooth muscle-specific knockout (KO): Gαq/11-KO, Gα12/13-KO and constitutive KO: thromboxane prostanoid (TP) receptor-KO, cyclooxygenase-1 (COX-1)-KO] mice and on human bladder samples. Contractions of detrusor strips were measured by myography. Bradykinin induced concentration-dependent contractions in both murine and human bladders, which were independent of secondary release of acetylcholine, ATP, or prostanoid mediators. B2 receptor antagonist HOE-140 markedly diminished contractile responses in both species, whereas B1 receptor antagonist R-715 did not alter BK's effect. Consistently with these findings, pharmacological stimulation of B2 but not B1 receptors resembled the effect of BK. Interestingly, both Gαq/11- and Gα12/13-KO murine bladders showed reduced response to BK, indicating that simultaneous activation of both pathways is required for the contraction. Furthermore, the Rho-kinase (ROCK) inhibitor Y-27632 markedly decreased contractions in both murine and human bladders. Our results indicate that BK evokes contractions in murine and human bladders, acting primarily on B2 receptors. Gαq/11-coupled and Gα12/13-RhoA-ROCK signaling appear to mediate these contractions simultaneously. Inhibition of ROCK enzyme reduces the contractions in both species, identifying this enzyme, together with B2 receptor, as potential targets for treating voiding disorders.

Calcium sensitization mechanisms in detrusor smooth muscles

The contraction of detrusor smooth muscles depends on the increase in intracellular calcium. The influx of calcium from the plasma membrane calcium channels and calcium release from the sarcoplasmic reticulum give rise to intracellular calcium. Under the pathophysiological conditions, the increased sensitivity of regulatory and contractile proteins to calcium also plays an important role in maintaining the spontaneous detrusor smooth muscle activity. Many proteins have been identified to play a role in calcium sensitization. Both the protein kinase C (PKC) and Rho-kinase (ROCK) signaling pathways are responsible for the induction of calcium sensitization in the detrusor smooth muscles. The balance between the myosin light chain kinase (MLCK) and myosin light chain phosphatase (MLCP) regulates the intracellular calcium-contractile force relationship. The inhibition of MLCP by PKC-mediated phosphatase inhibitor (CPI-17) and myosin phosphatase target subunit (MYPT-1) phosphorylation by both the PKC and ROCK are responsible for calcium sensitization in the detrusor smooth muscles. However, the ROCK pathway predominantly participates in the calcium sensitization induction under pathophysiological situations. Many kinases are well known nowadays to play a role in calcium sensitization. This review aims to enlighten the current understanding of the regulatory mechanisms of calcium sensitization with special reference to the PKC and ROCK pathways in the detrusor smooth muscles. It will also aid in the development of new pharmacological strategies to prevent and treat bladder diseases.

Inverse relationship of Rho kinase and myosin-light chain kinase expression in the aging human detrusor smooth muscle

Background

Rho kinase (ROCK) and myosin-light chain kinase (MLCK) are key enzymes in smooth muscle contraction. Previous data have suggested that ROCK contribution to human detrusor contraction is increasing with age. Here, we have analyzed the transcriptional expression of Rho kinase isoforms (ROCK1 and ROCK2) as well as MLCK in the aging human detrusor smooth muscle obtained from resected tissue.

Methods

Small pieces of macroscopically healthy human detrusor smooth muscle (urothelium-free) were prepared for quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR). Transcript expression (mRNA level) of the target genes ROCK1, ROCK2 and MLCK was normalized to three common reference genes (glyceraldehyde-3-phosphate dehydrogenase, β-actin, phosphoglycerate kinase 1).

Results

We found that across all ages the expression level of ROCK (i.e. ROCK1 and ROCK2 together) was almost equal to that of MLCK in the human bladder. Further, ROCK2 showed a significantly higher expression level than ROCK1. Among all subjects, there was no significant correlation of any single target gene to age, but expression levels of ROCK and MLCK were inversely correlated. Moreover, the within-subject analysis revealed that the ROCK-to-MLCK ratio showed a significantly negative correlation to age. Thus, within a given subject, there is a relative ROCK down-regulation and concomitant MLCK up-regulation.

Conclusions

Together with previous data in human detrusor specimens showing increased ROCK contribution to detrusor contraction, we speculate that the drop of the ROCK-to-MLCK ratio may occur as an attempt to compensate for the increased Rho kinase activity.

Aging changes agonist induced contractile responses in permeabilized rat bladder

Aging alters bladder functions where a decrease in filling, storage and emptying is observed. These changes cause urinary incontinence, especially in women. The aim of this study is to examine how aging affects the intracellular calcium movements due to agonist-induced contractions in permeabilized female rat bladder. Urinary bladder isolated from young and old female Sprague-Dawley rats were used. Small detrusor strips were permeabilized with β-escin. The contractile responses induced with agonists were compared between young and old groups. Carbachol-induced contractions were decreased in permeabilized detrusor from old rats compared to young group. Heparin and ryanodine decreased carbachol-induced contractions in young rats where only heparin inhibited these contractions in olds. Caffeine-induced contractions but not inositol triphosphate (IP3)-induced contractions were decreased in old group compared to youngs. The cumulative calcium response curves (pCa 8-4) were also decreased in old rats. Carbachol-induced calcium sensitization responses did not alter by age where GTP-β-S and GF-109203X but not Y-27632 inhibited these responses. Carbachol-induced contractions decrease with aging in rat bladder detrusor. It can be postulated as IP3-induced calcium release (IICR) is primarily responsible for the contractions in older rats where the decrease in carbachol contractions in aging may be as a result of a decrease in calcium-induced calcium release (CICR), rather than carbachol-induced calcium sensitization.

Pioneering drugs for overactive bladder and detrusor overactivity: Ongoing research and future directions

The ongoing research on pioneering drug candidates for the overactive bladder (OAB) aimed to overcome the limitations of currently licensed pharmacotherapies, such as antimuscarinics, β3-adrenergic agents, and botulinum neurotoxin, has been reviewed performing a systematic literature review and web search. The review covers the exploratory agents alternative to available medications for OAB and that may ultimately prove to be therapeutically useful in the future management of OAB patients based on preclinical and early clinical data. It emerges that many alternative pharmacological strategies have been discovered or are under investigation in disease-oriented studies. Several potential therapeutics are known for years but still find obstacles to pass the clinical stages of development, while other completely novel compounds, targeting new pharmacological targets, have been recently discovered and show potential to translate into clinical therapeutic agents for idiopathic and neurogenic OAB syndrome. The global scenario of investigational drugs for OAB gives promise for the development of innovative therapeutics that may ultimately prove effective as first, combined or second-line treatments within a realistic timescale of ten years.

Age-related decrease of adenosine-mediated relaxation in rat detrusor is a result of A2B receptor downregulation

OBJECTIVES

To analyze the effect of adenosine on detrusor smooth muscle contraction and to assess age-related changes of adenosine function.

METHODS

Sustained contractions were induced in young (10-30 days) and old (>60 days) rat detrusor muscle strips by application of 30 mmol/L K(+) and adenosine (0.1-400 µmol/L), which was either applied before raising the K(+) concentration or added to the precontracted muscle strip. Quantitative polymerase chain reaction analyses were used to study adenosine receptor expression in rat and human detrusor specimens.

RESULTS

Pretreatment with adenosine dose-dependently reduced subsequent K(+) -induced contraction in detrusor muscle strips from young rats (half-maximal effect = 40 µmol/L). The residual depolarization-induced contraction strength in young tissue was significantly smaller than in tissue from old animals, showing a greater potency of adenosine in young detrusor samples. Likewise, the relaxing effect of adenosine on precontracted detrusor muscle was also significantly more pronounced in young compared with older detrusor. Quantitative polymerase chain reaction showed an age-related downregulation of the adenosine A2B receptor in rat detrusor tissues, which could be confirmed in human detrusor samples. Furthermore, relaxation of both K(+) -induced as well as carbachol-induced contraction by the specific A2B receptor agonist BAY 60-6583 was significantly more pronounced in young than in old rats.

CONCLUSIONS

Adenosine powerfully counteracts contraction of detrusor smooth muscle, which is lost in the aging bladder. This is paralleled by an age-dependent transcriptional downregulation of the low-affinity A2B receptor. Hence, this might be pathophysiologically relevant in conditions of raised adenosine concentrations, such as hyperactive bladder contractility.