Detrusor contraction

Autonomic nervous control of the urinary bladder

The autonomic nervous system plays an important role in the regulation of the urinary bladder function. Under physiological circumstances, noradrenaline, acting mainly on β(3) -adrenoceptors in the detrusor and on α(1) (A) -adrenoceptors in the bladder outflow tract, promotes urine storage, whereas neuronally released acetylcholine acting mainly on M(3) receptors promotes bladder emptying. Under pathophysiological conditions, however, this system may change in several ways. Firstly, there may be plasticity at the levels of innervation and receptor expression and function. Secondly, non-neuronal acetylcholine synthesis and release from the urothelium may occur during the storage phase, leading to a concomitant exposure of detrusor smooth muscle, urothelium and afferent nerves to acetylcholine and noradrenaline. This can cause interactions between the adrenergic and cholinergic system, which have been studied mostly at the post-junctional smooth muscle level until now. The implications of such plasticity are being discussed.

The effect of hypercholesterolemia on carbachol-induced contractions of the detrusor smooth muscle in rats: increased role of L-type Ca2+ channels

To investigate a possible relation between hypercholesterolemia and detrusor smooth muscle function, we studied the contractile response to potassium challenge, carbachol (CCh), and the components of CCh-induced contractile mechanism in high-cholesterol diet-fed rats. Adult male Sprague-Dawley rats were fed with standard (control group, N = 17) or 4 % cholesterol diet (hypercholesterolemia group (HC), N = 16) for 4 weeks. Spontaneous contractions of detrusor muscle strips and their responses to potassium chloride (KCl) or cumulative dose-contraction curves to CCh were recorded. The effects of muscarinic receptor antagonists (methoctramin and/or 4-diphenylacetoxy-N-methylpiperidine), L-type Ca(+2) channel blocker (nifedipine), and/or rho-kinase inhibitor Y-27632 were investigated. Blood cholesterol level was increased in the HC group with no sign of atherosclerosis. The KCl-induced detrusor smooth muscle contractions were higher in HC, whereas spontaneous and CCh-induced responses were similar in both groups. Preincubation with receptor antagonist for M(3) but not for M(2) attenuated contraction significantly, shifting the dose-response curve to the right. This response was similar in both groups. Among two effector mechanisms of M(3)-mediated detrusor smooth muscle contraction, rho-kinase pathway was not affected by hypercholesterolemia, whereas blockade of L-type Ca(+2) channels potently reduced contractions. The results of this study point out a relation between hypercholesterolemia and contractile mechanism of detrusor smooth muscle likely to change urinary bladder function, via altering L-type Ca(+2) channels. Taken together with escalating incidence of hypercholesterolemia and lower urinary tract symptoms, it is a field which deserves to be investigated further.

Muscarinic acetylcholine receptors in the urinary tract

Muscarinic receptors comprise five cloned subtypes, encoded by five distinct genes, which correspond to pharmacologically defined receptors (M(1)-M(5)). They belong to the family of G-protein-coupled receptors and couple differentially to the G-proteins. Preferentially, the inhibitory muscarinic M(2) and M(4) receptors couple to G(i/o), whereas the excitatory muscarinic M(1), M(3), and M(5) receptors preferentially couple to G(q/11). In general, muscarinic M(1), M(3), and M(5) receptors increase intracellular calcium by mobilizing phosphoinositides that generate inositol 1,4,5-trisphosphate (InsP3) and 1,2-diacylglycerol (DAG), whereas M(2) and M(4) receptors are negatively coupled to adenylyl cyclase. Muscarinic receptors are distributed to all parts of the lower urinary tract. The clinical use of antimuscarinic drugs in the treatment of detrusor overactivity and the overactive bladder syndrome has focused interest on the muscarinic receptors not only of the detrusor, but also of other components of the bladder wall, and these have been widely studied. However, the muscarinic receptors in the urethra, prostate, and ureter, and the effects they mediate in the normal state and in different urinary tract pathologies, have so far not been well characterized. In this review, the expression of and the functional effects mediated by muscarinic receptors in the bladder, urethra, prostate, and ureters, under normal conditions and in different pathologies, are discussed.

Regional heterogeneity in expression of the sphingosine-1-phosphate pathway in the female rat lower urinary tract

OBJECTIVE

We investigated the existence and regional distribution of sphingosine-1-phosphate regulatory enzymes and receptors in the lower urinary tract and determined the functional role of sphingosine-1-phosphate receptors in the bladder.

STUDY DESIGN

Lower urinary tract tissue from 10 female rats was harvested for real-time reverse transcriptase-polymerase chain reaction or organ bath physiology, whereas blood serum was obtained for high-performance liquid chromatography determination of sphingosine-1-phosphate levels. Statistical analysis included the Student t test and analysis of variance.

RESULTS

All 3 sphingosine-1-phosphate receptors and major enzymes were expressed throughout the lower urinary tract, but expression and physiologic force generation varied among regions. Sphingosine-1-phosphate was detected in serum.

CONCLUSION

We provide novel data that the sphingosine-1-phosphate signaling pathway regulatory proteins exist throughout the female rat lower urinary tract, but that relative expression exhibits regional heterogeneity corresponding with lower urinary tract contractile response to sphingosine-1-phosphate. Our study suggests that sphingosine-1-phosphate signaling is important in the lower urinary tract and identifies this pathway as a possible target for altering bladder smooth muscle tone.

Inhibitory effects of different ATP-sensitive potassium channel openers on electrically generated and carbachol-induced contractions of porcine and human detrusor muscle

The inhibitory effects of different potassium channel openers (PCOs) on electrically generated and carbachol-induced contractions of porcine and human detrusor muscle were examined. PCOs could be an interesting substance class for treatment of detrusor overactivity. Experiments were performed on muscle strips suspended in a tissue bath. Human tissue originated from patients who underwent total cystectomy. The concentration-relaxation curves of the first-generation PCOs cromakalim and pinacidil and the untypical PCO minoxidil were performed using carbachol-precontracted detrusor muscle strips of pigs and humans. Additionally, the inhibitory effects of cromakalim, pinacidil and minoxidil on electrically generated contractions of porcine detrusor muscle were examined. Furthermore, the inhibitory effect of the second-generation, bladder-selective PCO ZM 226600 on electrically generated contractions of the human detrusor muscle was determined. Frequency-response curves were performed before and after incubation with one PCO used in two different concentrations. In humans, cromakalim and pinacidil led to a maximum decrease of 73.5 and 68.4% and showed mean pD2 values of 6.65 and 5.5, respectively. In pigs, cromakalim and pinacidil led to a maximum decrease of 90.6 and 93.6% and showed mean pD2 values of 6.39 and 5.01, respectively. Minoxidil did not significantly decrease the precontraction at the highest used concentration in both species. Cromakalim exhibited the biggest inhibitory effect being significant at 10(-5) and 10(-6) M. Pinacidil showed only a significant inhibitory effect at 10(-5) M which was smaller than that of cromakalim. At 3 x 10(-6) M only a very small effect occurred at 1 Hz. Minoxidil did not inhibit the contractions at both examined concentrations except for a very small effect at 1 Hz. In humans, ZM 226600 exhibited at 10(-6) and 10(-5) M a significant inhibitory effect. At 10(-7) M it was only significant at one frequency.

Contribution of Ca2+ influx to carbachol-induced detrusor contraction is different in human urinary bladder compared to pig and mouse

Carbachol-induced detrusor contractions are mainly mediated via M3 receptor subtype and depend not only on Ca2+ release from the intracellular calcium stores but also on Ca2+ influx via L-type Ca2+ channels. The purpose of this study was to examine the different contributions of Ca2+ influx and Ca2+ release underlying muscarinic receptor-mediated contractions in human, porcine and murine urinary bladder. Detrusor contractions were measured in urothelium-denuded detrusor strips as responses to cumulatively increasing carbachol concentrations, release of intracellular Ca2+ was determined in Chinese hamster ovary cells stably transfected with human muscarinic M3 (hM3) receptors. In human tissue, 1 microM of the L-type Ca2+-channel blocker nifedipine reduced carbachol contractions to 74%, in pig to 18% and in mouse to 27% of pre-drug controls. 2-aminoethoxyphenyl borate (2-APB, 300 microM), which impairs inositol trisphosphate (IP3)-induced release of Ca2+, reduced carbachol responses in human detrusor to 60%, in pig to 35% and in mouse to 20%, whereas block of the Ca2+-induced Ca2+ release with ryanodine had no significant effect on carbachol contractions in all three species. Carbachol-induced release of intracellular Ca2+ in Chinese hamster ovary cells expressing muscarinic hM3 receptors was completely prevented by 100 microM 2-APB. The direct intracellular IP3 receptor antagonist xestospongin C (10 microM) reduced carbachol-stimulated intracellular Ca2+ to 41% of the control value. Blockade of ATP-dependent Ca2+ uptake into intracellular stores with thapsigargin was associated with a concentration-dependent increase of detrusor contraction, but limited on-top contractions with carbachol. In conclusion, carbachol-induced contractions in human, porcine and mouse detrusor depend differently on Ca2+ influx, since potency of nifedipine reducing muscarinic receptor-mediated detrusor contraction is lower in human bladder. On the other hand, slight species differences are also found when inhibiting IP3-induced Ca2+ release and Ca2+ reuptake into intracellular stores. Taken together, our data show considerable species differences between human, porcine and murine detrusor regarding the relative contributions of Ca2+ influx and maybe also carbachol-induced Ca2+ release that could be of relevance when using different animal models.

Oxidative stress reduces the muscarinic receptor function in the urinary bladder

AIMS

Several pathophysiological conditions in the urinary bladder, for example, ischemia/reperfusion and inflammation are characterized by the formation of reactive oxygen species (ROS). The ROS are highly toxic because they can destroy proteins, DNA, and lipids. The aim of this study was to investigate the effect of oxidative stress on excitation-contraction coupling of detrusor smooth muscle.

MATERIALS AND METHODS

Smooth muscle strips were dissected from pig urinary bladder and mounted in organ baths. Oxidative stress was mimicked by the addition of Cumene hydroperoxide (CHP), a lipophilic hydroperoxide, to the organ baths. Contractile responses to electrical field stimulation (EFS: 4-32 Hz), carbachol (10(-8)-3 x 10(-5) M), potassium (65.3 mM), and ATP (1 mM) were monitored before and after the addition of CHP.

RESULTS

Responses of detrusor strips to EFS were for the greater part based on neurogenic stimulation and the release of acetylcholine. CHP diminished contractile responses to EFS and carbachol to the same extent. The pD(2) value of the carbachol concentration-response curve decreased significantly after exposure to 0.1 mM, 0.4 mM, 0.8 mM CHP. Furthermore the maximal effect obtained with carbachol was significantly reduced after 0.1 mM, 0.4 mM, and 0.8 mM CHP treatment. Contractions induced by potassium and ATP were significantly less affected by oxidative stress compared to EFS- and carbachol-induced responses of comparable amplitude.

CONCLUSIONS

The results of our study demonstrate that oxidative stress induced by CHP affects pig bladder contractility. The muscarinic receptor signaling system is severely damaged. L-type calcium channels and the contractile system are less affected and cholinergic nerves remain largely unaffected.

Molecular mechanisms of detrusor and corporal myocyte contraction: identifying targets for pharmacotherapy of bladder and erectile dysfunction

The Post-Genomic age presents many new challenges and opportunities for the improved understanding, diagnosis and treatment of human disease. The long-term goal is to identify molecular correlates of disease processes, and use this information to develop novel and more effective therapeutics. A major hurdle in this regard is ensuring that the molecular targets of interest are indeed relevant to the physiology and/or pathophysiology of the processes being studied, and, moreover, to determine if they are specific to the tissue/organ being investigated. As a first step in this direction, we have reviewed the literature pertaining to bladder and erectile physiology/pharmacology and dysfunction and attempted to summarize some of the critical molecular mechanisms regulating detrusor and corporal myocyte tone. Because of the vast amount of published data, we have limited the scope of this review to consideration of the calcium-mobilizing and calcium-sensitizing pathways in these cells. Despite obvious differences in phenotypic characteristics of the detrusor and corporal myocyte, there are some common molecular changes that may contribute to, for example, the increased myocyte contractility characteristic of bladder and erectile dysfunction (i.e. increased Rho kinase activity and decreased K(+) channel function). Of course, there are also some important distinctions in the pathways that modulate contractility in these two cell types (i.e. the contribution of ryanodine-sensitive calcium stores and the nitric oxide/cGMP pathways). This report highlights some of these similarities and distinctions in the hope that it will encourage scientific discourse and research activity in this area, eventually leading to an improved quality of life for those millions of individuals that are afflicted with bladder and erectile dysfunction.

The role of Ca2+influx and intracellular Ca2+release in the muscarinic-mediated contraction of mammalian urinary bladder smooth muscle

OBJECTIVE To study the involvement of extracellular Ca2+ and the properties of the intracellular Ca2+ ([Ca2+]i) stores on the carbachol-induced contraction of mammalian urinary bladder smooth muscle strips under polarized and depolarized conditions.

MATERIALS AND METHODS

Strips of bladder were suspended between platinum ring electrodes in a cylindrical organ bath (0.2 mL) and continuously superfused with Krebs' solution at 1 mL/min. The effect of nifedipine, cyclopiazonic acid (CPA), thapsigargin, procaine, ryanodine and caffeine before and during a 10-s application of 100 microm carbachol under polarized conditions were studied. The effect of these drugs was also assessed under depolarized conditions using a protocol that allowed a more detailed assessment of the role of [Ca2+]i stores, consisting of emptying the stores by exposure to Ca2+-free solution, rapidly refilling them by a 10-s application of 81.5 mm Ca2+ (priming), returning to the Ca2+-free solution for 3 min and then applying 100 microm carbachol (10 s) in Ca2+-free solution (store release).

RESULTS

Under polarized conditions, nifedipine and Ca2+ removal almost completely inhibited the carbachol-induced contractions. CPA increased the amplitude and duration of both carbachol- and electrical field stimulation-induced contractions. Although ryanodine had no inhibitory effect, caffeine and procaine significantly inhibited the carbachol-induced contraction. Under depolarized conditions nifedipine blocked both priming and store release contractions. CPA, thapsigargin, procaine and ryanodine significantly increased the priming and inhibited the store release contractions. However, caffeine virtually abolished both priming and store release contractions.

CONCLUSION

These results suggest that in guinea-pig urinary bladder smooth muscle the Ca2+ necessary for contraction enters the cell through voltage-dependent dihydropyridine-sensitive Ca2+ channels and is pumped into an intracellular store that is released by carbachol. Under polarized conditions, the blockade of sarco-endoplasmic reticulum calcium ATP-ase (SERCA) with CPA increases [Ca2+]i and carbachol-induced contractions. The effects of caffeine and procaine suggest that store release involves ryanodine receptors and calcium-induced calcium release. Under depolarized conditions, Ca2+ entry is blocked by nifedipine and the stores diminish. Stored Ca2+ is also greatly reduced by the blockade of SERCA with either CPA or thapsigargin. Procaine, ryanodine and caffeine blocked the store release contractions, suggesting that this involves ryanodine receptors and calcium-induced calcium release.

Urinary incontinence in women

Urinary incontinence is common in women, but is under-reported and under-treated. Urine storage and emptying is a complex coordination between the bladder and urethra, and disturbances in the system due to childbirth, aging, or other medical conditions can lead to urinary incontinence. The two main types of incontinence in women, stress urinary incontinence and urge urinary incontinence, can be evaluated by history and simple clinical assessment available to most primary care physicians. There is a wide range of therapeutic options, but the recent proliferation of new drug treatments and surgical devices for urinary incontinence have had mixed results; direct-to-consumer advertising has increased public awareness of the problem of urinary incontinence, but many new products are being introduced without long-term assessment of their safety and efficacy.