Atropine resistance of transmurally stimulated isolated human bladder muscle

Age-related changes of P2X(1) receptor mRNA in the bladder detrusor from men with and without bladder outlet obstruction

The urinary bladder purinergic system is reported to change with age and with bladder dysfunction. Here, we examined the expression of purinergic P2X(1) receptors in detrusor and mucosa (urothelium+lamina propria) from male control bladder and investigated age-related P2X(1) receptor mRNA expression in control and obstructed detrusor. Biopsy specimens were obtained at cystoscopy from control patients (n=46, age range 30-86years) and patients diagnosed with outlet obstruction (n=29, 46-88years). Calponin expression (measured by RT-PCR) was similar in control and obstructed detrusor and did not change with age. Quantitative competitive RT-PCR was used to measure P2X(1) receptor and GAPDH mRNA in control and obstructed detrusor. P2X(1) receptor mRNA expression was 9-fold (p<0.0001) higher in the detrusor than in the mucosa. Expression of mRNA for the internal control GAPDH remained stable with age and across control and obstructed detrusor. No difference in P2X(1) receptor expression was observed between control and obstructed detrusor (p=0.35). However, an age-related decrease in P2X(1) mRNA expression was observed in control (n=27; p=0.0054; Spearman coefficient r=-0.520) but not obstructed detrusor (n=19; p=0.093; r=-0.396). Downregulation of P2X(1) mRNA expression might occur as a result of an increased component of neural ATP release in the aging bladder.

New Unstable Bladder Model in Hypercholesterolemia Rats

OBJECTIVES

To evaluate the voiding function of the new vasculogenic erectile dysfunction (ED) model in hypercholesterolemic rats.

METHODS

We used 14 adult 12-week-old male Sprague-Dawley rats. The cholesterol group received a 1% cholesterol diet for 8 weeks. During the initial 2 weeks, they also drank water containing 3 mg/mL of NG-nitro-L-arginine methyl ester. After 8 weeks, we performed cystometrography, a detrusor strip contraction study, and pathologic examination of the detrusor to confirm voiding dysfunction. The results of the cholesterol and control groups were compared.

RESULTS

Compared with the control group values, the mean serum cholesterol and body weight were significantly elevated in the cholesterol group. The cholesterol group had shorter voiding intervals (377.6 +/- 205.4 versus 121.8 +/- 79.6 seconds, P <0.01) and a smaller functional bladder volume (1.4 +/- 0.7 versus 0.7 +/- 0.3 mL, P <0.05) on cystometrography compared with the control group. In the detrusor strip study, the cholesterol group had greater tension in spontaneous activities and an increase (13.1% +/- 5.6% versus 28.4% +/- 16.2%, P <0.05) in the proportion of purinergic components.

CONCLUSIONS

This vasculogenic ED rat model showed significantly frequent voiding on cystometrography. Considering the many epidemiologic and experimental data, in addition to the data from this model, ED and overactive bladder could share similar pathophysiologic features or be two symptoms of a systemic disorder. This rat model should be useful in evaluating the mechanism of ED and overactive bladder.

Purinoceptors as therapeutic targets for lower urinary tract dysfunction

Lower urinary tract symptoms (LUTS) are present in many common urological syndromes. However, their current suboptimal management by muscarinic and alpha(1)-adrenoceptor antagonists leaves a significant opportunity for the discovery and development of superior medicines. As potential targets for such therapeutics, purinoceptors have emerged over the last two decades from investigations that have established a prominent role for ATP in the regulation of urinary bladder function under normal and pathophysiological conditions. In particular, evidence suggests that ATP signaling via P2X(1) receptors participates in the efferent control of detrusor smooth muscle excitability, and that this function may be heightened in disease and aging. ATP also appears to be involved in bladder sensation, via activation of P2X(3) and P2X(2/3) receptors on sensory afferent neurons, both within the bladder itself and possibly at central synapses. Such findings are based on results from classical pharmacological and localization studies in non-human and human tissues, knockout mice, and studies using recently identified pharmacological antagonists--some of which possess attributes that offer the potential for optimization into candidate drug molecules. Based on recent advances in this field, it is clearly possible that the development of selective antagonists for these receptors will occur that could lead to therapies offering better relief of sensory and motor symptoms for patients, while minimizing the systemic side effects that limit current medicines.

Mechanisms of disease: role of purinergic signaling in the pathophysiology of bladder dysfunction

Although the 'purinergic nerve hypothesis' proposed by Burnstock in the early 1970s was met with considerable skepticism, it is now accepted that certain neurons use a purine nucleotide or nucleoside such as ATP or adenosine as a neurotransmitter. Likewise, early studies indicated that the human bladder is devoid of purinergic nerves mediating contraction; however, later studies demonstrated that purinergic nerve-mediated bladder contraction is increased in pathologic conditions such as interstitial cystitis. Cloning and sequencing studies have revealed four subtypes of adenosine receptors and eight subtypes of P2Y receptors, all of which are G-protein-coupled receptors. There are no reports of the cellular location of these receptors in the human bladder. P2X receptors are ligand-gated ion channels, and seven subunits have been cloned and sequenced. Immunohistochemical studies have determined that P2X(1,2,4) subunits are on detrusor-muscle cells, P2X(1-3,5) subunits are on bladder nerves and P2X(2,3,5) subunits are on bladder urothelial cells. Development of purinergic antagonist drugs with selectivity for P2X(1) receptors on detrusor muscle cells might be useful for treatment of detrusor overactivity. Antagonists with selectivity for P2X(3) receptors on bladder sensory nerves might be clinically beneficial for treatment of urinary urgency, and perhaps chronic pelvic pain.

Frequency encoding of cholinergic- and purinergic-mediated signaling to mouse urinary bladder smooth muscle: modulation by BK channels

In the urinary bladder, contractions of the detrusor muscle and urine voiding are induced by the neurotransmitters ACh and ATP, released from parasympathetic nerves. Activation of K(+) channels, in particular the large-conductance Ca(2+)-activated K(+) (BK) channels, opposes increases in excitability and contractility of urinary bladder smooth muscle (UBSM). We have shown that deleting the gene mSlo1 in mice (Slo(-/-)), encoding the BK channel, leads to enhanced nerve-mediated and neurotransmitter-dependent contractility of UBSM (38). Here, we examine the location of the BK channel in urinary bladder strips from mouse. Immunohistochemical analysis revealed that the channel is expressed in UBSM but not in nerves that innervate the smooth muscle. The relationship between electrical field stimulation and force generation of the cholinergic and purinergic pathways was examined by applying blockers of the respective receptors in UBSM strips from wild-type and from Slo(-/-) (knockout) mice. In wild-type strips, the stimulation frequency required to obtain a half-maximal force was significantly lower for the purinergic (7.2 +/- 0.3 Hz) than the cholinergic pathway (19.1 +/- 1.5 Hz), whereas the maximum force was similar. Blocking BK channels with iberiotoxin or ablation of the Slo gene increased cholinergic- and purinergic-mediated force at low frequencies, i.e., significantly decreased the frequency for a half-maximal force. Our results indicate that the BK channel has a very significant role in reducing both cholinergic- and purinergic-induced contractility and suggest that alterations in BK channel expression or function could contribute to pathologies such as overactive detrusor.

The overactive bladder: review of current pharmacotherapy in adults. Part 1: pathophysiology and anticholinergic therapy

Overactive bladder is a syndrome characterised by urinary urgency, with or without urge incontinence, and usually with frequency and nocturia. It affects millions of people of all ages worldwide and causes significant morbidity, especially in terms of health-related quality of life. It poses a huge economic burden on health resources. Managing such patients involves a thorough history, physical examination and the use of pertinent investigations before the initiation of treatment. Therapy consists of lifestyle changes, bladder training, anticholinergics, second-line agents such as resiniferatoxin instillation or botulinum toxin injections into the bladder in refractory cases and, finally, in intractable cases, surgery. In the first part of this review of pharmacotherapy for the treatment of this condition, the focus is on the pathophysiological factors potentially involved in overactive bladder and covers the wide range of currently available first-line anticholinergic agents. Treatment algorithms are suggested on the basis of current literature.

Pharmacological characterization of urinary bladder smooth muscle contractility following partial bladder outlet obstruction in pigs

Partial bladder outlet obstruction of the pig is considered as a valuable preclinical model for evaluating the profile of compounds for the treatment of bladder overactivity. In this study, we characterized the pharmacological properties of isolated bladder smooth muscle from pigs following partial outlet obstruction and its sensitivity to potassium channel openers. Bladder strips from obstructed animals showed significantly lower maximal efficacy (E(max)) and sensitivity to stimulation by ATP and carbachol, but not to those evoked by serotonin, compared to age-matched controls. Tissue strips from obstructed animals also showed a 2.5-fold increase in the potency and significantly reduced maximum response following K+ depolarization. With respect to spontaneous activity, bladder strips from control strips demonstrated little spontaneous phasic activity at all preloads examined. In contrast, bladder strips from obstructed animals showed large preload-dependent increases in spontaneous phasic activity at preload values of 16-32 g. The potencies of K(ATP) channel openers to relax carbachol-evoked contractions showed a good 1:1 correlation (r(2)=0.90) between obstructed and control bladder strips. These studies demonstrate that obstructed pig bladders show enhanced spontaneous phasic activity especially at elevated preloads, which may underlie unstable myogenic bladder contractions reported in cystometrographic measurements in vivo. The impaired responses to electrical field stimulation could be attributed to reduced efficacies and/or lower sensitivities of muscarinic and purinergic signaling pathways. K(ATP) channel sensitivities remain essentially unimpaired in the obstructed bladder and could be effectively modulated by openers with potential for the treatment of overactive bladder secondary to outlet obstruction.

A Role for the P2X Receptor in Urinary Tract Physiology and in the Pathophysiology of Urinary Dysfunction

OBJECTIVE

We provide a historical perspective of the P2X receptor class in bladder physiology and the pathophysiology of urinary dysfunction.

METHODS

A literature search was performed using the MEDLINE database.

RESULTS

Evidence suggests that P2X receptors serve a combined function in sensory and motor activity of human bladder. P2X receptors mediate excitation of sensory neurons and evoke muscle contraction in response to ATP release. Anatomical and functional defects in the P2X receptor signaling are associated with a variety of urologic diseases.

CONCLUSION

Current research underscores the importance of P2X receptors in urologic physiology. Potential applications exist in relation to the diagnosis and treatment of urinary dysfunction. However, the detailed mechanism of P2X receptor function in bladder physiology and in urinary tract disease remains unknown and warrants further investigation.

Pharmacology of the lower urinary tract: basis for current and future treatments of urinary incontinence

The lower urinary tract constitutes a functional unit controlled by a complex interplay between the central and peripheral nervous systems and local regulatory factors. In the adult, micturition is controlled by a spinobulbospinal reflex, which is under suprapontine control. Several central nervous system transmitters can modulate voiding, as well as, potentially, drugs affecting voiding; for example, noradrenaline, GABA, or dopamine receptors and mechanisms may be therapeutically useful. Peripherally, lower urinary tract function is dependent on the concerted action of the smooth and striated muscles of the urinary bladder, urethra, and periurethral region. Various neurotransmitters, including acetylcholine, noradrenaline, adenosine triphosphate, nitric oxide, and neuropeptides, have been implicated in this neural regulation. Muscarinic receptors mediate normal bladder contraction as well as at least the main part of contraction in the overactive bladder. Disorders of micturition can roughly be classified as disturbances of storage or disturbances of emptying. Failure to store urine may lead to various forms of incontinence, the main forms of which are urge and stress incontinence. The etiology and pathophysiology of these disorders remain incompletely known, which is reflected in the fact that current drug treatment includes a relatively small number of more or less well-documented alternatives. Antimuscarinics are the main-stay of pharmacological treatment of the overactive bladder syndrome, which is characterized by urgency, frequency, and urge incontinence. Accepted drug treatments of stress incontinence are currently scarce, but new alternatives are emerging. New targets for control of micturition are being defined, but further research is needed to advance the pharmacological treatment of micturition disorders.

Urodynamic properties and neurotransmitter dependence of urinary bladder contractility in the BK channel deletion model of overactive bladder

Overactive bladder and incontinence are major medical issues, which lack effective therapy. Previously, we showed (Meredith AL, Thornloe KS, Werner ME, Nelson MT, and Aldrich RW. J Biol Chem 279: 36746-36752, 2004) that the gene mSlo1 encodes large-conductance Ca2+-activated K+ (BK) channels of urinary bladder smooth muscle (UBSM) and that ablation of mSlo1 leads to enhanced myogenic and nerve-mediated contractility and increased urination frequency. Here, we examine the in vivo urodynamic consequences and neurotransmitter dependence in the absence of the BK channel. The sensitivity of contractility to nerve stimulation was greatly enhanced in UBSM strips from Slo-/- mice. The stimulation frequency required to obtain a 50% maximal contraction was 8.3 +/- 0.9 and 19.1 +/- 1.8 Hz in Slo-/- and Slo+/+ mice, respectively. This enhancement is at least partially due to alterations in UBSM excitability, as muscarinic-induced Slo-/- contractility is elevated in the absence of neuronal activity. Muscarinic-induced Slo-/- contractility was mimicked by blocking BK channels with iberiotoxin (IBTX) in Slo+/+ strips, whereas IBTX had no effect on Slo-/- strips. IBTX also enhanced purinergic contractions of Slo+/+ UBSM but was without effect on purinergic contractions of Slo-/- strips. In vivo bladder pressure and urine output measurements (cystometry) were performed on conscious, freely moving mice. Slo-/- mice exhibited increased bladder pressures, pronounced pressure oscillations, and urine dripping. Our results indicate that the BK channel in UBSM has a very significant role in urinary function and dysfunction and as such likely represents an important therapeutic target.

Potential therapeutic targets for the treatment of detrusor overactivity

Current treatments for the overactive detrusor are poorly tolerated and can exert significant adverse effects. Possible targets for the development of new treatments are considered. Potential targets in four locations are examined: detrusor smooth muscle, urothelium, peripheral nerves and the CNS. In the detrusor, the role of various muscarinic receptor subtypes is discussed and beta-adrenoceptor agonists, phosphodiesterase inhibitors and potassium channel openers, all of which inhibit detrusor contractility, are considered for drug development. In the urothelium, a number of substances are released that affect bladder function including ATP, acetylcholine and an inhibitory factor that has yet to be identified. All three systems have the potential to be novel targets for drug development. Other possible therapeutic targets are the mechanisms influencing transmitter release in the bladder, for example, prejunctional 5-hydroxytryptamine (5-HT) 4 receptors. Finally, targets within the CNS and spinal cord are considered, including opioid receptors, 5-HT receptors and alpha-adrenoceptors.

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.

Urinary bladder contraction and relaxation: physiology and pathophysiology

The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition. These processes are regulated by several external nervous and hormonal control systems, and the detrusor contains multiple receptors and signaling pathways. Functional changes of the detrusor can be found in several clinically important conditions, e.g., lower urinary tract symptoms (LUTS) and bladder outlet obstruction. The aim of this review is to summarize and synthesize basic information and recent advances in the understanding of the properties of the detrusor smooth muscle, its contractile system, cellular signaling, membrane properties, and cellular receptors. Alterations in these systems in pathological conditions of the bladder wall are described, and some areas for future research are suggested.

Signal Transduction Underlying Carbachol-Induced Contraction of Human Urinary Bladder

The present study was designed to reexamine the muscarinic acetylcholine receptor subtype mediating carbachol-induced contraction of human urinary bladder and to investigate the underlying signal transduction. Based upon the nonselective tolterodine, the highly M(2)-selective (R)-4-[2-[3-(4-methoxy-benzoylamino)-benzyl]-piperidin-1-ylmethyl]piperidine-1-carboxylic acid amide (Ro-320-6206), and the highly M(3)-selective darifenacin and 3-(1-carbamoyl-1,1-diphenylmethyl)-1-(4-methoxyphenylethyl)pyrrolidine (APP), contraction occurs via M(3) receptors. The phospholipase C inhibitor 1-(6-[([17beta]-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl)-1H-pyrrole-2,5-dione (U 73,122) (1-10 microM) did not significantly affect carbachol-stimulated bladder contraction. The phospholipase D inhibitor butan-1-ol relative to its negative control butan-2-ol (0.3% each) caused small but detectable inhibition of carbachol-induced bladder contraction. The Ca(2+) entry blocker nifedipine (10-100 nM) strongly inhibited carbachol-induced bladder contraction. In contrast, 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole HCl (SK&F 96,365) (1-10 microM), an inhibitor of store-operated Ca(2+) channels, caused little inhibition. The protein kinase C inhibitor bisindolylmaleimide I (1-10 microM) did not significantly affected carbachol-induced bladder contraction. In contrast, trans-4-[(1R)-1-aminoethyl]-N-4-pyridinylcyclohexanecarboxamide (Y 27,632) (1-10 microM), an inhibitor of rho-associated kinases, concentration dependently and effectively attenuated the carbachol responses. We conclude that carbachol-induced contraction of human urinary bladder via M(3) receptors largely depends on Ca(2+) entry through nifedipine-sensitive channels and activation of a rho kinase, whereas phospholipase D and store-operated Ca(2+) channels contribute only in a minor way. Surprisingly, phospholipase C or protein kinase C do not seem to be involved to a relevant extent.

Storage and voiding symptoms: pathophysiologic aspects

Lower urinary tract symptoms (LUTS) can be categorized as storage, voiding, and postmicturition symptoms. Although often associated with benign prostatic hyperplasia (BPH), they may also occur in women. This observation, the beneficial effects of alpha-adrenoceptor (AR) antagonists in men with BPH and LUTS, and the frail correlation between LUTS, and prostatic enlargement and/or outflow obstruction have focused interest on the role of extraprostatic alpha-ARs in the pathogenesis of LUTS. It has been suggested that an upregulation of contraction-mediating alpha-ARs and a downregulation of relaxation-mediating beta-ARs can contribute to LUTS generation. However, recent investigations on human bladder tissue could not confirm such a change. Antimuscarinic agents are effective for treatment of the overactive bladder, which is characterized by urge, frequency, urge incontinence, and nocturia (ie, LUTS). This suggests that muscarinic receptors are involved in the pathogenesis of LUTS, and there is recent evidence implicating purinergic receptors. Structural changes in the bladder, such as smooth muscle hypertrophy and connective tissue infiltration, are associated with detrusor overactivity in about 50% to 66% of patients with BPH. However, it is unclear whether this is caused by bladder outlet obstruction because the symptoms may remain in up to 33% of the patients after surgical removal of the obstruction. When outflow obstruction is reversed in rats, there is a subset (20%) that continues to have overactive voiding, despite a reversal of the bladder hypertrophy, suggesting that changes within the central nervous system may be a contributing factor. LUTS can be caused by many, often overlapping, pathophysiologic mechanisms, which may contribute to individual variation in response to treatment.

Signal transduction underlying carbachol-induced contraction of rat urinary bladder. I. Phospholipases and Ca2+ sources

We have reexamined the muscarinic receptor subtype mediating carbachol-induced contraction of rat urinary bladder and investigated the role of phospholipase (PL)C, D, and A2 and of intra- and extracellular Ca2+ sources in this effect. Based on the nonsubtype-selective tolterodine, the highly M2 receptor-selective (R)-4-[2-[3-(4-methoxy-benzoylamino)-benzyl]-piperidin-1-ylmethyl]-piperidine-1-carboxylic acid amide (Ro-320-6206), and the highly M3 receptor-selective darifenacin and 3-(1-carbamoyl-1,1-diphenylmethyl)-1-(4-methoxyphenylethyl)pyrrolidine (APP), contraction occurs via M3 receptors. Carbachol stimulated inositol phosphate formation in rat bladder slices, and this was abolished by the phospholipase C inhibitor 1-(6-[([17beta]-3-methoxyestra-1,3,5[10]-trien-17-yl)-amino]hexyl)-1H-pyrrole-2,5-dione (U 73,122; 10 microM). Nevertheless, U 73,122 (1-10 microM) did not significantly affect carbachol-stimulated bladder contraction. Carbachol had only little effect on PLD activity in bladder slices, but the PLD inhibitor butan-1-ol, relative to its negative control butan-2-ol (0.3% each), caused detectable inhibition of carbachol-induced bladder contraction. The cytosolic PLA2 inhibitor arachidonyltrifluoromethyl ketone weakly inhibited carbachol-induced contraction at a concentration of 300 microM, but the cyclooxygenase inhibitor indomethacin (1-10 microM) remained without effect. The Ca2+ entry blocker nifedipine (10-100 nM) almost completely inhibited carbachol-induced bladder contraction. In contrast, 1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole HCl (SKF 96,365; 10 microM), an inhibitor of store-operated Ca2+ channels, caused little inhibition. We conclude that carbachol-induced contraction of rat bladder largely depends on Ca2+ entry through nifedipine-sensitive channels and, perhaps, PLD, PLA2, and store-operated Ca2+ channels, whereas cyclooxygenase and, surprisingly, also PLC are not involved to a relevant extent.

Recent developments in the management of detrusor overactivity

PURPOSE OF REVIEW

Detrusor overactivity is a relatively common yet embarrassing symptom complex with significant impact on quality of life. The mainstay of current pharmacological treatment involves use of muscarinic receptor antagonists, but their therapeutic efficacy is limited by their troublesome side effects resulting in the non-continuance of treatment in a significant number of patients. Therefore, the development of new drugs can proceed by targeting alternative pathways affecting detrusor overactivity. In this article, the pharmacological basis for the current therapeutic alternatives for managing detrusor overactivity and possible future developments are discussed.

RECENT FINDINGS

It is clear that far from being a passive container for urine, the urothelium is a crucial part of the bladder. Its functions are complex, dynamic and important, and only now becoming understood. The release of ATP from urothelium in response to distension and its action on P2X receptors resulting in activating both motor and sensory neurons is being increasingly recognised. In the normal bladder, muscarinic receptor stimulation produces the main part of detrusor contraction. However, in functionally abnormal bladders, a non-cholinergic activation via the purinergic receptors may occur. The central nervous mechanisms controlling the micturition reflex have also recently attracted attention.

SUMMARY

Recent research has suggested that several transmitters may modulate voiding. However, few drugs with clinical benefits have been developed so far. Present treatments for overactive bladders have significant non-compliance rates. Hopefully, future research will lead to drugs with greater therapeutic benefits and better tolerance.

[Pharmacological analysis of neurotransmitters contributing to lower urinary tract function]

Lower urinary tract function is controlled by the autonomic nervous system, which consists of adrenergic, cholinergic, and non-adrenergic, non-cholinergic (NANC) neurons. We have measured the amount of various neurotransmitters (acetylcholine, ACh; noradrenaline, NA; adenosine triphosphate, ATP; and nitric oxide, NO) released from human and rabbit urinary tract smooth muscles by the microdialysis method coupled with HPLC. Muscle strips are isolated from human or rabbit bladder, urethra, and prostate. A microdialysis probe was inserted into each smooth muscle strip. Each muscle strip was connected to an isometric transducer, and tension development was measured. We have evaluated the changes in electrical field stimulation-induced neurotransmitter releases and functional responses in physiological and pathological conditions and the interactions between neurotransmitters or neurons. In this review, we present several of our results: 1) interactions between adrenergic and nitrergic neurons in rabbit urethra, 2) effect of NO on human bladder function, 3) effect of NO on human prostate function, and 4) effects of aging on acetylcholine and ATP releases from human bladder smooth muscles. These data may reveal physiological or pathological neurotransmitter control of lower urinary tract function and give us useful information for clinical intervention to treat lower urinary tract symptoms.

Electromyographic detection of purinergic activity in Guinea pig detrusor smooth muscle

PURPOSE

We recorded nerve mediated extracellular electrical activity from guinea pig detrusor smooth muscle strips using suction electrodes and determined the electrophysiological origins of this signal and its relationship to contractile activity.

MATERIALS AND METHODS

Mucosa-free detrusor strips were prepared from male guinea pigs sacrificed under Home Office license, physiologically superfused, attached to a pressure transducer and electrically stimulated (0.1 millisecond pulses). Electrical signals recorded using a bipolar reversible suction electrode were processed and recorded simultaneously with changes in strip tension. The effect of superfusion with alpha, beta-methylene adenosine triphosphate (ATP), atropine, extracellular [CaCl(2)] depletion and pharmacological Ca2+ channel blockade on the electrical and mechanical signals was determined.

RESULTS

A biphasic electrical signal was consistently recorded from 37 detrusor strips. The signal was sensitive to graded reduction in [CaCl(2)] of the superfusate and abolished by tetrodotoxin in 7 preparations. The signal was also abolished in 12 preparations by alpha, beta-methylene ATP in association with an attenuated contraction but not significantly reduced in amplitude (p = 0.77) despite a significant reduction in tension with atropine (mean plus or minus SD 74% +/- 14% of control, p <0.001). The signal was attenuated to a mean maximum of 9% +/- 3% of control by pharmacological Ca2+ channel blockade and the remaining signal was abolished by alpha, beta-methylene ATP.

CONCLUSIONS

The extracellular electrical signal recorded from guinea pig detrusor strips using suction electrodes originates from a purinergic mechanism. Although an atropine sensitive component may be present, the signal does not depend on cholinergic neuromuscular transmission and would not be expected to be generated by normal human detrusor. Provided that the electrophysiological basis of purinergic neurotransmission in guinea pig and human bladders is similar suction electrodes may be a valuable tool with which to evaluate in vitro and clinically by electromyography the pathological purinergic neuromuscular transmission that can be expressed in addition to normal cholinergic mechanisms in detrusor from dysfunctional human bladders.

Antimuscarinics and the overactive detrusor--which is the main mechanism of action?

Contraction of the bladder, voluntary or involuntary, involves stimulation of the muscarinic receptors on the detrusor by acetylcholine, released from activated cholinergic nerves. Antimuscarinics are the drugs of choice for treatment of detrusor overactivity and the overactive bladder (OAB) syndrome. However, antimuscarinics at clinically recommended doses have little effect on voiding contractions, and may act mainly during the bladder storage phase, during which there is normally no parasympathetic outflow from the spinal cord. Supporting this, antimuscarinics have been shown to reduce bladder tone during storage, and to increase cystometric bladder capacity. A basal release of acetylcholine from non-neuronal (urothelial) as well as neuronal sources has been demonstrated in isolated human detrusor muscle. It is suggested that this release, which is increased by stretching the muscle and in the aging bladder, contributes to detrusor overactivity and OAB by eventually increasing bladder afferent activity during storage.

Current and future pharmacological treatment for overactive bladder

PURPOSE

Urinary incontinence and overactive bladder are important and common conditions that have received little general medical attention. We reviewed the magnitude and impact of these conditions, and discuss pharmacotherapy as well as new drugs under investigation.

MATERIALS AND METHODS

The main emphasis of this review is pharmacological therapy for the bladder. We discuss currently available agents, drugs under development and pharmacological targets that would be suitable targets for treating overactive bladder. Drugs such as duloxetine that target not bladder smooth muscle, but rather central nervous system control of the micturition reflex are undergoing clinical trials. We also discuss intravesical therapy and alternative drug delivery methods, such as intravesical capsaicin and botulinum toxin, with special emphasis on approaches to modulate bladder afferent nerve function for preventing overactive bladder.

RESULTS

There are many advantages to advanced drug delivery systems, including long-term therapeutic efficacy, decreased side effects and improved patient compliance. Future speculation such as gene therapy holds great promise for overactive bladder because it is possible to access all genitourinary organs via endoscopy and other minimally invasive techniques that are ideally suited for gene therapy.

CONCLUSIONS

Traditional anticholinergic therapies are limited in their effectiveness. There is great hope for future research regarding voiding dysfunction and urinary incontinence through a focus on afferent nerve intervention for preventing overactive bladder.

Muscarinic receptor subtypes and management of the overactive bladder

Anticholinergic agents are the most widely used therapy for urge incontinence despite exerting adverse effects, such as constipation, tachycardia, and dry mouth, that limit their use. These adverse effects result from a lack of selectivity for the bladder over other organs. Although M2-muscarinic receptors are the predominant cholinoreceptor present in urinary bladder, the smaller population of M3-receptors appears to be the most functionally important and mediates direct contraction of the detrusor muscle. M2-receptors modulate detrusor contraction by several mechanisms and may contribute more to contraction of the bladder in pathologic states, such as bladder denervation or spinal cord injury. Prejunctional inhibitory M2-receptors or M4-receptors and prejunctional facilitatory M1-muscarinic receptors in the bladder have also been reported, but their relevance to the clinical effectiveness of muscarinic antagonists is unknown. In clinical studies, tolterodine, a nonselective muscarinic antagonist, has been reported to be equally effective to oxybutynin but to induce less dry mouth. Controlled-release and intravesical, intravaginal, and rectal administrations of oxybutynin have all been reported to cause fewer adverse effects. Conversely, darifenacin, a new M3-selective antagonist, has been reported to have selectivity for the bladder over the salivary gland in vivo. Whether M3-selective or nonselective muscarinic antagonists will be the most clinically effective for the overactive bladder-preserving the best balance between efficacy and tolerability-has yet to be established, and comparative clinical trials between compounds, such as darifenacin (M3 selective) and tolterodine (nonselective) will be required.

Different responses to drugs against overactive bladder in detrusor muscle of pig, guinea pig and mouse

Direct comparison of experimental data for drugs commonly used in the treatment of overactive bladder is difficult because of possible species differences. In this study, we compare the effects of atropine, propiverine, oxybutynin and tolterodine in strips of pig, guinea pig and mouse detrusor muscle. In the three species, we observed slight differences in potency of carbachol-induced biphasic contractile responses between the species (guinea pig>pig>mouse). Cumulative concentration-response curves for carbachol were shifted to the right by atropine, propiverine, oxybutynin and tolterodine. However, at higher concentrations of the latter three antagonists, the maximum response to carbachol was also reduced. Therefore, propiverine, oxybutynin and tolterodine must have additional pharmacological actions beyond competitive antagonism at muscarinic receptors. Electric field stimulation (30 Hz) of detrusor strips led to contraction amplitudes, which remained constant over time (210 min) in pig, decreased by 17+/-5% in guinea pig, and increased by 28+/-9% in mouse detrusor muscle. Electric field stimulation-evoked contractions were suppressed to 18% of pre-drug control by high concentrations of atropine (10 microM) in pig, but to a much lesser extent in guinea pig and mouse (to 46% and 70%, respectively). In all three species, a myogenic component of contraction was observed in the presence of tetrodotoxin (1 microM). Compared to atropine, the bladder spasmolytic agents propiverine, oxybutynin and tolterodine also reduced electrically evoked contractions in the three species, though higher concentrations were required. The differences in the reported effects of the spasmolytic agents commonly used for treating overactive bladder suggest that drug action is strongly dependent on the species. Thus, a comparison of drug effects is only feasible in the same animal model and the results cannot easily be transferred to humans.

Pharmacologic perspective on the physiology of the lower urinary tract

Myogenic activity, distention of the detrusor, and signals from the urothelium may initiate voiding. In the bladder, afferent nerves have been identified not only in the detrusor, but also suburothelially, where they form a plexus that lies immediately beneath the epithelial lining. Extracellular adenosine triphosphate (ATP) has been found to mediate excitation of small-diameter sensory neurons via P2X3 receptors, and it has been shown that bladder distention causes release of ATP from the urothelium. In turn, ATP can activate P2X3 receptors on suburothelial afferent nerve terminals to evoke a neural discharge. However, most probably, not only ATP but also a cascade of inhibitory and stimulatory transmitters and mediators are involved in the transduction mechanisms underlying the activation of afferent fibers during bladder filling. These mechanisms may be targets for future drugs. The central nervous control of micturition involves many transmitter systems, which may be suitable targets for pharmacologic intervention. gamma-Aminobutyric acid, dopamine, enkephalin, serotonin, and noradrenaline receptors and mechanisms are known to influence micturition, and potentially, drugs that affect these systems could be developed for clinical use. However, a selective action on the lower urinary tract may be difficult to obtain. Most drugs currently used for treatment of detrusor overactivity have a peripheral site of action, mainly the efferent (cholinergic) neurotransmission and/or the detrusor muscle itself. In the normal bladder, muscarinic receptor stimulation produces the main part of detrusor contraction, but evidence is accumulating that in disease states, such as neurogenic bladders, outflow obstruction, idiopathic detrusor instability, and interstitial cystitis, as well as in the aging bladder, a noncholinergic activation via purinergic receptors may occur. If this component of activation is responsible not only for part of the bladder contractions, but also for the symptoms of the overactive bladder, it should be considered an important target for therapeutic interventions.

Physiology of female micturition

Micturition is a dynamic physiologic process consisting of alternating storage and expulsion phases and is accomplished by complex interactions among innervation, smooth muscle, connective tissue, urothelium and supportive structures. Although our current understanding of the anatomy and physiology of the lower urinary tract is far from complete, intensive research over the last decade has dramatically improved our appreciation of the neural, biomechanical, biochemical, and morphologic properties of the bladder and urethra, as well as the hormonal influences and unique pelvic and perineal anatomy of women. Continued research related to the physiology of female micturition promises to offer new insights into the complex bladder-urethral interactions and to provide a basis for developing better management strategies for a variety of voiding dysfunctions in women.

Influence of nitric oxide signalling pathways on pre-contracted human detrusor smooth muscle in vitro

OBJECTIVES

To assess the effects of nitric oxide (NO) donors on human detrusor strips in vitro under conditions which attempt to mimic those occurring in vivo during the tonic phase of bladder contraction, as NO may promote relaxation by modulating parasympathetic excitation contraction coupling.

MATERIALS AND METHODS

With ethical approval from the local ethics committee, human detrusor tissue was obtained from a heterogeneous clinical group after obtaining informed consent. Detrusor strips were dissected and mounted in a 1-mL, superfused organ bath. After pre-contraction with carbachol, the effect of NO donors, sodium nitroprusside (SNP) and S-nitro-N-acetylpenicillamine, a cell-permeable cyclic nucleotide analogue (dibutyl-cGMP), and inhibitors (methylene blue and ibuprofen) on isometric tension were assessed. All drugs were dissolved in Tyrode solution (pH 7.4), passed through a thermostatically controlled (36 degrees C) warming jacket and bubbled with 95% O2/5% CO2.

RESULTS

Both NO donors and db-cGMP evoked a complex response in pre-contracted tissue, i.e. relaxation, contraction or a transient relaxation followed by contraction. Inhibition of soluble guanylyl cyclase significantly attenuated NO-mediated contraction, indicating the involvement of cGMP, but this inhibition did not significantly affect the relaxant response. The relaxant response was also potentiated by ibuprofen. SNP and db-cGMP evoked similar responses, although the occurrence of the responses (relaxation, contraction or biphasic) was significantly different in normal and pathological human detrusor.

CONCLUSIONS

NO donors and db-cGMP modulate carbachol-evoked contraction of human detrusor smooth muscle in vitro. There is probably a NO/cGMP signalling pathway, with inhibition of endogenous cGMP by methylene blue, suggesting that SNP evokes contraction via cGMP. However, NO donors and db-cGMP evoked a complex response (relaxant, contractile or biphasic), suggesting that NO and cGMP may also act independently and/or via several pathways.

The tachykinin NK-2 receptor antagonist SR48968 does not block noncholinergic contractions in unstable human bladder

Concentration-response curves to acetylcholine, and responses to electrical field stimulation (EFS) were compared in detrusor muscle strips, from control patients and those with idiopathic detrusor instability (IDI). Responses were similar in both groups. However, atropine abolished responses to EFS in 80% of control but only 33% of IDI patients (P>0.05), with the residual atropine-resistant response in most IDI patients abolished by tetrodotoxin. The post-atropine residual response was unaffected by the tachykinin NK-2 receptor antagonist SR48968. Despite the known existence of NK-2 receptors in the human detrusor, there was no evidence for tachykinin contribution to EFS-induced contractions.

A possible effect of sulfhydryl reagents on the contractile activity of the rat detrusor muscle

We aimed to investigate the effect of sulfhydryl (SH) inactivating agents, ethacrynic acid and N-ethylmaleimide, on the contractile activity of rat detrusor muscle. Wistar Kyoto rats weighing 150-250 g were anaesthetized with ketamine and bled to death. The urinary bladders were surgically removed and detrusor strips were mounted under 0.5 g tension in organ baths. The responses were recorded with isotonic transducers on polygraph paper. After an equilibrium period, the tissues were contracted by electrical field stimulation, acetylcholine, ethacrynic acid or N-ethylmaleimide and the effects of L-cysteine, glutathione, verapamil, Ca(2+)-free solution, sodium nitroprusside or atropine were then examined on these contractions. Verapamil, Ca(2+)-free solution or atropine significantly reduced the contractions elicited by electrical field stimulation and acetylcholine whereas L-cysteine, glutathione or sodium nitroprusside had no effect on the contractions in response to these stimuli. L-Cysteine, glutathione, verapamil or Ca(2+)-free solution significantly inhibited the contractions induced by ethacrynic acid or N-ethylmaleimide. Sodium nitroprusside slightly inhibited only the contraction induced by ethacrynic acid but not that with N-ethylmaleimide. Atropine has no action on the contractions in response to these SH reagents. These findings suggest that SH reagents may play a role in the contractile activity of rat detrusor muscle and this action seems to be related to the gating of Ca(2+) channels. Further experiments are needed to determine the cellular mechanism(s) of action by which these SH reagents act on the detrusor smooth muscle.

P2X receptors and their role in female idiopathic detrusor instability

PURPOSE

It is clear from previous studies that adenosine triphosphate is released as a contractile co-transmitter with acetylcholine from parasympathetic nerves supplying the mammalian bladder but the physiological significance of ligand gated purinergic P2X receptors in human bladder innervation has not been adequately investigated. We examined the role of these receptors in female patients with idiopathic detrusor instability.

MATERIALS AND METHODS

Female patients with idiopathic detrusor instability were recruited for cystoscopy and bladder biopsy with ethics approval. Control tissue was obtained from age and sex matched patients with a urodynamically proved stable bladder. We obtained 4 bladder biopsies per patient from the posterior wall. Samples were analyzed in an organ bath for functional studies of the detrusor muscle to assess the purinergic contribution to its contraction. In addition, we performed quantitative analysis using reverse transcriptase-polymerase chain reaction and immunohistochemical localization of P2X receptors.

RESULTS

In patients with idiopathic detrusor instability detrusor P2X2 receptors were significantly elevated, while other P2X receptor subtypes were significantly decreased. A purinergic component of nerve mediated contractions was not detected in control female bladder biopsy specimens but there was a significant component in unstable bladder specimens. It was particularly prominent at stimulation frequencies of 2 to 16 Hz. which are likely to be most relevant physiologically. Approximately 50% of nerve mediated contractions were purinergic in idiopathic detrusor instability cases.

CONCLUSIONS

In patients with idiopathic detrusor instability there is abnormal purinergic transmission in the bladder, which may explain symptoms. This pathway may be a novel target for the pharmacological treatment of overactive bladder.

A quantitative analysis of purinoceptor expression in the bladders of patients with symptomatic outlet obstruction

OBJECTIVE

To compare the expression of the seven known P2X receptors in human bladder from male patients with detrusor instability caused by symptomatic bladder outlet obstruction with that from control bladders, using a quantitative reverse transcription-polymerase chain reaction (RT-PCR) method.

PATIENTS AND METHODS

Real-time quantitative RT-PCR provides a system for detecting and analysing RNA. Bladder biopsies were obtained from nine patients undergoing prostate surgery and control biopsies were obtained from eight age-matched men undergoing routine bladder endoscopy studies, and who were asymptomatic. Total RNA was extracted from each sample and 10 ng of this used for individual PCR reactions. The expression levels of the seven P2X genes in the total RNA were then determined.

RESULTS

In the control bladder, P2X1 was by far the predominant purinergic receptor at the RNA level, the remainder consistently present in the order P2X1 >> P2X4 > P2X2 > P2X7 > P2X5 >> P2X3 = P2X6 = 0. Calponin, a smooth muscle-specific protein, was used as a marker for smooth muscle content. In bladder from symptomatic patients, the P2X1/calponin ratio was greater than that in controls (P = 0.016). There appeared to be no difference in P2X2, but P2X4, P2X5, and P2X7 were all greater in the symptomatic bladder than in the controls, although these differences were not significant.

CONCLUSION

P2X1 is the predominant purinoceptor subtype in the human male bladder, consistent with pharmacological evidence. The amount of P2X1 receptor per smooth muscle cell is greater in the obstructed than in control bladder, suggesting an increase in purinergic function in the unstable bladder arising from bladder outlet obstruction.

Bladder instability: a re-appraisal of classical experimental approaches and development of new therapeutic strategies

1 Despite the growing social interest in human urinary tract disorders, the aetiology of detrusor instability remains poorly understood. Myogenic and neural impairment of detrusor activity caused by CNS or autonomic injuries can results in dysfunctions of normal voiding of the bladder such as urinary incontinence. 2 The contractility of human detrusor smooth muscle is critically dependent on acetylcholine-induced muscarinic receptor activation. Biochemical and functional in vivo and in vitro studies suggest the presence of an heterogeneous population of muscarinic receptor subtypes (M1-M4) localized at muscular and neutral sites. There is increasing evidence on the prejunctional auto- and hetero-regulation of acetylcholine release from parasympathetic nerve endings in modulating detrusor muscle contraction during micturition. 3 Activation of P2X purinoreceptors closely associated with the parasympathetic varicosities seems to be implicated to varying extent in the contractility in normal or instable human detrusor. Interestingly, P2X(1) subtype expression on smooth muscle increases considerably in the symptomatically obstructed bladder. A striking absence of P2X(3) and P2X(5) subtypes was observed in the cholinergic innervation of detrusor from patients with urgent incontinence. Thus, it is likely that alteration of the neural acetylcholine control can play a critical role in pathological states. 4 If the failures in storage and voiding can be recognized urodynamically, considerable difficulties remain in investigating the underlying functional changes especially because the study of the pathophysiology requires techniques that can be justified in animals but not in humans. 5 Recently, to solve this problem an alternative technique using human smooth muscle cells in culture has been developed. Human cell lines may be relevant in investigating the molecular pathways in physiological and pathological conditions. 6 The potential development of novel molecular therapeutic strategies such as gene therapy and tissue engineering is also discussed.

Age-related changes in cholinergic and purinergic neurotransmission in human isolated bladder smooth muscles

We evaluated the correlation among age, cholinergic and purinergic neurotransmissions in the electrical field stimulation-induced contractions in human isolated urinary bladder smooth muscles, using the muscle bath technique. Human bladder specimens were divided into three groups (G1, under 50years; G2, 51-70years; G3, over 70years old), and each muscle strip was suspended in a thermostatically controlled organ bath filled with oxygenated Krebs-Henseleit solution, connected to an isometric force displacement transducer, and an isometric tension development was recorded. The contractile responses induced by KCl, carbachol, adenosine triphosphate (ATP) and electrical field stimulation, and the effects of atropine and alpha, beta methylene ATP on electrical field stimulation-induced contractions were observed. The contractile response to KCl and concentration-response curves for carbachol and ATP, and frequency-response curves for electrical field stimulation were not significantly different among the three groups. The atropine sensitive and resistant parts of contraction induced by electrical field stimulation were decreased and increased with age, respectively. There are significant positive and negative correlations between age and the purinergic, and age and the cholinergic neurotransmissions in human isolated bladder smooth muscles, respectively. The age-related changes in neurotransmissions may contribute to the changes in bladder function in the elderly.

P2X receptor expression in mouse urinary bladder and the requirement of P2X(1) receptors for functional P2X receptor responses in the mouse urinary bladder smooth muscle

1. We have used subtype selective P2X receptor antibodies to determine the expression of P2X(1 - 7) receptor subunits in the mouse urinary bladder. In addition we have compared P2X receptor mediated responses in normal and P2X(1) receptor deficient mice to determine the contribution of the P2X(1) receptor to the mouse bladder smooth muscle P2X receptor phenotype. 2. P2X(1) receptor immunoreactivity was restricted to smooth muscle of the bladder and arteries and was predominantly associated with the extracellular membrane. Diffuse P2X(2) and P2X(4) receptor immunoreactivity not associated with the extracellular membrane was detected in the smooth muscle and epithelial layers. Immunoreactivity for the P2X(7) receptor was associated with the innermost epithelial layers and some diffuse staining was seen in the smooth muscle layer. P2X(3), P2X(5) and P2X(6) receptor immunoreactivity was not detected. 3. P2X receptor mediated inward currents and contractions were abolished in bladder smooth muscle from P2X(1) receptor deficient mice. In normal bladder nerve stimulation evoked contractions with P2X and muscarinic acetylcholine (mACh) receptor mediated components. In bladder from the P2X(1) receptor deficient mouse the contraction was mediated solely by mACh receptors. Contractions to carbachol were unaffected in P2X(1) receptor deficient mice demonstrating that there had been no compensatory effect on mACh receptors. 4. These results indicate that homomeric P2X(1) receptors underlie the bladder smooth muscle P2X receptor phenotype and suggest that mouse bladder from P2X(1) receptor deficient and normal animals may be models of human bladder function in normal and diseased states.

Comparison of the effects of novel antimuscarinic drugs on human detrusor smooth muscle

OBJECTIVE

To evaluate the effects of tolterodine, vamicamide and temiverine, novel antimuscarinic drugs developed for the treatment of frequency and urinary incontinence, on human detrusor smooth muscle. Materials and methods Specimens of human urinary bladder were obtained from 20 patients who underwent total cystectomy for malignant bladder tumour. Using an organ-bath technique, the effects of various drugs on the contractions induced by carbachol, KCl, CaCl2 and electrical field stimulation in the detrusor strips were investigated.

RESULTS

Carbachol (0.001-10000 micromol/L) caused concentration-dependent contractions in human detrusor smooth muscles. Tolterodine (0.01-10 micromol/L), vamicamide (0.01-10 micromol/L), temiverine (0.01-1 micromol/L) and atropine (0.001-1 micromol/L) caused parallel shifts to the right of the concentration-response curves to carbachol. All slopes for the regression line of Schild plots were close to unity, and the rank order of pA2 values was atropine = tolterodine > vamicamide > temiverine. Tolterodine, vamicamide and atropine did not inhibit the maximum contractile responses to carbachol, while temiverine (10 micromol/L) significantly inhibited the maximum contractions. Tolterodine (0.001-1 micromol/L) and vamicamide (0.01-10 micromol/L) did not inhibit the KCl- (80 mmol/L) and CaCl2-induced (5 mmol/L) contractions, while temiverine (0.01-10 micromol/L) significantly inhibited the contractions. Electrical field stimulation (2-60 Hz) caused frequency-dependent contractions in human detrusor smooth muscles, which were significantly inhibited by various drugs. In the presence of 1 micromol/L atropine, tolterodine and vamicamide did not inhibit the contractions induced by electrical field stimulation at all frequencies, while temiverine (10 micromol/L) significantly inhibited the contractions.

CONCLUSION

Tolterodine and vamicamide inhibited contractions of human detrusor smooth muscles only through their antimuscarinic action, while temiverine had both antimuscarinic and calcium-antagonist actions. Furthermore, these novel drugs have different efficacies and potencies for inhibiting human detrusor smooth muscle.

Structural and functional denervation of human detrusor after spinal cord injury

The bladder receives an extensive nerve supply that is predominantly cholinergic, but several putative transmitters are present, some of which are colocalized. Previous studies have shown increased levels of sensory nerves, reduced inhibitory transmitters, and structural and functional changes in the excitatory input in unstable bladder conditions. The present study compared the end-organ nerve supply to the bladder in spinal cord injury (SCI) with uninjured controls. Acetylcholinesterase histochemistry and double-label immunofluorescence were used to investigate neurotransmitter content, with confocal laser scanning microscopy to assess colocalization. Organ bath studies provided functional correlates for the structural changes in the excitatory innervation. Control samples had dense innervation of the detrusor containing a diverse range of transmitters. Hyperreflexic SCI samples showed patchy denervation, and areflexic SCI samples were diffusely denervated. Vasoactive intestinal polypeptide-, neuropeptide Y-, neuronal nitric oxide synthase-, and galanin-immunoreactive nerve fibers were reduced from frequent or moderately frequent to infrequent or very infrequent in SCI. Calcitonin gene-related peptide-immunoreactive fibers were infrequent in controls and SCI samples. Patterns of colocalization were unchanged, but significantly fewer fibers expressed more than one transmitter. The subepithelial plexus was markedly reduced and several of the smaller coarse nerve trunks showed no immunoreactivity to the transmitters assessed. There was no reduction in sensitivity to electrical field stimulation of intrinsic nerves in SCI, but the maximum force generated by each milligram of bladder tissue and the peak force as a proportion of the maximum carbachol contraction were significantly reduced and the responses were protracted. There was no significant functional atropine-resistant neuromuscular transmission in controls or SCI. The reported findings have clinical implications in the management of chronic SCI and development of new treatments.

Pharmacological and molecular analysis of ATP-sensitive K(+) channels in the pig and human detrusor

The pharmacological and molecular properties of ATP-sensitive K(+) channels present in pig detrusor smooth muscle were investigated. In isolated pig detrusor strips, ATP-sensitive K(+) channel openers inhibited contractions elicited by low frequency field-stimulation in a concentration-dependent manner. The inhibitory effects of P1075 [N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine] were attenuated by glyburide with a pA(2) value of 7.38 (slope=1.08). The potency of the inhibitory effects of the K(+) channel openers on the field-stimulated contractions correlated well with those evoked by the muscarinic receptor agonist, carbachol (r=0.93) and furthermore, to relaxation of the pre-contracted (25 mM potassium chloride, KCl) human detrusor (r=0.95). Reverse transcriptase polymerase chain reaction (RT-PCR) analysis showed the presence of mRNA for sulfonylurea receptors SUR1 and SUR2B in both pig and human detrusor. Considering the similarities in the molecular and pharmacological profile of ATP-sensitive K(+) channels between the pig and the human detrusor, it is concluded that the pig detrusor may serve as a suitable in vitro model for the evaluation of novel K(+) channel openers with potential use in urological disorders in humans.

Simultaneous recording of mechanical and intracellular electrical activity in human urinary bladder smooth muscle

OBJECTIVE

To elucidate the role of the membrane potential in human detrusor smooth muscle contraction, by simultaneously recording mechanical and intracellular electrical activity in muscle strips. Materials and methods The agonists acetylcholine and carbachol were applied to induce a contraction on muscarinic receptor stimulation; to block the response, atropine was added to the bath. The Ca2+ necessary for activating the contractile machinery can be recruited via two pathways: release from intracellular stores or influx from the extracellular matrix. High potassium was applied to induce Ca2+ influx through voltage-sensitive Ca2+ channels.

RESULTS

There were significant changes in the force when agonist, antagonist and high potassium was administered. However, there were significant changes in membrane potential only when KCl was applied to the bath and not with muscarinic agonist or antagonist application. Activity in the form of spike potentials did not change significantly on applying any of the test substances.

CONCLUSION

The present results indicate that the Ca2+ mobilized on M3 receptor stimulation originates primarily from intracellular stores, with no systematic changes in membrane potential. Atropine only caused a relaxation in muscle previously contracted by M3-receptor agonist stimulation; it had no effect on relaxed muscle strips.