Gap junction channel activity in cultured human bladder smooth muscle cell pairs: gating and unitary conductances

[Physiopathology of overactive bladder syndrome]

The pathophysiology of OAB is complex, multifactorial and still largely unknown. Several pathophysiological mechanisms have been highlighted that may play a different role in different patient groups. There are now experimental evidences that support both the myogenic and neurogenic hypothesis, but in recent years the "integrative" hypothesis has been gaining more and more acceptance, where a disruption in the multiple interactions between different cell types (neurons, urothelium, interstitial cells, myocytes) and network functions represent a central element of lower urinary tract dysfunctions. Of utmost importance, a disorder in the urothelial sensory function and in the urothelial/suburothelial non-neural cholinergic system, favored by age and comorbidities, appears to be crucial for the development of the OAB. Neuroplastic and detrusor changes in OAB are broadly similar to those observed in bladders exposed to outlet obstruction, neuropathies, inflammation or aging, and may be driven by a common urothelial dysfunction. Several signaling substances and their receptors were found to be involved in central pathways of bidirectional communication between the different cell types in the bladder, and were shown to be modified in several animal models of OAB as well as in human models, indicating new potential therapeutic targets.

Overactive bladder in males

The prevalence of overactive bladder (OAB) symptoms is considerable in both men and women and the impact on quality of life (QOL) is equally substantial. Ironically, despite nearly equal prevalence, OAB symptoms in men are infrequently treated, and often with medical therapies aimed at bladder outlet obstruction (BOO). In this review, we examine the pathophysiology of OAB and its evaluation in the context of benign prostatic hypertrophy and concomitant BOO. We then consider the efficacy and safety of individual therapeutic options for lower urinary tract symptoms in men, focusing on the mainstays of medical therapy: α-adrenergic blockers, 5-α reductase inhibitors, and antimuscarinic agents. Finally, we aim to comment on new therapeutic strategies and targets that may one day be available for the treatment of male OAB.

Treatment-resistant detrusor overactivity--underlying pharmacology and potential mechanisms

Bladder function during filling and micturition is regulated by peripheral and central nervous and hormonal control systems. Micturition occurs in response to afferent signals from the lower urinary tract, and distention of the bladder wall is the primary stimulus. In the animal and human bladder, efferent adrenergic, cholinergic and nonadrenergic, noncholinergic (NANC) neurotransmission has been demonstrated. The most important receptors for activation of contraction are muscarinic (M3) and purinergic receptors (P2X1), however, the contribution of these receptors to contraction may differ between species, and may be changed in bladder dysfunction associated with detrusor overactivity (DO) and/or the overactive bladder (OAB) syndrome, such as outflow obstruction, neurogenic bladders, idiopathic DO and diabetes. The NANC component of the nerve-induced response in such disorders may be responsible for up to 40-50% of the total bladder contraction. Whether this in vitro'atropine-resistance' corresponds to DO/OAB seen in patients not responding to antimuscarinic treatment is not known. Afferent signalling from the urothelium may be involved in both normal bladder function and in DO/OAB, but its role in antimuscarinic-refractory patients remains to be established. Several central nervous system (CNS) transmitters/transmitter systems, including gamma aminobutyric acid (GABA), opioid, serotonin, noradrenaline, dopamine or glutamatergic receptors and mechanisms are known to be involved in micturition control. The contribution of these receptors and mechanisms in DO/OAB resistant to treatment with antimuscarinics is not known, but drugs acting at these sites may offer future treatment possibilities.

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.

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.