The effects and selectivity of beta-adrenoceptor agonists in rat myometrium and urinary bladder

Antagonism of α1-adrenoceptors by β3-adrenergic agonists: Structure-function relations of different agonists in prostate smooth muscle contraction

Effects of β₃-adrenergic agonists on prostate smooth muscle contraction are poorly characterized, although mirabegron is used for treatment of lower urinary tract symptoms. Off-target effects of several β₃-adrenergic agonists include antagonism of α₁-adrenoceptors. Proposed, but unconfirmed explanations include phenylethanolamine backbones, found in some β₃-adrenergic agonists and imparting interaction with catecholamine binding pockets of adrenoceptors. Here, we examined effects of β₃-adrenergic agonists on contractions of human prostate tissues, including ZD7114 (without phenylethanolamine moiety), ZD2079 (phenylethanolamine backbone), BRL37344 and CL316243 (chloride-substituted phenylethanolamine deriatives). Prostate tissues were obtained from radical prostatectomy. Contractions by α₁-adrenergic agonists and electric field stimulation (EFS) were studied in an organ bath. ZD7114 (10 µM) right-shifted concentration responses curves for α₁-adrenergic agonists, resulting in increased EC₅₀ values for phenylephrine, methoxamine and noradrenaline up to one magnitude, without affecting E_max values. ZD7114 (10 µM) inhibited EFS-induced contractions, resulting in reduced E_max values. All effects of ZD7114 were resistant to the β₃-adrenergic antagonist L-748337, including increases in EC₅₀ values for α₁-adrenergic agonists, up to more than two magnitudes. Using 10 µM, neither ZD2079, BRL37344 or CL316243 affected α₁-adrenergic or EFS-induced contractions. At escalated concentrations, BRL37344 (200 µM) right-shifted concentration response curves for phenylephrine, increased EC₅₀ values for phenylephrine, and inhibited EFS-induced contractions, while CL316243 (300 µM) did not affect phenylephrine- or EFS-induced contractions. In conclusion, phenylethanolamine backbones are not decisive to impart α₁-adrenoceptor antagonism to β₃-agonists. Effects of β₃-adrenergic agonists on prostate smooth muscle contraction are limited to off-target effects, including α₁-adrenoceptor antagonism by ZD7114 and BRL37344.

EFFECT OF PEPTIDOGLYCANE OF STAPHYLOCOCCUS AUREUS CELL WALL ON THE MECHANISM OF REGULATION OF CONTRACTILE ACTIVITY OF RAT MYOMETRIUM BY ADENYLATE CYCLASE SYSTEM

The revue deals with the role of each component of adenylate cyclase regulatory system in the rat myometrial contractile activity modulation by the peptidoglycane of Staphylococcus aureus. Noradrenalin and salbutamol were used to investigate peptidoglycane impact on the myometrial β-adrenergic receptors. It was shown that inhibited by these substances myometrial contractility increased to the initial level after peptidoglycane application. The same effect we observed under the cAMP level elevation by forscolin. Peptidoglycan’ s ability to strengthen contractions was inhibited by the 8-brom-cAMP and papaverine application. Stimulation of Gs-protein by the cholera toxin didn’t influence on the peptidoglycane effect while the blocking of Gi/o-protein by the pertussis toxin caused stopping it’s manifestation. We concluded that the modulating effect of peptidoglycane implemented via Gi/o-protein activation, which causes adenilatcyclase desensitization.

Effect of Suo Quan Wan on the bladder function of aging rats based on the β-adrenoceptor

Suo Quan Wan (SQW) has been used to treat lower urinary tract symptoms (LUTS) in elderly patients for hundreds of years in China. β-adrenoceptors (β-ARs), particularly β₃-adrenoceptor (β₃-AR), was reported to be important in the bladder dysfunction of the elderly. The present study was conducted to explore the effect of β-AR, and particularly the β₃-adrenoceptor, in aging rat bladder function in vitro and to test the therapeutic effect of SQW on LUTS in an aging rat model based on the β₃-adrenoceptor. Briefly, the bladder detrusor muscles of young (age, 3 months) and aging (age, 15 months) female rats were separated. A β-AR non-selective agonist, isoprenaline (ISO), subtype β₃-AR agonist (BRL37344A) and β₃-AR antagonist (SR59230A) were used to define the tension change of detrusor muscles between young and aging rats in vitro. For blank controls, 12 young rats were marked, and 48 aging female rats were randomly divided into four groups as follows: Model, SQW high, SQW middle and SQW low. Following oral administration of SQW for 6 weeks in aging rats, urodynamic and bladder detrusor tests were used to evaluate the therapeutic effect of SQW. The expression of β₃-AR mRNA was investigated using reverse transcription-quantitative polymerase chain reaction. Using ISO and BRL37344A in vitro, maximum relaxation (E_max), intrinsic activity (IA), and log (50% effective concentration) (PD₂) were significantly decreased in aging rats compared with that in young rats (P<0.05). Significant changes were also observed in the β₃-AR antagonist experiment, which blocked ISO-induced relaxation, with significant decreases observed in E_max, IA and PD₂, and a significant increase observed in PA₂ for the aging rats compared with the young controls (P<0.05). SQW was demonstrated to enhance bladder control, storage and contraction ability. Furthermore, SQW was able to increase the sensitivity and expression of β₃-AR in an aging rat. In conclusion, the decrease in β₃-AR sensitivity in aging rats and the expression resulted in bladder detrusor dysfunction. In addition, the therapeutic effect of SQW against LUTS relies on the former's effect on the urethral sphincter, bladder detrusor and β₃-AR.

β- and β-adrenergic receptors stimulation relaxes porcine myometrium in the peri-implantation period

These studies were to demonstrate whether the β-receptor is involved in regulating the contractility of the swine myometrium in the peri-implantation period and to compare a relaxing activity of selective β- and β-adrenergic agonists (salbutamol and BRL 37344, respectively). Myometrial strips were collected form the gilts ( = 8) on d 12 to 14 of pregnancy. Changes in the contractility of myometrial strips were assessed further to the administration of increasing concentrations of the agonists (10 to 10 ) with and without β-adrenergic receptor antagonists: butoxamine, propranolol, and bupranolol at 10 . Moreover, the -log EC (pD) of the agonists were compared. Following the incubation of myometrial strips with salbutamol and BRL 37344, a significant ( < 0.05 to 0.001) reduction in the contractility, seen as decreased tension, amplitude, and frequency of contractions, as compared to the pretreatment period was noted, although salbutamol induced these changes at a concentration of 10 to 10 , whereas BRL 37344 induced them at 10 to 10 . Salbutamol exerted a significantly ( < 0.001) more potent reduction of the tension (pD = 6.98 ± 0.93 [SD]) than BRL 37344 (pD = 3.41 ± 0.1.61). The impact of salbutamol was neutralized by all administered antagonists, while a relaxing effect of BRL 37344 was completely inhibited by bupranolol and partially by propranolol. The data indicate that the β-adenergic receptor is involved in the regulation of smooth muscle contractility in the swine uterus in the peri-implantation period and its activation triggers relaxation of the myometrium to a lesser degree than the activation of the β-adrenergic receptor.

β-Adrenoceptor-mediated Relaxation of Urinary Bladder Muscle in β2-Adrenoceptor Knockout Mice

Background and Objective: In order to characterize the β-adrenoceptor (AR) subtypes involved in agonist-stimulated relaxation of murine urinary bladder we studied the effects of (-)-isoprenaline and CL 316,243 on tonic contraction and spontaneous contractions in detrusor strips of wild-type (WT) and β₂-AR knockout (β₂-AR KO) mice.

Materials and Methods: Urinary bladders were isolated from male WT and β₂-AR KO mice. β-AR subtype expression was determined with quantitative real-time PCR. Intact muscle strips pre-contracted with KCl (40 mM) were exposed to cumulatively increasing concentrations of (-)-isoprenaline or β₃-AR agonist CL 316,243 in the presence and absence of the subtype-selective β-AR blockers CGP 20712A (β₁-ARs), ICI 118,551 (β₂-ARs), and L748,337 (β₃-ARs).

Results: Quantitative real-time PCR confirmed lack of β₂-AR expression in bladder tissue from β₂-AR KO mice. In isolated detrusor strips, pre-contraction with KCl increased basal tone and enhanced spontaneous activity significantly more in β₂-AR KO than in WT. (-)-Isoprenaline relaxed tonic tension and attenuated spontaneous activity with similar potency, but the concentrations required were two orders of magnitude higher in β₂-AR KO than WT. The concentration-response curves (CRCs) for relaxation were not affected by CGP 20712A (300 nM), but were shifted to the right by ICI 118,551 (50 nM) and L748,337 (10 μM). The -logEC₅₀ values for (-)-isoprenaline in WT and β₂-AR KO tissue were 7.98 and 6.00, respectively, suggesting a large receptor reserve of β₂-AR. (-)-CL 316,243 relaxed detrusor and attenuated spontaneous contractions from WT and β₂-AR KO mice with a potency corresponding to the drug’s affinity for β₃-AR. L743,337 shifted the CRCs to the right.

Conclusion: Our findings in β₂-AR KO mice suggest that there is a large receptor reserve for β₂-AR in WT mice so that this β-AR subtype will mediate relaxation of tone and attenuation of spontaneous activity under physiological conditions. Nevertheless, upon removal of this reserve, β₃-AR can also mediate murine detrusor relaxation.

Effect of β3 adrenoceptor activation in the basolateral amygdala on ethanol seeking behaviors

RATIONALE

The interaction between ethanol (EtOH) and anxiety plays an integral role in the development and maintenance of alcoholism. Many medications in pre-clinical or clinical trials for the treatment of alcoholism share anxiolytic properties. However, these drugs typically have untoward side effects, such as sedation or impairment of motor function that may limit their clinical use. We have recently demonstrated that BRL 37344 (BRL), a selective β3-adrenoceptor (AR) agonist, enhances a discrete population of GABAergic synapses in the basolateral amygdala (BLA) that mediates feed-forward inhibition from lateral paracapsular (LPC) GABAergic interneurons onto BLA pyramidal cells. Behavioral studies revealed that intra-BLA infusion of BRL significantly reduced measures of unconditioned anxiety-like behavior without locomotor depressant effects.

OBJECTIVES

The present studies tested the effect of BRL (0.1, 0.5, or 1.0 μg/side) on EtOH self-administration using an intermittent access home cage two-bottle choice procedure and limited access operant responding for EtOH or sucrose.

RESULTS

Intra-BLA infusion of BRL did not reduce home cage, intermittent EtOH self-administration. However, using an operant procedure that permits the discrete assessment of appetitive (seeking) and consummatory measures of EtOH self-administration, BRL reduced measures of EtOH and sucrose seeking, but selectively reduced operant responding for EtOH during extinction probe trials. BRL had no effect on consummatory behaviors for EtOH or sucrose.

CONCLUSIONS

Together, these data suggest that intra-BLA infusion of BRL significantly reduces motivation to seek EtOH and provide initial evidence that β3-ARs and LPC GABAergic synapses may represent promising targets for the development of novel pharmacotherapies for the treatment of alcoholism.

Modulation of nerve-evoked contractions by β3-adrenoceptor agonism in human and rat isolated urinary bladder

Activation of β3-adrenoceptors has been shown to have a direct relaxant effect on urinary bladder smooth muscle from both rats and humans, however there are very few studies investigating the effects of β3-adrenoceptor agonists on nerve-evoked bladder contractions. Therefore in the current study, the role of β3-adrenoceptors in modulating efferent neurotransmission was evaluated. The effects of β3-adrenoceptor agonism on neurogenic contractions induced by electrical field stimulation (EFS) were compared with effects on contractions induced by exogenous acetylcholine (Ach) and αβ-methylene adenosine triphosphate (αβ-meATP) in order to determine the site of action. Isoproterenol inhibited EFS-induced neurogenic contractions of human bladder (pD2=6.79; Emax=65%). The effect of isoproterenol was selectively inhibited by the β3-adrenoceptor antagonist L-748,337 (pKB=7.34). Contractions induced by exogenous Ach (0.5-1μM) were inhibited 25% by isoproterenol (3μM) while contractions to 10Hz in the same strip were inhibited 67%. The selective β3-adrenoceptor agonist CL-316,243 inhibited EFS-induced neurogenic contractions of rat bladder (pD2=7.83; Emax=65%). The effects of CL-316,243 were inhibited in a concentration dependent manner by L-748,337 (pA2=6.42). Contractions induced by exogenous Ach and αβ-meATP were significantly inhibited by CL-316,243, 29% and 40%, respectively. These results demonstrate that the activation of β3-adrenoceptors inhibits neurogenic contractions of both rat and human urinary bladder. Contractions induced by exogenously applied parasympathetic neurotransmitters are also inhibited by β3-agonism however the effect is clearly less than on neurogenic contractions (particularly in human), suggesting that in addition to a direct effect on smooth muscle, activation of prejunctional β3-adrenoceptors may inhibit neurotransmitter release.

Cardioprotective effect of beta-3 adrenergic receptor agonism: role of neuronal nitric oxide synthase

OBJECTIVES

The aim of this study was to determine whether activation of β3-adrenergic receptor (AR) and downstream signaling of nitric oxide synthase (NOS) isoforms protects the heart from failure and hypertrophy induced by pressure overload.

BACKGROUND

β3-AR and its downstream signaling pathways are recognized as novel modulators of heart function. Unlike β1- and β2-ARs, β3-ARs are stimulated at high catecholamine concentrations and induce negative inotropic effects, serving as a "brake" to protect the heart from catecholamine overstimulation.

METHODS

C57BL/6J and neuronal NOS (nNOS) knockout mice were assigned to receive transverse aortic constriction (TAC), BRL37344 (β3 agonist, BRL 0.1 mg/kg/h), or both.

RESULTS

Three weeks of BRL treatment in wild-type mice attenuated left ventricular dilation and systolic dysfunction, and partially reduced cardiac hypertrophy induced by TAC. This effect was associated with increased nitric oxide production and superoxide suppression. TAC decreased endothelial NOS (eNOS) dimerization, indicating eNOS uncoupling, which was not reversed by BRL treatment. However, nNOS protein expression was up-regulated 2-fold by BRL, and the suppressive effect of BRL on superoxide generation was abrogated by acute nNOS inhibition. Furthermore, BRL cardioprotective effects were actually detrimental in nNOS(-/-) mice.

CONCLUSIONS

These results are the first to show in vivo cardioprotective effects of β3-AR-specific agonism in pressure overload hypertrophy and heart failure, and support nNOS as the primary downstream NOS isoform in maintaining NO and reactive oxygen species balance in the failing heart.

Fenoterol functionally activates the β₃-adrenoceptor in human urinary bladder, comparison with rat and mouse: implications for drug discovery

Fenoterol has been reported to be a potent and selective β(2)-adrenoceptor agonist and is currently used clinically to treat asthma. Electrical field stimulation (EFS) of isolated urinary bladder mimics the voiding contraction by stimulating parasympathetic nerves, resulting in neurogenic contractions. To determine if stimulation of β(2)-adrenoceptors can inhibit this response, fenoterol was tested against EFS-induced contractions in human isolated urinary bladder and compared with mouse and rat. Bladder strips were mounted in organ baths and reproducible contractions induced by EFS. Fenoterol was added cumulatively in the presence of the β(2)-adrenoceptor antagonist ICI118551 or the β(3)-adrenoceptor antagonist L-748337. Fenoterol inhibited neurogenic contractions in all three species in a concentration-dependent manner with pEC(50) values of 6.66 ± 0.11, 6.86 ± 0.06 and 5.71 ± 0.1 in human, mouse and rat respectively. In human bladder strips ICI118551 (100 nM) did not affect responses to fenoterol, while L-748337 (0.3-3 μM) produced rightward shifts of the concentration-response curves with a pA(2) value of 8.10. In mouse bladder strips ICI118551 (30 nM) blocked the inhibitory effect of fenoterol (pA(2)=8.80), while L-748337 (10 μM) inhibited the response with a pA(2) of 5.79. In rat bladder ICI118551 (30 nM) was without effect, while L-748,337 (10 μM) inhibited the response to fenoterol with a pA(2) of 5.40. From these results it is clear that fenoterol potently activates β(3)-adrenoceptors in human isolated urinary bladder to inhibit EFS-induced contractions. Fenoterol also activates β(3)-adrenoceptors in rat, but β(2)-adrenoceptors in mouse bladder to inhibit EFS-induced contractions.

Effects and selectivity of CL 316243, beta-3-adrenoceptor agonist, in term-pregnant rat myometrium

BACKGROUND/AIMS

Recent evidence supports a predominant role of β(3)-adrenoceptors at the end of pregnancy in myometrium. This study was designed to characterize the pharmacology of the selective β(3)-adrenoceptor agonist CL 316243 on oxytocin-induced myometrial contractions and the levels of cAMP and cGMP of myometrial strips isolated from term-pregnant rats.

METHODS

Myometrial strips were obtained from term-pregnant Wistar albino rats (n = 10), mounted in organ baths and tested for changes in isometric tension in response to CL 316243 (10(-10)-10(-5) M) on oxytocin-induced myometrial contractions. Effects of CL 316243 on cAMP and cGMP levels in isolated myometrial strips (n = 8) were evaluated by radioimmunoassay kits. We evaluated the effect of increasing concentrations of CL 316243 on myometrial contractions and on contractions of myometrial smooth muscle pretreated with metoprolol, ICI 118.551 and SR 59230A (β(1)-, β(2)-, β(3)-adrenoceptor antagonists, respectively, 10(-6) M).

RESULTS

The inhibition of the amplitude of oxytocin-induced contractions by CL 316243 were antagonized with SR 59230A (10(-6) M), but they were not changed by metoprolol (10(-6) M) or ICI 118.551 (10(-6) M). CL 316243 increased cAMP levels compared to the control group. CL 316243 increased cGMP levels, in the CL 316243 group more than in the control group, but this increase is less significant than cAMP levels.

CONCLUSION

These results demonstrate that the inhibition of rat myometrial contractions with CL 316243 is mediated by β(3)-adrenoceptor subtype and increased cAMP and cGMP levels.

Hyperthyroidism and female urinary incontinence: a population-based cohort study

OBJECTIVE

The imbalanced autonomic nervous system present in hyperthyroidism may cause lower urinary tract symptoms. Urinary incontinence (UI) is the most bothersome lower urinary tract symptom; however, in the literature, reports regarding urinary dysfunction and/or incontinence among hyperthyroid patients are scarce. This population-based cohort study aimed to examine the relationship between hyperthyroidism in women and the risk of developing UI in Taiwan.

DESIGN

This study used data from the Longitudinal Health Insurance Database. For this study, 10,817 female patients diagnosed with hyperthyroidism from 2001 to 2005 were recruited together with a comparison cohort of 54,085 matched enrollees who did not have a history of hyperthyroidism. All patients were tracked for a 3-year period from their index date to identify those who had a subsequent UI. The stratified Cox proportional hazards models were used to compute the risk of UI between study and comparison cohorts.

RESULTS

During the follow-up period, of 64,169 patients, 173 (1·60%) from the hyperthyroidism group and 560 (1·04%) from the comparison group, had a diagnosis of UI. The regression analysis showed that, after adjusting for monthly income, geographic region, urbanization level of the community in which the patient resided, obesity and hysterectomy, patients with hyperthyroidism were more likely to have UI during the 3-year follow-up period than the comparison patients (hazard ratio = 1·54; 95% CI = 1·30-1·83; P < 0·001).

CONCLUSION

Our results suggest an increased risk of UI in patients with hyperthyroidism at the 3-year follow-up.

Enhanced sensitivity to afferent stimulation and impact of overactive bladder therapies in the conscious, spontaneously hypertensive rat

The spontaneously hypertensive rat (SHR) has been proposed as an overactive bladder model, driven, at least partially, by alterations in bladder innervation. To assess the functional role of sensory bladder afferents we evaluated the conscious cystometric response to prostaglandin E(2) (PGE(2)) or acetic acid (AA) bladder infusion. SHR demonstrated a hypersensitivity to PGE(2) and AA, as indicated by a greater reduction in both void volume (VV) and micturition interval (MI) compared with Sprague-Dawley controls. The heightened PGE(2) and AA responses in the SHR were inhibited by capsaicin desensitization, supporting a role for bladder afferents in facilitating the hypersensitivity. Furthermore, we characterized the SHR pharmacologically using overactive bladder therapeutic agents. In the SHR, both darifenacin and oxybutynin (M(3)-selective and nonselective muscarinic antagonists, respectively) reduced micturition pressure (MP) and functional bladder capacity (VV and MI). In sharp contrast, functional bladder capacity was significantly enhanced by β(3)-adrenoceptor agonism [5-[(2R)-2-[[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino]propyl]-1,3-benzodioxole-2,2-dicarboxylate (CL316243)], and by gabapentin, without effect on MP. These data provide the first functional evidence for hypersensitive bladder afferents in the SHR and provide a pharmacological benchmark in this model for overactive bladder therapeutics. These data also support the idea that β(3)-adrenoceptor agonism and gabapentin may provide a more effective overactive bladder therapy than muscarinic antagonism.

β(2)-Adrenergic activity of 6-methoxykaempferol-3-O-glucoside on rat uterus: in vitro and in silico studies

6-Methoxykaempferol-3-O-glucoside (6-MKG) was isolated from a Sudanese herb (El-hazha). The pharmacological effects of 6-MKG were tested on isolated non-pregnant or late-pregnant rat uteri in vitro, whilst docking studies were carried out modelling of the binding of 6-MKG to the rat β(2)-adrenoceptor in silico. In vitro studies revealed that 6-MKG was able to relax both the non-pregnant and the late-pregnant uterine contractility with 50% of the E(max) of terbutaline, whilst the EC(50) for 6-MKG was at least half than that of terbutaline. The β(2)-adrenoceptors antagonist 3-(isopropylamino)-1-[(7-methyl-4-indanyl)oxy]butan-2-ol(ICI118,551) competitively antagonised the relaxing effect of 6-MKG. Radioligand binding and cAMP studies confirmed the β(2)-adrenoceptors agonistic property of the compound. In in silico docking studies, 6-MKG bound to rat β(2)-adrenoceptors with low ∆G(bind) value (-11.53±0.06 kcal/mol) and it interacted with four residues of the active site (Asp(113), Asn(312), Cys(191)and Tyr(316)). It is concluded that 6-MKG exerts weak β(2)-adrenoceptor agonistic activity and can be considered a natural compound with potential therapeutic significance in the field of premature pregnant uterine contractions and asthmatic problems.

Progesterone decreases the relaxing effect of the beta3-adrenergic receptor agonist BRL 37344 in the pregnant rat myometrium

Although the published results regarding the function of the beta(3)-adrenergic receptors (beta(3)-ARs) in the regulation of smooth muscle activity are very promising, the question of the mechanism of beta(3)-ARs' action in the pregnant myometrium cannot be fully answered by human investigations. To assess whether it possesses an essential role in the regulation of uterine contractility in pregnant rats, as in humans, we performed functional, western blotting and molecular biology experiments on the late-pregnant rat myometrium. The influence of progesterone on the function of the beta(3)-ARs was also investigated. We demonstrated the presence and the functional activity of the beta(3)-ARs in the late-pregnant rat myometrium. The maximum dose-dependent uterus-relaxing effect of the selective beta(3)-agonist BRL 37344 was recorded at the end of pregnancy in rats, similarly as in humans. The extent of its relaxing action was regarded as moderate. The expression of beta(3)-AR protein and mRNA remained unchanged during the investigated period. The administration of progesterone had no effect on the beta(3)-AR mRNA and protein expression or the maximum relaxation effect of BRL 37344, but shifted the dose-response curve to the right and decreased the synthesis of the second messenger, cAMP. It can be concluded that the beta(3)-ARs play an additional role in the regulation of the contractile activity of the pregnant rat uterus. The inhibitory effect of progesterone on the functional activity of the beta(3)-ARs may have important consequences in the case of human application if this effect is also demonstrated in pregnant human myometrial tissue.

Stimulation of beta3-adrenoceptors relaxes rat urinary bladder smooth muscle via activation of the large-conductance Ca2+-activated K+ channels

We investigated the role of large-conductance Ca(2+)-activated K(+) (BK) channels in beta3-adrenoceptor (beta3-AR)-induced relaxation in rat urinary bladder smooth muscle (UBSM). BRL 37344, a specific beta3-AR agonist, inhibits spontaneous contractions of isolated UBSM strips. SR59230A, a specific beta3-AR antagonist, and H89, a PKA inhibitor, reduced the inhibitory effect of BRL 37344. Iberiotoxin, a specific BK channel inhibitor, shifts the BRL 37344 concentration response curves for contraction amplitude, net muscle force, and tone to the right. Freshly dispersed UBSM cells and the perforated mode of the patch-clamp technique were used to determine further the role of beta3-AR stimulation by BRL 37344 on BK channel activity. BRL 37344 increased spontaneous, transient, outward BK current (STOC) frequency by 46.0 +/- 20.1%. In whole cell mode at a holding potential of V(h) = 0 mV, the single BK channel amplitude was 5.17 +/- 0.28 pA, whereas in the presence of BRL 37344, it was 5.55 +/- 0.41 pA. The BK channel open probability was also unchanged. In the presence of ryanodine and nifedipine, the current-voltage relationship in response to depolarization steps in the presence and absence of BRL 37344 was identical. In current-clamp mode, BRL 37344 caused membrane potential hyperpolarization from -26.1 +/- 2.1 mV (control) to -29.0 +/- 2.2 mV. The BRL 37344-induced hyperpolarization was eliminated by application of iberiotoxin, tetraethylammonium or ryanodine. The data indicate that stimulation of beta3-AR relaxes rat UBSM by increasing the BK channel STOC frequency, which causes membrane hyperpolarization and thus relaxation.

New insights into the pharmacology of the bladder

PURPOSE OF REVIEW

Pharmacotherapy of a number of bladder disorders has traditionally focused on targeting the 'sensory' component or bladder nerves and the smooth muscle. This review aims to provide an insight into recent (experimental and clinical) developments in mechanisms of existing therapies as well as novel targets.

RECENT FINDINGS

Traditionally, sensory signaling in the urinary bladder has been attributed to activation of bladder afferents, but new findings have pointed to the urothelium and interstitial cells as key participants in the transduction of sensory events. Recent advances provide strong support for the development of subtype selective receptor agonists/antagonists, the modulation of signal transduction cascades and new and expanded uses for various neurotoxins.

SUMMARY

The development of therapeutic options for the treatment of a number of bladder disorders is complicated, and most treatments are associated with an increased incidence of side effects or lack of specificity. Recent studies suggest that selective targeting of receptors/ion channels or a disease-specific (i.e. phosphorylated) form of the receptor may represent a viable therapeutic target. Though the mechanisms regulating ion channel expression under pathological conditions are not fully known, an increased understanding of these pathways has important implications for drug development.