Involvement of Rho kinase and protein kinase C in carbachol-induced calcium sensitization in beta-escin skinned rat and guinea-pig bladders

The role of rhoA/rho-kinase and PKC in the inhibitory effect of L-cysteine/H2S pathway on the carbachol-mediated contraction of mouse bladder smooth muscle

We investigated the role of RhoA/Rho-kinase (ROCK) and PKC in the inhibitory effect of L-cysteine/hydrogen sulfide (H2S) pathway on the carbachol-mediated contraction of mouse bladder smooth muscle. Carbachol (10-8-10-4 M) induced a concentration-dependent contraction in bladder tissues. L-cysteine (H2S precursor; 10-2 M) and exogenous H2S (NaHS; 10-3 M) reduced the contractions evoked by carbachol by ~ 49 and ~ 53%, respectively, relative to control. The inhibitory effect of L-cysteine on contractions to carbachol was reversed by 10-2 M PAG (~ 40%) and 10-3 M AOAA (~ 55%), cystathionine-gamma-lyase (CSE) and cystathionine-β-synthase (CBS) inhibitor, respectively. Y-27632 (10-6 M) and GF 109203X (10-6 M), a specific ROCK and PKC inhibitor, respectively, reduced contractions evoked by carbachol (~ 18 and ~ 24% respectively), and the inhibitory effect of Y-27632 and GF 109203X on contractions was reversed by PAG (~ 29 and ~ 19%, respectively) but not by AOAA. Also, Y-27632 and GF 109203X reduced the inhibitory responses of L-cysteine on the carbachol-induced contractions (~ 38 and ~ 52% respectively), and PAG abolished the inhibitory effect of L-cysteine on the contractions in the presence of Y-27632 (~ 38%). Also, the protein expressions of CSE, CBS, and 3-MST enzymes responsible for endogenous H2S synthesis were detected by Western blot method. H2S level was increased by L-cysteine, Y-27632, and GF 109203X (from 0.12 ± 0.02 to 0.47 ± 0.13, 0.26 ± 0.03, and 0.23 ± 0.06 nmol/mg respectively), and this augmentation in H2S level decreased with PAG (0.17 ± 0.02, 0.15 ± 0.03, and 0.07 ± 0.04 nmol/mg respectively). Furthermore, L-cysteine and NaHS reduced carbachol-induced ROCK-1, pMYPT1, and pMLC20 levels. Inhibitory effects of L-cysteine on ROCK-1, pMYPT1, and pMLC20 levels, but not of NaHS, were reversed by PAG. These results suggest that there is an interaction between L-cysteine/H2S and RhoA/ROCK pathway via inhibition of ROCK-1, pMYPT1, and pMLC20, and the inhibition of RhoA/ROCK and/or PKC signal pathway may be mediated by the CSE-generated H2S in mouse bladder.

Determination of the roles of cADPR and NAADP as intracellular calcium mobilizing messengers in S1P-induced contractions in rat bladders having IC/PBS

AIMS

Interstitial cystitis/painful bladder syndrome (IC/PBS) is characterized by lower abdominal pain and increased frequency and urgency of urine. Sphingosine 1-phosphate (S1P) is a bioactive sphingolipid that plays role in calcium homeostasis in smooth muscle. The intracellular calcium mobilizing secondary messengers are also involved in smooth muscle contraction. The role of intracellular calcium storing depots in S1P-induced contraction was investigated in permeabilized detrusor smooth muscle having cystitis.

MAIN METHODS

IC/PBS was induced by cyclophosphamide injection. The detrusor smooth muscle strips isolated from rats were permeabilized with β-escin.

KEY FINDINGS

S1P-induced contraction was increased in cystitis. S1P-induced enhanced contraction was inhibited by cyclopiazonic acid, ryanodine and heparin showing involvement of sarcoplasmic reticulum (SR) calcium stores. Inhibition of S1P-induced contraction by bafilomycin and NAADP suggested the participation of lysosome-related organelles.

SIGNIFICANCE

IC/PBS triggers S1P-induced increase in intracellular calcium from SR and lysosome-related organelles in permeabilized detrusor smooth muscle.

Pharmacological characterization of DA-8010, a novel muscarinic receptor antagonist selective for urinary bladder over salivary gland

Several antimuscarinics have been commonly used for overactive bladder patients, but dry mouth as a major anticholinergic side effect remains a shortcoming to limit long-term use. The aim of this study was to elucidate the pharmacological properties of DA-8010, a novel muscarinic receptor antagonist selective for urinary bladder over salivary gland. DA-8010 exhibited a high binding affinity for human muscarinic M₃ receptor with pK_i of 8.81 ± 0.05 and great potencies for human M₃ receptor and rat bladder preparation. The potency of DA-8010 for bladder smooth muscle cells was 3.6-fold higher than that for salivary gland cells isolated from mice. Intravenous administration of DA-8010 dose-dependently inhibited rhythmic urinary bladder contractions induced by distension in rats, indicating the most potent activity (ID₃₀ = 0.08 mg/kg) among the antimuscarinics tested. Taken together with the inhibitory effects of DA-8010 and other antimuscarinics on carbachol-induced salivary secretion in rats, the in vivo functional selectivity of DA-8010 for urinary bladder over salivary gland was 3.1-fold, 3.2-fold and 5.2-fold greater than those observed for solifenacin, oxybutynin and darifenacin, respectively. Furthermore, oral administration of DA-8010 in mice resulted in more selective and persistent binding for muscarinic receptors in the bladder rather than in the submaxillary gland, in comparison with other antimuscarinics. These findings suggest that DA-8010 is a potent muscarinic M₃ receptor antagonist to be highly selective for bladder over salivary gland, which might be a promising agent with greater efficacy and less dry mouth in the treatment of overactive bladder.

Mirabegron induces relaxant effects via cAMP signaling-dependent and -independent pathways in detrusor smooth muscle

OBJECTIVE

We previously found that mirabegron exerts a relaxant effect in the presence of the β₃ -adrenoceptor antagonist SR58894A during carbachol-induced contraction in human and pig detrusor. The aim of this study was to explore the possible mechanism underlying the relaxant effects of mirabegron using detrusor smooth muscle.

METHODS

Human tissue was obtained from urinary bladders of patients undergoing radical cystectomy at Kyushu University and Harasanshin Hospital. Pig tissue was obtained from an abattoir. Tension force (organ bath experiments) was measured in intact or permeabilised (α-toxin or β-escin) detrusor smooth muscle strips. The contribution of cAMP-dependent signaling and the inhibition of Ca²⁺ sensitization to the relaxant effects of mirabegron were characterized using 1 μM SR58894A, 100 μM SQ22536 (an adenylyl cyclase inhibitor), 10 μM H-89 (a protein kinase [PK] A inhibitor), 10 μM Y-27632 (a selective Rho kinase inhibitor), and 10 μM GF-109203X (a selective PKC inhibitor).

RESULTS

30 μM Mirabegron impaired carbachol (0.03-1 μM)-induced contraction in human detrusor smooth muscle. SR58894A only partially attenuated the relaxant effects of mirabegron in human and pig detrusor strips precontracted with 1 μM carbachol. In α-toxin-permeabilized detrusor strips, tension force at 1 μM [Ca²⁺ ]_i was decreased by mirabegron in a concentration-dependent manner. The relaxant effect of mirabegron was only slightly attenuated by H-89 and not significantly affected by SQ22536. Y-27632 potentiated the relaxation response to mirabegron, but attenuated responses to cAMP; GF-109203X had little effect. Mirabegron but not cAMP had a notable relaxant effect in the pig detrusor smooth muscle permeabilized with β-escin.

CONCLUSIONS

Mirabegron-induced relaxation of pig and human detrusor smooth muscle occurs via both a β₃ -adrenoceptor/cAMP-dependent and -independent pathway.

Calcium sensitization mechanisms in detrusor smooth muscles

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

Regulation of urinary bladder function by protein kinase C in physiology and pathophysiology

BACKGROUND

Protein kinase C (PKC) is expressed in many tissues and organs including the urinary bladder, however, its role in bladder physiology and pathophysiology is still evolving. The aim of this review was to evaluate available evidence on the involvement of PKC in regulation of detrusor contractility, muscle tone of the bladder wall, spontaneous contractile activity and bladder function under physiological and pathophysiological conditions.

METHODS

This is a non-systematic review of the published literature which summarizes the available animal and human data on the role of PKC signaling in the urinary bladder under different physiological and pathophysiological conditions. A wide PubMed search was performed including the combination of the following keywords: "urinary bladder", "PKC", "detrusor contractility", "bladder smooth muscle", "detrusor relaxation", "peak force", "detrusor underactivity", "partial bladder outlet obstruction", "voltage-gated channels", "bladder nerves", "PKC inhibitors", "PKC activators". Retrieved articles were individually screened for the relevance to the topic of this review with 91 citations being selected and included in the data analysis.

DISCUSSION

Urinary bladder function includes the ability to store urine at low intravesical pressure followed by a subsequent release of bladder contents due to a rapid phasic contraction that is maintained long enough to ensure complete emptying. This review summarizes the current concepts regarding the potential contribution of PKC to contractility, physiological voiding, and related signaling mechanisms involved in the control of both the storage and emptying phases of the micturition cycle, and in dysfunctional voiding. Previous studies linked PKC activation exclusively with an increase in generation of the peak force of smooth muscle contraction, and maximum force generation in the lower urinary tract. More recent data suggests that PKC presents a broader range of effects on urinary bladder function including regulation of storage, emptying, excitability of the detrusor, and bladder innervation. In this review, we evaluated the mechanisms of peripheral and local regulation of PKC signaling in the urinary bladder, and their impact on different phases of the micturition cycle under physiological and pathophysiological conditions.

Aging changes agonist induced contractile responses in permeabilized rat bladder

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

Endogenous cardiac troponin T modulates Ca(2+)-mediated smooth muscle contraction

Mechanisms linked to actin filaments have long been thought to cooperate in smooth muscle contraction, although key molecules were unclear. We show evidence that cardiac troponin T (cTnT) substantially contributes to Ca²⁺-mediated contraction in a physiological range of cytosolic Ca²⁺ concentration ([Ca²⁺]_i). cTnT was detected in various smooth muscles of the aorta, trachea, gut and urinary bladder, including in humans. Also, cTnT was distributed along with tropomyosin in smooth muscle cells, suggesting that these proteins are ready to cause smooth muscle contraction. In chemically permeabilised smooth muscle of cTnT^+/− mice in which cTnT reduced to ~50%, the Ca²⁺-force relationship was shifted toward greater [Ca²⁺]_i, indicating a sizeable contribution of cTnT to smooth muscle contraction at [Ca²⁺]_i < 1 μM. Furthermore, addition of supplemental TnI and TnC reconstructed a troponin system to enhance contraction. The results indicated that a Tn/Tn-like system on actin-filaments cooperates together with the thick-filament pathway.

Signalling to contractile proteins by muscarinic and purinergic pathways in neurally stimulated bladder smooth muscle

Urinary bladder smooth muscle contraction is triggered by parasympathetic nerves, which release ATP and acetylcholine (ACh) that bind to purinergic and muscarinic receptors, respectively. Neuronal signalling may thus elicit myosin regulatory light chain (RLC) phosphorylation and contraction through the combined, but distinct contributions of these receptors. Both receptors mediate Ca2+ influx whereas muscarinic receptors may also recruit Ca2+-sensitization mechanisms. Using transgenic mice expressing calmodulin sensor myosin light chain kinase (MLCK) in smooth muscles, the effects of suramin/α,β-methylene ATP (α,β-meATP) (purinergic inhibition) or atropine (muscarinic inhibition) on neurally stimulated elevation of [Ca2+]i, MLCK activation, force and phosphorylation of RLC, myosin light chain phosphatase (MLCP) targeting subunit MYPT1 and MLCP inhibitor protein CPI-17 were examined. Electric field stimulation (EFS) increased [Ca2+]i, MLCK activation and concomitant force in a frequency-dependent manner. The dependence of force on [Ca2+]i and MLCK activation decreased with time suggesting increased Ca2+ sensitization in the late contractile phase. RLC and CPI-17 phosphorylation increased upon stimulation with maximal responses at 20 Hz; both responses were attenuated by atropine, but only RLC phosphorylation was inhibited by suramin/α,β-meATP. Antagonism of purinergic receptors suppressed maximal MLCK activation to a greater extent in the early contractile phase than in the late contractile phase; atropine had the opposite effect. A frequency- and time-dependent increase in MLCK phosphorylation explained the desensitization of MLCK to Ca2+, since MLCK activation declined more rapidly than [Ca2+]i. EFS elicited little or no effect on MYPT1 Thr696 or 850 phosphorylation. Thus, purinergic Ca2+ signals provide the initial activation of MLCK with muscarinic receptors supporting sustained responses. Activation of muscarinic receptors recruits CPI-17, but not MYPT1-mediated Ca2+ sensitization. Furthermore, nerve-released ACh also initiates signalling cascades leading to phosphorylation-dependent desensitization of MLCK.

Phase IIb, multicenter, double-blind, randomized, placebo-controlled, parallel-group study to determine effects of elocalcitol in women with overactive bladder and idiopathic detrusor overactivity

OBJECTIVE

To evaluate the efficacy and safety of elocalcitol in the treatment of women with overactive bladder and idiopathic detrusor overactivity.

METHODS

The study was a multicenter, double-blind, randomized, placebo-controlled, parallel-group trial of women with overactive bladder symptoms recruited from 48 European tertiary referral centers. The participants were randomized to receive either placebo or elocalcitol, 75 μg/d or 150 μg/d for 4 weeks. A 3-day bladder diary, the Urgency Perception Scale, the Patient's Perception of Bladder Condition, and urodynamics were used before and after treatment. Vital signs, laboratory blood tests, 24-hour urine collection, and electrocardiography were also performed to assess the safety. The analysis of covariance test was used to compare the treatment groups. The primary objective was to evaluate the change in bladder volume at the first involuntary detrusor contraction from baseline.

RESULTS

A total of 308 women were studied. No significant change was seen in the urodynamic parameters between the placebo and elocalcitol groups, except for the bladder volume at the first desire to void. The frequency of incontinence episodes was significantly reduced in the elocalcitol group compared with the placebo group (P = .02). The Patient's Perception of Bladder Condition score improved significantly after treatment for the women receiving elocalcitol compared with those receiving placebo (P = .02). Treatment with both doses of elocalcitol was well tolerated, and no differences versus placebo were observed.

CONCLUSION

Although the primary endpoint was not achieved, elocalcitol appears to be an effective and well-tolerated drug for the treatment of women with overactive bladder and idiopathic detrusor overactivity. However, the multicenter setting for the use of urodynamics might have biased the results of our study.

Perspective on the role of P2X-purinoceptor activation in human vas deferens contractility

The contractile actions of α,β-methylene ATP (α,β-meATP) and ATP and the effects of K(+) channel blockers in longitudinal and circular muscles of human vas deferens were investigated with a view to clarifying the functional importance of P2X(1)-purinoceptor activation and K(+) channels in modulating contractility of the tissues. The results provide an experiment-based perspective for resolving differing reports on purinergic activation of the tissues and uncertain roles of large-conductance Ca(2+)-activated K(+) (BK(Ca)) and voltage-gated delayed rectifier K(+) (K(V)) channels. α,β-Methylene ATP (3-100 μm) evoked suramin-sensitive contractions of longitudinal muscle but rarely of circular muscle. ATP (0.1-3 mm) less reliably activated only longitudinal muscle contractions. These were enhanced by ARL 67156 (100 μm), but a different ectonucleotidase inhibitor, POM 1, was ineffective. Both muscle types were unresponsive to ADP-βS (100 μm), a P2Y-purinoceptor agonist. Longitudinal muscle contractions in response to α,β-meATP were enhanced by FPL 64176 (1 μm), an L-type Ca(2+) agonist, TEA (1 mm), a non-specific K(+) channel blocker, 4-aminopyridine (0.3 mm), a selective blocker of K(V) channels, and iberiotoxin (0.1 μm), a selective blocker of BK(Ca) channels. Quiescent circular muscles responded to α,β-meATP reliably in the presence of FPL 64176 or iberiotoxin. Apamin (0.1 μm), a selective blocker of small conductance Ca(2+)-activated K(+) (SK(Ca)) channels had no effect in both muscle types. Y-27632 (1-10 μm) reduced longitudinal muscle contractions in response to α,β-meATP, suggesting involvement of Rho-kinase-dependent contractile mechanisms. The results indicate that P2X(1)-purinoceptor stimulation elicits excitatory effects that: (a) lead to longitudinal muscle contraction and secondary activation of 4-aminopyridine-sensitive (K(V)) and iberiotoxin-sensitive (BK(Ca)) K(+) channels; and (b) are subcontractile in circular muscle due to ancillary activation of BK(Ca) channels. The novel finding of differential action by P2X(1)-purinoceptor agonists in the muscle types has functional implication in terms of the purinergic contribution to overall contractile function of human vas deferens. The modulatory effects of K(V) and BK(Ca) channels following P2X(1)-purinoceptor activation may be pivotal in providing the crucial physiological mechanism that ensures temporal co-ordination of longitudinal and circular muscle contractility.

The Relaxing Effect of α-Defensin 1 on the Adrenergic Responses of Rat Bladder

Defensins, cysteine-rich cationic polypeptides released from neutrophils, are known to have powerful antimicrobial properties. In this study, we sacrificed 30 rats to investigate the effects of α-defensin 1 on detrusor muscle contractions in isolated rat bladder. From the experiments we found relaxing effects of α-defensin 1 on the contractions induced by phenylephrine (PE) but not by bethanechol (BCh) in the detrusor smooth muscles. To determine the mechanisms of the effects of α-defensin 1, the changes of effects on PE-induced contraction by α-defensin 1 pretreatment were observed after pretreatment of Rho kinase inhibitor (Y-27632), protein kinase C (PKC) inhibitor (Calphostin C), potent activator of PKC (PDBu; phorbol 12,13-dibutyrate), and NF-κB inhibitors (PDTC; pyrrolidinedithiocarbamate and sulfasalazine). The contractile responses of PE (10(-9)~10(-4) M) were significantly decreased in some concentrations of α-defensin 1 (5×10(-9) and 5×10(-8) M). When strips were pretreated with NF-κB inhibitors (PDTC and sulfasalazine; 10(-7)~10(-6) M), the relaxing responses by α-defensin 1 pretreatment were disappeared. The present study demonstrated that α-defensin 1 has relaxing effects on the contractions of rat detrusor muscles, through NF-κB pathway. Further studies in vivo are required to clarify whether α-defensin 1 might be clinically related with bladder dysfunction by inflammation process.

Hydrogen sulphide inhibits carbachol-induced contractile responses in β-escin permeabilized guinea-pig taenia caecum

Hydrogen sulphide (H(2)S) is an endogenous mediator producing a potent relaxation response in vascular and non-vascular smooth muscles. While ATP-sensitive potassium channels are mainly involved in this relaxant effect in vascular smooth muscle, the mechanism in other smooth muscles has not been revealed yet. In the present study, we investigated how H(2)S relaxes non-vascular smooth muscle by using intact and β-escin permeabilized guinea-pig taenia caecum. In intact tissues, concentration-dependent relaxation response to H(2)S donor NaHS in carbachol-precontracted preparations did not change in the presence of a K(ATP) channel blocker glibenclamide, adenylate cyclase inhibitor SQ-22536, guanylate cyclase inhibitor ODQ, protein kinase A inhibitor KT-5720, protein kinase C inhibitor H-7, tetrodotoxin, apamin/charybdotoxin, NOS inhibitor L-NAME and cyclooxygenase inhibitor indomethacin. We then studied how H(2)S affected carbachol- or Ca(2+)-induced contractions in permeabilized tissues. When Ca(2+) was clamped to a constant value (pCa6), a further contraction could be elicited by carbachol that was decreased by NaHS. This decrease in contraction was reversed by catalase but not by superoxide dismutase or N-acetyl cysteine. The sarcoplasmic reticulum Ca(2+)-ATPase pump inhibitor, cyclopiazonic acid, also decreased the carbachol-induced contraction that was further inhibited by NaHS. Mitochondrial proton pump inhibitor carbonyl cyanide p-trifluromethoxyphenylhydrazone also decreased the carbachol-induced contraction but this was not additionally changed by NaHS. The carbachol-induced Ca(2+) sensitization, calcium concentration-response curves, IP(3)- and caffeine-induced contractions were not affected by NaHS. In conclusion, we propose that hydrogen peroxide and mitochondria may have a role in H(2)S-induced relaxation response in taenia caecum.

Rho-kinase, a common final path of various contractile bladder and ureter stimuli

Normal urinary bladder function is based on the proper contraction and relaxation of smooth muscle (SM), which constitutes the majority of the bladder wall. The contraction and relaxation of all SM involves a phosphorylation-dephosphorylation pathway involving the enzymes smooth muscle myosin light chain kinase (SMMLCK) and smooth muscle myosin light chain phosphatase (SMMLCP), respectively. Although originally thought to function just as a passive opposition to SMMLCK-driven SM contraction, it is now clear that SMMLCP activity is under an extremely complex molecular regulation via which SMMLCP inhibition can induce "calcium sensitization." This review provides a thorough summary of the literature regarding the molecular regulation of the SMMLCP with a focus on one of its major inhibitory pathways that is RhoA/Rho-kinase (ROK) including its activation pathways, effector molecules, and its roles in various pathological conditions associated with bladder dysfunction. Newly emerging roles of ROK outside of SM contractility are also discussed. It is concluded that the RhoA/ROK pathway is critical for the maintenance of basal SM tone of the urinary bladder and serves as a common final pathway of various contractile stimuli in rabbits, rats, mice, and pigs as well as humans. In addition, this pathway is upregulated in response to a number of pathological conditions associated with bladder SM dysfunction. Similarly, RhoA/Rho-kinase signaling is essential for normal ureteral function and development and is upregulated in response to ureteral outlet obstruction. In addition to its critical role in bladder SM function, a role of ROK in the urothelium is also beginning to emerge as well as roles for ROK in bladder infection and invasion and metastasis of bladder cancer.

A complex of Ca(V)1.2/PKC is involved in muscarinic signaling in smooth muscle

Here we present functional and biochemical evidence for a Ca(2+) channel (Ca(V)1.2)/protein kinase C (PKC) signaling complex being a key player in muscarinic regulation of urinary bladder smooth muscle. Muscarinic stimulation induced Ca(2+) signals and concomitant contractions in detrusor muscle from mice that were dependent on functional Ca(2+) channels. These signals were still present in muscles being depolarized by 85 mM extracellular K(+). Muscarinic-induced contractions were reduced by a PKC inhibitor [bisindolylmaleimide I (BIM-I)] and a phospholipase D (PLD) inhibitor (1-butanol). A phorbol ester (PDBu) enlarged muscarinic-induced Ca(2+) signals and contractions. The effects of BIM-I and PDBu were inhibited by isradipine and/or absent in muscles from Ca(V)1.2-deficient mice. Both carbachol and PDBu increased Ca(V)1.2 channel currents in isolated bladder myocytes. Blue native-PAGE electrophoresis revealed that Ca(V)1.2, PKC, and PLD are closely associated in muscles being previously stimulated by carbachol. Immunoprecipitation using anti-Ca(V)1.2 followed by Western blotting demonstrated that Ca(V)1.2 and PKC are coupled in stimulated muscles from wild-type mice. Autoradiography on immunoprecipitates showed that Ca(V)1.2 is a substrate for PKC-mediated phosphorylation. These findings suggest that a signaling complex consisting of Ca(V)1.2, PKC, and, probably, PLD controls muscarinic-mediated phasic contraction of urinary bladder smooth muscle.

Clinical and experimental aspects of Adreno-muscarinic synergy in the bladder base and prostate

Recent clinical trials have shown that combination therapy using an alpha-receptor antagonist and an antimuscarinic is more effective than either agent alone in improving quality of life and objective urodynamic variables in men with bladder outflow obstruction. There appear to be no negative effects on bladder function. The mode of action of this combination is unknown but presumed to be an antimuscarinic reduction in detrusor overactivity and the alpha-receptor antagonist reduced outflow tract resistance. We have shown with in vitro experiments that in smooth muscles influencing outflow tract resistance (prostate, trigone) there is a profound contractile synergy between adrenergic and muscarinic pathways. We propose the hypothesis that both arms of the combination therapy reduce contractile tone of the outflow tract and that their simultaneous attenuation has a disproportionately large effect on outflow tract resistance. Our data from trigone muscle suggest that adrenergic and muscarinic receptor activation increase the intracellular [Ca(2+)] but the adrenergic pathway also operates through Ca(2+)-sensitisation of the contractile apparatus, primarily through a PKC-dependent pathway.

Calcium sensitization induced by sodium fluoride in permeabilized rat mesenteric arteries

It was hypothesized that NaF induces calcium sensitization in Ca(2+)-controlled solution in permeabilized rat mesenteric arteries. Rat mesenteric arteries were permeabilized with beta-escin and subjected to tension measurement. NaF potentiated the concentration-response curves to Ca(2+) (decreased EC(50) and increased E(max)). Cumulative addition of NaF (4.0, 8.0 and 16 mM) also increased vascular tension in Ca(2+)-controlled solution at pCa 7.0 or pCa 6.5, but not at pCa 8.0. NaF-induced vasocontraction and GTPgammaS-induced vasocontraction were not additive. NaF-induced vasocontraction at pCa 7.0 was inhibited by pretreatment with Rho kinase inhibitors H1152 or Y27632 but not with a MLCK inhibitor ML-7 or a PKC inhibitor Ro31-8220. NaF induces calcium sensitization in a Ca(2+)-dependent manner in beta-escin-permeabilized rat mesenteric arteries. These results suggest that NaF is an activator of the Rho kinase signaling pathway during vascular contraction.

Regulation of smooth muscle contraction by small GTPases

Next to changes in cytosolic [Ca(2+)], members of the Rho subfamily of small GTPases, in particular Rho and its effector Rho kinase, also known as ROK or ROCK, emerged as key regulators of smooth muscle function in health and disease. In this review, we will focus on the regulation of the contractile machinery by Rho/ROK signaling and its interaction with PKC and cyclic nucleotide signaling. We will briefly discuss the emerging evidence that remodeling of cortical actin is necessary for contraction.

Alteration of the PKC-mediated signaling pathway for smooth muscle contraction in obstruction-induced hypertrophy of the urinary bladder

Normal urinary bladder function requires contraction and relaxation of the detrusor smooth muscle (DSM). The DSM undergoes compensatory hypertrophy in response to partial bladder outlet obstruction (PBOO) in both men and animal models. Following bladder hypertrophy, the bladder either retains its normal function (compensated) or becomes dysfunctional (decompensated) with increased voiding frequency and decreased void volume. We analyzed the contractile characteristics of DSM in a rabbit model of PBOO. The protein kinase C (PKC) agonist phorbol 12, 13-dibutyrate (PDBu) elicited similar levels of contraction of DSM strips from normal and compensated bladders. However, PDBu-induced contraction decreased significantly in DSM strips from decompensated bladders. The expression and activity of PKC-alpha were also lowest in decompensated bladders. The PKC-specific inhibitor bisindolylmaleimide-1 (Bis) blocked PDBu-induced contraction and PKC activity in all three groups. Moreover, the phosphorylation of the phosphoprotein inhibitor CPI-17 (a 17-kDa PKC-potentiated inhibitory protein of protein phosphatase-1) was diminished in DSM from the decompensated bladder, which would result in less inhibitory potency of CPI-17 on myosin light chain phosphatase activity and contribute to less contractility. Immunostaining revealed the colocalization of PKC and phosphorylated CPI-17 in the DSM and confirmed the decreases of these signaling proteins in the decompensated bladder. Our results show a differential PKC-mediated DSM contraction with corresponding alterations of PKC expression, activity and the phosphorylation of CPI-17. Our finding suggests a significant correlation between bladder function and PKC pathway. An impaired PKC pathway appears to be correlated with severe bladder dysfunction observed in decompensated bladders.

Vardenafil modulates bladder contractility through cGMP-mediated inhibition of RhoA/Rho kinase signaling pathway in spontaneously hypertensive rats

INTRODUCTION

Phosphodiesterase type 5 inhibitors (PDE5i), the most widely used drugs for erectile dysfunction, could also improve lower urinary tract symptoms, essentially due to overactive bladder (OAB), a condition hypothesized to be a result of an increased RhoA/Rho-kinase (ROCK) signaling. Phosphorylation/inactivation of RhoA by cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG) activity has been described in vascular smooth muscle.

AIM

The aim of this paper was to investigate whether vardenafil-induced cGMP accumulation reduces RhoA/ROCK signaling in bladder.

METHODS

Spontaneously hypertensive rats (SHRs), a strain genetically prone to develop OAB, were treated with vardenafil (10 mg/kg/day) for 2 weeks. Wistar-Kyoto rats (WKY) were used as control. In vitro experiments were performed in human bladder smooth muscle cells (hBCs).

MAIN OUTCOME MEASURES

Urodynamic parameters were registered in vivo in anesthetized WKY and SHRs. RhoA/ROCK activity in bladder was evaluated by molecular and functional studies in tissues and cells.

RESULTS

The intercontraction interval and bladder capacity, and were decreased in SHRs and restored by vardenafil. The in vitro relaxant effect of the ROCK inhibitor Y-27632 was higher in bladder strips from SHR than from WKY and reduced by vardenafil. Nomega-nitro-L-arginine-methyl-ester (a NO-synthase inhibitor, 40 mg/kg/day during the last week of the 2-week treatment with vardenafil) partially antagonized vardenafil effect on Y-27632 responsiveness. Vardenafil prevented RhoA membrane translocation/activation, decreased ROCK activity, and increased cGMP levels in vivo (rat) and in vitro (hBCs). Exposing hBCs to vardenafil increased Ser(188) RhoA phosphorylation, to the same extent as the PDE5-insensitive PKG agonist Sp-8-Br-PET-cGMP. Moreover, vardenafil inhibited several RhoA-dependent functions in hBCs, including smooth muscle gene transcription and endothelin-1-induced migration. These effects were reverted by the PKG inhibitor KT 5823, further suggesting a cGMP/PKG-dependency. In hBCs, vardenafil was active in the low nanomolar range.

CONCLUSIONS

This is the first study demonstrating that the effect of vardenafil on OAB could be partially determined by a cGMP-dependent RhoA/ROCK signaling inhibition.

Phospholipase C mediated Ca2+ signals in murine urinary bladder smooth muscle

Muscarinic stimulation of urinary bladder induces contraction via an increase in intracellular Ca(2+) concentration that results from Ca(2+) influx through Ca(2+) channels and/or IP(3)-mediated Ca(2+) release controlled by phospholipase C (PLC) signalling. The significance of PLC/IP(3) signalling in this cascade has recently been questioned because PLC inhibitors were without effect on carbachol-induced contractions in detrusor muscle strips. However, PLC/IP(3)-mediated Ca(2+) release was clearly observed in recordings of Ca(2+) signals in isolated myocytes. Therefore, we investigated the presence of PLC/IP(3)-dependent Ca(2+) release by directly monitoring Ca(2+) signals in intact detrusor muscle strips. Concomitant Ca(2+) signals from Ca(2+) channel activity were eliminated by the Ca(2+) channel antagonist isradipine (3 microM) or by the use of muscles from Ca(v)1.2 channel-deficient (SMACKO) mice. In absence of Ca(2+) channel activity, carbachol elicited contractions and Ca(2+) signals in muscles from wild type and SMACKO mice that were inhibited by the PLC inhibitor U73122 (10 microM). The results show that PLC/IP(3)-dependent Ca(2+) release is activated by stimulation with carbachol in urinary bladder smooth muscle but has a minor contribution to overall carbachol-induced Ca(2+) signals.

Synergistic effects of cyclic strain and Th1-like cytokines on tenascin-C production by rheumatic aortic valve interstitial cells

Tenascin-C (TN-C) is a key component of extracellular matrix (ECM) and its expression process is poorly understood during rheumatic heart valvular disease (RHVD). In this study, we found that interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha and TN-C concentrations in patients with RHVD were significantly higher than in normal controls. More IFN-gamma receptors and TNF receptors were found being expressed on rheumatic aortic valves interstitial cells than on non-rheumatic ones and their expression was patients' sera dependent. Antibodies neutralizing IFN-gamma or TNF-alpha could attenuate patients' sera-induced TN-C transcription by isolated rheumatic aortic valves interstitial cells. By application with different protein kinase inhibitors, we found that combined with cyclic strain, TNF-alpha and IFN-gamma induced TN-C transcription through the RhoA/ROCK signalling pathway. At the same time, p38 mitogen-activated protein kinase was involved in TNF-alpha and IFN-gamma induced TN-C transcription. TNF-alpha also increased TN-C mRNA level by additional PKC and ERK 1/2 activation. Our finding revealed a new insight into ECM remodelling during RHVD pathogenesis and new mechanisms involved in the clinical anti-IFN-gamma and anti-TNF-alpha therapy.

Rho-kinase and effects of Rho-kinase inhibition on the lower urinary tract

Altered smooth muscle cell contractility/tone contributes, at least in part, to the lower urinary tract symptoms (LUTS) seen in men with benign prostatic obstruction (BPO). Accordingly, many of the therapies to date have focused largely on blockade of individual membrane receptors to diminish smooth muscle contractility and provide symptomatic relief. This pharmacologic approach has been associated with variable results, limited efficacy, and untoward side effects. Such limited clinical success is not surprising given the plethora of neurotransmitters, neuromodulators, and hormones that are now known to modulate LUT smooth muscle cell tone. In the pursuit of improved treatment options, more recent investigations have focused attention on intracellular signal transduction events that represent convergence points for membrane receptor activation. In particular, calcium sensitization and the role of the Rho-kinase pathway has received much attention. In this report, we review the literature on the role of the Rho-kinase pathway in the modulation of LUT smooth muscle cell tone. In short, the available data support an important role for Rho-kinase in the physiologic and pathophysiologic regulation of LUT smooth muscle cell tone. Rho-kinase inhibitors thus appear to represent a potentially attractive therapeutic possibility for the treatment of LUTS.

Signal transduction underlying the control of urinary bladder smooth muscle tone by muscarinic receptors and beta-adrenoceptors

The normal physiological contraction of the urinary bladder, which is required for voiding, is predominantly mediated by muscarinic receptors, primarily the M₃ subtype, with the M₂ subtype providing a secondary backup role. Bladder relaxation, which is required for urine storage, is mediated by β-adrenoceptors, in most species involving a strong β₃-component. An excessive stimulation of contraction or a reduced relaxation of the detrusor smooth muscle during the storage phase of the micturition cycle may contribute to bladder dysfunction known as the overactive bladder. Therefore, interference with the signal transduction of these receptors may be a viable approach to develop drugs for the treatment of overactive bladder. The prototypical signaling pathway of M₃ receptors is activation of phospholipase C (PLC), and this pathway is also activated in the bladder. Nevertheless, PLC apparently contributes only in a very minor way to bladder contraction. Rather, muscarinic-receptor-mediated bladder contraction involves voltage-operated Ca²⁺ channels and Rho kinase. The prototypical signaling pathway of β-adrenoceptors is an activation of adenylyl cyclase with the subsequent formation of cAMP. Nevertheless, cAMP apparently contributes in a minor way only to β-adrenoceptor-mediated bladder relaxation. BK_Ca channels may play a greater role in β-adrenoceptor-mediated bladder relaxation. We conclude that apart from muscarinic receptor antagonists and β-adrenoceptor agonists, inhibitors of Rho kinase and activators of BK_Ca channels may have potential to treat an overactive bladder.

Evolving mechanisms of action of alverine citrate on phasic smooth muscles

BACKGROUND AND PURPOSE

We have investigated the mechanisms underlying the paradoxical ability of the antispasmodic, alverine, to enhance spontaneous activity in smooth muscles while suppressing evoked activity.

EXPERIMENTAL APPROACH

The effects of alverine on spontaneous and induced contractile activity were examined in preliminary experiments with various smooth muscles. More detailed effects were also investigated by recording membrane potential, intracellular Ca2+ concentration ([Ca2+]i) and tension from single-bundle detrusor smooth muscle (DSM) of the guinea-pig urinary bladder.

KEY RESULTS

Alverine (10 microM) increased the frequency and amplitude of spontaneous action potentials, transient increases in [Ca2+]i and associated contractions. Alverine also decreased action potential rate of decay, suggesting inhibition of L-type Ca channel inactivation. Charybdotoxin (50 nM) but neither cyclopiazonic acid (10 microM) nor Bay K 8644 (10 microM) attenuated alverine-induced enhancement of spontaneous contractions. Alverine suppressed contractions produced by high K (40 mM) or ACh (10 microM), without affecting electrical responses and with little suppression of increases in [Ca2+]i. This feature was very similar to that of the effects of the Rho kinase inhibitor Y-27632 (10 microM).

CONCLUSIONS AND IMPLICATIONS

Alverine may increase Ca influx during action potentials due to inhibition of the inactivation of L-type Ca channels, but may also suppress evoked activity by inhibiting the sensitivity of contractile proteins to Ca2+. The proportional contribution of Ca-dependent and Ca-independent contractions in DSM may differ between spontaneous and evoked activity, necessitating further investigations into the interactions between these pathways for assessing the therapeutic potential of alverine to treat DSM dysfunction.

Comparative pharmacological analysis of Rho-kinase inhibitors and identification of molecular components of Ca2+ sensitization in the rat lower urinary tract

We aimed to compare the expression and function of molecular components of the RhoA/Rho-kinase signaling pathway in the contractile responses of detrusor, trigonal and urethral smooth muscle, using selective Rho-kinase inhibitors. Contractility studies and molecular approaches were employed to demonstrate the expression patterns and functional activity of the RhoA/Rho-kinase signaling pathway in the lower urinary tract. Frequency-response curves (1-32 Hz) and concentration-response curves (CRC) to carbachol (CCh, 0.01-30 microM), phenylephrine (PE, 0.01-300 microM) and endothelin-1 (ET-1, 0.01-100 nM) were significantly attenuated (p<0.01) following incubation with the Rho-kinase inhibitors H-1152 (0.1-1 microM), Y-27632 (1-10 microM) or HA-1077 (10 microM). Addition of Rho-kinase inhibitors also markedly reduced (p<0.01) the contractions evoked by either KCl (80 mM) or alpha,beta-methylene ATP (alpha,beta-mATP, 10 microM). Among the Rho-kinase inhibitors tested, H-1152 was approximately 9-16 times more potent than Y-27632 or HA-1077. In addition, basal tone of detrusor and trigonal strips was reduced following addition of Y-27632 (10 microM), H-1152 (1 microM) and HA-1077 (10 microM). The expression of RhoA, RhoGDI, leukemia-associated RhoGEF (LARG) and p115RhoGEF was similar among the detrusor, trigone and urethra, whereas Rho-kinase alpha, Rho-kinase beta and PDZ-RhoGEF protein levels were significantly lower in the urethra. Components of the RhoA/Rho-kinase signaling are expressed in detrusor, trigonal and urethral smooth muscle and dynamically regulate contraction and tone. Manipulation of RhoGEF expression may provide further understanding of mechanisms involving Ca(2+) sensitization in the lower urinary tract.

Intracellular calcium stores in beta-escin skinned rat and guinea-pig bladders

Intracellular Ca2+ stores in rat and guinea-pig bladders and taenia caecum were studied in beta-escin skinned smooth muscle strips. 30 min of skinning with 40 microM and 80 microM beta-escin were the best parameters found to obtain good calcium response curves (10(-7)-10(-4) M) in rat and guinea pig, respectively. Calmodulin (1 microM) increased the calcium contractions significantly. pCa 6 was used to load intracellular stores and application of carbachol (50 microM) in all tissues then only contracted the tissues in the presence of guanosine-5'-triphosphate (GTP; 100 microM). Inositol triphosphate (IP3; 50 microM), applied after pCa 6, contracted all tissues. Carbachol added after IP3 or heparin (1 mg/ml) no longer caused a contraction in any of them. In bladders, caffeine (30 mM) but not ryanodine (5 microM) prevented the subsequent carbachol contraction. A slowly rising contraction with carbachol was elicited after caffeine (30 mM) or ryanodine (5 microM) in the taenia and after ryanodine in the bladders. Caffeine (30 mM) suppressed the calcium response curves in all tissues. Procaine (30 mM) blocked the carbachol (50 microM) contractions in bladders but not in taenia. These results suggest that calcium induced calcium release (CICR) and IP3 induced calcium release (IICR) release calcium from a common store in bladder but two different compartments in taenia.

Long term partial bladder outlet obstruction induced contractile dysfunction in male rabbits: A role for Rho-kinase

AIMS

In this study we examined the expression of Rho-kinase (ROK) isoforms in rabbit detrusor smooth muscle during the progression of partial bladder outlet obstruction and correlated them with the time course of obstruction.

METHODS

Detrusor samples were obtained from bladders after 1, 2, 4, and 8 weeks of obstruction and also sham operated control rabbits. Contractile responses to field stimulation (FS) and also the smooth muscle (SM) to collagen ratio were determined in isolated bladder strips. Reverse transcriptase-polymerase chain reaction, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting were used to determine the relative levels of ROK isoform expression at the mRNA and protein levels.

RESULTS

Bladder weight increased gradually and contractile responses were reduced significantly over the course of obstruction. The smooth muscle/collagen ratio increased significantly during the course of obstruction. The expression of ROKalpha increased significantly to approximately the same extent in 1-4-week obstructed groups and increased further in the 8-week obstructed group, both at the mRNA and protein levels. In contrast, there was a significant decrease in the expression of ROKbeta in the obstructed groups, which gradually decrease during the course of 1-4-week obstruction period and are slightly upregulated at the decompensated stage at 8-week obstruction.

CONCLUSIONS

The change in the isoforms of ROK may be part of the molecular mechanism for bladder compensation following partial bladder outlet obstruction.