Carbachol-induced sustained tonic contraction of rat detrusor muscle

Developmental changes in contractile responses to cholinergic stimuli: role of calcium sensitization and related pathways

This study was performed to analyze the developmental changes in bladder response to cholinergic stimulation in detail, highlighting calcium sensitization (CS) and its related pathways. Rats were divided into three groups in accordance with reported time of developmental milestones (newborns, days 1–4; youngsters, days 5–14; and grown-ups, days 15–28). Following cholinergic stimulation (carbachol, 5 µM), the contractile response to detrusor was analyzed with respect to three phases (initial phasic, tonic, and superimposed phasic contractions). Contractile responses were analyzed by their dynamic and kinetic aspects. The responses were further compared in varying external calcium concentrations and in the presence of inhibitors of protein kinase C (PKC) and Rho kinase (ROCK), which are involved in CS. The responses of newborns contrasted with the others by their short and brisk initial phasic contractions, prominent tonic contractions, and delayed participation of irregular superimposed phasic contractions. With development, phasic contractions became prominent, and tonic contractions diminished. These developmental changes in phasic contractions were reproduced when exposed to increasing calcium concentrations. Application of specific inhibitors and molecular phasic analysis revealed that PKC was functional in tonic contractions of the newborns, whereas ROCK took over its role with development. Within a few days of birth, rats’ bladders experienced drastic changes in contractile mechanisms. This included dominance of phasic contractions over tonic contractions due to increased calcium dependence and the maturational shift of the calcium sensitivity mechanism from PKC to ROCK.

The validation of a functional, isolated pig bladder model for physiological experimentation

Characterizing the integrative physiology of the bladder requires whole organ preparations. The purpose of this study was to validate an isolated large animal (pig) bladder preparation, through arterial and intravesical drug administration, intravesical pressure recording, and filming of surface micromotions. Female pig bladders were obtained from the local abattoir and arterially perfused in vitro. Arterial and intravesical pressures were recorded at varying volumes. Bladder viability was assessed histologically and by monitoring inflow and outflow pH. Arterial drug administration employed boluses introduced into the perfusate. Intravesical administration involved slow instillation and a prolonged dwell-time. Surface micromotions were recorded by filming the separation of surface markers concurrently with intravesical pressure measurement. Adequate perfusion to all bladder layers was achieved for up to 8 h; there was no structural deterioration nor alteration in inflow and effluent perfusate pH. Arterial drug administration (carbachol and potassium chloride) showed consistent dose-dependent responses. Localized movements (micromotions) occurred over the bladder surface, with variable correlation with fluctuations of intravesical pressure. The isolated pig bladder is a valid approach to study integrative bladder physiology. It remains viable when perfused in vitro, responds to different routes of drug administration and provides a model to correlate movements of the bladder wall directly to variation of intravesical pressure.

Commonly used intravenous anesthetics decrease bladder contractility: An in vitro study of the effects of propofol, ketamine, and midazolam on the rat bladder

Aim:

This study was designed to test the hypothesis that propofol, ketamine, and midazolam could alter the contractile activity of detrusor smooth muscle.

Materials and Methods:

Four detrusor muscle strips isolated from each rat bladder (n = 12) were placed in 4 tissue baths containing Krebs-Henseleit solution. The carbachol (10 ⁻⁸to 10⁻⁴mol/L)-induced contractile responses as well as 5, 10, 20, 30, 40, 50 Hz electrical field stimulation (EFS)-evoked contractile responses of the detrusor muscles were recorded using isometric contraction measurements. After obtaining basal responses, the in vitro effects of propofol, ketamine, midazolam (10⁻⁵ to 10⁻³ mol/L), and saline on the contractile responses of the detrusor muscle strips were recorded and evaluated.

Results:

All the 3 drugs reduced the carbachol-induced and/or EFS-evoked contractile responses of rat detrusor smooth muscles in different degrees. Midazolam (10⁻⁴ to 10⁻³ mol/L) caused a significant decrease in the contractile responses elicited by either EFS or carbachol (P=0.000−0.013). Propofol (10⁻³mol/L) caused a decrease only in EFS-evoked contractile responses (P=0.001−0.004) and ketamine (10⁻³mol/L) caused a decrease only in carbachol-induced contractile responses (P=0.001−0.034).

Conclusion:

We evaluated the effects of the 3 different intravenous anesthetics on detrusor contractile responses in vitro and found that there are possible interactions between anesthetic agents and detrusor contractile activity. The depressant effects of midazolam on the contractile activity were found to be more significant than ketamine and propofol. Despite the necessity of further studies, it could be a piece of wise advice to clinicians to keep the probable alterations due to intravenous anesthetics in mind, while evaluating the results of urodynamic studies in children under sedation.

Animal models in overactive bladder research

Overactive bladder syndrome (OAB) is a symptom-based diagnosis characterised by the presence of urinary urgency. It is highly prevalent and overlaps with the presence of bladder contractions during urine storage, which characterises the urodynamic diagnosis of detrusor overactivity. Animal models are needed to understand the pathophysiology of OAB, but the subjective nature of the symptom complex means that interpretation of the findings in animals requires caution. Because urinary urgency cannot be ascertained in animals, surrogate markers such as frequency, altered toileting areas, and non-micturition contractions have to be used instead. No model can recapitulate the subjective, objective, and related factors seen in the clinical setting. Models used include partial bladder outlet obstruction, the spontaneous hypertensive rat, the hyperlipidaemic rat, various neurological insults and some gene knock-outs. Strengths and weaknesses of these models are discussed in the context of the inherent difficulties of extrapolating subjective symptoms in animals.

The extracorporeal perfusion of the female pig detrusor as an experimental model for the study of bladder contractility

AIMS

The objective of the study was to establish an experimental model for the extracorporeal perfusion of the pig detrusor. In order to validate this model we examined some biochemical parameters and determined the effect of carbachol on the contractility of perfused female pig bladders.

METHODS

Twenty-six pig bladders were perfused with Krebs-Ringer bicarbonate-glucose buffer for a period up to 5 hr with the aim to preserve a viable organ, which would be responsive to contraction-inducing agents. The intravesical pressure of the bladder as well as the intraarterial pressure of the vesical arteries were recorded before and after administration of carbachol.

RESULTS

The perfusate pH, lactate, partial carbon dioxide tension, and the ATP content in the perfused tissue, all indicators of tissue ischemia or cell necrosis, showed a good preservation of the organ for up to 5 hr. Carbachol was able to induce contractions of the prefilled bladder with a complete draining of the bladder throughout the whole perfusion period.

CONCLUSIONS

We could demonstrate that this perfusion system was able to preserve the pig bladder in a functional condition, appropriate for the study of physiological questions.

Two-step Ca2+ intracellular release underlies excitation-contraction coupling in mouse urinary bladder myocytes

The relative contributions of Ca(2+)-induced Ca(2+) release (CICR) versus Ca(2+) influx through voltage-dependent Ca(2+) channels (VDCCs) to excitation-contraction coupling has not been defined in most smooth muscle cells (SMCs). The present study was undertaken to address this issue in mouse urinary bladder (UB) smooth muscle cells (UBSMCs). Confocal Ca(2+) images were obtained under voltage- or current-clamp conditions. When UBSMCs were activated by a 30-ms depolarization to 0 mV, intracellular Ca(2+) concentration ([Ca(2+)](i)) increased in several small, discrete areas just beneath the cell membrane. These Ca(2+) "hot spots" then spread slowly through the myoplasm as Ca(2+) waves, which continued even after repolarization. Shorter depolarizations (5 ms) elicited only a few Ca(2+) sparks, which declined quickly. The number of Ca(2+) sparks, or hot spots, was closely related to the depolarization duration in the range of approximately 5-20 ms. There was an apparent threshold depolarization duration of approximately 10 ms within which to induce enough Ca(2+) transients to spread globally and then induce a contraction. Application of 100 microM ryanodine to the pipette solution did not change the resting [Ca(2+)](i) or the VDCC current, but it did abolish Ca(2+) hot spots elicited by depolarization. Application of 3 microM xestospongin C reduced ACh-induced Ca(2+) release but did not affect depolarization-induced Ca(2+) events. The addition of 100 microM ryanodine to tissue segments markedly reduced the amplitude of contractions triggered by direct electrical stimulation. In conclusion, global [Ca(2+)](i) rise triggered by a single action potential is not due mainly to Ca(2+) influx through VDCCs but is attributable to the subsequent two-step CICR.

Mechanisms of neurokinin A- and substance P-induced contractions in rat detrusor smooth musclein vitro

OBJECTIVE

To investigate the mechanisms of neurokinin A- and substance P-induced contractions of rat urinary bladder smooth muscle, and to compare them with those of the muscarinic agonist carbachol.

MATERIALS AND METHODS

Rat urinary bladder strips were suspended under 1 g of tension in a physiological buffer at 37 degrees C, gassed with 95% O(2)/5% CO(2). Mechanical activity was recorded isometrically during exposure to neurokinin A and substance P.

RESULTS

Both agents produced concentration-dependent contractions of smooth muscle strips which were unaffected by tetrodotoxin (1 micro mol/L), peptidase inhibitors (captopril, thiorphan and bestatin; 1 micro mol/L each) or piroxicam (10 micro mol/L). The rank order of potency of agonists was neurokinin A > substance P > carbachol. Contractile responses to neurokinin A and substance P, like the contractile responses to carbachol, were abolished in a nominally Ca(2+)-free medium and significantly reduced by nifedipine (1 micro mol/L). SKF-96365 (60 micro mol/L), an inhibitor of receptor-mediated Ca(2+) entry, abolished the nifedipine-resistant response to substance P and carbachol, and significantly attenuated the response to neurokinin A. Depleting intracellular Ca(2+) stores with thapsigargin (1 micro mol/L) significantly attenuated neurokinin A-induced contractions but had no effect on substance P- or carbachol- induced contractions. The Rho-kinase inhibitor, Y-27632 (10 micro mol/L), significantly reduced both phasic and tonic components of the contractile responses to neurokinin A, substance P and carbachol.

CONCLUSION

The contractile responses induced by tachykinins in rat urinary bladder smooth muscle strips involve a direct action on smooth muscle and are not modulated by peptidases or prostanoids. Neurokinin A and substance P, like carbachol-induced contractions, depend on extracellular Ca(2+) influx largely through voltage-operated and partly through receptor-operated Ca(2+) channels. Intracellular Ca(2+) release contributes to the contractile response to neurokinin A but appears to have no involvement in substance P- and carbachol-induced contractions. Rho-kinase activation contributes to contractions induced by substance P, neurokinin A and carbachol.

Mitochondrial metabolism in the rat during bladder regeneration induced by small intestinal submucosa

OBJECTIVE

To assess mitochondrial metabolism of bladder tissue induced by small-intestinal submucosa (SIS), by comparing the mitochondrial enzyme metabolism in this tissue with that in normal bladder tissue and thus evaluate intracellular normality.

MATERIAL AND METHODS

In all, 70 rats were grouped into healthy controls (10), surgical controls with a simple bladder incision (15) and rats treated by partial cystectomy with replacement by the SIS graft (45). At 1, 3 and 6 months the rats were killed, the enzymes of mitochondrial respiratory chain complexes assayed, and the respiration of permeabilized bladder fibres assessed using polarographic analysis.

RESULTS

The enzyme activities of control and treated rats at 3 months were identical. The results from the polarographic analysis of respiration were also similar to that in normal tissue apart from a decrease in the number of mitochondria. Histologically, there was complete regeneration at 6 months.

CONCLUSION

After a phase of inflammation the bladder regenerates after a patch is placed. The new tissue has the same enzymatic and histological features as normal bladder tissue.

Preconditioning protects the guinea-pig urinary bladder against ischaemic conditions in vitro

AIMS

To investigate the ability of ischaemic preconditioning (IPC) to protect guinea-pig detrusor from damage caused by a subsequent more prolonged exposure to ischaemic conditions.

MATERIALS AND METHODS

Smooth muscle strips were mounted for tension recording in small organ baths continuously superfused with Krebs' solution at 37 degrees C. Ischaemia was mimicked by removing oxygen and glucose from the superfusing solution. Contractile responses to electrical field stimulation (EFS) and carbachol were monitored. Three regimes of preconditioning were examined: 15, 10, and 5 min of ischaemic conditions followed by 15, 10, and 5 min of normal conditions, respectively.

RESULTS

Without preconditioning, nerve-mediated responses were significantly and proportionally reduced by periods of ischaemic conditions lasting for 45, 60, and 90 min, but recovered fully after exposure to ischaemic conditions for 30 min. The recovery of the responses to EFS was significantly improved in preconditioned strips when the period of ischaemic conditions was 45 or 60 min. However, no significant differences were seen with preconditioning when the period of ischaemic conditions was 90 min. The recovery of responses to carbachol was much greater than for the responses to EFS, and no significant differences were found between control and preconditioned strips.

CONCLUSIONS

It is suggested that in vivo short periods of transient ischaemia may be able to protect the guinea-pig bladder from the impairment associated with longer periods of ischaemia and reperfusion, which might happen in obstructed micturition. Our results also indicate that the phenomenon affects mainly the intrinsic nerves, which are more susceptible to ischaemic damage than the smooth muscle.

EFFECTS OF LOCAL ANESTHETICS ON THE CONTRACTILITY OF RAT BLADDERS

PURPOSE

We investigated the effect of local anesthetic agents on the detrusor muscle in rats.

MATERIALS AND METHODS

In vitro isometric contraction of rat detrusor strips was measured. We investigated the effects of tetracaine, bupivacaine and lidocaine on baseline spontaneous contractions and contractions induced by various stimuli, including 60 mM. KCl, carbachol and electricalal field stimulation with a pulse duration of 0.8 or 100 milliseconds.

RESULTS

Local anesthetic agents have complex effects on baseline spontaneous contractility that depend on the type of agent used and its concentration. These agents inhibited nerve mediated contraction resulting from electricalal field stimulation with a pulse duration of 0.8 milliseconds in a concentration dependent manner and also inhibited nonnerve mediated detrusor contractions induced by KCl, carbachol or electricalal field stimulation with a pulse duration of 100 milliseconds Higher concentrations of local anesthetic agents were needed to inhibit nonnerve than nerve mediated contractions. In rat detrusor muscle carbachol induced a sustained tonic contraction even after the depletion of internal and external Ca2+ sources, which was also inhibited by local anesthetic agents.

CONCLUSIONS

These results show that local anesthetic agents have a wide spectrum of inhibitory effects on the contraction of bladder smooth muscle induced by various stimulants at different concentrations, which may be potentially useful for treating overactive bladder.

Active properties of the urinary bladder: in vitro comparative studies between adult and neonatal rats

OBJECTIVE

To determine, using in vitro comparative studies, developmental aspects associated with the active properties of the urinary bladder in neonatal and adult rats.

MATERIALS AND METHODS

Urinary bladders were removed from neonatal (1-3 days old) and adult (15 weeks old) male Sprague-Dawley rats. Anterior longitudinal muscle strips were obtained from each group and isometric tensions recorded. Nerve-mediated contractions elicited by electrical field stimulation (0.8 ms pulse) or carbachol-induced contractile responses in neonatal and adult bladder strips were compared. Contractile tensions were normalized using the wet weight of the bladder strip or by using the percentage contraction induced by 60 mmol/L KCl.

RESULTS

Nerve-mediated contractile responses showed that the muscarinic component predominated in the neonatal rat bladder, which contrasted with the predominant purinergic components in adult bladder. The pattern of spontaneous activity and carbachol-induced contraction differed in the two groups. Small spontaneous contractions in the basal state occurred in adult bladder strips, while short-lived large spontaneous contractions were present in neonatal strips. The amplitude of carbachol-induced contractions generated in the neonatal bladder was larger than that in the adult bladder. In addition, the time to achieve peak contraction elicited by carbachol (5 micromol/L) was shorter in the neonatal bladder. Repetitive carbachol applications induced an attenuation of the contractile response (desensitization), but the neonatal bladder was more resistant to desensitization than the adult bladder.

CONCLUSIONS

These results show that nerve-mediated or agonist-induced contractile patterns, and spontaneous activity, in the neonatal bladder differ from those of the adult bladder in rats. The results suggest that in addition to neural immaturity, there are functional differences between the bladders of adult and neonatal rats.