Role of calcium ion antagonists of the bladder detrusor muscle: in vitro and in vivo study

Effects of combined use of trospium chloride and melatonin on in vitro contractility of rat urinary bladder

OBJECTIVES

To examine the effects of combined use of trospium chloride and melatonin on in vitro contractility of rat urinary bladder.

METHODS

Isolated bladder strips from 20 male Wistar rats were examined in an organ bath. Contractions were evoked by acetylcholine (ACh). Initially, effective concentrations of trospium and melatonin to inhibit the contractions were determined. We subsequently tested the effects of combined use of melatonin and trospium on agonist-induced contractions.

RESULTS

Exposure of bladder strips to 10 microM ACh significantly increased the contractions. After cumulative administration of increasing concentrations of trospium (1, 3, and 5 microM), agonist-induced contractions decreased significantly (P <.05). Similarly, the mean peak amplitude of contractions evoked by ACh was significantly inhibited by melatonin in a concentration-dependent manner (100, 200, and 300 microM) (P <.05). Further evaluation of the effects of combined use of trospium and melatonin on ACh-induced contractions of bladder strips revealed that one-tenth of initially applied dose of trospium (500 nM) in addition to the lowest inhibitory dose of melatonin (100 microM) significantly lowered both the peak amplitude and area under the contractility curve of contractions (P <.05).

CONCLUSIONS

Our results showed that combined use of low dose trospium and melatonin had strong in vitro inhibitory capability on agonist-induced contractions of rat bladder strips. The present findings may offer an insight into lowering the dose of an antimuscarinic by combining it with an antioxidant and endogenous hormone, melatonin.

Inhibitory effects of L- and T-type calcium antagonists on contractions of human detrusor muscle

The inhibitory and relaxant effects of the L-type calcium antagonists nifedipine, nimodipine, verapamil and diltiazem, and of the T-type calcium antagonist mibefradil, on contractions of isolated human detrusor muscle were investigated. The tissue was obtained from 10 patients undergoing cystectomy due to bladder cancer. Effects of the calcium antagonists at different concentrations on the concentration-response curves for carbachol were investigated. Furthermore, concentration-relaxation curves were performed using potassium-precontracted muscle strips. All L-type calcium antagonists suppressed the mean concentration-response curve of carbachol significantly at a concentration of 10(-6) M. Mibefradil up to 10(-5) M did not significantly suppress it. Nifedipine significantly reduced the carbachol-induced maximum contraction to 75% and 44%, verapamil to 75% and 67% of the appropriate control value at concentrations of 10(-7) and 10(-6) M, respectively. Diltiazem reduced it insignificantly to 96% and 71% at the above-mentioned concentrations. The concentration-relaxation experiments revealed following pD2-values and maximum relaxations of nifedipine, nimodipine, verapamil and diltiazem, respectively: 6.23, 6.37, 5.66, 5.81 and 85%, 83%, 82%, 90%. Maximum relaxations and pD2-values were not significantly different from each other. The lowest concentration, for which a significant effect compared to control in Student;s t-test was found, amounted to 10(-10) M, 10(-9) M, 10(-7) M, 10(-6.5) M and 10(-4) M for nimodipine, nifedipine, diltiazem, verapamil and mibefradil, respectively. L-type calcium antagonists are very potent relaxant agents of the human detrusor muscle in vitro.

Inhibitory effects of various L-type and T-type calcium antagonists on electrically generated, potassium-induced and carbachol-induced contractions of porcine detrusor muscle

The inhibitory effects of different calcium antagonists on contractions of isolated porcine detrusor muscle were investigated. Suppression of the maximum potassium-induced contraction and electrically generated contractions by nifedipine, verapamil and diltiazem were investigated. Furthermore, concentration-response curves of carbachol after pretreatment with the L-type antagonists nifedipine, verapamil, diltiazem, nimodipine and the T-type antagonist mibefradil at different concentrations were performed. Nifedipine significantly reduced the potassium-induced maximum contraction to 89, 60, 21, 8 and 4% (10(-9)-10(-5) M). Verapamil and diltiazem significantly reduced it to 64, 30 and 5% (10(-7)-10(-5) M) or 79, 27, 7 and 1% (10(-7)-10(-4) M), respectively. Nifedipine, verapamil and diltiazem significantly reduced the electrically generated contraction to 55, 36, 34 and 25% (10(-7)-10(-4) M), 71, 32 and 2% (10(-6)-10(-4) M), 96, 78, 38 and 5% (10(-7)-10(-4) M), respectively. pD2 values of nifedipine, verapamil and diltiazem amounted to 7.07, 5.56 and 5.40 and differed significantly. After pretreatment with nifedipine at 10(-6) M, the concentration-response curve of carbachol was nearly suppressed. The effects of nimodipine, verapamil and diltiazem were smaller. Mibefradil caused only at 10(-5) M a significant reduction. All investigated L-type calcium antagonists were strong inhibitors of the examined contractions. Nifedipine showed the biggest inhibitory effect.

The inhibitory role of melatonin on isolated guinea-pig urinary bladder: an endogenous hormone effect

OBJECTIVE

To investigate the effects of melatonin, an endogenous hormone, on acetylcholine and KCl-induced contractions of isolated guinea-pig detrusor muscle.

MATERIALS AND METHODS

Detrusor smooth muscle strips isolated from guinea-pig bladders were placed in an organ bath containing physiological saline at 37 degrees C and pH 7.4, constantly bubbled with 95% oxygen and 5% CO2. The effects of cumulatively applied melatonin on the acetylcholine- and KCl-induced contractions of isolated bladder strips were examined using isometric contraction measurements.

RESULTS

Melatonin (100 and 300 micromol/L) significantly inhibited the peak amplitude of both acetylcholine (10 micromol/L) and KCl (30 mmol/L)-induced contraction of the isolated bladder strips (P < 0.05). Similarly, melatonin caused a significant reduction in the contractile frequency induced by KCl (eight strips) in a concentration-dependent manner, while having no significant effect on the frequency of contractile response to acetylcholine, even at the highest concentration (300 micromol/L) used (P = 0.58, 14 strips).

CONCLUSIONS

These results suggest that melatonin inhibits acetylcholine- and KCl-induced contractions in isolated bladder strips from guinea pigs. The endogenous nature of melatonin, with its low side-effect profile, makes it a potentially useful agent to be considered in the medical management of the overactive bladder.

Effect of partial outlet obstruction of the rabbit urinary bladder on ryanodine binding to microsomal membranes

1. Partial outlet of obstruction of the rabbit urinary bladder results in a significant increase in the ability of ryanodine to inhibit field stimulated contraction. The current study determined the effect of outlet obstruction on ryanodine binding to microsomal membranes. 2. The results demonstrate: (i) Ryanodine binding is linear showing one set of ryanodine binding sites (Bmax = 28 +/- 3.5 fmol/mg protein; Kd = 4.2 nM). (ii) Total ryanodine binding was slightly increased at 1 and 3 day following obstruction. (iii) Binding increased approx 4-fold at 5 and 7 days post obstruction. (iv) No change in the Kds were noted at any time period. 3. The results of these studies indicate that smooth muscle hypertrophy secondary to partial outlet obstruction induces a marked increase in the role of intracellular calcium in the mediation of the contractile response to field stimulation.

The binding and functional properties of voltage dependent calcium channel receptors in pediatric normal and myelodysplastic bladders

The present study was designed to compare the binding and functional properties of calcium channel receptors in normal and myelodysplastic bladders. Normal bladders were obtained from children with vesicoureteral reflux undergoing ureteral reimplantation. Myelodysplastic bladder specimens were obtained from patients undergoing bladder augmentation. The functional studies included agonist (calcium chloride) dose response experiments and the determination of apparent antagonist dissociation constants for various calcium channel antagonists. The receptor binding studies were performed using the ligand (+)-3H-PN200-110 (specific activity 86.6 Ci./mmol.). The mean maximal response of myelodysplastic bladders to calcium ions was 31% less than normal bladders (p greater than 0.05). The mean EC50 for calcium mediated isometric tension and the mean -log antagonist dissociation constant values of nifedipine, diltiazem and verapamil were similar in normal and myelodysplastic bladders. The radioligand receptor binding studies demonstrated that the equilibrium dissociation constant of (+)-3H-PN200-110 in myelodysplastic bladders was 4-fold greater than in normal bladders. The density of dihydropyridine binding sites in myelodysplastic and normal bladders was similar. Our study demonstrated that the pathophysiology of the poorly compliant hyperreflexic bladder is not related to up regulation of dihydropyridine calcium channel receptors or alterations in the response of detrusor muscle to calcium ions. The relative abundance of calcium channel receptors in the normal and myelodysplastic bladders, and the regulation of detrusor contraction by calcium ions suggest that calcium channel receptors have a meaningful role in detrusor function.

Effect of extracellular Ca2+ on cholinergic, KCl and phorbol ester-mediated phosphoinositide turnover and guinea pig urinary bladder contraction

The effect of extracellular Ca2+ ([Ca2+]o) on cholinergic, KCl and phorbol ester-mediated detrusor contractions was related to phosphoinositide (PI) breakdown in guinea pig urinary bladder. Carbachol (1.0 mM) elicited a 20-fold increase in inositol phosphate (IP) accumulation both in presence and absence of [Ca2+]o yielding the same EC50 value (approximately 12 microM). In contrast, carbachol-induced detrusor contractions were reduced by 35% without [Ca2+]o, but maximal efficacy was restored with Ca2+ replenishment. In absence of [Ca2+]o, repeated cholinergic stimulation yielded contractions only if tissues were intermittently equilibrated in [Ca2+]o. High K+ and PDBu evoked [Ca2+]o-dependent contractions. Ca2+ channel antagonists and divalent metal cations inhibited high K+ more potently than carbachol-mediated contractions. Together, these findings suggest multiple sources of Ca2+ for urinary bladder contraction, where voltage-sensitive responses depend primarily on [Ca2+]o and PI-linked muscarinic responses involved Ca2+ mobilization from intracellular stores as well. Clinical agents used for the treatment of urinary incontinence inhibited both carbachol-induced PI turnover and muscle contraction with the same rank order of potency both in presence and absence of [Ca2+]o. These findings suggest that the cholinergic mechanism of action of these agents involves the PI-Ca2+ effector system.

The effect of raveron on the detrusor muscle

Raveron (a European pharmaceutical consisting of swine prostate extract and m-creosal) was studied in vivo in female mongrel dogs and in vitro bladder studies were conducted on male New Zealand rabbits. Intravenous administration of raveron reduced both the passive and active pressure in dog detrusor in vivo. It did not act in a dose dependent fashion. Chronic treatment with raveron for three to four months caused changes in in rabbits with vesical neck obstruction. An increase in contractility along with a reduced rate of increase in passive force (measurement of bladder stiffness) was observed in relation to obstructed rabbits without treatment. Parallel morphological changes were also observed in this group, consisting of increased muscular hypertrophy, decreased bladder wall thickness and reduced collagen content (readings taken from Masson-Trichrome sections). No influence was observed with bladder specimens from rabbits with six to eight week vesical obstruction or normals that received treatment. In vitro dose response studies showed that a 3.3% dose of raveron significantly reduced passive force in two groups (treated normals and treated rabbits with six to eight week vesical obstruction). Pharmacology studies with potassium chloride and acetylcholine suggest that raveron acts as a calcium antagonist by blocking the influx of extracellular calcium.

The effect of nifedipine on spontaneous, drug-induced and reflexly-activated contractions of the rat urinary bladder: evidence for the participation of an intracellular calcium store to micturition contraction

1. The effect of nifedipine on spontaneous and stimulated motility of the rat urinary bladder has been investigated in vitro (isolated detrusor strips) and in vivo (micturition reflex). 2. Nifedipine inhibited tone and spontaneous activity of the isolated rat bladder, its effect being greater in indomethacin-treated preparations. Nifedipine suppressed the KCl induced phasic and tonic contraction and inhibited by 60-80% the carbachol- or ATP- induced contractions. Nifedipine reduced by about 70% amplitude of the nerve-mediated bladder contractions. 3. Exposure to Ca free medium containing EDTA suppressed tone and spontaneous activity of the rat bladder. In these conditions the response to KCl or ATP was rapidly abolished while a response to carbachol was still evident even after a long exposure to the Ca free medium. 4. In vivo, nifedipine affected reflex micturition e.g. increased volume threshold and slightly reduced amplitude of micturition contraction. In addition, nifedipine reduced voiding efficiency e.g. increased residual volume after micturition. These effects were evident following ligation of the ureters because in normal conditions nifedipine induced a marked diuresis which masked its effect on volume threshold. 5. These findings indicate that in the rat urinary bladder Ca from both intra- and extracellular pools is mobilized during spontaneous or stimulated contractions. Mobilization of an intracellular Ca pool by cholinomimetics or other neurotransmitter(s) may be responsible for the nifedipine-resistant component of the voiding contraction in vivo.