Regional differences in responses of rabbit detrusor to electrical and adrenergic stimulation: influence of outlet obstruction

Dog and human bladders have different neurogenic and nicotinic responses in inner versus outer detrusor muscle layers

The aim of this study was to investigate layer and species variations in detrusor muscle strip responses to myogenic, neurogenic, and nicotinic, and muscarinic receptor stimulations. Strips from bladders of 9 dogs and 6 human organ transplant donors were dissected from inner and outer longitudinal muscle layers, at least 1 cm above urethral orifices. Strips were mounted in muscle baths and maximal responses to neurogenic stimulation using electrical field stimulation (EFS) and myogenic stimulation using potassium chloride (KCl, 120 mM) determined. After washing and re-equilibration was completed, responses to nicotinic receptor agonist epibatidine (10 μM) were determined followed by responses to EFS and muscarinic receptor agonist bethanechol (30 μM) in continued presence of epibatidine. Thereafter, strips and full-thickness bladder sections from four additional dogs and three human donors were examined for axonal density and intramural ganglia. In dog bladders, contractions to KCl, epibatidine, and bethanechol were 1.5- to 2-fold higher in the inner longitudinal muscle layer, whereas contractions to EFS were 1.5-fold higher in the outer (both pre- and post-epibatidine). Human bladders showed 1.2-fold greater contractions to epibatidine in the inner layer and to EFS in the outer, yet no layer differences to KCl or bethanechol were noted. In both species, axonal density was 2- to 2.5-fold greater in the outer layer. Dogs had more intramural ganglia in the adventitia/serosa layer, compared with more internal layers and to humans. These findings indicate several layer-dependent differences in receptor expression or distribution, and neurogenic responses in dog and human detrusor muscles, and myogenic/muscarinic differences between dog versus humans.

Assessment of local structural disorders of the bladder wall in partial bladder outlet obstruction using polarized light imaging

Partial bladder outlet obstruction causes prominent morphological changes in the bladder wall, which leads to bladder dysfunction. In this paper, we demonstrate that polarized light imaging can be used to identify the location of obstruction induced structural changes that other imaging modalities fail to detect. We induced 2-week and 6-week partial outlet obstruction in rats, harvested obstructed bladders, then measured their retardances while distended to high pressures and compared them to controls. Our results show that the retardance of the central part of the ventral side (above the ureters) closer to the urethra can be used as a potential metric of the distending bladder obstruction.

Berberine improves neurogenic contractile response of bladder detrusor muscle in streptozotocin-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Coptidis Rhizoma has been used to treat diabetes mellitus for more than 1400 years in China. Berberine, one of the main alkaloids of Coptidis Rhizoma, is a principal antidiabetic component of Coptidis Rhizoma. To investigate the effects of berberine on impaired neurogenic contractility of detrusor muscle from urinary bladder of rats with early stage diabetes.

MATERIALS AND METHODS

The detrusor muscle strips were isolated from urinary bladders of streptozotocin-induced diabetic rats, 5% sucrose-induced diuretic rats or normal rats, and were placed in organ bath. The contractions induced by electrical field stimulation (EFS), carbachol, KCl, adenosine triphosphate, and the effects of berberine on those contractions were measured.

RESULTS

The EFS- or KCl-induced contraction of detrusor muscle was significantly decreased in diabetic rats as compared with diuretic or normal rats. Atropine and suramin inhibited EFS-induced contraction. In diabetic rats, the atropine sensitive components were decreased in EFS-induced contraction of detrusor muscle, and the adenosine triphosphate-induced contraction was significantly increased. The carbachol-induced contrations were not different among groups. Berberine significantly potentiated EFS-induced contractions of detrusor muscle both from normal and diabetic rats, but the potentiated effect of BBR was more sensitive to atropine in diabetic rats. Berberine also potentiated adenosine triphosphate-induced contraction of detrusor muscle, but did not change carbachol- or KCl-induced contraction.

CONCLUSION

The neurogenic contraction of urinary bladder detrusor muscle is decreased while purinergic contraction of bladder detrusor muscle is increased in rats with early stage diabetes. Berberine increases the neurogenic contractile response to EFS possibly via both presynaptic increasing neurotransmitters release and postsynaptic potentiation of purinergic transmitter-regulated response in rat urinary bladder detrusor; and in diabetic rats, berberine increases neurogenic contractile response mainly via the presynaptic increasing acetylcholine release.

Effects of imidazolines on neurogenic contraction in isolated urinary bladder detrusor strips from rabbit

Moxonidine and clonidine, which are imidazoline compounds, are sympathetic modulators used as centrally acting antihypertensive drugs. Moxonidine, clonidine, and agmatine produce extensive effects in mammalian tissues via imidazoline recognition sites (or receptors) or α(2)-adrenoceptors. To investigate the effects of imidazolines on the function of the urinary bladder, we tested the effects of moxonidine, clonidine, and agmatine on the neurogenic contraction induced by electric field stimulation, and on the post-synaptic receptors in isolated urinary bladder detrusor strips from rabbit. Both moxonidine at 1.0-10.0 µmol/L and clonidine at 0.1-10.0 µmol/L inhibited electric-field-stimulation-induced contraction in a concentration-dependent manner, but not agmatine (10.0-1000.0 µmol/L). Both moxonidine and clonidine failed to affect carbachol or adenosine-triphosphate-induced contractions; however, 1000.0 µmol/L agmatine significantly increased these contractions. Our study indicates that (i) moxonidine and clonidine produce a concentration-dependent inhibition of the neurogenic contractile responses to electric field stimulation in isolated detrusor strips from male New Zealand rabbits; (ii) post-synaptic muscarinic receptor and purinergic receptor stimulation are not involved in the responses of moxinidine and clonidine in this study; (iii) the inhibitory effects of these agents are probably not mediated by presynaptic imidazoline receptors.

Inducible knockout mutagenesis reveals compensatory mechanisms elicited by constitutive BK channel deficiency in overactive murine bladder

The large-conductance, voltage-dependent and Ca(2+)-dependent K(+) (BK) channel links membrane depolarization and local increases in cytosolic free Ca(2+) to hyperpolarizing K(+) outward currents, thereby controlling smooth muscle contractility. Constitutive deletion of the BK channel in mice (BK(-/-)) leads to an overactive bladder associated with increased intravesical pressure and frequent micturition, which has been revealed to be a result of detrusor muscle hyperexcitability. Interestingly, time-dependent and smooth muscle-specific deletion of the BK channel (SM-BK(-/-)) caused a more severe phenotype than displayed by constitutive BK(-/-) mice, suggesting that compensatory pathways are active in the latter. In detrusor muscle of BK(-/-) but not SM-BK(-/-) mice, we found reduced L-type Ca(2+) current density and increased expression of cAMP kinase (protein kinase A; PKA), as compared with control mice. Increased expression of PKA in BK(-/-) mice was accompanied by enhanced beta-adrenoceptor/cAMP-mediated suppression of contractions by isoproterenol. This effect was attenuated by about 60-70% in SM-BK(-/-) mice. However, the Rp isomer of adenosine-3',5'-cyclic monophosphorothioate, a blocker of PKA, only partially inhibited enhanced cAMP signaling in BK(-/-) detrusor muscle, suggesting the existence of additional compensatory pathways. To this end, proteome analysis of BK(-/-) urinary bladder tissue was performed, and revealed additional compensatory regulated proteins. Thus, constitutive and inducible deletion of BK channel activity unmasks compensatory mechanisms that are relevant for urinary bladder relaxation.

Design, synthesis, and BK channel-opening activity of hexahydrodibenzazepinone derivatives

In order to explore new scaffolds for large-conductance Ca2+ -activated K+ channel (BK channel) openers, we carried out molecular design and synthesis on the basis of the following two concepts: (1) introduction of a heteroatom into the dehydroabietic acid (BK channel opener) skeleton would allow easier introduction of substituents. (2) Because of the fourfold symmetrical structure of BK channels, dimeric compounds in which two pharmacophores are linked through a tether are expected to have a greater binding probability to the channels, resulting in increased channel-opening activity. Herein, we explore the usefulness of the hexahydrodibenzazepinone structure as a new scaffold for BK channel openers. The synthesized monomer compounds of hexahydrodibenzazepinone derivatives, which can be derived from dehydroabietic acid, were subjected to electrophysiological patch-clamp studies, followed by Magnus contraction-relaxation assay using rabbit urinary bladder smooth muscle strips to assess overall activities. Dimeric compounds were designed by linking the monomeric hexahydrodibenzazepinone derivatives through a diacetylenebenzene tether, and their channel-opening activities were evaluated by electrophysiological methods. Finally, we concluded that the critical structure for BK channel-opening activity is the hexahydrodibenzazepinone monomer substituted with a phenyl-bearing alkynyl substituent on the lactam amide.