Signaling Pathways Mediating Bradykinin-Induced Contraction in Murine and Human Detrusor Muscle

Kinin B1- and B2-Receptor Subtypes Contract Isolated Bovine Ciliary Muscle: Their Role in Ocular Lens Function and Intraocular Pressure Reduction

Background: Bradykinin is an endogenously produced nonapeptide with many physiological and pathological functions that are mediated by two pharmacologically defined receptor subtypes, B1- and B2-receptors. Current studies sought to characterize the functional bradykinin (BK) receptors present in freshly isolated bovine ciliary muscle (BCM) using an organ-bath tissue contraction system. Methods: Cumulative longitudinal isometric tension responses of BCM strips (4-5 mm) were recorded before and after the addition of test compounds to BCM strips hooked up to an isometric strain gauge transducer system. Results: BK and its analogs (7-11 concentrations) contracted BCM in a biphasic concentration-dependent manner. The first high affinity/potency phase accounted for 40-60% of the maximal contraction by each of BK (potency, EC50 = 0.9 ± 0.3 nM), Lys-BK (EC50 = 0.7 ± 0.1 nM), Met-Lys-BK (EC50 = 1 ± 0.1 nM), Hyp3-BK (EC50 = 1 ± 0.2 nM), RMP-7 (EC50 = 3.5 ± 0.5 nM), and Des-Arg9-BK (EC50 = 10 ± 0.4nM) (mean ± SEM, n = 3-8). The second lower activity phase of contraction potency values for these peptides ranged between 100 nM and 3 µM. In the presence of a selective B1-receptor antagonist (R715; 0.1-10 µM), the concentration-response curves to Des-Arg9-BK (B1-receptor agonist) were still observed, indicating activation of B2-receptors by this kinin. Likewise, when B2-receptors were completely blocked by using a B2-selective antagonist (WIN-64338; 1-10 µM), BK still induced BCM contraction, now by stimulating B1-receptors. Conclusions: This agonist/antagonist profile of BCM receptors indicated the presence of both B1- and B2-receptor subtypes, both being responsible for contracting this smooth muscle. The BCM kinin receptors may be involved in changing the shape of the ocular lens to influence accommodation, and since the ciliary muscle is attached to the trabecular meshwork through which aqueous humor drains, endogenously released kinins may regulate intraocular pressure.

Intracellular signaling pathways of muscarinic acetylcholine receptor-mediated detrusor muscle contractions

Acetylcholine plays an essential role in the regulation of detrusor muscle contractions, and antimuscarinics are widely used in the management of overactive bladder syndrome. However, several adverse effects limit their application and patients' compliance. Thus, this study aimed to further analyze the signal transduction of M2 and M3 receptors in the murine urinary bladder to eventually find more specific therapeutic targets. Experiments were performed on adult male wild-type, M2, M3, M2/M3, or Gαq/11 knockout (KO), and pertussis toxin (PTX)-treated mice. Contraction force and RhoA activity were measured in the urinary bladder smooth muscle (UBSM). Our results indicate that carbamoylcholine (CCh)-induced contractions were associated with increased activity of RhoA and were reduced in the presence of the Rho-associated kinase (ROCK) inhibitor Y-27632 in UBSM. CCh-evoked contractile responses and RhoA activation were markedly reduced in detrusor strips lacking either M2 or M3 receptors and abolished in M2/M3 KO mice. Inhibition of Gαi-coupled signaling by PTX treatment shifted the concentration-response curve of CCh to the right and diminished RhoA activation. CCh-induced contractile responses were markedly decreased in Gαq/11 KO mice; however, RhoA activation was unaffected. In conclusion, cholinergic detrusor contraction and RhoA activation are mediated by both M2 and M3 receptors. Furthermore, whereas both Gαi and Gαq/11 proteins mediate UBSM contraction, the activation at the RhoA-ROCK pathway appears to be linked specifically to Gαi. These findings may aid the identification of more specific therapeutic targets for bladder dysfunctions.NEW & NOTEWORTHY Muscarinic acetylcholine receptors are of utmost importance in physiological regulation of micturition and also in the development of voiding disorders. We demonstrate that the RhoA-Rho-associated kinase (ROCK) pathway plays a crucial role in contractions induced by cholinergic stimulation in detrusor muscle. Activation of RhoA is mediated by both M2 and M3 receptors as well as by Gi but not Gq/11 proteins. The Gi-RhoA-ROCK pathway may provide a novel therapeutic target for overactive voiding disorders.

Editorial: Kinin 2022 Meeting, Annecy, France

The Kinin 2022 meeting took place at the Imperial Palace, Annecy, France, from 5-8 June 2022 [...].

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.

Gardnerella Exposures Alter Bladder Gene Expression and Augment Uropathogenic Escherichia coli Urinary Tract Infection in Mice

The anaerobic actinobacterium Gardnerella was first isolated from the bladder by suprapubic aspiration more than 50 years ago. Since then, Gardnerella has been increasingly recognized as a common and often abundant member of the female urinary microbiome (urobiome). Some studies even suggest that the presence of Gardnerella is associated with urological disorders in women. We recently reported that inoculation of Gardnerella into the bladders of mice results in urothelial exfoliation. Here, we performed whole bladder RNA-seq in our mouse model to identify additional host pathways involved in the response to Gardnerella bladder exposure. The transcriptional response to Gardnerella reflected the urothelial turnover that is a consequence of exfoliation while also illustrating the activation of pathways involved in inflammation and immunity. Additional timed exposure experiments in mice provided further evidence of a potentially clinically relevant consequence of bladder exposure to Gardnerella-increased susceptibility to subsequent UTI caused by uropathogenic Escherichia coli. Together, these data provide a broader picture of the bladder's response to Gardnerella and lay the groundwork for future studies examining the impact of Gardnerella on bladder health.