Changes in the function and expression of T-type and N-type calcium channels in the rat bladder after bladder outlet obstruction

Inhibition of Contractility of Isolated Caprine Detrusor by the Calcium Channel Blocker Cilnidipine and Reversal by Calcium Channel Openers

Background

Cilnidipine is a fourth-generation calcium channel blocker that is clinically used to treat hypertension. It is a dihydropyridine that blocks L- and N-type calcium channels. The inhibitory effect of cilnidipine on isolated detrusor muscle contractility has not been studied. This study investigated the inhibitory effect of cilnidipine on isolated caprine (goat) detrusor muscle contractility and the reversal of the inhibition by calcium channel openers.

Methods

Fourteen caprine detrusor strips were made to contract using 80 mM potassium chloride before and after addition of three concentrations (20, 40, and 60 µM) of cilnidipine. Two reversal agents, the L-type calcium channel opener FPL64716, and the N-type calcium channel opener GV-58, were investigated for their ability to reverse the inhibitory effect of 40 µΜ cilnidipine on potassium chloride-induced detrusor contractility.

Results

Cilnidipine caused a dose-dependent and statistically significant inhibition of detrusor contractility at all concentrations of cilnidipine used (20, 40, and 60 µΜ). The inhibitory effect of 40 µM cilnidipine on detrusor contractility was significantly reversed by the addition of FPL64716 and GV-58.

Conclusions

Cilnidipine inhibits the contractility of the isolated detrusor by blocking L- and N-type calcium channels. Cilnidipine could be evaluated for treating clinical conditions requiring relaxation of the detrusor such as overactive bladder.

The T-type calcium channel Ca V 3.2 regulates bladder afferent responses to mechanical stimuli

ABSTRACT

The bladder wall is innervated by a complex network of afferent nerves that detect bladder stretch during filling. Sensory signals, generated in response to distension, are relayed to the spinal cord and brain to evoke physiological and painful sensations and regulate urine storage and voiding. Hyperexcitability of these sensory pathways is a key component in the development of chronic bladder hypersensitivity disorders including interstitial cystitis/bladder pain syndrome and overactive bladder syndrome. Despite this, the full array of ion channels that regulate bladder afferent responses to mechanical stimuli have yet to be determined. Here, we investigated the role of low-voltage-activated T-type calcium (Ca V 3) channels in regulating bladder afferent responses to distension. Using single-cell reverse-transcription polymerase chain reaction and immunofluorescence, we revealed ubiquitous expression of Ca V 3.2, but not Ca V 3.1 or Ca V 3.3, in individual bladder-innervating dorsal root ganglia neurons. Pharmacological inhibition of Ca V 3.2 with TTA-A2 and ABT-639, selective blockers of T-type calcium channels, dose-dependently attenuated ex-vivo bladder afferent responses to distension in the absence of changes to muscle compliance. Further evaluation revealed that Ca V 3.2 blockers significantly inhibited both low- and high-threshold afferents, decreasing peak responses to distension, and delayed activation thresholds, thereby attenuating bladder afferent responses to both physiological and noxious distension. Nocifensive visceromotor responses to noxious bladder distension in vivo were also significantly reduced by inhibition of Ca V 3 with TTA-A2. Together, these data provide evidence of a major role for Ca V 3.2 in regulating bladder afferent responses to bladder distension and nociceptive signalling to the spinal cord.

Deletion of the lysyl oxidase-like 1 gene induces impaired elastin fiber synthesis and inefficient urethral closure in rats

We investigated the bladder and urethral function in a rat model lacking the protein lysyl oxidase-like 1 (Loxl1). Female nulliparous rats of Loxl1^-/- or age-matched wild type (WT) rats had leak-point pressure testing, cystometry, histopathological analyses of lower urinary tract, and contractile response of isolated detrusor strips to carbachol and electric field stimulation. The Loxl1^-/- rats showed increased looseness and redundancy of the skin, the decreased intercontraction interval and voided volume in cystometry, the lower leak-point pressure, thinner elastic fibers of the mesentery, bladder, urethra and vagina, and smaller contractile response of detrusor strips to carbachol when compared to the WT rats. Thus, the insufficient hydrostatic mechanism of urethra via submucosal impaired elastin synthesis might reduce the resting urethral closure pressure and the diminished cholinergic contractile response of detrusor smooth muscle might be involved in bladder activity in the Loxl1^-/- rats.

Gabapentin reduces painful bladder hypersensitivity in rats with lipopolysaccharide-induced chronic cystitis

Although interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic condition causing bladder pain and urinary symptoms, effective treatments have not been established. The aim of this study was to adapt a chronic cystitis model in rats using lipopolysaccharide (LPS), which reflects IC/BPS pathology, and characterize the model's histological and behavioral effects. Furthermore, we investigated the effect of an α2 δ subunit ligand, gabapentin (GBP), on bladder hypersensitivity of rats with chronic cystitis. Cystitis models were created by repeated intravesical injections of LPS. In the histological examination, the LPS-injected group had greater inflammatory response, fibrosis, and abnormally thick re-epithelialization. In the LPS-injected group, LPS prompted hyperalgesia in both the lower abdomen and hind paw regions after day 1 of the first injection compared with the saline-injected controls, without any recovery for 21 days at least. During cystometry, the LPS-injected group showed bladder hyperactivity at all times. Systemic administration of GBP reduced cystitis-related pain due to chronic inflammation and reduced the increased frequency of voiding in the LPS-injected group. These results suggest that repeated intravesical injections of LPS induce long-lasting bladder inflammation, pain, and overactivity in rats, while GBP is effective in the management of those symptoms in this chronic cystitis model. The current study identifies a relatively simple method to develop an animal model for chronic cystitis and provides evidence that GBP may be an effective treatment option for patients with IC/BPS.

Effectiveness of Gabapentinoids for Cancer-related Rectal and Vesical Tenesmus: Report of Four Cases

Gabapentinoids could be assumed to relieve cancer-related rectal/vesical tenesmus based on their pharmacological mechanism. Four patients were refractory for cancer-related rectal/vesical tenesmus although their opioid doses were titrated up. Symptom intensity difference (SID) between initiation and follow-up after 24, 48, and 72 h and daily changes in the frequency of urination, defecation, opioid rescue doses, presence of sleep disruption, and dose of regular opioid medication were evaluated. The median reductions in daily discomfort measured as SID between baseline and follow-up after 24, 48, and 72 h were 87.5%, 70.0%, and 80.0%, respectively, while those in daily pain intensity were 75%, 66.7%, and 66.7%, respectively. The initiation dose of gabapentin was 200 or 400 mg/day and that of pregabalin was 75 mg/day in one patient. Gabapentinoids were effective at low doses administered over a short duration to patients with refractory cancer-related rectal/vesical tenesmus.

Urinary bladder smooth muscle ion channels: expression, function, and regulation in health and disease

Urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, forms the bladder wall and ultimately determines the two main attributes of the organ: urine storage and voiding. The two functions are facilitated by UBSM relaxation and contraction, respectively, which depend on UBSM excitability shaped by multiple ion channels. In this review, we summarize the current understanding of key ion channels establishing and regulating UBSM excitability and contractility. They include excitation-enhancing voltage-gated Ca2+ (Cav) and transient receptor potential channels, excitation-reducing K+ channels, and still poorly understood Cl- channels. Dynamic interplay among UBSM ion channels determines the overall level of Cav channel activity. The net Ca2+ influx via Cav channels increases global intracellular Ca2+ concentration, which subsequently triggers UBSM contractility. Here, for each ion channel type, we describe UBSM tissue/cell expression (mRNA and protein) profiles and their role in regulating excitability and contractility of UBSM in various animal species, including the mouse, rat, and guinea pig, and, most importantly, humans. The currently available data reveal certain interspecies differences, which complicate the translational value of published animal research results to humans. This review highlights recent developments, findings on genetic knockout models, pharmacological data, reports on UBSM ion channel dysfunction in animal bladder disease models, and the very limited human studies currently available. Among all gaps in present-day knowledge, the unknowns on expression and functional roles for ion channels determined directly in human UBSM tissues and cells under both normal and disease conditions remain key hurdles in the field.

Evaluation of a rat model of functional urinary bladder outlet obstruction produced by chronic inhibition of nitric oxide synthase

AIMS

Ligation of the urethra to create partial bladder outlet obstruction has widely been used as an animal model of bladder obstruction, although obstructive bladder dysfunction may be due to both mechanical and functional obstruction. Previous studies in rodents have demonstrated that long-term nitric oxide (NO) deficiency can lead to detrusor overactivity, and lack of NO may thus cause impairment of bladder outlet relaxation. The aim of this study was to define the characteristics of bladder and urethral dysfunction induced by chronic NO deficiency through both in vivo and in vitro investigations.

MAIN METHODS

Rats were divided into two groups, and one group received an NO synthase inhibitor (N_ω-nitro-L-arginine methyl ester hydrochloride: L-NAME) in the drinking water for 4 weeks. Bladder and urethral function were evaluated by continuous cystometry and isovolumetric cystometry. In vitro functional studies of detrusor strips and measurement of the mRNA and protein expression of an ischemic marker and a gap junction protein were also performed in separate rats.

KEY FINDINGS

L-NAME administration raised blood pressure and decreased plasma nitrite/nitrate level compared to the control group. L-NAME treatment increased the frequency of bladder contractions and the residual volume, and elevated urethral pressure and bladder contraction pressure. In addition, carbachol-induced contraction was reduced in isolated detrusor strips from the L-NAME group, and bladder expression of HIF-1 and connexin 43 showed upregulation.

SIGNIFICANCE

These findings suggest that chronic administration of L-NAME to rats induces bladder hyperactivity with residual urine, and may provide a useful model of functional bladder obstruction.

Attenuated lipopolysaccharide-induced inflammatory bladder hypersensitivity in mice deficient of transient receptor potential ankilin1

Transient receptor potential ankyrin 1 (TRPA1) channel expressed by urothelial cells and bladder sensory nerve fibers might act as a bladder mechanosensor and nociceptive transducer. To disclose the role of TRPA1 in bladder function and inflammation-associated hypersensitivity, we evaluated in vitro and in vivo bladder function and inflammatory mechanosensory and nociceptive responses to intravesical lipopolysaccharide (LPS)-instillation in wild type (WT) and TRPA1-knock out (KO) mice. At baseline before treatment, no significant differences were observed in frequency volume variables, in vitro detrusor contractility, and cystometric parameters between the two groups in either sex. LPS-instillation significantly increased voiding frequency and decreased mean voided volume at 24-48 hours after instillation in WT but not in TRPA1-KO mice. LPS-instillation also significantly increased the number of pain-like behavior at 24 hours after instillation in WT mice, but not in TRPA1-KO mice. Cystometry 24 hours after LPS-instillation revealed shorter inter-contraction intervals in the WT mice compared with TRPA1-KO mice. In contrast, inflammatory cell infiltration in the bladder suburothelial layer was not significantly different between the two groups. These results indicate that TRPA1 channels are involved in bladder mechanosensory and nociceptive hypersensitivity accompanied with inflammation but not in physiological bladder function or development of bladder inflammation.

Involvement of Voltage-Gated Calcium Channels in Inflammation and Inflammatory Pain

Voltage-gated calcium channels (VGCCs) are classified into high-voltage-activated (HVA) channels and low-voltage-activated channels consisting of Ca_v3.1-3.3, known as T ("transient")-type VGCC. There is evidence that certain types of HVA channels are involved in neurogenic inflammation and inflammatory pain, in agreement with reports indicating the therapeutic effectiveness of gabapentinoids, ligands for the α₂δ subunit of HVA, in treating not only neuropathic, but also inflammatory, pain. Among the Ca_v3 family members, Ca_v3.2 is abundantly expressed in the primary afferents, regulating both neuronal excitability at the peripheral terminals and spontaneous neurotransmitter release at the spinal terminals. The function and expression of Ca_v3.2 are modulated by a variety of inflammatory mediators including prostanoids and hydrogen sulfide (H₂S), a gasotransmitter. The increased activity of Ca_v3.2 by H₂S participates in colonic, bladder and pancreatic pain, and regulates visceral inflammation. Together, VGCCs are involved in inflammation and inflammatory pain, and Ca_v3.2 T-type VGCC is especially a promising therapeutic target for the treatment of visceral inflammatory pain in patients with irritable bowel syndrome, interstitial cystitis/bladder pain syndrome, pancreatitis, etc., in addition to neuropathic pain.

Increased Expression of TREK-1 K+ Channel in the Dorsal Root Ganglion of Rats with Detrusor Overactivity After Partial Bladder Outlet Obstruction

Background

Changes in expression and activity of ion channels are important pathophysiological mechanisms underlying detrusor overactivity (DO) in partial bladder outlet obstruction (PBOO). The objective of this study was to examine the expression of TREK-1 channel in the bladder and central nervous system of DO rats.

Material/Methods

Thirty Sprague-Dawley rats were subjected to PBOO operations and those displaying non-voiding contractions (NVCs) in cystometry were classified as DO. Sham-operated rats without NVCs in cystometry served as controls. The expression and distribution of TREK-1 in the bladder, spinal cord, and dorsal root ganglion (DRG) were detected by real time-PCR, western blot, and immunohistochemistry.

Results

TREK-1 channel expression in the DRG was significantly increased at the mRNA level (11.20±3.762 vs. 3.209±1.505, P<0.01) and protein level (2.195±0.058 vs. 1.713±0.066, P<0.01) in DO rats as compared to control rats. However, the expression of TREK-1 mRNA in the bladder (1.380±0.810 vs. 4.206±3.827, P>0.05) and spinal cord (0.764±0.357 vs. 0.696±0.188, P>0.05) was comparable between the 2 groups. Immunohistochemistry showed enhanced immunoreactive signals of TREK-1 channel in the DRG, but not in the spinal cord and bladder.

Conclusions

TREK-1 channel was upregulated in the DRG of DO rats after chronic PBOO, which might suppress neuronal excitability and play a protective role in bladder overactivity in PBOO.

Age-related changes in function and gene expression of the male and female mouse bladder

We investigated age-related changes in in vivo and in vitro functions and gene expression of the bladder of male and female mice. Mature and aged (12 and 27–30 month old) C57BL/6 mice of both sexes were used. Frequency volume, conscious free-moving cystometry and detrusor contractile and relaxant properties in in vitro organ bath were evaluated. mRNA expression level of muscarinic, purinergic, and β-adrenergic receptors and gene expression changes by cDNA microarray analysis of the bladder were determined. Cystometry demonstrated storage and voiding dysfunctions with ageing in both sexes. Detrusor strips from aged mice showed weaker contractile responses particularly in the cholinergic component and weaker relaxant responses to isoproterenol. These age-related impairments were generally severer in males. mRNA expression of bladder tissue was decreased for M3 muscarinic receptors in aged males and β2-adrenoceptors in aged females. cDNA microarray analysis results, albeit substantial sex difference, indicated “cell-to-cell signaling and interaction” as the most common feature of age-related gene expression. In summary, aged mice demonstrated voiding and storage dysfunctions resembling to detrusor hyperactivity with impaired contractility (DHIC), which were more pronounced in males. Genomic changes associated with aging may contribute to the age-related bladder functional deterioration in mice.

Enhanced expression of TWIK-related arachidonic acid-activated K+ channel in the spinal cord of detrusor overactivity rats after partial bladder outlet obstruction

Background

Detrusor overactivity (DO) secondary to partial bladder outlet obstruction (PBOO) is closely associated with alteration of ion channels. The objective of this study is to investigate the expression of the TWIK-related arachidonic acid-activated K⁺ channel (TRAAK) in the L6-S1 spinal cord of DO rats after PBOO.

Methods

Female Sprague–Dawley rats undergoing PBOO surgery were screened for DO by cystometry. Sham-operated rats served as controls. The expression of TRAAK in the L6-S1 spinal cord was detected by real-time polymerase chain reaction, western blotting and immunohistochemistry.

Results

DO was successfully induced after chronic PBOO in rats, with an incidence rate of 62.5 %. Compared with sham-operated rats, the expression of TRAAK in the L6-S1 spinal cord of DO rats was significantly increased at the mRNA (1.886 ± 0.710 versus 0.790 ± 0.679, P < 0.05) and protein level (0.510 ± 0.087 versus 0.255 ± 0.107, P < 0.05). Immunohistochemical staining showed increased expression of TRAAK in the dorsal horn and ventral horn of the spinal cord.

Conclusions

Upregulation of TRAAK was observed in the spinal cord of DO rats after chronic PBOO, which may exert a protective effect against DO by suppressing the excitability of neurons.

Long-term caloric restriction in rats may prevent age related impairment of in vitro bladder function

PURPOSE

Bladder function is often impaired with aging. In other organs caloric restriction has had a prophylactic effect on the biological changes associated with aging. We tested the hypothesis that long-term caloric restriction can prevent age related impaired bladder function in the rat.

MATERIALS AND METHODS

Fisher 344 male rats were divided into 3 groups, including 16 young rats at age 6 months with free access to normal food, 15 old rats at age 25 to 28 months with free access to normal food and 16 old rats at age 25 to 28 months fed with normal food 3 days per week since age 6 weeks (caloric restriction). We performed frequency volume measurements, in vitro organ bath functional studies using full-thickness longitudinal detrusor strips, evaluation of muscarinic and purinergic receptor mRNA expression, and histological examination with Masson trichrome staining of bladder tissue.

RESULTS

Frequency volume changes did not significantly differ among the 3 groups. The old group fed normal food showed weaker contractile responses to carbachol and electrical field stimulation (especially in the cholinergic component), lower M3 receptor mRNA expression and higher collagen deposition compared to the young group. These age related bladder changes were milder in the old group with caloric restriction than in the old group fed normal food.

CONCLUSIONS

This study suggests that in the rat long-term caloric restriction has a preventive effect against age related functional and morphological bladder changes. These changes include impaired detrusor contractility that may be related to decreased expression of M3 receptors and to bladder wall fibrosis.

T-type Ca2+ channels and the urinary and male genital tracts

T-type Ca(2+) channels are widely expressed throughout the urinary and male genital tracts, generally alongside L-type Ca(2+) channels. The use of pharmacological blockers of these channels has suggested functional roles in all regions, with the possible exception of the ureter. Their functional expression is apparent not just in smooth muscle cells but also in interstitial cells that lie in close proximity to muscle, nerve and epithelial components of these tissues. Thus, T-type Ca(2+) channels can contribute directly to modulation of muscle function and indirectly to changes of epithelial and nerve function. T-type Ca(2+) channel activity modulates phasic contractile activity, especially in conjunction with Ca(2+)-activated K(+) channels, and also to agonist-dependent responses in different tissues. Upregulation of channel density occurs in pathological conditions associated with enhanced contractile responses, e.g. overactive bladder, but it is unclear if this is causal or a response to the pathological state. Moreover, T-type Ca(2+) channels may have a role in the development of prostate tumours regulating the secretion of mitogens from neuroendocrine cells. Although a number of selective channel blockers exist, their relative selectivity over L-type Ca(2+) channels is often low and makes evaluation of T-type Ca(2+) channel function in the whole organism difficult.