Attenuated BK channel function promotes overactive bladder in a rat model of obesity

SKA-31-induced activation of small-conductance calcium-activated potassium channels decreased modulation of detrusor smooth muscle function in a rat model of obesity

Increased excitability and contractility of detrusor smooth muscle (DSM) cells are associated with overactive bladder (OAB), which is often induced by obesity. Small-conductance Ca²⁺-activated K⁺ (SK) channels regulate the excitability and contractility of DSM cells. Selective pharmacological activation of SK channels attenuates hyperpolarization and the decreased relaxation effect in DSM cells in obesity-induced OAB. However, additional data are needed to confirm the regulatory effect of SK channels on the function of DSM cells in obesity-related OAB. The tested hypothesis was that activation of SK channels decreases modulation of DSM function in a rat model of obesity-related OAB. Female Sprague Dawley rats were fed a normal diet (ND) or a high-fat diet (HFD), weighed after 12 weeks, and subjected to urodynamic study, patch-clamp electrophysiology, and isometric tension recording. The average body weight and incidence of OAB were increased in the HFD group. Patch-clamp studies revealed that pharmacological activation of SK channels with SKA-31 had attenuated hyperpolarization of DSM cells. In addition, isometric tension recordings indicated that SKA-31 decreased relaxation of spontaneous phasic contractions of DSM strips in the HFD group. Attenuated function of SK channels increased the excitability and contractility of DSM cells, which contributed to the occurrence of OAB, suggesting that SK channels are potential therapeutic targets for control of OAB.

A Comprehensive Review of the Therapeutic Value of Urine-Derived Stem Cells

Stem cells possess regenerative powers and multidirectional differentiation potential and play an important role in disease treatment and basic medical research. Urine-derived stem cells (USCs) represent a newly discovered type of stem cell with biological characteristics similar to those of mesenchymal stromal cells (MSCs), including their doubling time and immunophenotype. USCs are noninvasive and can be readily obtained from voided urine and steadily cultured. Based on advances in this field, USCs and their secretions have increasingly emerged as ideal sources. USCs may play regulatory roles in the cellular immune system, oxidative stress, revascularization, apoptosis and autophagy. This review summarizes the applications of USCs in tissue regeneration and various disease treatments. Furthermore, by analysing their limitations, we anticipate the development of more feasible therapeutic strategies to promote USC-based individualized treatment.

Solifenacin/Mirabegron Induces an Acute Compliance Increase in the Filling Phase of the Capacity-Reduced Urinary Bladder: A Pressure-Volume Analysis in Rats

Aims: Pressure in the bladder, which is a high compliance organ, is only slightly elevated to a considerable filling volume during storage. Although cystometry off-line offers mean compliance, no protocol is available for real-time assays of the dynamics of bladder compliance, and the potential impact of solifenacin and mirabegron on dynamic bladder compliance has not been established.

Methods: Along with constantly infused cystometry, a pressure-volume analysis (PVA) was performed by plotting intra-vesical volume against pressure in Sprague-Dawley rats. The instant compliance was assayed as the slope of the trajectory, and the mean compliance (Cm) was determined by the slope of the line produced by regression of the data points at the end of the first, second, and third quarters of the filling phase.

Results: Under a steady-state, the PVA trajectory moved clockwise which shaped coincident enclosed loops with stable compliance. Though administering to naïve animals solifenacin, but not mirabegron (both 1 × 10⁻⁵−1 × 10⁻¹ mg/kg, i.a.) decreased the peak pressure, both of these reagents exhibited acute increments in the trajectory slope and Cm of the filling phase in a dose-dependent manner (ED₅₀ = 1.4 × 10⁻⁴ and 2.2 × 10⁻⁵ mg/kg, respectively). Resembling urine frequency/urgency in OAB patients, the voiding frequency of a capacity-reduced bladder was increased in association with decreased compliance which was ameliorated by both acute solifenacin and mirabegron injections (both 1 × 10−1 mg/kg).

Conclusion: In addition to their well-known anti-inotropic/relaxative effects, solifenacin, and mirabegron induce an acute increase in bladder compliance to ameliorate OAB-like syndromes. Together with time-domain cystometry, PVA offers a platform for investigating the physiology/pathophysiology/pharmacology of bladder compliance which is crucial for urine storage.

Female mice are resilient to age-related decline of substantia nigra dopamine neuron firing parameters

Degeneration of substantia nigra pars compacta dopamine neurons is a central feature in the pathology of Parkinson's disease, which is characterized by progressive loss of motor and cognitive functions. The largest risk factors for Parkinson's disease are age and sex; most cases occur after age 60 and males have nearly twice the incidence as females. Preclinical work has scarcely considered the influence of these 2 factors to disease risk and presentation. Here, we observed a progressive decline in dopamine neuron firing activity in male C57BL/6 mice by 18 months of age, while dopamine neurons from females remained largely unaffected. This was accompanied by increased mRNA expression of PINK1 in both males and females, and PARK2 primarily in males, both of which have been linked to Parkinson's. Since the declining cell properties were accompanied by only slight decreases in locomotion in both sexes, it is likely that these age-related impairments in males represent a vulnerability to further insults that could predispose the neurons to neurodegenerative processes such as in Parkinson's.

Attenuated regulatory function of the small-conductance Ca2+-activated K+ channel in detrusor smooth muscle cells excitability in an obese rat model

PURPOSE

Overactive bladder (OAB) is related to detrusor overactivity (DO), which is caused by the increased detrusor smooth muscle (DSM) cells excitability. Small-conductance Ca²⁺-activated K⁺ (SK) channels is a fundamental regulator of excitability and contractility in DSM cells. Obesity-related OAB is associated with the decreased expression and regulatory function of SK channels in DSM layer. However, the regulation role of SK channels in obesity-related OAB DSM cell excitability is still unknown. Here, we tested the hypothesis that obesity-related OAB is associated with reduced expression and activity of SK channels in DSM cells.

METHODS

Female Sprague-Dawley rats were fed a normal diet (ND) or a high-fat diet (HFD) and weighed after 12 weeks. We performed urodynamic study, single-cell quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and patch-clamp electrophysiology.

RESULTS

Increased average body weights and urodynamically demonstrated OAB were observed in HFD rats. Single-cell qRT-PCR experiments discovered the decreased mRNA expression level of SK channel in DSM cell from HFD rats. Patch-clamp studies revealed that NS309, a SK channel activator, had an attenuated effect on membrane potential hyperpolarization in HFD DSM cells. In addition, the reduced whole cell SK channel currents were recorded in HFD DSM cells.

CONCLUSIONS

Attenuated SK channels expression and function, which results in the increased DSM cells excitability and contributes to DO, is discovered in obesity-related OAB DSM cells, suggesting that SK channels might be potential therapeutic targets to control OAB.

Reduced Ca2+ spark activity contributes to detrusor overactivity of rats with partial bladder outlet obstruction

We tested whether or not altered Ca²⁺ spark activity accounted for detrusor overactivity (DO) of Wistar rats after partial bladder outlet obstruction (PBOO). We constructed a DO model through PBOO and studied the Ca²⁺ spark activity of detrusor. By way of using confocal microscopy and the patch-clamp technique, Ca²⁺ sparks and spontaneous transient outward currents (STOCs) in detrusor myocytes were measured respectively. Our results indicated that Ca²⁺ spark activity and STOCs were significantly reduced in the DO detrusor myocytes compared to unafflicted control cells, and both of these had levels that were remarkably increased by applications of caffeine (10 μM), a RyR agonist, in DO myocytes. In addition, measures of detrusor contractions were also recorded by using freshly isolated detrusor strips. These results indicated that the spontaneous contraction of DO detrusor was significantly enhanced, and that the effect of caffeine (10 μM) upon detrusor contractions was reversed by applications of iberiotoxin (100 nM) which is a BK channel blocker. Western blotting (WB) analyses indicated that the levels of expression of ryanodine receptor type 2 (RyR2) and FK506 binding protein 12.6 (FKBP12.6) in bladder muscle were respectively decreased and increased in the samples from DO rats. Thus, we considered in the rat DO model wherein PBOO, the reduced Ca²⁺ spark activity in detrusor myocytes partly contributed to overactive detrusor contractions. The impaired Ca²⁺ spark activity may have resulted from decreased RyR2 expression and increased FKBP12.6 expression. Such novel findings in our research might help to provide means for better treatment outcomes for patients afflicted by bladder dysfunction.