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Lee N, Kim S, Lee NY, Jo H, Jeong P, Pagire HS, Pagire SH, Ahn JH, Jin MS, Park CS. Activation mechanism and novel binding sites of the BK Ca channel activator CTIBD. Life Sci Alliance 2024; 7:e202402621. [PMID: 39089879 PMCID: PMC11294680 DOI: 10.26508/lsa.202402621] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Revised: 07/12/2024] [Accepted: 07/15/2024] [Indexed: 08/04/2024] Open
Abstract
The large-conductance calcium-activated potassium (BKCa) channel, which is crucial for urinary bladder smooth muscle relaxation, is a potential target for overactive bladder treatment. Our prior work unveiled CTIBD as a promising BKCa channel activator, altering V 1/2 and G max This study investigates CTIBD's activation mechanism, revealing its independence from the Ca2+ and membrane voltage sensing of the BKCa channel. Cryo-electron microscopy disclosed that two CTIBD molecules bind to hydrophobic regions on the extracellular side of the lipid bilayer. Key residues (W22, W203, and F266) are important for CTIBD binding, and their replacement with alanine reduces CTIBD-mediated channel activation. The triple-mutant (W22A/W203A/F266A) channel showed the smallest V 1/2 shift with a minimal impact on activation and deactivation kinetics by CTIBD. At the single-channel level, CTIBD treatment was much less effective at increasing P o in the triple mutant, mainly because of a drastically increased dissociation rate compared with the WT. These findings highlight CTIBD's mechanism, offering crucial insights for developing small-molecule treatments for BKCa-related pathophysiological conditions.
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Affiliation(s)
- Narasaem Lee
- https://ror.org/024kbgz78 School of Life Sciences, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Subin Kim
- https://ror.org/024kbgz78 School of Life Sciences, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Na Young Lee
- https://ror.org/024kbgz78 School of Life Sciences, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Heeji Jo
- https://ror.org/024kbgz78 School of Life Sciences, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | | | - Haushabhau S Pagire
- https://ror.org/024kbgz78 Department of Chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Suvarna H Pagire
- https://ror.org/024kbgz78 Department of Chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Jin Hee Ahn
- https://ror.org/024kbgz78 Department of Chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Mi Sun Jin
- https://ror.org/024kbgz78 School of Life Sciences, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
| | - Chul-Seung Park
- https://ror.org/024kbgz78 School of Life Sciences, Gwangju Institute of Science and Technology (GIST), Gwangju, Republic of Korea
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Discovery and characterization of a potent activator of the BK Ca channel that relives overactive bladder syndrome in rats. Eur J Pharmacol 2022; 927:175055. [PMID: 35644420 DOI: 10.1016/j.ejphar.2022.175055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 05/13/2022] [Accepted: 05/19/2022] [Indexed: 11/21/2022]
Abstract
The large-conductance Ca2+-activated K+ channel (BKCa channel) is involved in repolarizing the membrane potential and has a variety of cellular functions. The BKCa channel is highly expressed in bladder smooth muscle and mediates muscle relaxation. Compounds that activate the BKCa channel have therapeutic potential against pathological symptoms associated with the overactivity of bladder smooth muscle. In this regard, we screened a chemical library of 9938 compounds to identify novel BKCa channel activators. A cell-based fluorescence assay identified a structural family of compounds containing a common tricyclic quinazoline ring that activated the BKCa channel. The most potent compound TTQC-1 (7-bromo-N-(3-methylphenyl)-5-oxo-1-thioxo-4,5-dihydro[1,3]thiazolo[3,4-a]quinazoline-3-carboxamide) directly and reversibly activated the macroscopic current of BKCa channels expressed in Xenopus oocytes from both sides of the cellular membrane. TTQC-1 increased the maximum conductance and shifted the half activation voltage to the left. The apparent half-maximal effective concentration and dissociation constant were 2.8 μM and 7.95 μM, respectively. TTQC-1 delayed the kinetics of channel deactivation without affecting channel activation. The activation effects were observed over a wide range of intracellular Ca2+ concentrations and dependent on the co-expression of β1 and β4 auxiliary subunits, which are highly expressed in urinary bladder. In the isolated smooth muscle cells of rat urinary bladder, TTQC-1 increased the K+ currents which can be blocked by iberiotoxin. Finally, oral administration of TTQC-1 to hypertensive rats decreased the urination frequency. Therefore, TTQC-1 is a BKCa channel activator with a novel structure that is a potential therapeutic candidate for BKCa channel-related diseases, such as overactive bladder syndrome.
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The intracellular Ca 2+ release channel TRPML1 regulates lower urinary tract smooth muscle contractility. Proc Natl Acad Sci U S A 2020; 117:30775-30786. [PMID: 33199609 PMCID: PMC7720193 DOI: 10.1073/pnas.2016959117] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
TRPML1 (transient receptor potential mucolipin 1) is a Ca2+-permeable, nonselective cation channel that is localized to late endosomes and lysosomes. Here, we investigated the function of TRPML1 channels in regulating lower urinary tract (LUT) smooth muscle cell (SMC) contractility. We found that TRPML1 forms a stable signaling complex with ryanodine receptors (RyRs) in the sarcoplasmic reticulum (SR). We further showed that TRPML1 channels are important for initiating an essential Ca2+-signaling negative feedback mechanism between RyRs on SR membranes and K+ channels on the plasma membrane. Knockout of TRPML1 channels in mice impaired this pathway, resulting in LUT smooth muscle hypercontractility and symptoms of overactive bladder. Our findings demonstrate a critical role for TRPML1 in LUT function. TRPML1 (transient receptor potential mucolipin 1) is a Ca2+-permeable, nonselective cation channel that is predominantly localized to the membranes of late endosomes and lysosomes (LELs). Intracellular release of Ca2+ through TRPML1 is thought to be pivotal for maintenance of intravesicular acidic pH as well as the maturation, fusion, and trafficking of LELs. Interestingly, genetic ablation of TRPML1 in mice (Mcoln1−/−) induces a hyperdistended/hypertrophic bladder phenotype. Here, we investigated this phenomenon further by exploring an unconventional role for TRPML1 channels in the regulation of Ca2+-signaling activity and contractility in bladder and urethral smooth muscle cells (SMCs). Four-dimensional (4D) lattice light-sheet live-cell imaging showed that the majority of LELs in freshly isolated bladder SMCs were essentially immobile. Superresolution microscopy revealed distinct nanoscale colocalization of LEL-expressing TRPML1 channels with ryanodine type 2 receptors (RyR2) in bladder SMCs. Spontaneous intracellular release of Ca2+ from the sarcoplasmic reticulum (SR) through RyR2 generates localized elevations of Ca2+ (“Ca2+ sparks”) that activate plasmalemmal large-conductance Ca2+-activated K+ (BK) channels, a critical negative feedback mechanism that regulates smooth muscle contractility. This mechanism was impaired in Mcoln1−/− mice, which showed diminished spontaneous Ca2+ sparks and BK channel activity in bladder and urethra SMCs. Additionally, ex vivo contractility experiments showed that loss of Ca2+ spark–BK channel signaling in Mcoln1−/− mice rendered both bladder and urethra smooth muscle hypercontractile. Voiding activity analyses revealed bladder overactivity in Mcoln1−/− mice. We conclude that TRPML1 is critically important for Ca2+ spark signaling, and thus regulation of contractility and function, in lower urinary tract SMCs.
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Malysz J, Petkov GV. Detrusor Smooth Muscle K V7 Channels: Emerging New Regulators of Urinary Bladder Function. Front Physiol 2020; 11:1004. [PMID: 33041840 PMCID: PMC7526500 DOI: 10.3389/fphys.2020.01004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 07/23/2020] [Indexed: 01/21/2023] Open
Abstract
Relaxation and contraction of the urinary bladder smooth muscle, also known as the detrusor smooth muscle (DSM), facilitate the micturition cycle. DSM contractility depends on cell excitability, which is established by the synchronized activity of multiple diverse ion channels. K+ channels, the largest family of channels, control DSM excitability by maintaining the resting membrane potential and shaping the action potentials that cause the phasic contractions. Among the members of the voltage-gated K+ (KV) channel superfamily, KV type 7 (KV7) channels - KV7.1-KV7.5 members encoded by KCNQ1-KCNQ5 genes - have been recently identified as functional regulators in various cell types including vascular, cardiac, and neuronal cells. Their regulatory roles in DSM, however, are just now emerging and remain to be elucidated. To address this gap, our research group has initiated the systematic investigation of human DSM KV7 channels in collaboration with clinical urologists. In this comprehensive review, we summarize the current understanding of DSM Kv7 channels and highlight recent discoveries in the field. We describe KV7 channel expression profiles at the mRNA and protein levels, and further elaborate on functional effects of KV7 channel selective modulators on DSM excitability, contractility, and intracellular Ca2+ dynamics in animal species along with in vivo studies and the limited data on human DSM. Within each topic, we highlight the main observations, current gaps in knowledge, and most pressing questions and concepts in need of resolution. We emphasize the lack of systematic studies on human DSM KV7 channels that are now actively ongoing in our laboratory.
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Affiliation(s)
- John Malysz
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, United States
| | - Georgi V. Petkov
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, TN, United States
- Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, United States
- Department of Urology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, United States
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Malysz J, Petkov GV. Urinary bladder smooth muscle ion channels: expression, function, and regulation in health and disease. Am J Physiol Renal Physiol 2020; 319:F257-F283. [PMID: 32628539 PMCID: PMC7473901 DOI: 10.1152/ajprenal.00048.2020] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 06/21/2020] [Accepted: 06/28/2020] [Indexed: 12/17/2022] Open
Abstract
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.
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Affiliation(s)
- John Malysz
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee
| | - Georgi V Petkov
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee
- Department of Urology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee
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Fry CH, Chakrabarty B, Hashitani H, Andersson KE, McCloskey K, Jabr RI, Drake MJ. New targets for overactive bladder-ICI-RS 2109. Neurourol Urodyn 2020; 39 Suppl 3:S113-S121. [PMID: 31737931 PMCID: PMC8114459 DOI: 10.1002/nau.24228] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2019] [Accepted: 10/31/2019] [Indexed: 12/16/2022]
Abstract
AIM To review evidence for novel drug targets that can manage overactive bladder (OAB) symptoms. METHODS A think tank considered evidence from the literature and their own research experience to propose new drug targets in the urinary bladder to characterize their use to treat OAB. RESULTS Five classes of agents or cellular pathways were considered. (a) Cyclic nucleotide-dependent (cyclic adenosine monophosphate and cyclic guanosine monophosphate) pathways that modulate adenosine triphosphate release from motor nerves and urothelium. (b) Novel targets for β3 agonists, including the bladder wall vasculature and muscularis mucosa. (c) Several TRP channels (TRPV1 , TRPV4 , TRPA1 , and TRPM4 ) and their modulators in affecting detrusor overactivity. (d) Small conductance Ca2+ -activated K+ channels and their influence on spontaneous contractions. (e) Antifibrosis agents that act to modulate directly or indirectly the TGF-β pathway-the canonical fibrosis pathway. CONCLUSIONS The specificity of action remains a consideration if particular classes of agents can be considered for future development as receptors or pathways that mediate actions of the above mentioned potential agents are distributed among most organ systems. The tasks are to determine more detail of the pathological changes that occur in the OAB and how the specificity of potential drugs may be directed to bladder pathological changes. An important conclusion was that the storage, not the voiding, phase in the micturition cycle should be investigated and potential targets lie in the whole range of tissue in the bladder wall and not just detrusor.
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Affiliation(s)
- Christopher Henry Fry
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Basu Chakrabarty
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Hikaru Hashitani
- Department of Cell Physiology, Nagoya City University, Nagoya, Japan
| | - Karl-Erik Andersson
- Institute of Laboratory Medicine, Lund University, Lund, Sweden
- Institute for Regenerative Medicine, Wake Forest University School of Medicine, Winston-Salem, North Carolina
| | - Karen McCloskey
- School of Medicine, Dentistry and Biomedical Sciences, Queens University Belfast, Belfast, UK
| | - Rita I. Jabr
- Division of Biochemical Sciences, Faculty of Health and Biomedical Sciences, University of Surrey, Guildford, UK
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Li N, Ding H, Zhang P, Li Z, Liu Y, Wang P. Attenuated BK channel function promotes overactive bladder in a rat model of obesity. Aging (Albany NY) 2019; 11:6199-6216. [PMID: 31480021 PMCID: PMC6738405 DOI: 10.18632/aging.102182] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Accepted: 08/10/2019] [Indexed: 12/17/2022]
Abstract
Overactive bladder (OAB) is mostly observed in obese individuals, and is associated with enhanced excitability and contractility of the detrusor smooth muscle (DSM). Large-conductance voltage- and Ca2+-activated K+ (BK) channels reduce the excitability and contractility of the DSM. We tested whether obesity-induced OAB is associated with altered BK channel expression and activity in the DSM. Seven-week-old female Sprague-Dawley rats (N=80) were fed a normal or high-fat diet (HFD) for 12 weeks. HFD-fed rats exhibited a higher average bodyweight and urodynamically established detrusor overactivity. mRNA levels of the Kcnma1 (BKα subunit) and Kcnmb1 (BKβ1 subunit) in whole tissues and cells from the DSM were reduced in HFD-fed rats. A selective BK channel opener, NS1619, was then applied to DSM cells from the two groups of rats. Patch-clamp techniques revealed that spontaneous transient outward currents, NS1619-induced activation of spontaneous transient outward currents, and whole-cell BK currents, as well as NS1619-induced membrane hyperpolarization, were attenuated in DSM cells from HFD-fed rats. The relaxation effect of NS1619 on contractility was reduced in DSM strips from HFD-fed rats. Thus, impaired expression of Kcnma1 and Kcnmb1 in the DSM contributes to obesity-induced OAB, suggesting that BK channels could be a useful treatment targets in OAB.
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Affiliation(s)
- Ning Li
- Department of Urology, Fourth Affiliated Hospital, China Medical University, Shenyang, Liaoning, China
| | - Honglin Ding
- Department of Urology, Fourth Affiliated Hospital, China Medical University, Shenyang, Liaoning, China.,Department of Urology, Affiliated Hospital, Chifeng University, Chifeng, Neimeng, China
| | - Peng Zhang
- Department of General Surgery, Shenyang 242 Hospital, Shenyang, Liaoning, China
| | - Zizheng Li
- Department of Urology, Fourth Affiliated Hospital, China Medical University, Shenyang, Liaoning, China
| | - Yili Liu
- Department of Urology, Fourth Affiliated Hospital, China Medical University, Shenyang, Liaoning, China
| | - Ping Wang
- Department of Urology, Fourth Affiliated Hospital, China Medical University, Shenyang, Liaoning, China
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Fry CH, McCloskey KD. Spontaneous Activity and the Urinary Bladder. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2019; 1124:121-147. [PMID: 31183825 DOI: 10.1007/978-981-13-5895-1_5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The urinary bladder has two functions: to store urine, when it is relaxed and highly compliant; and void its contents, when intravesical pressure rises due to co-ordinated contraction of detrusor smooth muscle in the bladder wall. Superimposed on this description are two observations: (1) the normal, relaxed bladder develops small transient increases of intravesical pressure, mirrored by local bladder wall movements; (2) pathological, larger pressure variations (detrusor overactivity) can occur that may cause involuntary urine loss and/or detrusor overactivity. Characterisation of these spontaneous contractions is important to understand: how normal bladder compliance is maintained during filling; and the pathophysiology of detrusor overactivity. Consideration of how spontaneous contractions originate should include the structural complexity of the bladder wall. Detrusor smooth muscle layer is overlain by a mucosa, itself a complex structure of urothelium and a lamina propria containing sensory nerves, micro-vasculature, interstitial cells and diffuse muscular elements.Several theories, not mutually exclusive, have been advanced for the origin of spontaneous contractions. These include intrinsic rhythmicity of detrusor muscle; modulation by non-muscular pacemaking cells in the bladder wall; motor input to detrusor by autonomic nerves; regulation of detrusor muscle excitability and contractility by the adjacent mucosa and spontaneous contraction of elements of the lamina propria. This chapter will consider evidence for each theory in both normal and overactive bladder and how their significance may vary during ageing and development. Further understanding of these mechanisms may also identify novel drug targets to ameliorate the clinical consequences of large contractions associated with detrusor overactivity.
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Affiliation(s)
- Christopher H Fry
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK.
| | - Karen D McCloskey
- School of Medicine, Dentistry and Biomedical Sciences, Queen's University Belfast, Belfast, UK
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Kullmann FA, Beckel JM, McDonnell B, Gauthier C, Lynn AM, Wolf-Johnston A, Kanai A, Zabbarova IV, Ikeda Y, de Groat WC, Birder LA. Involvement of TRPM4 in detrusor overactivity following spinal cord transection in mice. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2018; 391:1191-1202. [PMID: 30054681 PMCID: PMC6186176 DOI: 10.1007/s00210-018-1542-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Accepted: 07/17/2018] [Indexed: 12/31/2022]
Abstract
Transient receptor potential cation channel subfamily M member 4 (TRPM4) has been shown to play a key role in detrusor contractility under physiological conditions. In this study, we investigated the potential role of TRPM4 in detrusor overactivity following spinal cord transection (SCT) in mice. TRPM4 expression and function were evaluated in bladder tissue with or without the mucosa from spinal intact (SI) and SCT female mice (T8-T9 vertebra; 1-28 days post SCT) using PCR, western blot, immunohistochemistry, and muscle strip contractility techniques. TRPM4 was expressed in the urothelium (UT) and detrusor smooth muscle (DSM) and was upregulated after SCT. Expression levels peaked 3-7 days post SCT in both the UT and DSM. Pharmacological block of TRPM4 with the antagonist, 9-Phenanthrol (30 μM) greatly reduced spontaneous phasic activity that developed after SCT, regardless of the presence or absence of the mucosa. Detrusor overactivity following spinal cord injury leads to incontinence and/or renal impairment and represents a major health problem for which current treatments are not satisfactory. Augmented TRPM4 expression in the bladder after chronic SCT supports the hypothesis that TRPM4 channels play a role in DSM overactivity following SCT. Inhibition of TRPM4 may be beneficial for improving detrusor overactivity in SCI.
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Affiliation(s)
- F Aura Kullmann
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA.
| | - Jonathan M Beckel
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Bronagh McDonnell
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Christian Gauthier
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, 15260, USA
| | - Andrew M Lynn
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Amanda Wolf-Johnston
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Anthony Kanai
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Irina V Zabbarova
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Youko Ikeda
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - William C de Groat
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
| | - Lori A Birder
- Department of Medicine/Renal and Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15261, USA
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Li N, Ding H, Li Z, Liu Y, Wang P. Effect of high-fat diet-induced obesity on the small-conductance Ca 2+-activated K + channel function affecting the contractility of rat detrusor smooth muscle. Int Urol Nephrol 2018; 51:61-72. [PMID: 30361965 DOI: 10.1007/s11255-018-2016-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2018] [Accepted: 10/19/2018] [Indexed: 12/01/2022]
Abstract
PURPOSE Obesity usually induces overactive bladder (OAB) associated with detrusor overactivity, which is related to increased contractility of the detrusor smooth muscle (DSM). Small-conductance Ca2+-activated K+ (SK) channels play a constitutive role in the regulation of DSM contractility. However, the role of SK channels in the DSM changes in obesity-related OAB is still unknown. Here, we tested the hypothesis that obesity-related OAB is associated with reduced expression and activity of SK channels in DSM and that SK channels activation is a potential treatment for OAB. METHODS Female Sprague-Dawley rats were fed a normal diet (ND) or a high-fat diet (HFD) and weighed after 12 weeks. Urodynamic studies, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and isometric tension recording were performed. RESULTS Increased average body weights and urodynamically demonstrated OAB were observed in HFD rats. qRT-PCR experiments revealed a decrease in the mRNA expression level of SK channel in DSM tissue of the HFD rats. Isometric tension recordings indicated an attenuated relaxation effect of NS309 on the spontaneous phasic and electrical field stimulation-induced contractions that occurred via SK channel activation in HFD DSM strips. CONCLUSIONS Reduced expression and activity of SK channels in the DSM contribute to obesity-related OAB, indicating that SK channels are a potential therapeutic target for OAB.
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Affiliation(s)
- Ning Li
- Department of Urology, Fourth Affiliated Hospital, China Medical University, 4 Chongshan East Road, Shenyang, Liaoning, China
| | - Honglin Ding
- Department of Urology, Fourth Affiliated Hospital, China Medical University, 4 Chongshan East Road, Shenyang, Liaoning, China.,Department of Urology, Affiliated Hospital, Chifeng University, 42 Wangfu Street, Chifeng, Neimeng, China
| | - Zizheng Li
- Department of Urology, Fourth Affiliated Hospital, China Medical University, 4 Chongshan East Road, Shenyang, Liaoning, China
| | - Yili Liu
- Department of Urology, Fourth Affiliated Hospital, China Medical University, 4 Chongshan East Road, Shenyang, Liaoning, China.
| | - Ping Wang
- Department of Urology, Fourth Affiliated Hospital, China Medical University, 4 Chongshan East Road, Shenyang, Liaoning, China
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Regulation of Spontaneous Contractions in Intact Rat Bladder Strips and the Effects of Hydrogen Peroxide. BIOMED RESEARCH INTERNATIONAL 2018; 2018:2925985. [PMID: 29511675 PMCID: PMC5817331 DOI: 10.1155/2018/2925985] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 12/01/2017] [Accepted: 12/31/2017] [Indexed: 01/07/2023]
Abstract
Enhanced spontaneous contractions are associated with overactive bladder. Elevated levels of reactive oxygen species might contribute to enhanced spontaneous contractions. We investigated the regulation of spontaneous contractions and the effects of hydrogen peroxide (H2O2) in intact rat bladder strips. The spontaneous contractions were measured using a tissue bath system. The vehicle or the specific activators/blockers were applied and followed by the application of 0.003 g% H2O2. The basal tension, amplitude, and frequency of spontaneous contractions were quantified. Nisoldipine and bisindolylmaleimide 1 had no effects on spontaneous contractions. SKF96365 and Y27632 decreased basal tension and amplitude. Ryanodine slightly increased frequency. Both iberiotoxin and NS-1619 increased amplitude. Apamin reduced frequency but increased amplitude. NS-309 inhibited both the amplitude and frequency. The basal tension and amplitude increased when H2O2 was applied. Pretreatment with NS-309 inhibited H2O2-elicited augmented amplitude and frequency, while pretreatment with Y-27632 inhibited the augmented basal tension. The combined application of NS-309 and Y27632 almost eliminated spontaneous contractions and its augmentation induced by H2O2. In conclusion, Ca2+ influx, Rho kinase activation, and SK channel inactivation play important roles in spontaneous contractions in intact bladder strips, whereas only latter two mechanisms may be involved in H2O2-elicited increased spontaneous contractions.
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12
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Kitney DG, Jabr RI, Vahabi B, Fry CH. Mild external heating and reduction in spontaneous contractions of the bladder. BJU Int 2017; 120:724-730. [PMID: 28609582 PMCID: PMC5643226 DOI: 10.1111/bju.13933] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES To measure the effect of external heating on bladder wall contractile function, histological structure and expression of proteins related to tissue protection and apoptosis. MATERIAL AND METHODS In vitro preparations of bladder wall and ex vivo perfused pig bladders were heated from 37 to 42°C, 46 and 50°C for 15 min. Isolated preparations were heated by radiant energy and perfused bladders were heated by altering perfusate temperature. Spontaneous contractions or pressure variations were recorded, as well as responses to the muscarinic agonist carbachol or motor nerve excitation in vitro during heating. Tissue histology in control and after heating was analysed using haematoxylin and eosin staining and 4'-6-diamidino-2-phenylindole (DAPI) nuclear labelling. The effects of heating on protein expression levels of (i) heat shock proteins HSP27-pSer82 and inducible-HSP70 and (ii) caspase-3 and its downstream DNA-repair substrate poly-[ADP-ribose] polymerase (PARP) were measured. RESULTS Heating to 42°C reduced spontaneous contractions or pressure variations by ~70%; effects were fully reversible. There were no effects on carbachol or nerve-mediated responses. Tissue histology was unaffected by heating, and expression of heat shock proteins as well as caspase-3 and PARP were also unaltered. A TRPV1 antagonist had no effect on the reduction of spontaneous activity. Heating to 46°C had a similar effect on spontaneous activity and also reduced the carbachol contracture. Urothelial structure was damaged, caspase-3 levels were increased and inducible-HSP70 levels declined. At 50°C evoked contractions were abolished, the urothelium was absent and heat shock proteins and PARP expression was reduced with raised caspase-3 expression. CONCLUSIONS Heating to 42°C caused a profound, reversible and reproducible attenuation of spontaneous activity, with no tissue damage and no initiation of apoptosis pathways. Higher temperatures caused tissue damage and activation of apoptotic mechanisms. Mild heating offers a novel approach to reducing bladder spontaneous activity.
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Affiliation(s)
- Darryl G Kitney
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Rita I Jabr
- Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
| | - Bahareh Vahabi
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
- Department of Biological, Biomedical and Analytical Sciences, University of the West of England, Bristol, UK
| | - Christopher H Fry
- School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol, UK
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Age Related Differences in Responsiveness to Sildenafil and Tamsulosin are due to Myogenic Smooth Muscle Tone in the Human Prostate. Sci Rep 2017; 7:10150. [PMID: 28860509 PMCID: PMC5578961 DOI: 10.1038/s41598-017-07861-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 07/03/2017] [Indexed: 11/08/2022] Open
Abstract
Lower urinary tract symptoms (LUTS) due to Benign Prostatic Hyperplasia (BPH) are highly prevalent in older men, having a profound impact on patient quality of life. Current therapeutics for BPH/LUTS target neurogenic smooth muscle tone, but response is unpredictable and many patients fail to respond. Spontaneous myogenic tone is another component of smooth muscle contractility that is uncharacterized in human prostate. To better understand and improve the predictability of patient response, we defined myogenic contractility using human prostate specimens and examined the effect of existing therapeutics. We show that myogenic activity is present in the human prostate with the frequency of contractions in transition zone (TZ) specimens from BPH diagnosed patients approximately 160% greater than matched controls. α1-adrenoreceptor antagonists (Tamsulosin) and PDE5 inhibitors (Sildenafil) both significantly reduced myogenic contractile parameters, including frequency, with notable interpatient variability. Tamsulosin was more effective in older patients (R2 = 0.36, p < 0.01) and men with larger prostate volumes (R2 = 0.41, p < 0.05), while Sildenafil was more effective in younger men (R2 = 0.45, p < 0.05). As myogenic tone is significantly increased in BPH, therapeutics targeting this mechanism used with reference to patient characteristics could improve clinical outcomes and better predict patient response.
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Hoshi T, Heinemann SH. Modulation of BK Channels by Small Endogenous Molecules and Pharmaceutical Channel Openers. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2016; 128:193-237. [PMID: 27238265 DOI: 10.1016/bs.irn.2016.03.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Voltage- and Ca(2+)-activated K(+) channels of big conductance (BK channels) are abundantly found in various organs and their relevance for smooth muscle tone and neuronal signaling is well documented. Dysfunction of BK channels is implicated in an array of human diseases involving many organs including the nervous, pulmonary, cardiovascular, renal, and urinary systems. In humans a single gene (KCNMA1) encodes the pore-forming α subunit (Slo1) of BK channels, but the channel properties are variable because of alternative splicing, tissue- and subcellular-specific auxiliary subunits (β, γ), posttranslational modifications, and a multitude of endogenous signaling molecules directly affecting the channel function. Initiatives to develop drugs capable of activating BK channels (channel openers) therefore need to consider the tissue-specific variability of BK channel structure and the potential interference with endogenously produced regulatory factors. The atomic structural basis of BK channel function is only beginning to be revealed. However, building on detailed knowledge of BK channel function, including its single-channel characteristics, voltage- and Ca(2+) dependence of channel gating, and modulation by diffusible messengers, a multi-tier allosteric model of BK channel gating (Horrigan and Aldrich (HA) model) has become a valuable tool in studying modulation of the channel. Using the conceptual framework of the HA model, we here review the functional impact of endogenous modulatory factors and select small synthetic compounds that regulate BK channel activity. Furthermore, we devise experimental approaches for studying BK channel-drug interactions with the aim to classify BK-modulating substances according to their molecular mode of action.
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Affiliation(s)
- T Hoshi
- University of Pennsylvania, Philadelphia, PA, United States.
| | - S H Heinemann
- Friedrich Schiller University Jena & Jena University Hospital, Jena, Germany
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15
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Molecular mechanisms underlying the effect of the novel BK channel opener GoSlo: involvement of the S4/S5 linker and the S6 segment. Proc Natl Acad Sci U S A 2015; 112:2064-9. [PMID: 25653338 DOI: 10.1073/pnas.1400555112] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
GoSlo-SR-5-6 is a novel large-conductance Ca(2+)-activated K(+) (BK) channel agonist that shifts the activation V1/2 of these channels in excess of -100 mV when applied at a concentration of 10 μM. Although the structure-activity relationship of this family of molecules has been established, little is known about how they open BK channels. To help address this, we used a combination of electrophysiology, mutagenesis, and mathematical modeling to investigate the molecular mechanisms underlying the effect of GoSlo-SR-5-6. Our data demonstrate that the effects of this agonist are practically abolished when three point mutations are made: L227A in the S4/S5 linker in combination with S317R and I326A in the S6C region. Our data suggest that GoSlo-SR-5-6 interacts with the transmembrane domain of the channel to enhance pore opening. The Horrigan-Aldrich model suggests that GoSlo-SR-5-6 works by stabilizing the open conformation of the channel and the activated state of the voltage sensors, yet decouples the voltage sensors from the pore gate.
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16
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Bayrak S, Balkanci ZD, Pehlivanoğlu B, Karabulut İ, Karaismailoğlu S, Erdem A. Does hypercholesterolemia affect the relaxation of the detrusor smooth muscle in rats? In vitro and in vivo studies. Naunyn Schmiedebergs Arch Pharmacol 2014; 388:761-71. [PMID: 25344203 DOI: 10.1007/s00210-014-1060-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Accepted: 10/13/2014] [Indexed: 12/22/2022]
Abstract
To evaluate the effects of hypercholesterolemia on the relaxation function of the urinary bladder, we examined the physiological mechanisms involved in the isoproterenol-induced relaxation in isolated detrusor strips in vitro and voiding behavior in vivo in rats. Adult male Sprague-Dawley rats were fed standard (control, N = 16) or 4 % cholesterol diet (hypercholesterolemia, N = 17) for 4 weeks. Concentration-response curves for isoproterenol-induced relaxations in carbachol-precontracted detrusor muscle strips were recorded. The contributions of β2- and β3-adrenoceptors and ATP-dependent and Ca(2+)-dependent potassium channels to the relaxation response were investigated by using selective adrenergic agonists salbutamol and BRL 37344 and specific potassium channel inhibitors glibenclamide and charybdotoxin, respectively. Cystometrography was performed to assess bladder function. Hypercholesterolemic rats had higher serum cholesterol and low- and high-density lipoprotein levels than the controls with no sign of atherosclerosis. Isoproterenol-induced relaxation was significantly enhanced in the hypercholesterolemia group. Preincubation with the M2 receptor antagonist attenuated the relaxation response in both groups. The relaxation responses to isoproterenol and salbutamol were similar in both groups, while BRL 37344 appeared to produce a greater relaxant effect in the hypercholesterolemic rats. Also, the inhibitory effects of potassium channel inhibitors on relaxation responses were comparable among the groups. The cystometric findings revealed that threshold and basal pressure values were higher in the hypercholesterolemia group compared with controls. We showed that hypercholesterolemia leads to greater relaxation responses to isoproterenol, appears to impair the braking function of M2 cholinergic receptors on adrenoceptor-induced relaxations in the isolated detrusor muscle, and affects the voiding function in rats.
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Affiliation(s)
- Sibel Bayrak
- Department of Physiology, Faculty of Medicine, Hacettepe University, 39, 06100, Sihhiye, Ankara, Turkey,
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17
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Bentzen BH, Olesen SP, Rønn LCB, Grunnet M. BK channel activators and their therapeutic perspectives. Front Physiol 2014; 5:389. [PMID: 25346695 PMCID: PMC4191079 DOI: 10.3389/fphys.2014.00389] [Citation(s) in RCA: 113] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Accepted: 09/19/2014] [Indexed: 01/05/2023] Open
Abstract
The large conductance calcium- and voltage-activated K+ channel (KCa1.1, BK, MaxiK) is ubiquitously expressed in the body, and holds the ability to integrate changes in intracellular calcium and membrane potential. This makes the BK channel an important negative feedback system linking increases in intracellular calcium to outward hyperpolarizing potassium currents. Consequently, the channel has many important physiological roles including regulation of smooth muscle tone, neurotransmitter release and neuronal excitability. Additionally, cardioprotective roles have been revealed in recent years. After a short introduction to the structure, function and regulation of BK channels, we review the small organic molecules activating BK channels and how these tool compounds have helped delineate the roles of BK channels in health and disease.
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Affiliation(s)
- Bo H Bentzen
- Department of Biomedical Sciences, Faculty of Health Sciences, Danish Arrhythmia Research Centre, University of Copenhagen Copenhagen, Denmark ; Acesion Pharma Copenhagen, Denmark
| | - Søren-Peter Olesen
- Department of Biomedical Sciences, Faculty of Health Sciences, Danish Arrhythmia Research Centre, University of Copenhagen Copenhagen, Denmark
| | | | - Morten Grunnet
- Acesion Pharma Copenhagen, Denmark ; H. Lundbeck A/S Copenhagen, Denmark
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Kyle BD, Braun AP. The regulation of BK channel activity by pre- and post-translational modifications. Front Physiol 2014; 5:316. [PMID: 25202279 PMCID: PMC4141542 DOI: 10.3389/fphys.2014.00316] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Accepted: 08/02/2014] [Indexed: 11/17/2022] Open
Abstract
Large conductance, Ca2+-activated K+ (BK) channels represent an important pathway for the outward flux of K+ ions from the intracellular compartment in response to membrane depolarization, and/or an elevation in cytosolic free [Ca2+]. They are functionally expressed in a range of mammalian tissues (e.g., nerve and smooth muscles), where they can either enhance or dampen membrane excitability. The diversity of BK channel activity results from the considerable alternative mRNA splicing and post-translational modification (e.g., phosphorylation) of key domains within the pore-forming α subunit of the channel complex. Most of these modifications are regulated by distinct upstream cell signaling pathways that influence the structure and/or gating properties of the holo-channel and ultimately, cellular function. The channel complex may also contain auxiliary subunits that further affect channel gating and behavior, often in a tissue-specific manner. Recent studies in human and animal models have provided strong evidence that abnormal BK channel expression/function contributes to a range of pathologies in nerve and smooth muscle. By targeting the upstream regulatory events modulating BK channel behavior, it may be possible to therapeutically intervene and alter BK channel expression/function in a beneficial manner.
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Affiliation(s)
- Barry D Kyle
- Department of Physiology and Pharmacology, Cumming School of Medicine, Libin Cardiovascular Research Institute, University of Calgary Calgary, AB, Canada
| | - Andrew P Braun
- Department of Physiology and Pharmacology, Cumming School of Medicine, Libin Cardiovascular Research Institute, University of Calgary Calgary, AB, Canada
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Petkov GV. Central role of the BK channel in urinary bladder smooth muscle physiology and pathophysiology. Am J Physiol Regul Integr Comp Physiol 2014; 307:R571-84. [PMID: 24990859 DOI: 10.1152/ajpregu.00142.2014] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The physiological functions of the urinary bladder are to store and periodically expel urine. These tasks are facilitated by the contraction and relaxation of the urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, which comprises the bladder wall. The large-conductance voltage- and Ca(2+)-activated K(+) (BK, BKCa, MaxiK, Slo1, or KCa1.1) channel is highly expressed in UBSM and is arguably the most important physiologically relevant K(+) channel that regulates UBSM function. Its significance arises from the fact that the BK channel is the only K(+) channel that is activated by increases in both voltage and intracellular Ca(2+). The BK channels control UBSM excitability and contractility by maintaining the resting membrane potential and shaping the repolarization phase of the spontaneous action potentials that determine UBSM spontaneous rhythmic contractility. In UBSM, these channels have complex regulatory mechanisms involving integrated intracellular Ca(2+) signals, protein kinases, phosphodiesterases, and close functional interactions with muscarinic and β-adrenergic receptors. BK channel dysfunction is implicated in some forms of bladder pathologies, such as detrusor overactivity, and related overactive bladder. This review article summarizes the current state of knowledge of the functional role of UBSM BK channels under normal and pathophysiological conditions and provides new insight toward the BK channels as targets for pharmacological or genetic control of UBSM function. Modulation of UBSM BK channels can occur by directly or indirectly targeting their regulatory mechanisms, which has the potential to provide novel therapeutic approaches for bladder dysfunction, such as overactive bladder and detrusor underactivity.
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Affiliation(s)
- Georgi V Petkov
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina
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20
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Wang Y, Tar MT, Fu S, Melman A, Davies KP. Diabetes attenuates urothelial modulation of detrusor contractility and spontaneous activity. Int J Urol 2014; 21:1059-64. [PMID: 24846346 DOI: 10.1111/iju.12491] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 04/13/2014] [Indexed: 02/04/2023]
Abstract
OBJECTIVES To investigate the effect of diabetes on urothelial modulation of bladder contractility. METHODS Bladder strips (urothelium intact or denuded) were prepared from 8-week-old streptozotocin-induced diabetic (n = 19) and non-diabetic control rats (n = 10). The effect of modulators of MaxiK (iberiotoxin and tetraethylammonium) and Kv7 (XE991 and retigabine) potassium channel activity were investigated for their effects on both carbachol-induced force generation and spontaneous contractile activity. RESULTS In bladder strips from non-diabetic animals, the presence of the urothelium resulted in marked sensitivity to carbachol-induced force generation by modulators of MaxiK and Kv7 channel activity, whereas in the diabetic animal urothelial sensitivity to these agents was significantly diminished. Urothelial-intact bladder strips from non-diabetic animals were more sensitive to modulators of Kv7 activity in reducing the amplitude of spontaneous phasic contractions than urothelial-denuded bladder strips, whereas in diabetic animals the presence or absence of the urothelium did not alter the sensitivity to modulators of Kv7 activity. Spontaneous activity in the presence of tetraethylammonium was not affected by the urothelium in bladder strips from either diabetic or non-diabetic animals. CONCLUSIONS The presence of the urothelium in bladders from non-diabetic animals modulates the activity of potassium blockers to affect bladder contractility, whereas in the diabetic bladder this effect is attenuated. These findings could help to explain the lack of success of pharmaceutical treatments targeting potassium channels to treat bladder pathology in patients with diseases imparing urothelial function.
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Affiliation(s)
- Yi Wang
- Department of Urology, Albert Einstein College of Medicine, Bronx, New York, USA
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21
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Stimulation of large-conductance calcium-activated potassium channels inhibits neurogenic contraction of human bladder from patients with urinary symptoms and reverses acetic acid-induced bladder hyperactivity in rats. Eur J Pharmacol 2014; 735:68-76. [PMID: 24747752 DOI: 10.1016/j.ejphar.2014.03.060] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 03/10/2014] [Accepted: 03/30/2014] [Indexed: 11/23/2022]
Abstract
We have analysed the effects of large-conductance calcium-activated potassium channel (BK) stimulation on neurogenic and myogenic contraction of human bladder from healthy subjects and patients with urinary symptoms and evaluated the efficacy of activating BK to relief bladder hyperactivity in rats. Bladder specimens were obtained from organ donors and from men with benign prostatic hyperplasia (BPH). Contractions elicited by electrical field stimulation (EFS) and carbachol (CCh) were evaluated in isolated bladder strips. in vivo cystometric recordings were obtained in anesthetized rats under control and acetic acid-induced hyperactive conditions. Neurogenic contractions of human bladder were potentiated by blockade of BK and small-conductance calcium-activated potassium channels (SK) but were unaffected by the blockade of intermediate calcium-activated potassium channels (IK). EFS-induced contractions were inhibited by BK stimulation with NS-8 or NS1619 or by SK/IK stimulation with NS309 (3µM). CCh-induced contractions were not modified by blockade or stimulation of BK, IK or SK. The anti-cholinergic agent, oxybutynin (0.3µM) inhibited either neurogenic or CCh-induced contractions. Neurogenic contractions of bladders from BPH patients were less sensitive to BK inhibition and more sensitive to BK activation than healthy bladders. The BK activator, NS-8 (5mg/kg; i.v.), reversed bladder hyperactivity induced by acetic acid in rats, while oxybutynin was ineffective. NS-8 did not significantly impact blood pressure or heart rate. BK stimulation specifically inhibits neurogenic contractions in patients with urinary symptoms and relieves bladder hyperactivity in vivo without compromising bladder contractile capacity or cardiovascular safety, supporting its potential therapeutic use for relieving bladder overactivity.
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22
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Tseng CH. Metformin may reduce bladder cancer risk in Taiwanese patients with type 2 diabetes. Acta Diabetol 2014; 51:295-303. [PMID: 24509842 DOI: 10.1007/s00592-014-0562-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/22/2013] [Accepted: 01/25/2014] [Indexed: 12/13/2022]
Abstract
Whether metformin therapy affects bladder cancer risk in patients with type 2 diabetes mellitus (T2DM) has not been extensively investigated. The reimbursement databases of all Taiwanese patients with a new diagnosis of T2DM between 1998 and 2002 (n = 940,708) were retrieved from the National Health Insurance for follow-up of bladder cancer up to the end of 2009. Metformin was treated as a time-dependent variable, and of these patients, 532,519 were never-users and 408,189 were ever-users of metformin. A time-dependent approach was applied in the calculation of bladder cancer incidence and in the estimation of hazard ratios by Cox regression for ever-users, never-users, and subgroups of metformin exposure (using tertile cutoffs of cumulative duration of therapy and cumulative dose). During the study period, 1,847 (0.45%) metformin ever-users and 6,213 (1.17%) metformin never-users developed bladder cancer, representing an incidence of 72.03 and 189.22 per 100,000 person-years, respectively. The age-sex-adjusted and multivariable-adjusted hazard ratios (95% confidence intervals) for ever- versus never-users were 0.382 (0.360-0.405) and 0.600 (0.564-0.638), respectively. The multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative duration of metformin therapy were 1.034 (0.954-1.120), 0.696 (0.632-0.766), and 0.258 (0.229-0.291), respectively (P trend <0.0001). Similarly, the multivariable-adjusted hazard ratios for the first, second, and third tertiles of cumulative dose of metformin were 0.997 (0.920-1.080), 0.615 (0.559-0.677), and 0.285 (0.253-0.321), respectively (P trend <0.0001). This study suggests that metformin use is associated with a decreased risk of bladder cancer in patients with T2DM.
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Affiliation(s)
- Chin-Hsiao Tseng
- Department of Internal Medicine, National Taiwan University College of Medicine, Taipei, Taiwan,
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Hristov KL, Smith AC, Parajuli SP, Malysz J, Petkov GV. Large-conductance voltage- and Ca2+-activated K+ channel regulation by protein kinase C in guinea pig urinary bladder smooth muscle. Am J Physiol Cell Physiol 2013; 306:C460-70. [PMID: 24352333 DOI: 10.1152/ajpcell.00325.2013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Large-conductance voltage- and Ca(2+)-activated K(+) (BK) channels are critical regulators of detrusor smooth muscle (DSM) excitability and contractility. PKC modulates the contraction of DSM and BK channel activity in non-DSM cells; however, the cellular mechanism regulating the PKC-BK channel interaction in DSM remains unknown. We provide a novel mechanistic insight into BK channel regulation by PKC in DSM. We used patch-clamp electrophysiology, live-cell Ca(2+) imaging, and functional studies of DSM contractility to elucidate BK channel regulation by PKC at cellular and tissue levels. Voltage-clamp experiments showed that pharmacological activation of PKC with PMA inhibited the spontaneous transient BK currents in native freshly isolated guinea pig DSM cells. Current-clamp recordings revealed that PMA significantly depolarized DSM membrane potential and inhibited the spontaneous transient hyperpolarizations in DSM cells. The PMA inhibitory effects on DSM membrane potential were completely abolished by the selective BK channel inhibitor paxilline. Activation of PKC with PMA did not affect the amplitude of the voltage-step-induced whole cell steady-state BK current or the single BK channel open probability (recorded in cell-attached mode) upon inhibition of all major Ca(2+) sources for BK channel activation with thapsigargin, ryanodine, and nifedipine. PKC activation with PMA elevated intracellular Ca(2+) levels in DSM cells and increased spontaneous phasic and nerve-evoked contractions of DSM isolated strips. Our results support the concept that PKC activation leads to a reduction of BK channel activity in DSM via a Ca(2+)-dependent mechanism, thus increasing DSM contractility.
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Affiliation(s)
- Kiril L Hristov
- Department of Drug Discovery and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, South Carolina
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24
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Neurogenic detrusor overactivity is associated with decreased expression and function of the large conductance voltage- and Ca(2+)-activated K(+) channels. PLoS One 2013; 8:e68052. [PMID: 23861849 PMCID: PMC3702577 DOI: 10.1371/journal.pone.0068052] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 05/24/2013] [Indexed: 11/23/2022] Open
Abstract
Patients suffering from a variety of neurological diseases such as spinal cord injury, Parkinson’s disease, and multiple sclerosis often develop neurogenic detrusor overactivity (NDO), which currently lacks a universally effective therapy. Here, we tested the hypothesis that NDO is associated with changes in detrusor smooth muscle (DSM) large conductance Ca2+-activated K+ (BK) channel expression and function. DSM tissue samples from 33 patients were obtained during open bladder surgeries. NDO patients were clinically characterized preoperatively with pressure-flow urodynamics demonstrating detrusor overactivity, in the setting of a clinically relevant neurological condition. Control patients did not have overactive bladder and did not have a clinically relevant neurological disease. We conducted quantitative polymerase chain reactions (qPCR), perforated patch-clamp electrophysiology on freshly-isolated DSM cells, and functional studies on DSM contractility. qPCR experiments revealed that DSM samples from NDO patients showed decreased BK channel mRNA expression in comparison to controls. Patch-clamp experiments demonstrated reduced whole cell and transient BK currents (TBKCs) in freshly-isolated DSM cells from NDO patients. Functional studies on DSM contractility showed that spontaneous phasic contractions had a decreased sensitivity to iberiotoxin, a selective BK channel inhibitor, in DSM strips isolated from NDO patients. These results reveal the novel finding that NDO is associated with decreased DSM BK channel expression and function leading to increased DSM excitability and contractility. BK channel openers or BK channel gene transfer could be an alternative strategy to control NDO. Future clinical trials are needed to evaluate the value of BK channel opening drugs or gene therapies for NDO treatment and to identify any possible adverse effects.
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Soder RP, Parajuli SP, Hristov KL, Rovner ES, Petkov GV. SK channel-selective opening by SKA-31 induces hyperpolarization and decreases contractility in human urinary bladder smooth muscle. Am J Physiol Regul Integr Comp Physiol 2012; 304:R155-63. [PMID: 23174857 DOI: 10.1152/ajpregu.00363.2012] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Overactive bladder (OAB) is often associated with increased involuntary detrusor smooth muscle (DSM) contractions during the bladder-filling phase. To develop novel therapies for OAB, it is critical to better understand the mechanisms that control DSM excitability and contractility. Recent studies showed that small-conductance Ca(2+)-activated K(+) (SK) channels, SK3 channels, in particular, regulate human DSM function. However, the concept that SK channel-selective pharmacological activation can decrease the excitability and contractility directly in human DSM needs further exploration. Here, we studied the effect of the novel and potent SK channel activator, SKA-31 (or naphtho [1,2-d]thiazol-2-ylamine), on human DSM excitability and contractility at the cellular and tissue level. We used isometric tension recordings on human DSM-isolated strips and the perforated patch-clamp technique on freshly isolated native human DSM cells. SKA-31 significantly decreased spontaneous phasic contractions of DSM-isolated strips. In the presence of the SK channel blocker, apamin, the inhibitory effects of SKA-31 on the DSM spontaneous phasic contractions were significantly reduced. SKA-31 decreased the carbachol- and KCl-induced contractions in human DSM strips. Electrical field stimulation-induced contractions were significantly attenuated in the presence of SKA-31 at all stimulation frequencies (0.5-50 Hz). SKA-31 hyperpolarized the resting membrane potential of human DSM cells. Apamin abolished the hyperpolarizing effect of SKA-31, indicating the involvement of SK channel activation. These results support the concept that pharmacological activation of SK channels with selective openers may represent an attractive new pharmacological approach for decreasing DSM excitability and contractility, thus controlling OAB.
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Affiliation(s)
- Rupal P Soder
- Dept. of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, Univ. of South Carolina, Columbia, SC 29208, USA
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Xin W, Soder RP, Cheng Q, Rovner ES, Petkov GV. Selective inhibition of phosphodiesterase 1 relaxes urinary bladder smooth muscle: role for ryanodine receptor-mediated BK channel activation. Am J Physiol Cell Physiol 2012; 303:C1079-89. [PMID: 22992675 DOI: 10.1152/ajpcell.00162.2012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The large conductance voltage- and Ca(2+)-activated K(+) (BK) channel is a major regulator of detrusor smooth muscle (DSM) excitability and contractility. Recently, we showed that nonselective phosphodiesterase (PDE) inhibition reduces guinea pig DSM excitability and contractility by increasing BK channel activity. Here, we investigated how DSM excitability and contractility changes upon selective inhibition of PDE type 1 (PDE1) and the underlying cellular mechanism involving ryanodine receptors (RyRs) and BK channels. PDE1 inhibition with 8-methoxymethyl-3-isobutyl-1-methylxanthine (8MM-IBMX; 10 μM) increased the cAMP levels in guinea pig DSM cells. Patch-clamp experiments on freshly isolated DSM cells showed that 8MM-IBMX increased transient BK currents and the spontaneous transient hyperpolarization (STH) frequency by ∼2.5- and ∼1.8-fold, respectively. 8MM-IBMX hyperpolarized guinea pig and human DSM cell membrane potential and significantly decreased the intracellular Ca(2+) levels in guinea pig DSM cells. Blocking BK channels with 1 μM paxilline or inhibiting RyRs with 30 μM ryanodine abolished the STHs and the 8MM-IBMX inhibitory effects on the DSM cell membrane potential. Isometric DSM tension recordings showed that 8MM-IBMX significantly reduced the spontaneous phasic contraction amplitude, muscle force integral, duration, frequency, and tone of DSM isolated strips. The electrical field stimulation-induced DSM contraction amplitude, muscle force integral, and duration were also attenuated by 10 μM 8MM-IBMX. Blocking BK channels with paxilline abolished the 8MM-IBMX effects on DSM contractions. Our data provide evidence that PDE1 inhibition relaxes DSM by raising cellular cAMP levels and subsequently stimulates RyRs, which leads to BK channel activation, membrane potential hyperpolarization, and decrease in intracellular Ca(2+) levels.
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Affiliation(s)
- Wenkuan Xin
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Coker Life Sciences Bldg., Rm. 609D, 715 Sumter St, Columbia, SC 29208, USA
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Xin W, Cheng Q, Soder RP, Rovner ES, Petkov GV. Constitutively active phosphodiesterase activity regulates urinary bladder smooth muscle function: critical role of KCa1.1 channel. Am J Physiol Renal Physiol 2012; 303:F1300-6. [PMID: 22896041 DOI: 10.1152/ajprenal.00351.2012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Pharmacological blockade of cyclic nucleotide phosphodiesterase (PDE) can relax human urinary bladder smooth muscle (UBSM); however, the underlying cellular mechanism is unknown. In this study, we investigated the effects of PDE pharmacological blockade on human UBSM excitability, spontaneous and nerve-evoked contractility, and determined the underlying cellular mechanism mediating these effects. Patch-clamp electrophysiological experiments showed that 3-isobutyl-1-methylxanthine (10 μM), a nonselective PDE inhibitor, caused ∼3.6-fold increase in the transient K(Ca)1.1 channel current frequency and ∼2.5-fold increase in the spontaneous transient hyperpolarization frequency in UBSM-isolated cells. PDE blockade also caused ∼5.6-mV hyperpolarization of the UBSM cell membrane potential. Blocking the K(Ca)1.1 channels with paxilline abolished the spontaneous transient hyperpolarization and the hyperpolarization effect of PDE blockade on the UBSM cell membrane potential. Live cell Ca(2+)-imaging experiments showed that PDE blockade significantly decreased the global intracellular Ca(2+) levels. Attenuation of PDE activity significantly reduced spontaneous phasic contraction amplitude, muscle force integral, duration, frequency, and muscle tone of human UBSM isolated strips. Blockade of PDE also significantly reduced the contraction amplitude, muscle force integral, and duration of the nerve-evoked contractions induced by 20-Hz electrical field stimulation. Pharmacological inhibition of K(Ca)1.1 channels abolished the relaxation effects of PDE blockade on both spontaneous and nerve-evoked contractions in human UBSM-isolated strips. Our data provide strong evidence that in human UBSM PDE is constitutively active, thus maintaining spontaneous UBSM contractility. PDE blockade causes relaxation of human UBSM by increasing transient K(Ca)1.1 channel current activity, hyperpolarizing cell membrane potential, and decreasing the global intracellular Ca(2+).
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Affiliation(s)
- Wenkuan Xin
- Dept. of Pharmaceutical & Biomedical Sciences, South Carolina College of Pharmacy, Univ. of South Carolina, Columbia, SC 29208, USA
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Afeli SAY, Rovner ES, Petkov GV. SK but not IK channels regulate human detrusor smooth muscle spontaneous and nerve-evoked contractions. Am J Physiol Renal Physiol 2012; 303:F559-68. [PMID: 22592639 DOI: 10.1152/ajprenal.00615.2011] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Animal studies suggest that the small (SK) and intermediate (IK) conductance Ca(2+)-activated K(+) channels may contribute to detrusor smooth muscle (DSM) excitability and contractility. However, the ability of SK and IK channels to control DSM spontaneous phasic and nerve-evoked contractions in human DSM remains unclear. We first investigated SK and IK channels molecular expression in native human DSM and further assessed their functional role using isometric DSM tension recordings and SK/IK channel-selective inhibitors. Quantitative PCR experiments revealed that SK3 channel mRNA expression in isolated DSM single cells was ∼12- to 44-fold higher than SK1, SK2, and IK channels. RT-PCR studies at the single-cell level detected mRNA messages for SK3 channels but not SK1, SK2, and IK channels. Western blot and immunohistochemistry analysis further confirmed protein expression for the SK3 channel and lack of detectable protein expression for IK channel in whole DSM tissue. Apamin (1 μM), a selective SK channel inhibitor, significantly increased the spontaneous phasic contraction amplitude, muscle force integral, phasic contraction duration, and muscle tone of human DSM isolated strips. Apamin (1 μM) also increased the amplitude of human DSM electrical field stimulation (EFS)-induced contractions. However, TRAM-34 (1 μM), a selective IK channel inhibitor, had no effect on the spontaneous phasic and EFS-induced DSM contractions suggesting a lack of IK channel functional role in human DSM. In summary, our molecular and functional studies revealed that the SK, particularly the SK3 subtype, but not IK channels are expressed and regulate the spontaneous and nerve-evoked contractions in human DSM.
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Affiliation(s)
- Serge A Y Afeli
- Dept. of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, Univ. of South Carolina, Columbia, SC 29208, USA
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Hristov KL, Parajuli SP, Soder RP, Cheng Q, Rovner ES, Petkov GV. Suppression of human detrusor smooth muscle excitability and contractility via pharmacological activation of large conductance Ca2+-activated K+ channels. Am J Physiol Cell Physiol 2012; 302:C1632-41. [PMID: 22422396 DOI: 10.1152/ajpcell.00417.2011] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Overactive bladder syndrome is frequently associated with increased detrusor smooth muscle (DSM) contractility. We tested the hypothesis that pharmacological activation of the large-conductance voltage- and Ca(2+)-activated K(+) (BK) channel with NS-1619, a selective BK channel opener, reduces the excitability and contractility of human DSM. We used the amphotericin-perforated whole cell patch-clamp technique on freshly isolated human DSM cells, live-cell Ca(2+) imaging, and isometric DSM tension recordings of human DSM strips obtained from open bladder surgeries. NS-1619 (30 μM) significantly increased the amplitude of the voltage step-induced whole cell BK currents, and this effect was abolished by pretreatment with 200 nM iberiotoxin (IBTX), a selective BK channel inhibitor. In current-clamp mode, NS-1619 (30 μM) significantly hyperpolarized the resting membrane potential, and the hyperpolarization was reversed by IBTX (200 nM). NS-1619 (30 μM) significantly decreased the intracellular Ca(2+) level in isolated human DSM cells. BK channel activation with NS-1619 (30 μM) significantly inhibited the amplitude, muscle force, frequency, duration, and tone of the spontaneous phasic and pharmacologically induced DSM contractions from human DSM isolated strips. IBTX (200 nM) suppressed the inhibitory effects of NS-1619 on spontaneous contractions. The amplitude of electrical field stimulation (0.5-50 Hz)-induced contractions was significantly reduced by NS-1619 (30 μM). Our data suggest that pharmacological activation of BK channels could represent a novel treatment option to control bladder dysfunction in humans.
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Affiliation(s)
- Kiril L Hristov
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, USA
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Inhibitory effects of the ATP-sensitive potassium channel openers cromakalim, pinacidil and minoxidil on the carbachol-response curve in porcine detrusor muscle. Arab J Urol 2012; 10:207-15. [PMID: 26558027 PMCID: PMC4442889 DOI: 10.1016/j.aju.2011.12.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2011] [Revised: 12/13/2011] [Accepted: 12/14/2011] [Indexed: 12/05/2022] Open
Abstract
Aims ATP-sensitive potassium channels represent promising drug targets for treating specific bladder diseases. The inhibitory effects of ATP-selective potassium channel openers (PCOs) on the carbachol–response curve in porcine detrusor muscle were examined. Materials and methods Each of the three substances used in the study represent one prototype of a different class of PCO: cromakalim belongs to the benzopyran series, pinacidil is a cyanoguanidine derivative, and minoxidil represents a pyrimidine derivative. The porcine detrusor muscle represents one of the best models for human detrusor. Experiments were conducted on muscle strips of porcine detrusor muscle suspended in a tissue bath. Concentration–response curves of carbachol were constructed after pretreatment with cromakalim at 10−7, 10−6 and 10−5 M, and with pinacidil and minoxidil at 10−6, 10−5.5 and 10−5 M, respectively. Each muscle strip was only used to examine one concentration of one substance. Results Cromakalim had the greatest inhibitory effect, significantly suppressing the carbachol–response curve at 10−6 and 10−5 M. Pinacidil showed a significant inhibitory effect at 10−5.5 and 10−5 M, which was smaller than that of cromakalim. Minoxidil did not significantly inhibit the contractions at all examined concentrations. Conclusions The examined ATP-sensitive PCOs belonging to the benzopyrans and cyanoguanidines significantly suppressed detrusor contractions. The development of derivatives of these prototypes could open new possibilities for the pharmacological treatment of selected bladder diseases.
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Petkov GV. Role of potassium ion channels in detrusor smooth muscle function and dysfunction. Nat Rev Urol 2011; 9:30-40. [PMID: 22158596 DOI: 10.1038/nrurol.2011.194] [Citation(s) in RCA: 126] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Contraction and relaxation of the detrusor smooth muscle (DSM), which makes up the wall of the urinary bladder, facilitates the storage and voiding of urine. Several families of K(+) channels, including voltage-gated K(+) (K(V)) channels, Ca(2+)-activated K(+) (K(Ca)) channels, inward-rectifying ATP-sensitive K(+) (K(ir), K(ATP)) channels, and two-pore-domain K(+) (K(2P)) channels, are expressed and functional in DSM. They control DSM excitability and contractility by maintaining the resting membrane potential and shaping the action potentials that determine the phasic nature of contractility in this tissue. Defects in DSM K(+) channel proteins or in the molecules involved in their regulatory pathways may underlie certain forms of bladder dysfunction, such as overactive bladder. K(+) channels represent an opportunity for novel pharmacological manipulation and therapeutic intervention in human DSM. Modulation of DSM K(+) channels directly or indirectly by targeting their regulatory mechanisms has the potential to control urinary bladder function. This Review summarizes our current state of knowledge of the functional role of K(+) channels in DSM in health and disease, with special emphasis on current advancements in the field.
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Affiliation(s)
- Georgi V Petkov
- Department of Pharmaceutical and Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Coker Life Sciences Building, Room 609D, 715 Sumter Street, Columbia, SC 29208, USA.
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ATP enhances spontaneous calcium activity in cultured suburothelial myofibroblasts of the human bladder. PLoS One 2011; 6:e25769. [PMID: 21998694 PMCID: PMC3187810 DOI: 10.1371/journal.pone.0025769] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2011] [Accepted: 09/11/2011] [Indexed: 11/19/2022] Open
Abstract
Background Suburothelial myofibroblasts (sMF) are located underneath the urothelium in close proximity to afferent nerves. They express purinergic receptors and show calcium transients in response to ATP. Therefore they are supposed to be involved in afferent signaling of the bladder fullness. Since ATP concentration is likely to be very low during the initial filling phase, we hypothesized that sMF Ca2+ activity is affected even at very low ATP concentrations. We investigated ATP induced modulation of spontaneous activity, intracellular calcium response and purinergic signaling in cultured sMF. Methodology/Principal Findings Myofibroblast cultures, established from cystectomies, were challenged by exogenous ATP in presence or absence of purinergic antagonist. Fura-2 calcium imaging was used to monitor ATP (10−16 to 10−4 mol/l) induced alterations of calcium activity. Purinergic receptors (P2X1, P2X2, P2X3) were analysed by confocal immunofluorescence. We found spontaneous calcium activity in 55.18%±1.65 of the sMF (N = 48 experiments). ATP significantly increased calcium activity even at 10−16 mol/l. The calcium transients were partially attenuated by subtype selective antagonist (TNP-ATP, 1 µM; A-317491, 1 µM), and were mimicked by the P2X1, P2X3 selective agonist α,β-methylene ATP. The expression of purinergic receptor subtypes in sMF was confirmed by immunofluorescence. Conclusions/Significance Our experiments demonstrate for the first time that ATP can modulate spontaneous activity and induce intracellular Ca2+ response in cultured sMF at very low concentrations, most likely involving P2X receptors. These findings support the notion that sMF are able to register bladder fullness very sensitively, which predestines them for the modulation of the afferent bladder signaling in normal and pathological conditions.
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Soder RP, Petkov GV. Large conductance Ca2+ -activated K+ channel activation with NS1619 decreases myogenic and neurogenic contractions of rat detrusor smooth muscle. Eur J Pharmacol 2011; 670:252-9. [PMID: 21914438 DOI: 10.1016/j.ejphar.2011.08.013] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2011] [Revised: 07/23/2011] [Accepted: 08/17/2011] [Indexed: 02/07/2023]
Abstract
Large conductance voltage- and Ca(2+)-activated K(+) (BK) channels are important in regulating detrusor smooth muscle (DSM) function. Here, we examined systematically how the BK channel pharmacological activation modulates DSM contractility. NS1619, a potent BK channel activator, was utilized as a pharmacological tool to investigate the effect of BK channel activation on rat DSM contractility. Isometric tension recordings of DSM strips isolated from rat urinary bladder were performed systematically under various experimental conditions. NS1619 (30 μM) substantially diminished DSM spontaneous contraction amplitude, muscle force integral, frequency, duration and muscle tone. This effect was blocked by iberiotoxin, a BK channel selective inhibitor. NS1619 inhibited the phasic and tonic contractions in DSM strips pre-contracted with either the cholinergic agonist, carbachol (0.1 μM), or the depolarizing agent, KCl (20mM). In the presence of elevated KCl (60 mM KCl), the inhibitory effect of NS1619 was significantly reduced, indicating that BK channel activation is the underlying mechanism of NS1619 action. BK channel activation with NS1619 dramatically decreased the amplitude of electrical field stimulation (EFS)-induced contractions under a range of stimulation frequencies (0.5-50 Hz). In the presence of specific neurotransmitter inhibitors, BK channel activation with NS1619 significantly decreased both cholinergic and purinergic components of EFS-induced contractions. We conclude that BK channel activation with NS1619 significantly inhibited spontaneous, pharmacologically induced and nerve-evoked DSM contractions. Targeting the BK channel with selective openers may offer a unique opportunity to control DSM contractile activity, including pathophysiological conditions such as overactive bladder and detrusor overactivity, regardless of the underlying cause.
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Affiliation(s)
- Rupal P Soder
- Pharmaceutical & Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA
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