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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Torrente AG, Zhang R, Wang H, Zaini A, Kim B, Yue X, Philipson KD, Goldhaber JI. Contribution of small conductance K + channels to sinoatrial node pacemaker activity: insights from atrial-specific Na + /Ca 2+ exchange knockout mice. J Physiol 2017; 595:3847-3865. [PMID: 28346695 DOI: 10.1113/jp274249] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2017] [Accepted: 03/22/2017] [Indexed: 12/14/2022] Open
Abstract
KEY POINTS Repolarizing currents through K+ channels are essential for proper sinoatrial node (SAN) pacemaking, but the influence of intracellular Ca2+ on repolarization in the SAN is uncertain. We identified all three isoforms of Ca2+ -activated small conductance K+ (SK) channels in the murine SAN. SK channel blockade slows repolarization and subsequent depolarization of SAN cells. In the atrial-specific Na+ /Ca2+ exchanger (NCX) knockout mouse, cellular Ca2+ accumulation during spontaneous SAN pacemaker activity produces intermittent hyperactivation of SK channels, leading to arrhythmic pauses alternating with bursts of pacing. These findings suggest that Ca2+ -sensitive SK channels can translate changes in cellular Ca2+ into a repolarizing current capable of modulating pacemaking. SK channels are a potential pharmacological target for modulating SAN rate or treating SAN dysfunction, particularly under conditions characterized by abnormal increases in diastolic Ca2+ . ABSTRACT Small conductance K+ (SK) channels have been implicated as modulators of spontaneous depolarization and electrical conduction that may be involved in cardiac arrhythmia. However, neither their presence nor their contribution to sinoatrial node (SAN) pacemaker activity has been investigated. Using quantitative PCR (q-PCR), immunostaining and patch clamp recordings of membrane current and voltage, we identified all three SK isoforms (SK1, SK2 and SK3) in mouse SAN. Inhibition of SK channels with the specific blocker apamin prolonged action potentials (APs) in isolated SAN cells. Apamin also slowed diastolic depolarization and reduced pacemaker rate in isolated SAN cells and intact tissue. We investigated whether the Ca2+ -sensitive nature of SK channels could explain arrhythmic SAN pacemaker activity in the atrial-specific Na+ /Ca2+ exchange (NCX) knockout (KO) mouse, a model of cellular Ca2+ overload. SAN cells isolated from the NCX KO exhibited higher SK current than wildtype (WT) and apamin prolonged their APs. SK blockade partially suppressed the arrhythmic burst pacing pattern of intact NCX KO SAN tissue. We conclude that SK channels have demonstrable effects on SAN pacemaking in the mouse. Their Ca2+ -dependent activation translates changes in cellular Ca2+ into a repolarizing current capable of modulating regular pacemaking. This Ca2+ dependence also promotes abnormal automaticity when these channels are hyperactivated by elevated Ca2+ . We propose SK channels as a potential target for modulating SAN rate, and for treating patients affected by SAN dysfunction, particularly in the setting of Ca2+ overload.
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Affiliation(s)
- Angelo G Torrente
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
| | - Rui Zhang
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
| | - Heidi Wang
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
| | - Audrey Zaini
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
| | - Brian Kim
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
| | - Xin Yue
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
| | - Kenneth D Philipson
- Department of Physiology, David Geffen School of Medicine at UCLA, 650 Charles Young Drive South, Los Angeles, CA, 90095-1751, USA
| | - Joshua I Goldhaber
- Cedars-Sinai Heart Institute, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA.,Department of Biomedical Sciences, Cedars-Sinai Medical Center, 8700 Beverly Blvd, Los Angeles, CA, 90048, USA
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