title: NS309 decreases rat detrusor smooth muscle membrane potential and phasic contractions by activating SK3 channels.
abstract: OBJECTIVE
  Overactive bladder (OAB) is often associated with abnormally increased detrusor smooth muscle (DSM) contractions. We used NS309, a selective and potent opener of the small or intermediate conductance Ca(2+) -activated K(+) (SK or IK, respectively) channels, to evaluate how SK/IK channel activation modulates DSM function.
  
  
  METHODS
  We employed single-cell RT-PCR, immunocytochemistry, whole cell patch-clamp in freshly isolated rat DSM cells and isometric tension recordings of isolated DSM strips to explore how the pharmacological activation of SK/IK channels with NS309 modulates DSM function.
  
  
  RESULTS
  We detected SK3 but not SK1, SK2 or IK channels expression at both mRNA and protein levels by RT-PCR and immunocytochemistry in DSM single cells. NS309 (10 μM) significantly increased the whole cell SK currents and hyperpolarized DSM cell resting membrane potential. The NS309 hyperpolarizing effect was blocked by apamin, a selective SK channel inhibitor. NS309 inhibited the spontaneous phasic contraction amplitude, force, frequency, duration and tone of isolated DSM strips in a concentration-dependent manner. The inhibitory effect of NS309 on spontaneous phasic contractions was blocked by apamin but not by TRAM-34, indicating no functional role of the IK channels in rat DSM. NS309 also significantly inhibited the pharmacologically and electrical field stimulation-induced DSM contractions.
  
  
  CONCLUSIONS
  Our data reveal that SK3 channel is the main SK/IK subtype in rat DSM. Pharmacological activation of SK3 channels with NS309 decreases rat DSM cell excitability and contractility, suggesting that SK3 channels might be potential therapeutic targets to control OAB associated with detrusor overactivity.
authors.affiliation: Department of Pharmaceutical & Biomedical Sciences, South Carolina College of Pharmacy, University of South Carolina, Columbia, SC 29208, USA.
authors.forename: Shankar P
authors.initials: SP
authors.lastname: Parajuli
authors.forename: Kiril L
authors.initials: KL
authors.lastname: Hristov
authors.forename: Rupal P
authors.initials: RP
authors.lastname: Soder
authors.forename: Whitney F
authors.initials: WF
authors.lastname: Kellett
authors.forename: Georgi V
authors.initials: GV
authors.lastname: Petkov
mesh_terms: D000818:Animals; D001030:Apamin / Q000494:pharmacology; D048429:Cell Size / Q000187:drug effects; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology*; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015640:Ion Channel Gating; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D010091:Oximes / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology
chemical_list: C493327:6,7-dichloro-1H-indole-2,3-dione 3-oxime; D007211:Indoles; D051660:Intermediate-Conductance Calcium-Activated Potassium Channels; C496901:Kcnn3 protein, rat; D010091:Oximes; D011720:Pyrazoles; D012333:RNA, Messenger; D051640:Small-Conductance Calcium-Activated Potassium Channels; C411671:TRAM 34; D001030:Apamin