Abstract
Calcium-activated potassium channels are attractive targets for the development of therapeutics for overactive bladder. In the current study, we addressed the role of calcium-activated potassium channels of small (SK; KCa2) and intermediate (IK; KCa3) conductance in bladder function pharmacologically. We identified and characterized a novel positive modulator of SK/IK channels, 4,5-dichloro-1,3-diethyl-1,3-dihydro-benzoimidazol-2-one (NS4591). In whole-cell patch-clamp experiments, NS4591 doubled IK-mediated currents at a concentration of 45 ± 6 nM(n = 16), whereas 530 ± 100 nM (n = 7) was required for doubling of SK3-mediated currents. In acutely dissociated bladder primary afferent neurons, the presence of SK channels was verified using apamin and 1-ethyl-2-benzimidazolinone. In these neurons, NS4591 (10 μM) inhibited the number of action potentials generated by suprathreshold depolarizing pulses. NS4591 also reduced carbachol-induced twitches in rat bladder detrusor rings in an apamin-sensitive manner. In vivo, NS4591 (30 mg/kg) inhibited bladder overactivity in rats and cats induced by capsaicin and acetic acid, respectively. In conclusion, the present study supports the involvement of calcium-activated potassium channels in bladder function and identifies NS4591 as a potent modulator of IK and SK channels that is effective in animal models of bladder overactivity.
Footnotes
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C.H. and M.O.F. contributed equally to this work.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.143123.
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ABBREVIATIONS: KATP, ATP-sensitive K+; SK, calcium-activated potassium channels of small conductance; IK, calcium-activated potassium channels of intermediate conductance; BK, calcium-activated potassium channels of large conductance; HEK, human embryonic kidney; DC-EBIO, 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one; 1-EBIO, 1-ethyl-2-benzimidazolinone; DMSO, dimethyl sulfoxide; OxyHb, oxyhemoglobin; h, human; DRG, dorsal root ganglion; IB4, isolectin B4; Fast DiI, 1,1′-dilinoleyl-3,3,3′,3′-tetramethylinocarbocyanine perchlorate; AP, action potential; RMP, resting membrane potential; Rin, input resistance; ANOVA, analysis of variance; PE, polyethylene; CMG, continuous cystometry; MP, maximal micturition pressure; MV, micturition volume; ICI, intercontraction interval; BP, basal pressure; TP, threshold pressure; AHP, afterhyperpolarization; CTL, control; ZD6169, (S)-N-(4-benzoylphenyl)-3,3,3-trifluoro-2-hydroxy-2-methylpropionamide; NS-8, 2-amino-3-cyano-5-(2-fluorophenyl)-4-methylpyrrole.
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↵1 Current affiliation: Urogenix Inc., Durham, North Carolina.
- Received July 4, 2008.
- Accepted September 25, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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