title: A-272651, a nonpeptidic blocker of large-conductance Ca2+-activated K+ channels, modulates bladder smooth muscle contractility and neuronal action potentials.
abstract: OBJECTIVE
  The large-conductance Ca(2+)-activated K(+) channel (BK(Ca), K(Ca)1.1) links membrane excitability with intracellular Ca(2+) signaling and plays important roles in smooth muscle contraction, neuronal firing, and neuroendocrine secretion. This study reports the characterization of a novel BK(Ca) channel blocker, 2,4-dimethoxy-N-naphthalen-2-yl-benzamide (A-272651).
  
  
  METHODS
  (86)Rb(+) efflux in HEK-293 cells expressing BK(Ca) was measured. Effects of A-272651 on BK(Ca) alpha- and BK(Ca) alphabeta1-mediated currents were evaluated by patch-clamp. Effects on contractility were assessed using low-frequency electrical field stimulated pig detrusor and spontaneously contracting guinea pig detrusor. Effects of A-272651 on neuronal activity were determined in rat small diameter dorsal root ganglia (DRG).
  
  
  RESULTS
  A-272651 (10 microM) inhibited (86)Rb(+) efflux evoked by NS-1608 in HEK-293 cells expressing BK(Ca) currents. A-272651 concentration-dependently inhibited BK(Ca) currents with IC(50) values of 4.59 microM (Hill coefficient 1.04, measured at +40 mV), and 2.82 microM (Hill coefficient 0.89), respectively, for BK(Ca) alpha and BK(Ca) alphabeta1-mediated currents. Like iberiotoxin, A-272651 enhanced field stimulated twitch responses in pig detrusor and spontaneous contractions in guinea pig detrusor with EC(50) values of 4.05+/-0.05 and 37.95+/-0.12 microM, respectively. In capsaicin-sensitive DRG neurons, application of A-272651 increased action potential firing and prolonged action potential duration.
  
  
  CONCLUSIONS
  These data demonstrate that A-272651 modulates smooth muscle contractility and neuronal firing properties. Unlike previously reported peptide BK(Ca) blockers, A-272651 represents one of the first small molecule BK(Ca) channel blockers that could serve as a useful tool for further characterization of BK(Ca) channels in physiological and pathological states.
authors.affiliation: Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064, USA. char-chang.shieh@abbott.com
authors.forename: C-C
authors.initials: CC
authors.lastname: Shieh
authors.forename: S C
authors.initials: SC
authors.lastname: Turner
authors.forename: X-F
authors.initials: XF
authors.lastname: Zhang
authors.forename: I
authors.initials: I
authors.lastname: Milicic
authors.forename: A
authors.initials: A
authors.lastname: Parihar
authors.forename: T
authors.initials: T
authors.lastname: Jinkerson
authors.forename: J
authors.initials: J
authors.lastname: Wilkins
authors.forename: S A
authors.initials: SA
authors.lastname: Buckner
authors.forename: M
authors.initials: M
authors.lastname: Gopalakrishnan
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D001549:Benzamides / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005727:Ganglia, Spinal; D006168:Guinea Pigs; D006801:Humans; D066298:In Vitro Techniques; D020128:Inhibitory Concentration 50; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors*; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects; D009281:Naphthalenes / Q000008:administration & dosage / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D013552:Swine; D001743:Urinary Bladder / Q000187:drug effects* / Q000294:innervation / Q000378:metabolism
chemical_list: C523735:2,4-dimethoxy-N-naphthalen-2-yl-benzamide; D001549:Benzamides; D051036:Large-Conductance Calcium-Activated Potassium Channels; D009281:Naphthalenes; D010455:Peptides; C064719:iberiotoxin