title: Selective, direct activation of high-conductance, calcium-activated potassium channels causes smooth muscle relaxation.
abstract: High-conductance calcium-activated potassium (Maxi-K) channels are present in smooth muscle where they regulate tone. Activation of Maxi-K channels causes smooth muscle hyperpolarization and shortening of action-potential duration, which would limit calcium entry through voltage-dependent calcium channels leading to relaxation. Although Maxi-K channels appear to indirectly mediate the relaxant effects of a number of agents, activators that bind directly to the channel with appropriate potency and pharmacological properties useful for proof-of-concept studies are not available. Most agents identified to date display significant polypharmacy that severely compromises interpretation of experimental data. In the present study, a high-throughput, functional, cell-based assay for identifying Maxi-K channel agonists was established and used to screen a large sample collection (>1.6 million compounds). On the basis of potency and selectivity, a family of tetrahydroquinolines was further characterized. Medicinal chemistry efforts afforded identification of compound X, from which its two enantiomers, Y and Z, were resolved. In in vitro assays, Z is more potent than Y as a channel activator. The same profile is observed in tissues where the ability of either agent to relax precontracted smooth muscles, via a potassium channel-dependent mechanism, is demonstrated. These data, taken together, suggest that direct activation of Maxi-K channels represents a mechanism to be explored for the potential treatment of a number of diseases associated with smooth muscle hyperexcitability.
authors.affiliation: Department of Biotechnology, Instituto Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Cristiano G
authors.initials: CG
authors.lastname: Ponte
authors.forename: Owen B
authors.initials: OB
authors.lastname: McManus
authors.forename: William A
authors.initials: WA
authors.lastname: Schmalhofer
authors.forename: Dong-Ming
authors.initials: DM
authors.lastname: Shen
authors.forename: Ge
authors.initials: G
authors.lastname: Dai
authors.forename: Andra
authors.initials: A
authors.lastname: Stevenson
authors.forename: Sylvie
authors.initials: S
authors.lastname: Sur
authors.forename: Tarak
authors.initials: T
authors.lastname: Shah
authors.forename: Laszlo
authors.initials: L
authors.lastname: Kiss
authors.forename: Min
authors.initials: M
authors.lastname: Shu
authors.forename: James B
authors.initials: JB
authors.lastname: Doherty
authors.forename: Ravi
authors.initials: R
authors.lastname: Nargund
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Kaczorowski
authors.forename: Guilherme
authors.initials: G
authors.lastname: Suarez-Kurtz
authors.forename: Maria L
authors.initials: ML
authors.lastname: Garcia
mesh_terms: D000818:Animals; D016466:CHO Cells; D002853:Chromatography, Liquid; D006224:Cricetinae; D003412:Cricetulus; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D009126:Muscle Relaxation; D009130:Muscle, Smooth / Q000502:physiology*
chemical_list: D051036:Large-Conductance Calcium-Activated Potassium Channels