title: Molecular mechanisms for large conductance Ca2+-activated K+ channel activation by a novel opener, 12,14-dichlorodehydroabietic acid.
abstract: Our recent study has revealed that 12,14-dichlorodehydroabietic acid (diCl-DHAA), which is synthetically derived from a natural product, abietic acid, is a potent opener of large conductance Ca(2+)-activated K(+) (BK) channel. Here, we examined, by using a channel expression system in human embryonic kidney 293 cells, the mechanisms underlying the BK channel opening action of diCl-DHAA and which subunit of the BK channel (alpha or beta1) is the site of action for diCl-DHAA. BK channel activity was significantly enhanced by diCl-DHAA at concentrations of 0.1 microM and higher in a concentration-dependent manner. diCl-DHAA enhanced the activity of BKalpha by increasing sensitivity to both Ca(2+) and membrane potential without changing the single channel conductance. It is notable that the increase in BK channel open probability by diCl-DHAA showed significant inverse voltage dependence, i.e., larger potentiation at lower potentials. Since coexpression of beta1 subunit with BKalpha did not affect the potency of diCl-DHAA, the site of action for diCl-DHAA is suggested to be BKalpha subunit. Moreover, kinetic analysis of single channel currents indicates that diCl-DHAA opens BKalpha mainly by decreasing the time staying in a long closed state. Although reconstituted voltage-dependent Ca(2+) channel current was significantly reduced by 1 microM diCl-DHAA, BK channels were selectively activated at lower concentrations. These results indicate that diCl-DHAA is one of the most potent BK channel openers acting on BKalpha and a useful prototype compound to develop a novel BK channel opener.
authors.affiliation: Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences, Nagoya City University, 3-1 Tanabedori, Mizuhoku, Nagoya 467-8603, Japan.
authors.forename: Kazuho
authors.initials: K
authors.lastname: Sakamoto
authors.forename: Taro
authors.initials: T
authors.lastname: Nonomura
authors.forename: Susumu
authors.initials: S
authors.lastname: Ohya
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Muraki
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Ohwada
authors.forename: Yuji
authors.initials: Y
authors.lastname: Imaizumi
mesh_terms: D045784:Abietanes / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005822:Genetic Vectors; D006801:Humans; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000235:genetics; D018408:Patch-Clamp Techniques; D010616:Phenanthrenes / Q000494:pharmacology*; D014162:Transfection
chemical_list: C119118:12,14-dichlorodehydroabietic acid; D045784:Abietanes; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D051036:Large-Conductance Calcium-Activated Potassium Channels; D010616:Phenanthrenes