title: The amiodarone derivative 2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl)benzofuran (KB130015) opens large-conductance Ca2+-activated K+ channels and relaxes vascular smooth muscle.
abstract: 2-methyl-3-(3,5-diiodo-4-carboxymethoxybenzyl)benzofuran (KB130015) has been developed to retain the antiarrhythmic properties of the parent molecule amiodarone but to eliminate its undesired side effects. In patch-clamp experiments, KB130015 activated large-conductance, Ca2+-activated BK(Ca) channels formed by hSlo1 (alpha) subunits in HEK 293 cells. Channels were reversibly activated by shifting the open-probability/voltage (P(o)/V) relationship by about -60 mV in 3 muM intracellular free Ca2+ ([Ca2+]in). No effect on the single-channel conductance was observed. KB130015-mediated activation of BK(Ca) channels was half-maximal at 20 microM with a Hill coefficient of 2.8. BK(Ca) activation by KB130015 did not require the presence of Ca2+ and still occurred with saturating (100 microM) [Ca2+]in. Effects of the prototypic BK(Ca) activator NS1619 (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one) and those of KB130015 were not additive suggesting that both activators may at least partially share a common mechanism of action. KB130015-mediated activation was observed also for BK(Ca) channels from insects and for human BK(Ca) channels with already profoundly left-shifted voltage-dependence. In contrast, human intermediate conductance Ca2+-activated channels were inhibited by KB130015. Using segments of porcine pulmonary arteries, KB130015 induced endothelium-independent vasorelaxation, half-maximal at 43 microM KB130015. Relaxation was inhibited by 1 mM tetraethylammonium, suggesting that KB130015 can activate vascular smooth muscle type BK(Ca) channels under physiological conditions. Interestingly, the shift in the P(o)/V relationship was considerably stronger (-90 mV in 3 microM [Ca2+]in) for BK(Ca) channels containing Slo-beta1 subunits. Thus, KB130015 belongs to a novel class of BK(Ca) channel openers that exert an effect depending on the subunit composition of the channel complex.
authors.affiliation: Center for Molecular Biomedicine, Department of Biophysics, Friedrich Schiller University Jena, Drackendorfer St. 1, D-07747 Jena, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Gessner
authors.forename: Regine
authors.initials: R
authors.lastname: Heller
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hoshi
authors.forename: Stefan H
authors.initials: SH
authors.lastname: Heinemann
mesh_terms: D000638:Amiodarone; D000818:Animals; D001572:Benzofurans / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D045744:Cell Line, Tumor; D006801:Humans; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000819:agonists* / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology; D011651:Pulmonary Artery / Q000187:drug effects / Q000502:physiology; D013552:Swine; D014664:Vasodilation / Q000187:drug effects
chemical_list: D001572:Benzofurans; C446946:KB 130015; D051036:Large-Conductance Calcium-Activated Potassium Channels; D000638:Amiodarone; D002118:Calcium