title: Propafenone blocks human cardiac Kir2.x channels by decreasing the negative electrostatic charge in the cytoplasmic pore.
abstract: Human cardiac inward rectifier current (IK1) is generated by Kir2.x channels. Inhibition of IK1 could offer a useful antiarrhythmic strategy against fibrillatory arrhythmias. Therefore, elucidation of Kir2.x channels pharmacology, which still remains elusive, is mandatory. We characterized the electrophysiological and molecular basis of the inhibition produced by the antiarrhythmic propafenone of the current generated by Kir2.x channels (IKir2.x) and the IK1 recorded in human atrial myocytes. Wild type and mutated human Kir2.x channels were transiently transfected in CHO and HEK-293 cells. Macroscopic and single-channel currents were recorded using the patch-clamp technique. At concentrations >1μM propafenone inhibited IKir2.x the order of potency being Kir2.3∼IK1>Kir2.2>Kir2.1 channels. Blockade was irrespective of the extracellular K(+) concentration whereas markedly increased when the intracellular K(+) concentration was decreased. Propafenone decreased inward rectification since at potentials positive to the K(+) equilibrium potential propafenone-induced block decreased in a voltage-dependent manner. Importantly, propafenone favored the occurrence of subconductance levels in Kir2.x channels and decreased phosphatidylinositol 4,5-bisphosphate (PIP2)-channel affinity. Blind docking and site-directed mutagenesis experiments demonstrated that propafenone bound Kir2.x channels at the cytoplasmic domain, close to, but not in the pore itself, the binding site involving two conserved Arg residues (residues 228 and 260 in Kir2.1). Our results suggested that propafenone incorporated into the cytoplasmic domain of the channel in such a way that it decreased the net negative charge sensed by K(+) ions and polyamines which, in turn, promotes the appearance of subconductance levels and the decrease of PIP2 affinity of the channels.
authors: Department of Pharmacology, School of Medicine, Universidad Complutense, 28040 Madrid, Spain.
authors: Irene
authors: I
authors: Amorós
authors: Pablo
authors: P
authors: Dolz-Gaitón
authors: Ricardo
authors: R
authors: Gómez
authors: Marcos
authors: M
authors: Matamoros
authors: Adriana
authors: A
authors: Barana
authors: Marta González
authors: MG
authors: de la Fuente
authors: Mercedes
authors: M
authors: Núñez
authors: Marta
authors: M
authors: Pérez-Hernández
authors: Ignacio
authors: I
authors: Moraleda
authors: Enrique
authors: E
authors: Gálvez
authors: Isabel
authors: I
authors: Iriepa
authors: Juan
authors: J
authors: Tamargo
authors: Ricardo
authors: R
authors: Caballero
authors: Eva
authors: E
authors: Delpón
mesh_terms: D000368:Aged; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003593:Cytoplasm / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D008297:Male; D008875:Middle Aged; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors*; D011405:Propafenone / Q000494:pharmacology*; D055672:Static Electricity
chemical_list: D024661:Potassium Channels, Inwardly Rectifying; D011405:Propafenone