title: Effects of class III antiarrhythmic drugs on transient outward and ultra-rapid delayed rectifier currents in human atrial myocytes.
abstract: A variety of class III antiarrhythmic agents have been shown to block the delayed rectifier current, but their effects on other K+ currents, particularly in human tissues, are less clear. We studied the concentration-dependent actions of the class III compounds d-sotalol, E-4031 and ambasilide on the transient outward current (I(to)) and the ultra-rapid delayed rectifier current (I(Kur)) in human atrial myocytes. d-Sotalol and E-4031 failed to alter I(to) or I(Kur) at concentrations up to 500 and 50 microM, respectively. In contrast, ambasilide produced a concentration-dependent inhibition of I(to) and I(Kur), with statistically significant effects at 10 microM and maximum effects at 100 microM. The 50% inhibitory concentration of ambasilide averaged 23 +/- 2 microM and 34 +/- 3 microM for I(to) and I(Kur) respectively. Ambasilide did not alter the voltage-dependence of activation or inactivation of I(to), or the voltage-dependence of I(Kur), and it did not affect I(to) recovery from inactivation. On the other hand, ambasilide accelerated I(to) inactivation, by introducing a more rapid component that accelerated with increasing drug concentration. Furthermore, block of both I(to) and I(Kur) developed over time after the onset of depolarization, with time constants of 5.8 +/- 0.8 msec and 2.5 +/- 0.4 msec at concentrations of 10 and 50 microM for I(to) and 6.1 +/- 0.8 msec and 2.1 +/- 0.3 msec at 10 and 50 microM for I(Kur). We conclude that neither d-sotalol nor E-4031 affects I(to) or I(Kur), whereas ambasilide produces efficacious open-channel block of both currents, in human atrial myocytes.
authors.affiliation: Department of Medicine, University of Montreal, Quebec, Canada.
authors.forename: J
authors.initials: J
authors.lastname: Feng
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: G R
authors.initials: GR
authors.lastname: Li
authors.forename: S
authors.initials: S
authors.lastname: Nattel
mesh_terms: D062365:Aminobenzoates / Q000494:pharmacology; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006325:Heart Atria / Q000187:drug effects*; D006801:Humans; D008875:Middle Aged; D010880:Piperidines / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D011725:Pyridines / Q000494:pharmacology; D013015:Sotalol / Q000494:pharmacology
chemical_list: D062365:Aminobenzoates; D000889:Anti-Arrhythmia Agents; D019086:Bridged Bicyclo Compounds, Heterocyclic; D010880:Piperidines; D015221:Potassium Channels; D011725:Pyridines; C075113:ambasilide; C063968:E 4031; D013015:Sotalol