Inhibition of HERG K+ current and prolongation of the guinea-pig ventricular action potential by 4-aminopyridine.
4-Aminopyridine (4-AP) has been used extensively to study transient outward K+ current (ITO,1) in cardiac cells and tissues. We report here inhibition by 4-AP of HERG (the human ether-à-go-go-related gene) K+ channels expressed in a mammalian cell line, at concentrations relevant to those used to study ITO,1. Under voltage clamp, whole cell HERG current (IHERG) tails following commands to +30 mV were blocked with an IC50 of 4.4 +/- 0.5 mM. Development of block was contingent upon HERG channel gating, with a preference for activated over inactivated channels. Treatment with 5 mM 4-AP inhibited peak IHERG during an applied action potential clamp waveform by ~59 %. It also significantly prolonged action potentials and inhibited resurgent IK tails from guinea-pig isolated ventricular myocytes, which lack an ITO,1. We conclude that by blocking the alpha-subunit of the IKr channel, millimolar concentrations of 4-AP can modulate ventricular repolarisation independently of any action on ITO,1.
Ridley
J M
JM
Department of Physiology and Cardiovascular Research Laboratories, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.
Milnes
J T
JT
Zhang
Y H
YH
Witchel
H J
HJ
Hancox
J C
JC
D015761:4-Aminopyridine / Q000494:pharmacology*; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D027682:Cation Transport Proteins; D002460:Cell Line; D002469:Cell Separation; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D032342:Muscle Cells / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D016276:Ventricular Function
D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; C072312:ERG protein, human; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C092509:KCNH6 protein, human; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D015761:4-Aminopyridine