State-dependent barium block of wild-type and inactivation-deficient HERG channels in Xenopus oocytes.
The effects of Ba2+ on current resulting from the heterologous expression of the human ether-à-go-go related gene (HERG) (IHERG) was studied with two-electrode voltage clamp techniques in Xenopus oocytes. Ba2+ produced time- and voltage-dependent block of IHERG. Significant inhibition was seen at concentrations as low as 1 microM. Inhibition was greatest at step potentials between -40 and 0 mV; at more positive potentials, inhibition decreased in association with time-dependent unblocking of channels. An inactivation-attenuated mutant of HERG (S631A) was prepared and expressed in Xenopus oocytes. Ba2+ block of S631A differed from that of HERG in that extensive unblocking was no longer seen at positive potentials and the voltage dependence of step current block was greatly attenuated. A mathematical model was applied to analyse quantitatively the inhibitory effects of Ba2+ on IHERG. The model suggested similar voltage-dependent affinity of Ba2+ for the open and closed states, along with absence of binding to the inactivated state, and accounted well for Ba2+ effects on both wild-type and S631A channels. We conclude that Ba2+ potently inhibits IHERG in a characteristic state-dependent fashion, with strong unblocking at positive potentials related to the presence of an intact C-type inactivation mechanism.
Weerapura
M
M
Research Center, Departments of Medicine and Anesthesia, Montreal Heart Institute, 5000 Belanger Street East, Montreal, Canada.
Nattel
S
S
Courtemanche
M
M
Doern
D
D
Ethier
N
N
Hebert
T
T
D019943:Amino Acid Substitution; D000818:Animals; D001464:Barium / Q000494:pharmacology*; D027682:Cation Transport Proteins; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D005260:Female; D006801:Humans; D007700:Kinetics; D008133:Long QT Syndrome / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008962:Models, Theoretical; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014982:Xenopus laevis
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; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D001464:Barium