Blockade of HERG channels expressed in Xenopus laevis oocytes by external divalent cations.
We have investigated actions of various divalent cations (Ba2+, Sr2+, Mn2+, Co2+, Ni2+, Zn2+) on human ether-a-go-go related gene (HERG) channels expressed in Xenopus laevis oocytes using the voltage clamp technique. All divalent cations inhibited HERG current dose-dependently in a voltage-dependent manner. The concentration for half-maximum inhibition (Ki) decreased at more negative potentials, indicating block is facilitated by hyperpolarization. Ki at 0 mV for Zn2+, Ni2+, Co2+, Ba2+, Mn2+, and Sr2+ was 0.19, 0.36, 0. 50, 0.58, 2.36, and 6.47 mM, respectively. The effects were manifested in four ways: 1) right shift of voltage dependence of activation, 2) decrease of maximum conductance, 3) acceleration of current decay, and 4) slowing of activation. However, each parameter was not affected by each cation to the same extent. The potency for the shift of voltage dependence of activation was in the order Zn2+ > Ni2+ >/= Co2+ > Ba2+ > Mn2+ > Sr2+, whereas the potency for the decrease of maximum conductance was Zn2+ > Ba2+ > Sr2+ > Co2+ > Mn2+. The kinetics of activation and deactivation were also affected, but the two parameters are not affected to the same extent. Slowing of activation by Ba2+ was most distinct, causing a marked initial delay of current onset. From these results we concluded that HERG channels are nonselectively blocked by most divalent cations from the external side, and several different mechanism are involved in their actions. There exist at least two distinct binding sites for their action: one for the voltage-dependent effect and the other for reducing maximum conductance.
Ho
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Department of Physiology, Seoul National University College of Medicine, Seoul 110-799, Republic of Korea. wonkyung@plaza.snu.ac.kr
Kim
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Lee
C O
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Youm
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JB
Lee
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Earm
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D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D027682:Cation Transport Proteins; D002413:Cations, Divalent / Q000494:pharmacology; D004268:DNA-Binding Proteins; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; D005260:Female; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000235:genetics / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated; D015534:Trans-Activators; D000071230:Transcriptional Regulator ERG; D014982:Xenopus laevis
D027682:Cation Transport Proteins; D002413:Cations, Divalent; 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