The voltage dependence of hEag currents is not determined solely by membrane-spanning domains.
The ether-à-go-go potassium channels hEag1 and hEag2 are highly homologous. Even though both possess identical voltage-sensing domain S4, the channels act differently in response to voltage. Therefore we asked whether transmembrane domains other than the voltage sensor could contribute to the voltage-dependent behaviour of these potassium channels. For this chimaeras were created, in which each single transmembrane domain of hEag1 was replaced by the corresponding segment of hEag2. The voltage-dependent properties of the chimaeras were analysed after expression in Xenopus laevis oocytes using the two-electrode voltage-clamp method. By this we found, that only the mutations in transmembrane domains S5 and S6 are able to change the voltage sensitivity of hEag1 by shifting the half-activation potential (V(50)) to values intermediate between the two wild types. Moreover, the presence of Mg2+ has strong effects on the voltage sensitivity of hEag2 shifting V(50) by more than 50 mV to more positive values. Interestingly, despite the identical binding site Mg2+ showed only little effects on hEag1 or the chimaeras. Altogether, our data suggest that not only transmembrane spanning regions, but also non-membrane spanning regions are responsible for differences in the behaviour of the hEag1 and hEag2 potassium channels.
Lörinczi
Eva
E
Max-Planck Institute of Experimental Medicine, Hermann-Rein Str. 3, 37075 Göttingen, Germany.
Napp
Joanna
J
Contreras-Jurado
Constanza
C
Pardo
Luis A
LA
Stühmer
Walter
W
D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D051638:Ether-A-Go-Go Potassium Channels / Q000235:genetics / Q000502:physiology*; D006801:Humans; D015640:Ion Channel Gating; D008274:Magnesium / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary; D014982:Xenopus laevis
D051638:Ether-A-Go-Go Potassium Channels; C496884:KCNH1 protein, human; C485729:KCNH5 protein, human; D008274:Magnesium