Regulation of Human Ether À Go-Go 1 (hEAG1) Potassium Channels

Abstract

Human ether à go-go (hEAG1) channel is a voltage-gated potassium channel that is only expressed in brain tissue. This channel consists of four transmembrane α helices, in which each α subunit has six domains (S1-6), S1-4 as voltage sensors and S5 and S6 are pore-forming domains. When action potential generated and subsequently the membrane potentials (Vm) depolarized, this channel repolarizes the cell back to resting potential. To date, little is known about the physiological role of EAG1 channel. In regard to diseases, ~ 70% of cancers exhibit hEAG1 overexpression. hEAG1 channel contributes to cancer proliferation indirectly through control of cytoplasmic Ca2+ (Ca2+ i). The aberrant overexpression of this channel in cancers prompted us to study its regulation by Ca2+ and hemin. To study hEAG1 regulation, currents from hEAG1-expressing Xenopus oocytes were measured by two-electrode voltage clamp (TEVC) technique. The results showed that hEAG1 currents substantially inhibited in response to increased Ca2+ i with maximal inhibition of 93.2± 2.9 %. In addition, the gating properties of hEAG1 currents in I and T was changed, in which the activation was clearly slowed without exhibition of rectification. Whereas the activity of hEAG1 channel with a deletion of PAS-cap domain in I and T substantially potentiated with 9± 1.4–fold compared to the control currents. Surprisingly, we found that upon application of extracellular hemin (5 µM) into hEAG1-expressing oocytes, the channel current significantly reduced with percentage of maximal inhibition of 24.8±5.2%. The gating of hEAG1-expressing oocytes upon persistent application of extracellular hemin interestingly resembles the gating of hEAG1 inhibited by an increase in Ca2+ i. Injection of hemin (1 µM) into hEAG1-expressing oocytes, however, showed no current inhibition. This study provides the first evidence that hemin inhibits hEAG1 channel from the extracellular side.