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J Gen Physiol December 1, 2004; 124 (6): 703-18.
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Gating charges in the activation and inactivation processes of the HERG channel.

Zhang M , Liu J , Tseng GN .

The hERG channel has a relatively slow activation process but an extremely fast and voltage-sensitive inactivation process. Direct measurement of hERG''s gating current (Piper, D.R., A. Varghese, M.C. Sanguinetti, and M. Tristani-Firouzi. 2003. PNAS. 100:10534-10539) reveals two kinetic components of gating charge transfer that may originate from two channel domains. This study is designed to address three questions: (1) which of the six positive charges in hERG''s major voltage sensor, S4, are responsible for gating charge transfer during activation, (2) whether a negative charge in the cytoplasmic half of S2 (D466) also contributes to gating charge transfer, and (3) whether S4 serves as the sole voltage sensor for hERG inactivation. We individually mutate S4''s positive charges and D466 to cysteine, and examine (a) effects of mutations on the number of equivalent gating charges transferred during activation (z(a)) and inactivation (z(i)), and (b) sidedness and state dependence of accessibility of introduced cysteine side chains to a membrane-impermeable thiol-modifying reagent (MTSET). Neutralizing the outer three positive charges in S4 and D466 in S2 reduces z(a), and cysteine side chains introduced into these positions experience state-dependent changes in MTSET accessibility. On the other hand, neutralizing the inner three positive charges in S4 does not affect z(a). None of the charge mutations affect z(i). We propose that the scheme of gating charge transfer during hERG''s activation process is similar to that described for the Shaker channel, although hERG has less gating charge in its S4 than in Shaker. Furthermore, channel domain other than S4 contributes to gating charge involved in hERG''s inactivation process.

PubMed ID: 15545400
PMC ID: PMC2234031
Article link: J Gen Physiol
Grant support: [+]

Species referenced: Xenopus laevis
Genes referenced: kcnh1 kcnh2 rps3a tbx2

Article Images: [+] show captions
References [+] :
Aggarwal, Contribution of the S4 segment to gating charge in the Shaker K+ channel. 1996, Pubmed, Xenbase