Thouta S , Lo G , Grajauskas L , Claydon T .

	Figure 1. hERG I663P trapped open channels exhibit inactivation that is similar to that in WT channels. (A–C) Typical hERG WT, I663P and I663P/S620T current traces evoked during 4 s repolarizing voltage steps from +40 to −120 mV applied following a 500 ms step to +60 mV to activate channels (holding potential was −80 mV for WT and −30 mV for I663P and I663P/S620T). (D) Fully activated hERG WT, I663P and I663P/S620T I-V relations constructed from peak tail currents. Current amplitudes were normalized in order to compare rectification in the two constructs. (E) Voltage-dependence of inactivation of hERG WT and I663P channels. Rectification factor was calculated (see Materials and Methods) from the fully activated tail current data in (D). Data were fitted with a Boltzmann function. V1/2 and k values were −62 ± 3.1 and 17 ± 0.4 mV for WT (n = 6), and −58.6 ± 0.5 and 5.4 ± 0.5 mV for I663P (n = 6), respectively.
	Figure 2. WT-like ion selectivity is preserved in I663P trapped open channels. (A and B) Plot of the permeability ratio (PX/PK) for each ion (see Materials and Methods section) in hERG WT (A) and I663P (B) channels. PX/PK ratios for WT were: PLi/PK = 0.02 ± 0.002; PNa/PK = 0.06 ± 0.01; PRb/PK = 1.2 ± 0.01; and PCs/PK = 0.42 ± 0.01 (n = 5). PX/PK ratios for I663P were: PLi/PK = 0.03 ± 0.004; PNa/PK = 0.06 ± 0.01; PRb/PK = 0.97 ± 0.03; and PCs/PK = 0.47 ± 0.09 (n = 3). n numbers are shown in parenthesis. The error bars are displayed behind the data points and some are so small that they are not visible.
	Figure 3. High affinity block by terfenadine and cisapride is preserved in I663P trapped open channels. (A–D) Typical WT and I663P currents recorded with 30 mM external K+ evoked during repetitive application of the voltage protocol shown in the insets and in the presence of the indicated concentration of terfenadine (A and B) or cisapride (C and D). The pulse frequency was 0.14 Hz, such that channels were held at the holding potential for 1 s between successive sweeps. In both WT and I663P channels, peak tail current was inhibited in a concentration dependent manner. Traces shown represent steady-state conditions at each concentration. (E and F) Concentration-effect relationship for block of WT and I663P channels by terfenadine (E) and cisapride (F), plotted from peak tail current amplitudes recorded in experiments such as in (A–D). Peak tail current amplitudes in the presence of drug were normalized to peak tail currents in the absence of drug. Fits of WT data to the Hill equation (see Material and Methods) yielded values for IC50 and n of: 4.4 ± 3.0 µM and 0.7 ± 0.04 for terfenadine block (n = 5); 1.1 ± 2.0 µM and 1.3 ± 0.09 for cisapride block (n = 5). Fits of I663P data yielded equivalent values of: 4.0 ± 4.0 µM and 0.4 ± 0.03 for terfenadine block (n = 4); 0.85 ± 0.2 µM and 0.7 ± 0.05 for cisapride block (n = 4).
	Figure 4. State-dependence of drug binding in trapped open hERG I663P channels. (A and B) Plots of percentage block by terfenadine (A) or cisapride (B) versus membrane voltage for I663P channels collected using the protocols shown. Pulse frequency was 0.5 Hz, such that channels were held at the holding potential indicated for 1.5 s between sweeps. n numbers are shown in parenthesis. Dashed lines in (A and B) represent the rectification factor calculated from hERG I663P fully activated currents (Fig. 1E).

Barrows, Extracellular potassium dependency of block of HERG by quinidine and cisapride is primarily determined by the permeant ion and not by inactivation. 2009, Pubmed, Xenbase

Barrows, Extracellular potassium dependency of block of HERG by quinidine and cisapride is primarily determined by the permeant ion and not by inactivation. 2009, Pubmed , Xenbase
Chen, Position of aromatic residues in the S6 domain, not inactivation, dictates cisapride sensitivity of HERG and eag potassium channels. 2002, Pubmed , Xenbase
Curran, A molecular basis for cardiac arrhythmia: HERG mutations cause long QT syndrome. 1995, Pubmed
Fernandez, Physicochemical features of the HERG channel drug binding site. 2004, Pubmed , Xenbase
Ficker, Molecular determinants of inactivation and dofetilide block in ether a-go-go (EAG) channels and EAG-related K(+) channels. 2001, Pubmed , Xenbase
Ficker, Molecular determinants of dofetilide block of HERG K+ channels. 1998, Pubmed , Xenbase
Guo, Molecular determinants of cocaine block of human ether-á-go-go-related gene potassium channels. 2006, Pubmed
Herzberg, Transfer of rapid inactivation and sensitivity to the class III antiarrhythmic drug E-4031 from HERG to M-eag channels. 1998, Pubmed
Kamiya, Molecular determinants of hERG channel block by terfenadine and cisapride. 2008, Pubmed , Xenbase
Kamiya, Molecular determinants of HERG channel block. 2006, Pubmed , Xenbase
Kiehn, Molecular physiology and pharmacology of HERG. Single-channel currents and block by dofetilide. 1996, Pubmed , Xenbase
Lees-Miller, Molecular determinant of high-affinity dofetilide binding to HERG1 expressed in Xenopus oocytes: involvement of S6 sites. 2000, Pubmed , Xenbase
Lin, Intracellular K+ is required for the inactivation-induced high-affinity binding of cisapride to HERG channels. 2005, Pubmed
Macdonald, Probing the molecular basis of hERG drug block with unnatural amino acids. 2018, Pubmed , Xenbase
McPate, Pharmacology of the short QT syndrome N588K-hERG K+ channel mutation: differential impact on selected class I and class III antiarrhythmic drugs. 2008, Pubmed
Mitcheson, Trapping of a methanesulfonanilide by closure of the HERG potassium channel activation gate. 2000, Pubmed , Xenbase
Mitcheson, A structural basis for drug-induced long QT syndrome. 2000, Pubmed , Xenbase
Mitcheson, Molecular determinants of high-affinity drug binding to HERG channels. 2003, Pubmed
Mitcheson, hERG potassium channels and the structural basis of drug-induced arrhythmias. 2008, Pubmed
Myokai, Topological mapping of the asymmetric drug binding to the human ether-à-go-go-related gene product (HERG) potassium channel by use of tandem dimers. 2008, Pubmed , Xenbase
Numaguchi, Probing the interaction between inactivation gating and Dd-sotalol block of HERG. 2000, Pubmed
Pareja, Role of the activation gate in determining the extracellular potassium dependency of block of HERG by trapped drugs. 2013, Pubmed
Perrin, Drug binding to the inactivated state is necessary but not sufficient for high-affinity binding to human ether-à-go-go-related gene channels. 2008, Pubmed
Perry, Hydrophobic interactions between the voltage sensor and pore mediate inactivation in Kv11.1 channels. 2013, Pubmed , Xenbase
Raschi, The hERG K+ channel: target and antitarget strategies in drug development. 2008, Pubmed
Roden, Cardiac ion channels. 2002, Pubmed
Sánchez-Chapula, Molecular determinants of voltage-dependent human ether-a-go-go related gene (HERG) K+ channel block. 2002, Pubmed , Xenbase
Sanguinetti, hERG potassium channels and cardiac arrhythmia. 2006, Pubmed
Sanguinetti, A mechanistic link between an inherited and an acquired cardiac arrhythmia: HERG encodes the IKr potassium channel. 1995, Pubmed , Xenbase
Saxena, New potential binding determinant for hERG channel inhibitors. 2016, Pubmed
Spector, Class III antiarrhythmic drugs block HERG, a human cardiac delayed rectifier K+ channel. Open-channel block by methanesulfonanilides. 1996, Pubmed , Xenbase
Stork, State dependent dissociation of HERG channel inhibitors. 2007, Pubmed , Xenbase
Thouta, Proline scan of the HERG channel S6 helix reveals the location of the intracellular pore gate. 2014, Pubmed , Xenbase
Trudeau, HERG, a human inward rectifier in the voltage-gated potassium channel family. 1995, Pubmed
Wang, Modulation of HERG affinity for E-4031 by [K+]o and C-type inactivation. 1997, Pubmed , Xenbase
Wang, A quantitative analysis of the activation and inactivation kinetics of HERG expressed in Xenopus oocytes. 1997, Pubmed , Xenbase
Wang, Cryo-EM Structure of the Open Human Ether-à-go-go-Related K+ Channel hERG. 2017, Pubmed
Weerapura, Dofetilide block involves interactions with open and inactivated states of HERG channels. 2002, Pubmed , Xenbase
Wu, The Link between Inactivation and High-Affinity Block of hERG1 Channels. 2015, Pubmed , Xenbase
Yang, Inactivation gating determines drug potency: a common mechanism for drug blockade of HERG channels. 2004, Pubmed , Xenbase