Abstract
The hERG potassium channel influences ventricular action potential duration. Extracellular acidosis occurs in pathological states including cardiac ischaemia. It reduces the amplitude of hERG current and speeds up deactivation, which can alter cardiac excitability. This study aimed to identify the site of action by which extracellular protons regulate the amplitude of macroscopic hERG current. Recordings of macroscopic and single hERG1a and 1b channel activity, mutagenesis, and the recent cryoEM structure for hERG were employed. Single hERG1a and 1b channels displayed open times that decreased with membrane depolarization, suggestive of a blocking mechanism that senses approximately 20% of the membrane electric field. This mechanism was sensitive to pH; extracellular acidosis reduced both hERG1a and1b channel open time and conductance. The effects of acidosis on macroscopic current amplitude and deactivation displayed different sensitivities to protons. Point mutation of a pair of residues (E575/H578) in the pore turret abolished the acidosis-induced decrease of current amplitude, without affecting the change in current deactivation. In single hERG1a channel recordings, the conductance of the double-mutant channel was unaffected by extracellular acidosis. These findings identify residues in the outer turret of the hERG channel that act as a proton sensor to regulate open time and channel conductance.
Highlights
The hERG potassium channel influences ventricular action potential duration
The macroscopic hERG conductance was reduced by extracellular acidosis, with maximal conductance (Gmax) of hERG1a current reduced by 29 ± 0.9% (n = 8, P = 0.0003) and hERG1b current by 69 ± 3.5% (n = 7, P < 0.0001)
The proportion of deactivating current described by the fast time-constant increased at acidic pHe, at potentials positive to −90 mV (Supplementary Fig. S1a) In contrast, only the slow component of hERG1b current deactivation was clearly accelerated by acidic pHe (Fig. 1biv), whilst the proportion of fast/slow deactivating current did not change (Supplementary Fig. S1b)
Summary
The hERG potassium channel influences ventricular action potential duration. Extracellular acidosis occurs in pathological states including cardiac ischaemia. Extracellular acidosis occurs during myocardial ischemia and reperfusion and is well recognized to be responsible for changes in myocardial ion handling that can cause arrhythmias[6,7] It reduces the peak amplitude, shifts the voltage dependence of activation, and accelerates deactivation of IKr/IhERG8–15. Mutagenesis studies have confirmed that residues in S2 (D456 and D460) and S3 (D509) transmembrane helices of the hERG voltage sensor domain bind cations[16,17,18], with mutation of all three residues abolishing the shift in activation but retaining the reduction in current amplitude and acceleration of deactivation evoked by pHe18. Mutation of likely histidine residues failed to reveal how the amplitude and deactivation of hERG-mediated current are affected by pHe10,15 It is not known whether the entire effect of extracellular acidosis on macroscopic current amplitude is attributable to reduction of single channel current amplitude[15]. These data reveal that hERG channels are novel in utilising an outer turret amino acid motif that connects to a mechanism to regulate conductance and open time
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
