Sinusoidal voltage protocols for rapid characterisation of ion channel kinetics

Rationale Understanding the roles of ion currents is crucial to predict the action of pharmaceuticals and mutations in different scenarios, and thereby to guide clinical interventions in the heart, brain and other electrophysiological systems. Our ability topredict how ion currents contribute to cellular electrophysiology is in turn critically dependent on our characterization of ion channel kinetics — the voltage-dependent rates of transition between open, closed and inactivated channel states. Objective The hERG potassium channel plays a fundamental role in controlling electrical activity in the heart and many other tissues. There is a well-established link between hERG mutations, or block by pharmaceuticals, and increased arrhythmic risk. We present a new method for rapidly exploring and characterizing ion channel kinetics, applying it to the hERG channel as an example, with the aim of generating a quantitatively predictive representation of the ion current. Methods & Results We fit a mathematical model to currents evoked by a novel 8 secand sinusoidal voltage clamp in CHO cells over-expressing hERG1a. The model is then used to predict over 5 minutes of recordings in the same cell in response to further protocols: a series of traditional square step voltage clamps, and also a novel voltage clamp comprised of a collection of physiologically-relevant action potentials. We demonstrate that we can make predictive cell-specific models that outperform the use of averaged data from a number of different cells, and thereby examine which changes in gating are responsible for cell-cell variability in current kinetics. Conclusions Our technique allows rapid collection of consistent and high quality data, from single cells, and produces more predictive mathematical ion channel models than traditional approaches. The approach will be widely applicable to other voltage-gatedion currents both in the heart and other electrophysiological systems. Subject Terms Ion Channels/Membrane Transport; Electrophysiology; Computational Biology. Non-standard Abbreviations and Acronyms CHO — Chinese Hamster Ovary [cells]. GKr — maximal conductance of IKr. HEK — Human Embryonic Kidney [cells]. hERG — human Ether-a-go-go Related Gene. IKr — rapid delayed rectifying potassium current, carried by the Kv11.1 ion channel whose primary subunit is encoded by hERG.