Investigating dynamic protocol-dependence of hERG potassium channel inhibition at 37 degrees C: Cisapride versus dofetilide

Milnes, James T, Witchel, Harry J, Leaney, Joanne L, Leishman, Derek J and Hancox, Jules C (2010) Investigating dynamic protocol-dependence of hERG potassium channel inhibition at 37 degrees C: Cisapride versus dofetilide. Journal of Pharmacological and Toxicological Methods, 61 (2). pp. 178-191. ISSN 1056-8719

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Abstract

INTRODUCTION

Pharmacological inhibition of cardiac potassium channels encoded by hERG (human ether-à-go-go-related gene) is associated with QT interval prolongation and torsades de pointes arrhythmia. Electrophysiological assays of hERG channel inhibition are integral to the safety testing of novel drug candidates. This study was conducted to compare, for the high affinity hERG inhibitors dofetilide and cisapride, hERG blockade between action potential (AP) and conventional (step and step-ramp) screening waveforms. Furthermore, it evaluated dynamic (pulse-by-pulse) protocol-dependence of hERG channel inhibition by these drugs.

METHODS

Whole-cell patch-clamp recordings were made at 37 degrees C from hERG-expressing HEK 293 cells. Half-maximal inhibitory concentrations (IC(50) values) for I(hERG) blockade were obtained using conventional voltage clamp and action potential clamp, using previously digitised ventricular and Purkinje fibre (PF) AP waveforms.

RESULTS

A more marked variation in IC(50) values with different command waveforms was observed for cisapride (ranging from 7 to 72 nM) than for dofetilide (ranging from 4 to 15 nM), with higher IC(50)s obtained with AP than step or step-ramp commands. The two drugs differed little from one another in effects on voltage-dependent activation; however, I(hERG) blockade by each drug was initially voltage-dependent, but at steady-state was only voltage-dependent for cisapride. There was comparatively little difference between the two drugs in effects on I(hERG) availability or time constants of development of inactivation. Features of time-dependence of blockade and the use of protocols employing varying rest periods in drug or commands of alternating duration highlighted a pronounced ability of cisapride, but not dofetilide, to dissociate and reassociate from hERG on a pulse-by-pulse basis.

DISCUSSION

Protocols described here that demonstrated dynamic variation (drug dissociation/reassociation) in hERG channel current blockade at 37 degrees C for cisapride may have future value for investigating drug interactions with the hERG channel. Downloadable digitised ventricular and PF AP waveforms that can be used in AP clamp experiments also accompany this article

Item Type: Article
Keywords: Action potential; Cisapride; Dofetilide; hERG; Methods; QT interval; Torsades de points; Screening
Schools and Departments: Brighton and Sussex Medical School > Clinical and Laboratory Investigation
Subjects: R Medicine > RM Therapeutics. Pharmacology
R Medicine > RS Pharmacy and materia medica
Depositing User: Patricia Butler
Date Deposited: 09 Nov 2012 14:15
Last Modified: 13 Nov 2012 10:31
URI: http://sro.sussex.ac.uk/id/eprint/42063
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