Impact of the whole-cell patch-clamp configuration on the pharmacological assessment of the hERG channel: Trazodone as a case example

IntroductionVoltage- and state-dependent blocks are important mechanisms by which drugs affect voltage-gated ionic channels. However, spontaneous (i.e. drug-free) time-dependent changes in the activation and inactivation of hERG and Na+ channels have been reported when using conventional whole-cell patch-clamp in HEK-293 cells.MethodshERG channels were heterologously expressed in HEK-293 cells and in Xenopus laevis oocytes. hERG current (IhERG) was recorded using both conventional and perforated whole-cell patch-clamp (HEK-293 cells), and two microelectrode voltage-clamp (Xenopus oocytes) in drug-free solution, and in the presence of the drug trazodone.ResultsIn conventional whole-cell setup, we observed a spontaneous time-dependent hyperpolarizing shift in the activation curve of IhERG. Conversely, in perforated patch whole-cell (HEK-293 cells) or in two microelectrode voltage-clamp (Xenopus oocytes) activation curves of IhERG were very stable for periods ~50 min. Voltage-dependent inactivation of IhERG was not significantly altered in the three voltage clamp configurations tested. When comparing voltage- and state-dependent effects of the antidepressant drug trazodone on IhERG, similar changes between the three voltage clamp configurations were observed as under drug-free conditions.DiscussionThe comparative analysis performed in this work showed that only under conventional whole-cell voltage-clamp conditions, a leftward shift in the activation curve of IhERG occurred, both in the presence and absence of drugs. These spontaneous time-dependent changes in the voltage activation gate of IhERG are a potential confounder in pharmacological studies on hERG channels expressed in HEK-293 cells.