Aldo A Rodriguez-Menchaca1, Tania Ferrer2, Ricardo A Navarro-Polanco2, Jose A Sanchez-Chapula2, Eloy G Moreno-Galindo3. 1. Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad Autónoma de San Luis Potosí, San Luis Potosí, Mexico. 2. Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico. 3. Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Col., Mexico. Electronic address: eloy@ucol.mx.
Abstract
INTRODUCTION: Voltage- 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. METHODS: hERG 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. RESULTS: In 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 ~50min. 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. DISCUSSION: The 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.
INTRODUCTION: Voltage- 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. METHODS:hERG 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. RESULTS: In 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 ~50min. 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. DISCUSSION: The 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.