Channel:
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Application NotehERG
CHO
Port-a-Patch®

Pharmacology of hERG recorded onNanion's Port-a-Patch®
The electrophysiology team at Nanion Technologies GmbH, Munich.
Cells were kindly provided by Cytomyx Millipore, UK.

SummaryResults

The hERG gene (KCNH2) encodes a potassium ion

Current responses of an individual cell expressing thechannel responsible for the repolarizing IKr current in thehERG channel is shown in Figure 1. Figure 2 shows thecardiac action potential (Sanguinetti et al., 1995).

corresponding current-voltage relation.

Abnormalities in this channel may lead to either Long QT
syndrome (LQT2) (with loss-of-function mutations) or Short
QT syndrome (with gain-of-function mutations), bothpotentially fatal cardiac arrhythmia, due to repolarization
disturbances of the cardiac action potential.
Given the importance of this channel in maintaining
cardiac function, it has become an important target incompound safety screening.
A large range of therapeutic agents with diverse chemical
structures have been reported to induce long QT

Figure 1:
hERG whole cell current as recorded in CHO cells.

syndrome. These include antihistamines (e.g. Terfenadine),
gastrointestinal prokinetic agents (e.g. Cisapride) andothers.
Here we present data collected on the Port-a-Patch®.
Astemizole, Terfenadine, Cisapride and Flunarizinedose-response curves on hERG expressed in CHO cells
are shown. The mean current amplitude in these cells was1076 ± 79 pA (n= 88) at -40 mV.
Figure 2:
Current-voltage response of the recording shown in Fig. 1. The holding
potential was -80 mV.

Download more Application Notes from www.nanion.deApplication NoteFigure 3 shows representative traces from an individual
cell in the absence and presence of increasing concentrations of Astemizole. The inhibitor was applied using apipettor. The recording was stable and a full concentration
response of Astemizole ranging from 0.5 nM to 10 nM wasachieved.

Figure 3:
Full dose response curve to Astemizole acting on the hERG channel.
Example traces in the absence and presence of increasing concentrationsof Astemizole of one cell.

The IC50 value was calculated to a value of 1.27 nM

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of the half maximal block is IC50 = 1.27 nM (Astemizole), IC50 = 11.0 ± 3 nM
(Terfenadine, Lit. val. 5-300 nM), IC50 = 8.9 nM (Cisapride, Lit. val. 5-60 nM)
and IC50 = 163.7 nM (Flunarizine, Lit. val. 344 nM).

(Fig. 4), which is in good agreement with the literature
values, which range between 0.9 nM and 69 nM (e.g.

In conclusion, we have demonstrated stable recordings

Zhou et al. 1999).

of the hERG channel on a planar patch clamp system.

Besides Astemizole, also the typical hERG blockers
Terfenadine, Cisapride and Flunarizine have been tested(Fig. 4).

References

Methods

1. Sanguinetti, M. C., Jiang, C., Curran, M. E., Keating,Cells

M. T., 1995. A mechanistic link between an inherited andCHO cells stably expressing hERG were used.

an acquired arrhythmia: HERG encodes the IKr potassium
Cell culturechannel. Cell. 81: 299-3072.
2. Zhou, Z., Vorperian, V. R., Gong, O., Zhang, S., andJanuary, C. T., 1999. Block of HERG Potassium Channels
by the Antihistamine Astemizole and its Metabolites
Desmethylastemizole and Norastemizole Journal of
Cardiovascular Electrophysiology, Volume 10, Issue 6.

Cells were cultured and harvested according to Nanion'sstandard cell culture protocol.
Electrophysiology
Whole cell patch clamp recordings were conductedaccording to Nanion’s standard procedure for thePort-a-Patch®. Currents for inhibiton experiments wereelicited using a voltage step protocol from a holding
potential of -80 mV to +40 mV for 500 ms followed by astep to -40 mV for 500 ms and back to the holding potential. The step was repeated every 20 s. Before applicationof an inhibitor, the current amplitude had to be stable forat least 3 minutes.

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