Assay Method Information

Assay Name:  hERG Analysis-Method 1
Description:  Cell CultureThe hERG-expressing Chinese hamster ovary K1 (CHO) cells described by (Persson, Carlsson, Duker, & Jacobson, 2005) were grown to semi-confluence at 37 C. in a humidified environment (5% CO2) in F-12 Ham medium containing L-glutamine, 10% foetal calf serum (FCS) and 0.6 mg/mL hygromycin (all available from Sigma-Aldrich). Prior to use, the monolayer was washed using a pre-warmed (37 C.) 3 mL aliquot of Versene 1:5,000 (Invitrogen) After aspiration of this solution the flask was incubated at 37 C. in an incubator with a further 2 mL of Versene 1:5,000 for a period of 6 minutes. Cells were then detached from the bottom of the flask by gentle tapping and 10 mL of Dulbecco's Phosphate-Buffered Saline containing calcium (0.9 mM) and magnesium (0.5 mM) (PBS; Invitrogen) was then added to the flask and aspirated into a 15 mL centrifuge tube prior to centrifugation (50 g, for 4 mins). The resulting supernatant was discarded and the pellet gently re-suspended in 3 mL of PBS. A 0.5 mL aliquot of cell suspension was removed and the number of viable cells (based on trypan blue exclusion) was determined in an automated reader (Cedex; Innovatis) so that the cell re-suspension volume can be adjusted with PBS to give the desired final cell concentration. It is the cell concentration at this point in the assay that is quoted when referring to this parameter. CHO-Kv1.5 cells, which were used to adjust the voltage offset on IONWORKS HT, were maintained and prepared for use in the same way.ElectrophysiologyThe principles and operation of this device have been described by (Schroeder, Neagle, Trezise, & Worley, 2003). Briefly, the technology is based on a 384-well plate (PATCHPLATE) in which a recording was attempted in each well by using suction to position and hold a cell on a small hole separating two isolated fluid chambers. Once sealing had taken place, the solution on the underside of the PATCHPLATE was changed to one containing amphotericin B. This permeablises the patch of cell membrane covering the hole in each well and, in effect, allowed a perforated, whole-cell patch clamp recording to be made.A β-test IONWORKS HT from Essen Instrument was used. There is no capability to warm solutions in this device hence it is operated at r.t. (21 C.), as follows. The reservoir in the Buffer position was loaded with 4 mL of PBS and that in the Cells position with the CHO-hERG cell suspension described above. A 96-well plate (V-bottom, Greiner Bio-one) containing the compounds to be tested (at 3-fold above their final test concentration) was placed in the Plate 1 position and a PATCHPLATE was clamped into the PATCHPLATE station. Each compound plate was laid-out in 12 columns to enable ten, 8-point concentration-effect curves to be constructed; the remaining two columns on the plate were taken up with vehicle (final concentration 0.33% DMSO), to define the assay baseline, and a supra-maximal blocking concentration of cisapride (final concentration 10 μM) to define the 100% inhibition level. The fluidics-head (F-Head) of IONWORKS HT then added 3.5 μL of PBS to each well of the PATCHPLATE and its underside was perfused with internal solution that had the following composition (in mM): K-Gluconate (100 parts), KCl (40 parts), MgCl2 (3.2 parts), EGTA (3 parts) and HEPES (5 parts, pH 7.25-7.30 using 10M KOH) After priming and de-bubbling, the electronics-head (E-head) then moved around the PATCHPLATE performing a hole test (i.e. applying a voltage pulse to determine whether the hole in each well is open). The F-head then dispensed 3.5 μL of the cell suspension described above into each well of the PATCHPLATE and the cells were given 200 seconds to reach and seal to the hole in each well. Following this, the E-head moved around the PATCHPLATE to determine the seal resistance obtained in each well.
Affinity data for this assay
 

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