Assay Method Information

Assay Name:  In Vitro Electrophysiology
Description:  Electrophysiological studies are performed with an IonWorks Quattro (Molecular Devices Corp.) automated patch-clamp electrophysiology platform as described by (Schroeder K et al. Journal of Biomolecular Screening 2003, 8 (1), 50-64). Buffers for the experiments have the following composition (mM): Internal solution; K-gluconate 100, KCl 40, MgCl2 3.2, HEPES 5, EGTA 3, pH 7.3. To this amphotericin B is added to final concentration of 0.1 mg/ml to generate access solution. External solution; Dulbecco's Phosphate buffered saline (D-PBS) NaCl 137.93, KCl 2.67, KH2PO4 1.47, Na2HPO4 8.06, CaCl2 0.90, MgCl2 0.49. Prior to the experiment the cells expressing the voltage-gated ion channel of interest are detached from the tissue culture flasks, centrifuged and resuspended in D-PBS. Compounds are prepared and serially diluted in DMSO and finally diluted 1:100 in D-PBS. Cells are exposed to compounds through the pipetting system integrated into the platform and the voltage-gated ion channel of interest is activated with specific voltage stimulation protocols. The following voltage stimulation protocol is used for testing compounds against the voltage-gated sodium channel Nav1.7; from a holding potential of −100 mV a train of eight 60 ms depolarising steps to −20 mV at a frequency of 14 Hz are employed followed by a further step to −20 mV for 2000 ms. After which the voltage is returned to −100 mV for 10 ms before another voltage step to −20 mV for 60 ms is applied. The following voltage stimulation protocol is used for testing compounds against the voltage-gated sodium channel Nav1.5; from a holding potential of −120 mV a train of twenty-six 120 ms depolarising steps to −20 mV at a frequency of 5 Hz are employed. Recordings are made before and after compound addition with the compound incubation time being 5 minutes. Percent block was calculated for each concentration in duplicate for peak 1 and peak 10 and peak 1 and 25 for Nav 1.7 and Nav 1.5 respectively in order to assess compound activity at close and inactivated states and IC50 curves were fitted to percent block as a function of concentration.
Affinity data for this assay
 

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