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Assay Method Information

Assay Name:  Electrophysiological Assay (In Vitro Assay)
Description:  Patch voltage clamp electrophysiology allows for the direct measurement and quantification of block of voltage-gated sodium channels (NaV's), and allows the determination of the time- and voltage-dependence of block which has been interpreted as differential binding to the resting, open, and inactivated states of the sodium channel (Hille, B., Journal of General Physiology (1977), 69: 497-515).The following patch voltage clamp electrophysiology studies were performed on representative compounds of the invention using human embryonic kidney cells (HEK), permanently transfected with an expression vector containing the full-length cDNA coding for the desired human sodium channel α-subunit, grown in culture media containing 10% FBS, 1% PSG, and 0.5 mg/mL G418 at 37° C. with 5% CO2. HEK cells used for the electrophysiology (EP) recordings had a passage number of less than 40 for all studies and were used within three days from the time of plating. NaV1.7 and NaV1.5 cDNAs (NM_002977 and AC137587; SCN5A, respectively) were stably expressed in HEK-293 cells. The β1 subunit was coexpressed in both the NaV1.7 and NaV1.5 cell lines.Sodium currents were measured using the patch clamp technique in the whole-cell configuration using either a PatchXpress automated voltage clamp or manually using an Axopatch 200B (Axon Instruments) or Model 2400 (A-M systems) amplifier. The manual voltage clamp protocol was as follows:Borosilicate glass micropipettes were fire-polished to a tip diameter yielding a resistance of 2-4 Mohms in the working solutions. The pipette was filled with a solution comprised of: 5 mM NaCl, 10 mM CsCl, 120 mM CsF, 0.1 mM CaCl2, 2 mM MgCl2, 10 mM HEPES, 10 mM EGTA; and adjusted to pH 7.2 with CsOH. The external solution had the following composition: 140 mM NaCl, 5 mM KCl, 2 mM CaCl2, 1 mM MgCl2, 10 mM HEPES; and adjusted to pH 7.4 with NaOH. In some studies, the external sodium was reduced by equimolar replacement with choline. Osmolarity in the CsF internal and NaCl external solutions was adjusted to 300 mOsm/kg and 310 mOsm/kg with glucose, respectively. All recordings were performed at ambient temperature in a bath chamber with a volume of 150 μL. Control sodium currents were measured in 0.5% DMSO. Controls and representative compounds of the invention were applied to the recording chamber through a 4-pinch or 8-pinch valve bath perfusion system manufactured by ALA Scientific Instruments.Currents were recorded at 40 kHz sampling frequency, filtered at 5 Hz, and stored using a Digidata-1322A analogue/digital interface with the pClamp software (Axon Instruments). Series resistance compensation was applied (60-80%). Cells were rejected if currents showed inadequate voltage control (as judged by the IV relationship during stepwise activation). All statistics in this study are given as meanąSD.The membrane potential was maintained at a voltage where inactivation of the channel is complete (which was −60 mV for both NaV1.7 and NaV1.5). The voltage is then stepped back to a very negative (Vhold=150 mV) voltage for 20 ms and then a test pulse is applied to quantify the compound block. The 20 ms brief repolarization was long enough for compound-free channels to completely recover from fast inactivation, but the compound-bound channels recovered more slowly such that negligible recovery could occur during this interval. The percent decrease in sodium current following wash-on of compound was taken as the percent block of sodium channels.
Affinity data for this assay
 

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Last update November 1, 2007
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