Whole-cell recordings were performed on differentiated ReN cells with an Axopatch 200A amplifier (Molecular Devices) and fire polished patch pipettes with resistances of 233 MO. Pipette solution was 140 mM KCl, 2 mM MgCl2, 1 mM EGTA, 10 mM HEPES, 4 mM MgATP, 0.3 mM NaGTP, and 0.1 mM Na2PhosCr, pH 7.2, adjusted with KOH. The external solution was 140 mM NaCl, 5 mM KCl, 2 mM CaCl2, 2 mM MgCl2, 10 mM HEPES, and 10 mM D-glucose, pH 7.4, adjusted with NaOH. Command protocols were generated and data were digitized with a Digidata 1440A A/D interface with pCLAMP10 software (Molecular Devices). Voltage errors were minimized by series resistance compensation (80%). During the recording, 500 nM tetrodotoxin (TTX) was applied to isolate Na+ currents by subtracting currents after and before TTX application. The data was analyzed by Clampfit (Molecular Devices) and Sigmaplot.
