Instantaneous (IInst) and near steady-state (ISt-St) current-voltage relationships of HEK293 cells in whole-cell patch-clamp configuration. Green symbols show I-V relationships obtained with NMDG-Cl in bath. Blue symbols show I-V relationships obtained with NaCl in bath. IInst was recorded immediately after the voltage step from the holding potential, Vhold = 0 mV, to the new Vm. ISt-St was recorded toward the end of the 1-s voltage pulse. Thus, rather than estimating the PNa/PCl of each cell from a reversal potential obtained by interpolation, we could take advantage of IInst-Vm data points covering a broader range about Vrev. Current-voltage relationships are shown for the following (all permeabilities in units of 10−14 cm3/s/pF). (A) HEK293 cells expressing TMEM16F-WT (with NMDG-Cl in bath, PCl = 12.9 ± 0.6; with NaCl in bath, PCl = 31.7 ± 1.0 and PNa = 9.7 ± 0.5). (B) HEK293 cells expressing the neutral mutant TMEM16F-I342A (with NMDG-Cl in bath, PCl = 19.8 ± 0.8; with NaCl in bath, PCl = 93.8 ± 4.2 and PNa = 13.3 ± 3.6). (C) HEK293 cells expressing the anion sequence modifying TMEM16F-R636E mutant (with NMDG-Cl in bath, PCl = 16.9 ± 1.5; with NaCl in bath, PCl = 22.9 ± 1.7 and PNa = 8.0 ± 1.4). It is noted that for all three ISt-St/Vm relationships obtained with NMDG-Cl in bath that Vrev ≈ ECl, whereas the reversal potentials with NaCl in bath are significantly displaced to the right of ECl, which is emphasized by the insets of expanded axis scales.
