Validation of ψ quantification by FACS. Representative trace of a CHO-Kv1.3 cell treated with different concentrations of [K+]e recorded by patch-clamp (A) or by FACS (B). (C) Dependence of absolute ψ of CHO-Kv1.3 cells on the [K+]e determined by FACS (●) and patch-clamp (Δ) techniques. Data of ψ against increasing [K+]e (5–145 mM) were plotted and fitted with a Boltzman equation. Data represent mean ± SE of four experiments. (D) CHO-Kv1.3 cells were treated with different concentrations (1, 3 and 10 nM) of MgTx (black bars) or IbTx (grey bars) and their ψ was measured by FACS. Data represent mean ± SD of three experiments.