Reversal potential and Equilibrium potential

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Reversal potential and Equilibrium potential

Hi !

I've recorded Na+ currents from neurons and I'm trying to fit activation and steady-state deactivation curve.

External sodium conc. was 127mM and internal  was 8.6 mM.
ENa is 67.8 mV predicted by the Nernst equation
but actual extrapolated reversal potential was near +42 mV
This deviation possibly arose from contamination outward currents or non-linearity arising form Goldman-type rectification.

Here is my question.
When I fit the activation curve, which value should I use for VNa in cord conductance equation
( GNa = INa(Vm-VNa) ? ....42 mV (actual reversal potential) or 67.8 mV (preducted ENa)

Thanks in advance.