equilibrium potential question

You are recording currents using an intracellular electrode and voltage-clamp from a squid giant axon. You change the membrane voltage from resting potential to 0 mV and manipulate external Na+. Sketch both the Na & K currents on a current (I) vs. time plot under three conditions (outward current up, inward current down):

a) Extracellular Na+ concentration normal

b) Extracellular Na+ concentration equal to the interior concentration

c) Extracellular Na+ concentration at zero