Imagine an artificial cell with a plasma membrane permeable only to na+ due to the presence of a na+ leak channel in the plasma membrane. the artificial cell rests in a buffer with a [na+] of 150 mm. if the intracellular [na+] of this cell is 15 mm, what is the net direction of na+ cation movement when the electrical potential of the plasma membrane is at the equilibrium potential (ena+)? "