: 4 k in and 4 na out= neutral. Membrane potential (-70mv) or membrane potential: a voltmeter is used to measure the electrical difference (membrane potential versus time) between the inside of the cell and the outside of the cell in volts or microvolt. The reference electrode is placed in the extracellular fluid (in the diagram, it is in a saline bath). This makes it possible for k to leave since the membrane is impermeable to ions. Since there is no k in the extracellular fluid, it is so easy for it to go outside of the cell (concentration gradient). Since the k and proteins are attracted to each other, due to charge, the proteins want to leave the cell as well. Because opposite charges attract each other, the negative proteins are going to attract the k ions back into the cell, its calling in. its e-ion will be -90mv.