The failure of the action potential at the end-plate membrane to reach the sodium equilibrium potential is due to the stimulating action of acetylcholine on Na⁺-K⁺ pump. This action of acetylcholine causes an enormous increase in the K⁺ transport rate. The quantitative amount of potassium ions in the inside of the end-plate membrane prevented the permeability of sodium ions during the depolarization phase of the action potential. It would favor the changes in the shape of action potential by acetylcholine which are always toward a fixed potential slightly below the zero line. The increased Na⁺-K⁺ pump activity by acetylcholine is responsible for the hypopolarization of membrane. This reduces the membrane resistance of the end-plate during transmitter activity.