Therefore, both the maintenance of the rest and the ability to fire action potentials depend on an active and cotninuous interplay with the cell's medium. A manipulation of the external ionic concentrations, for example by raising K+ concentrations, breaks down the internal mechanism for firing action potentials. If the intervention blocks the ionic pumping mechanism (located at the boundary between cell and world), the mechanism is also interfered importantly and cannot function as it does in the physiological situation.