sentences:  Therefore, it requires large concentrations of Ca2+ to be effective, but is useful for ridding the cell of large amounts of Ca2+ in a short time, as is needed in a neuron after an action potential.Thus, the exchanger also likely plays an important role in regaining the cell's normal calcium concentrations after an excitotoxic insult.Such a primary transporter of calcium ions is present in the plasma membrane of most animal cells.