There is a very large transmembrane electrochemical gradient

Electrochemical gradient

An electrochemical gradient is a spatial variation of both electrical potential and chemical concentration across a membrane; that is, a combination of the membrane potential and the pH gradient...

 of Ca²⁺ driving the entry of the ion

Ion

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

 into cells, yet it is very important for cells to maintain low concentration

Concentration

In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...

s of Ca²⁺ for proper cell signalling; thus it is necessary for the cell to employ ion pumps to remove the Ca²⁺.

The PMCA and the sodium calcium exchanger (NCX) are together the main regulators of intracellular Ca²⁺ concentrations.