The crucial role played by calcium as a cellular messenger has become increasingly evident, as has the recognition that cells spend much energy in maintaining the cytosolic concentration of this cation both constant and low. It is thought they do this to avoid precipitating phosphate, needed as a source of bond energy and to modulate protein structure. Moreover, since calcium that does enter the cell must be disposed with, processes that utilize calcium have evolved, e.g. secretion, contraction, signaling, to name just some. New knowledge concerning the processes of cellular calcium entry,...