The regulation of cytosolic Ca2+ concentration in a mammalian cell

The assumptions governing the regulation of free Ca2+ in a mammalian cell are presented. There is a possibility that mitochondria, microsomes and plasma membrane play a major role, by regulation of the very low concentration of free Ca2+ in cytosol, as the signal to biochemical activities. The possibility of the loss of very high-affinity Ca2(+)-binding and the number of its sites by preparation has not been taken into consideration in previous hypotheses.