Cytosolic free calcium (Cai 2+) is controlled by several calcium transporters located at the plasma membrane, the inner membrane of the mitochondria and in the endoplasmic reticulum. Fig. 1 shows the various ATP-dependent pumps and antiporters involved in the control of Cai 2+ and Nai + (In this figure, the plasmalemmal Na+-Ca2+ antiporter is conventionally assumed to operate in the forward mode i.e. Ca2+ efflux energized by Na+ influx). Since Ca2+ transport out of the cell can be energized by ATP or by the Na+ electrochemical potential ΔμNa+, a fall in cellular ATP or a drop in ΔμNa+ would be expected to depress Ca2+ efflux, raise Cai 2+ and increase the cell Ca2+ content. In recent experiments (1,2) performed with cultured monkey kidney cells (LLC-MK2), my collaborators Dr. K.W. Snowdowne, C.C. Freudenrich and I found that only one of these three predictions was proved correct.KeywordsKidney CellCalcium InfluxBiological ChemistReverse ModeCytosolic Free CalciumThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.