Kinetic analysis of calcium movements in cell culture

Summary The distribution of intracellular calcium was determined in isolated kidney cells by kinetic analyses of⁴⁵Ca fluxes. Isotopic desaturation curves reveal an intracellular calcium compartment with a very slow time constant. The size of this calcium compartment is markedly increased by raising the extracellular calcium, by increasing the extracellular phosphate and may contain up to 99% of the intracellular exchangeable calcium. Accumulation of calcium in this pool is completely abolished by two specific inhibitors of mitochondrial calcium uptake, Antimycin A and Warfarin^®. These results suggest that this compartment represents a pool of calcium in the cell mitochondria. The sudden removal of phosphate from the medium immediately stimulates calcium efflux from the cell. Conversely, an increase in medium phosphate immediately inhibits calcium efflux. Both effects are rapidly reversible. Finally, calcium efflux from the cells is stimulated after the cells are exposed to low temperature suggesting that calcium transport out of the cell may be regulated by the cytoplasmic calcium activity. These experiments are consistent with the view that mitochondria play an important role in the control and regulation of cytoplasmic calcium activity and of calcium transport.