Phosphate modulation of calcium transport by a calcium-phospholipid-phosphate complex of calcifying tissues.

The ionophoretic activities of a stable Ca-PS-Pi complex were examined in a three-compartment lipid-aqueous phase transport system. It was found that the complex transported Ca2+ at a slower rate than free PS. Analysis of the transport process, using an equilibrium partitioning model, revealed that Ca2+ binding to the complex was the rate-limiting step. This inhibition was overcome by the addition of exogeneous Pi. It was concluded that the complex acted as an ionophore and that the presence of coordinated Ca and P atoms facilitated Pi modulation of Ca2+ transport.