SODIUM-DEPENDENT TRANSPORT OF PHOSPHATE IN NEURONAL AND RELATED CELLS

Sodium-dependent phosphate entry into neuronal cells was demonstrated in synaptic plasma membrane vesicles and synaptosomes prepared from ra t brains, in PC12 cells and in primary culture of pituitary cells. The extent of the sodium-dependent phosphate transport in the synaptic pl asma membrane preparation, at [Na](out) = 110 mM and [P-i](out) = 0.1 mM, varied between 0.28 to 1.02 nmol phosphate/mg membrane protein/min . In pituitary cells the value was only about 0.05 nmol P-i/mg protein /min. In PC12 cells the activity increased from 0.0085 to 0.26 nmol P- i/mg protein/min in the transit from undifferentiated to differentiate d cells. The dependence of phosphate on sodium concentrations fits a m odel in which two sodium ions are required to transfer the phosphate i nto the cells with a k([Na]0.5) of 43 mM. The K-n for the phosphate tr ansport in the synaptic plasma membrane preparations was between 0.1 a nd 0.45 mM. It is concluded that sodium-driven active transport of pho sphate is a ubiquitous activity in various types of neuronal cells.