Sodium-dependent transport of orthophosphate in nerve fibres.

The mechanism by which orthophosphate is concentrated in cells against an electrochemical concentration gradient has so far not been studied in detail. At first sight, such studies appear difficult and laborious, since transmembrane fluxes of phosphate are small (1) and since phosphate is involved in numerous metabolic reactions. An indication that a Na-dependent mechanism might be involved comes from experiments of Chambers (2) who observed that the uptake of labelled phosphate in sea urchin eggs is decreased when the Na of the sea-water is replaced by other cations. Later, Harrison and Harrison (3) observed a similar effect of Na on phosphate transport in rat intestine. At that time, however, little was known on Na-dependent transport processes so that these authors did not study the effect of Na in more detail.