Characterization of phosphate uptake in primary cultures of rat hepatocytes

Phosphate uptake across the plasma membrane of rat hepatocytes was characterized in primary cultures of rat hepatocytes. Phosphate uptake by cultured rat hepatocytes consisted of a Na(+)-dependent and Na(+)-independent component. A major portion of the uptake was Na(+)-dependent, which was saturable and exhibited Michaelis-Menten kinetics. Kinetic analysis showed that the apparent Km value for phosphate at 137 mM Na+ was 0.25 mM and Vmax was 13.3 pmol/microgram protein for 30 min. Hill coefficient was 1.76. This study is the first to demonstrate the presence of a phosphate carrier on the plasma membrane of hepatocytes.