Kinetics of p-aminohippurate transport in rabbit kidney slices. Role of Na+.

Active accumulation of p-aminohippurate by cortex slices of rabbit kidney in vitro requires 2.5-3 h at 25 degrees C to attain a steady-state value. The uptake process can be divided into a rapid and a slow component. The slow component makes the largest contribution to the final accumulation of p-aminohippurate. Rapid uptake is dependent on oxidative metabolism, but is not affected by Na+ or ouabain. By way of contrast, Na+ is required for the slow uptake process to occur. Efflux of p-aminohippurate accumulated in the presence of Na+ is stimulated by transfer to media with a low concentration of Na+. On the other hand, there is only evidence of a stimulatory effect of Na+ on p-aminohippurate influx at medium concentrations above 30 mM. The results indicate the existence of both Na+-dependent and Na+-independent p-aminohippurate transport, respectively.