Orthophosphate Turnover in the Extracellular and Intracellular Space of Mouse Liver

The flux rates of Pi from blood plasma into the extracellular and intracellular space of mouse liver have been measured in vivo with the [32P]Pi-tracer technique. The specific radioactivities of plasma Pi and total liver Pi have been measured 0.1–4 min after injection of carrier-free [32P]Pi. The results have been treated with the analogue computer technique. The main conclusions are: 1 The flux rate of Pi from blood plasma into the extracellular liver space amounts to 1.14 μmoles and that from the extracellular into the intracellular liver space to 0.39 μmoles per g fresh liver per min. 2 The influx of Pi through the liver cell membrane takes place without transient transformation into another phosphate compound rapidly exchangeable with large intracellular phosphate pools. 3 The specific radioactivity of intracellular Pi is somewhat higher than that of [γ-32P]ATP, thus indicating the absence of intracellular Pi-compartmentation with isotope kinetic relevance.