Phosphate concentration and transport in Ehrlich ascites tumor cells: Effect of sodium

✍ Scribed by Jesse W. Bowen; Charles Levinson

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 619 KB
• Volume: 110
• Category: Article
• ISSN: 0021-9541
• DOI: 10.1002/jcp.1041100207

✦ Synopsis

The effects of extracellular P, and Na' on cellular Pi concentration and transport were studied. Steady-state P, exchange flux was measured by 3zP uptake in the presence and absence of Na'. Model experiments were also conducted to assess t h e possibility that hydrolysis of organic phosphate esters contributes to the chemically measured intracellular P, concentration of Ehrlich ascites tumor cells. The results of these experiments indicate that hydrolysis of labile organic phosphate esters does not contribute to the measured intracellular pool of P,. The P, transport system exhibits an apparent K, of 0.1 15 mM Pi and a maximal flux of 1.73 mmole min-' (kg dry wt)-l. When incubated in a phosphate-buffered choline chloride medium (5 mM Pi) t h e intracellular Pi and the P, influx fall by 65 and 88%, respectively. At 5 mM extracellular Pi, the Na+-dependent component of Pi transport fits Michaelis-Menten kinetics with the maximal flux equal to 2.46 mmole min-' (kg dry wt)-' and an apparent K,of 35.4 mM Na'. In addition, a Na+-independent component of Pi transport, comprising about 12% of the total Pi flux, was identified. The data support the hypothesis that a Pi transport system, dependent on Na+, plays a principal role in the maintenance of intracellular Pi concentration.