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Phosphate concentration and transport in Ehrlich ascites tumor cells: Effect of sodium
Author(s) -
Bowen Jesse W.,
Levinson Charles
Publication year - 1982
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/jcp.1041100207
Subject(s) - pi , extracellular , intracellular , sodium , phosphate , chemistry , flux (metallurgy) , hydrolysis , kinetics , extracellular fluid , steady state (chemistry) , biochemistry , biophysics , chromatography , biology , organic chemistry , physics , quantum mechanics
The effects of extracellular P i and Na + on cellular P i concentration and transport were studied. Steady‐state P i exchange flux was measured by 32 P uptake in the presence and absence of Na + . Model experiments were also conducted to assess the possibility that hydrolysis of organic phosphate esters contributes to the chemically measured intracellular P i concentration of Ehrlich ascites tumor cells. The results of these experiments indicate that hydroloysis of labile organic phosphate esters does not contribute to the measured intracellular pool of P i . The P i transport system exhibits an apparent K s of 0.115 mM P i and a maximal flux of 1.73 mmole min −1 (kg dry wt) −1 . When incubated in a phosphate‐buffered choline chloride medium (5 mM P i ) the intracellular P i and the P i influx fall by 65 and 88%, respectively. At 5 mM extracellular P i , the Na + ‐dependent component of P i transport fits Michaelis‐Menten kinetics with the maximal flux equal to 2.46 mmole min −1 (kg dry wt) −1 and an apparent K s of 35.4 mM Na + . In addition, a Na + ‐independent component of P i transport, comprising about 12% of the total P i flux, was identified. The data support the hypothesis that a P i transport system, dependent on Na + , plays a principal role in the maintenance of intracellular P i concentration.