AJP - Cell Physiology, Vol 236, Issue 5 202-C210, Copyright © 1979 by American Physiological Society

ARTICLES

Determination of unidirectional fluxes of phosphate across plasma membrane in isolated perfused rat liver

L. Sestoft and L. O. Kristensen

In livers labeled with 32P by intraperitoneal injection 18 h before perfusion the unidirectional efflux of inorganic phosphate (Pi) was a linear function of the concentration of Pi in the intracellular exchangeable pool of Pi (range, 0--1 mumol/g liver). Calculations of the efflux were based on determination of the specific radioactivity of Pi in the intracellular exchangeable pool of Pi by a new method. Zero efflux was found at biopsy concentrations of Pi of about 1.8 mumol/g liver. The influx of Pi was calculated from the efflux and the net uptake of Pi; it was found to be related to the extracellular concentration of Pi in a fashion that was approximately linear. An increase in the concentration of Pi in the input medium gave rise to an increased influx and, with a time delay, also to a gradually increasing efflux. The increased efflux could be explained as a consequence of an increased intracellular concentration of exchangeable Pi.

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