AJP - Gastrointestinal and Liver Physiology, Vol 246, Issue 1 48-G55, Copyright © 1984 by American Physiological Society
Copper efflux kinetics from rat hepatocytes
H. M. Darwish, R. C. Schmitt, J. C. Cheney and M. J. Ettinger
The kinetics of copper efflux from rat hepatocytes were determined to
further characterize the hepatic Cu(II) transport system. Efflux was
biphasic. Net efflux was rapid for 1-5 min, and 35-45% of preloaded copper
was lost by 40 min. Efflux was negligible after 40 min. The retained
percentage was independent of the preloading concentration, but the total
amount of intracellular copper that was available for efflux gradually
decreased as the duration of the preloading period increased. Unlabeled
extracellular Cu(II) displaced 64Cu from intracellular pools, but exchange
with intracellular Cu was not required for uptake. Zinc also displaced
copper but less effectively than copper. This implies some specificity in
intracellular binding components. No transstimulation of uptake or efflux
was detected. Copper efflux was strictly passive. Extracellular Cu(II)
decreased the rate of efflux and preloading inhibited Cu(II) uptake.
Metabolic inhibitors had no effect on the rate or total amount of 64Cu
efflux, and significant efflux occurred at 4 degrees C. Moreover, when a
steady state was attained at the end of a preloading period, the effective
intracellular concentration of free copper approximated the Cu(II)
concentration in the extracellular medium. By use of this estimate for the
intracellular concentration of free copper, efflux kinetic parameters were
obtained from initial (1-min) rate data (Km = 5.5 +/- 0.8 microM; Vmax =
1.1 +/- 0.1 nmol X min-1 X mg prot-1). These parameters are similar to
those obtained for Cu(II) uptake, and the saturation kinetics observed are
consistent with specific facilitated efflux by this copper transport
system.(ABSTRACT TRUNCATED AT 250 WORDS)
