Kinetics of zinc uptake and exchange by primary cultures of rat hepatocytes.
The kinetics of 65Zn2+ uptake and exchange by hepatocytes in primary culture have been examined in detail to provide a basis for analyzing hormonal regulation of hepatic zinc metabolism. 65Zn2+ uptake was found to be a biphasic process. The slow phase represents an exchange between Zn2+ in the medium and preexisting, intracellular zinc pools. This exchange rate was saturable with a medium zinc concentration of 9.5 microM eliciting one-half the maximum exchange rate and a maximum exchange rate of 9.9 pmol Zn2+ . min-1 . mg protein-1 in the presence of bovine serum albumin. In the absence of albumin, a secondary, nonsaturable uptake rate was observed. The slow phase was relatively selective, and of the divalent transition metal ions tested, only Cd2+ and Mn2+ caused inhibition. The rate of exchange suggests total hepatocyte zinc has a turnover rate of approximately 30 h. The fast phase of 65Zn2+ reflects net Zn2+ accumulation into a labile pool. The initial rates for this process were too fast to be measured accurately, but steady-state measurements allowed determination of the labile pool size. The pool dimensions saturated in the presence [Kapp = 28.6 microM; pool capacity = 0.44 nmol Zn2+/mg protein] and absence [Kapp = 11.8 microM; pool capacity = 0.34 nmol Zn2+/mg protein] of bovine serum albumin. Kinetics and equilibria of Zn2+ uptake into the labile pool suggest that the latter acts as a source of Zn2+ for the slow-exchange phase. Dexamethasone stimulated slow Zn2+ exchange and also increased the labile pool size. The data suggest physiological factors alter hepatic zinc metabolism by influencing both intracellular Zn2+ pools.
D000818:Animals; D002413:Cations, Divalent; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008345:Manganese / Q000494:pharmacology; D051381:Rats; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism*; D015037:Zinc Radioisotopes
D002413:Cations, Divalent; D015037:Zinc Radioisotopes; D012710:Serum Albumin, Bovine; D008345:Manganese; D003907:Dexamethasone; D004492:Edetic Acid; D015032:Zinc