Studies on the mechanism of zinc uptake by human fibroblasts.
The mechanisms of zinc uptake from a complete culture medium by human fibroblasts have been studied. The metal is accumulated in a biphasic pattern; an initial rapid phase followed by a slower linear phase. We suggest that the former represents binding to carriers or receptors on the cell surface followed by uptake to within the cell, or at least to a compartment inaccessible to proteolytic digestion. The uptake correlates well with estimates of the zinc requirement of a growing fibroblast. The process of uptake is saturable, with an apparent association constant of 1.1 X 10(7) M-1. Interestingly, there appears to be a very large number of binding sites, 2 X 10(7) per cell. No explanation for this observation is immediately apparent. The mechanism of uptake is not dependent on metabolic energy, or at least on ATP levels within the cell, but N-ethyl maleimide does block uptake in a dose-dependent manner. Weak bases and ionophores, apart from nigericin, do not affect uptake. The results suggest that zinc is not taken up by a receptor-mediated endocytic pathway as has been described for transferrin and iron.
Ackland
M L
ML
Murdoch Institute for Research into Birth Defects, Royal Children's Hospital, Parkville, Victoria, Australia.
Danks
D M
DM
McArdle
H J
HJ
D000963:Antimetabolites / Q000494:pharmacology; D003080:Cold Temperature; D003470:Culture Media; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D011402:Pronase / Q000378:metabolism; D013997:Time Factors; D015032:Zinc / Q000493:pharmacokinetics*
D000963:Antimetabolites; D003470:Culture Media; D011402:Pronase; D015032:Zinc