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Biophys J, September 2000, p. 1298-1309, Vol. 79, No. 3

*Centre de Recherche Paul Pascal, CNRS, 33600 Pessac, France, and
Laboratoire de Physique des Interactions Ondes
Matière, ENSCPB BP 108, 33402 Talence Cedex, France
We have characterized the binding of multilamellar
colloids to J774 cells. Cationic colloids were shown to bind much more efficiently than neutral ones. Particle uptake by cells was followed by
flow cytometry and fluorescence microscopy. Analysis of the kinetics of
uptake of cationic particles indicated that binding on the cell surface
occurred with two characteristic times. Analysis of the dissociation
properties allowed discriminating between several alternative models
for adsorption and led us to propose a mechanism that involved two
independent classes of binding sites on the cell surface. One class of
sites appeared to be governed by a classic mass action law describing a
binding equilibrium. The other sites were populated irreversibly by
particles made of 10% cationic lipids. This was observed in the
absence of endocytosis, under conditions where both the equilibrium and
the irreversible binding occurred at the cell surface. We determined
the rate constants for the different steps. We found that the
reversible association occurred with a characteristic time of the order
of tens of seconds, whereas the irreversible binding took a hundred
times longer. The presence of serum proteins in the incubation medium
did not drastically affect the final uptake of the particles. In
contrast, the capture of the particles by cells significantly dropped
when the fraction of positively charged lipids contained in the
colloids was decreased from 10% to 5%. Finally, the results will be
discussed within a comprehensive model where cationic particles find
labile binding sites in the volume of the pericellular network
(glycocalyx and extracellular matrix) and less-accessible irreversible
binding sites at the cell membrane itself.
Biophys J, September 2000, p. 1298-1309, Vol. 79, No. 3
© 2000 by the Biophysical Society 0006-3495/00/09/1298/12 $2.00
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