Fj. Burczynski et al., EFFECT OF BINDING-PROTEIN SURFACE-CHARGE ON PALMITATE UPTAKE BY HEPATOCYTE SUSPENSIONS, British Journal of Pharmacology, 120(7), 1997, pp. 1215-1220
1 Studies were directed at determining whether hepatocytes, isolated f
rom female Sprague-Dawley rats, facilitate the uptake of protein-bound
long-chain fatty acids. We postulated one form of facilitated uptake
may occur through an ionic interaction between the protein-ligand comp
lex and the cell surface. These interactions are expected to supply ad
ditional ligand to the cell for uptake. 2 The clearance rate of [H-3]-
palmitate in the presence of alpha(1)-acid-glycoprotein (pI = 2.7), al
bumin (pI = 4.9) and lysozyme (pI = 11.0) was investigated. Palmitate
uptake was determined in the presence of protein concentrations that r
esulted in similar unbound ligand fractions (= 0.03). The experimental
clearance rates were compared to the theoretical predictions based up
on the diffusion-reaction model. 3 By use of our experimentally determ
ined equilibrium binding and dissociation rate constants for the vario
us protein-palmitate complexes, the diffusion-reaction model predicted
clearance rates were 4.9 mu l s(-1)/10(6) cells, 4.8 mu l s(-1)/10(6)
cells and 5.5 mu l s(-1)/10(6) cells for alpha(1)-acid-glycoprotein,
albumin and lysozyme, respectively; whereas the measured hepatocyte pa
lmitate clearance rates were 1.2+/-0.1 mu l s(-1)/10(6) cells, 2.3+/-0
.3 mu l s(-1)/10(6) cells and 7.1+/-0.7 mu l s(-1)/10(6), respectively
. 4 Hepatocyte palmitate clearance was significantly faster (P<0.01) i
n the presence of lysozyme than albumin which was significantly faster
than alpha(1)-acid-glycoprotein (P<0.01). The marked difference in cl
earance rates could not be explained by considering differences in sol
ution viscosity. 5 Our results are consistent with the notion that ion
ic interactions between protein-ligand complexes and the cell surface
facilitate the ligand uptake by decreasing the diffusional distance of
the unbound ligand and/or by facilitating the protein-ligand dissocia
tion rate.