title: Hepatocyte [3H]-palmitate uptake: effect of albumin surface charge modification.
abstract: The role of plasma proteins on the cellular uptake of lipophilic substrates has perplexed investigators for many years. We tested the hypothesis that an ionic interaction between the protein-ligand complex and hepatocyte surface may be responsible for supplying more ligand to the cell for uptake. The surface-charged groups on albumin were modified to yield proteins having a range of isoelectric points (ALB, ALBs, ALBm, ALBe had values of 4.8-5.0, 4.5-4.7, 3.0-3.5, 8.4-8.6, respectively). [3H]-Palmitate uptake studies were performed with adult rat hepatocyte suspensions using similar unbound ligand fractions in the presence of the different binding proteins. Mass spectrometry, isoelectric focusing (pI), and heptane:water partitioning were used to determine protein molecular weight, pI, and protein-palmitate equilibrium binding constant, respectively. Hepatocyte [3H]-palmitate clearance in the presence of ALBs and ALBm were significantly lower (p < 0.05) than ALB, whereas [3H]-palmitate clearance in the presence of ALBe was significantly higher (p < 0.05) than ALB. The data were consistent with the notion that ionic interactions between extracellular protein-ligand complexes and the hepatocyte surface facilitate the uptake of long-chain fatty acids.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada. burczyn@cc.umanitoba.ca
authors.forename: F J
authors.initials: FJ
authors.lastname: Burczynski
authors.forename: G Q
authors.initials: GQ
authors.lastname: Wang
authors.forename: B
authors.initials: B
authors.lastname: Elmadhoun
authors.forename: Y M
authors.initials: YM
authors.lastname: She
authors.forename: M S
authors.initials: MS
authors.lastname: Roberts
authors.forename: K G
authors.initials: KG
authors.lastname: Standing
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000465:Algorithms; D000818:Animals; D002412:Cations; D005227:Fatty Acids / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007525:Isoelectric Focusing; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008298:Maleates / Q000138:chemical synthesis / Q000378:metabolism; D008970:Molecular Weight; D010168:Palmitates / Q000378:metabolism*; D011487:Protein Conformation; D051381:Rats; D017207:Rats, Sprague-Dawley; D021241:Spectrometry, Mass, Electrospray Ionization; D013386:Succinates / Q000138:chemical synthesis / Q000378:metabolism; D013499:Surface Properties
chemical_list: D000418:Albumins; D002412:Cations; D005227:Fatty Acids; D008298:Maleates; D010168:Palmitates; D013386:Succinates