Receptor for Albumin on the Liver Cell Surface May Mediate Uptake of Fatty Acids and Other Albumin-Bound Substances

Abstract

Kinetic analysis of the uptake of carbon-14-labeled oleate in a single-pass perfusion of rat liver and saturable and specific binding of iodine-125-labeled albumin to hepatocytes in suspension suggest the existence of a receptor for albumin on the liver cell surface. The putative receptor appears to mediate uptake of albumin-bound fatty acids by the cell and may account for the efficient hepatic extraction of many other substances tightly bound to albumin.

Effects of albumin and .ALPHA.1-acid glycoprotein on the transport of imipramine and desipramine through the blood-brain barrier in rats.

“…For instance, Weisiger et al 13,16) presented the albumin receptor-mediated transport concept to account for the transport of fatty acid, sulfobromophthalein and bilirubin into the liver, and Forker and Luxon14, 15) suggested the presence of albumin-mediated transport in the liver for rose bengal and taurocholate. Subsequently, we also found an albumin-mediated hepatic uptake of warfarin using the multiple indicator dilution method.31) Pardridge et al 18,19) suggested a "free intermediate model" to explain the transport of many substances such as steroid hormone and l-propranolol (PL) into the brain.…”

Initial heme uptake from albumin by short-term cultured rat hepatocytes is mediated by a transport mechanism differing from that of other organic anions

“…BSP uptake by hepatocytes in the presence of albumin requires the presence of extracellular Cl Ϫ , while a large fraction of taurocholate uptake requires the presence of Na ϩ . 15,17,25 Isosmotic substitution of NaCl by sucrose failed to affect the initial uptake of 55 Fe-heme (Fig. 4B), indicating that heme transport by short-term cultured rat hepatocytes does not require Na ϩ or Cl Ϫ (n ϭ 3).…”

“…It is controversial whether albumin plays a role in the uptake of organic anions by hepatocytes. [25][26][27] One possibility is that the affinity of albumin for the organic anion is a determining factor for the uptake rate. We investigated the effects of albumins with different affinities for heme on the transport of this organic anion.…”

“…Various concepts of how albumin could be involved in the process of extracting organic anions from the circulation exist, one even suggesting an ''albumin receptor.'' 25 The initial albumin receptor concept has been modified considerably over the years and is still controversial. 27 Mechanisms for obtaining ''albumin receptor''-type kinetics in the absence of albumin receptors have recently been elucidated.…”

“…These studies were performed at heme concentrations of 0.09 to 0.9 µmol/L in rat albumin, keeping the ratio of heme to albumin constant at 1:10 in an attempt to minimize changes in the fraction of unbound ligand. 17,25 Uptake of 55 Fe-heme was determined at 4°C or 37°C over the initial 5 minutes of uptake. In these and subsequent studies, the small amount of residual cell-associated radioactivity at 4°C was subtracted as a blank from the uptake data at 37°C (see below).…”