Palmitate uptake by neonatal rat myocytes and hepatocytes - Role of extracellular protein

The role of extracellular binding proteins in the rate of [H-3]palmitate up take by neonatal cardiac myocytes and hepatocytes was investigated using a model-independent approach. Binding proteins used in this study included oi l-acid glycoprotein [isoelectric point (pI) approximate to 2.7], conalbumin (pI approximate to 6.4), lysozyme (pI approximate to 11.0), albumin (pI ap proximate to 4.9), and albumin which had been modified to yield proteins wi th pi values of 3.5, 4.7, 7.5 and 8.6. All uptake studies were conducted at similar unbound ligand fractions. There was a linear relationship between the rate of neonatal hepatocyte [H-3]palmitate clearance and protein pI (r( 2) = 0.98). In contrast, there was an overall poor relationship between neo natal cardiac myocyte [H-3]palmitate-clearance rate and protein pI (r(2) = 0.48). However, the relationship improved when the data on [H-3]palmitate-c learance were analyzed using only the modified albumins. The study indicate s that an ionic interaction between extracellular proteins and the hepatocy te surface enhances the overall uptake of [H-3]palmitate. This interaction may be limited to albumin for neonatal cardiac myocytes.