Some properties of the chylomicron remnant uptake by rat hepatocyte monolayers

The effect of mild proteolytic treatment on chylomicron remnant uptake by rat hepatocyte monolayers was studied both at 4 degrees C and at 37 degrees C. At 4 degrees C binding of remnants to the cells was considerably lower than at 37 degrees C, and preincubation of the cells with pronase (2 micrograms/ml) further descreased binding of remnants at 4 degrees C by 63%. At 37 degrees C the effect of preincubation of pronase was less marked, suggesting that reconstruction of remnant binding structures(s) may occur. Only marginal effects on remnant catabolism by cytochalasin B in hepatocyte monolayers were evident. There was thus no positive evidence for a role of microfilaments during interiorization of remnant particles by the cells. Remnant uptake in hepatocytes was not inhibited by EDTA, the presence of asialofetuin, or treatment of the cells with neuraminidase. This indicates that remnant binding sites are different from the hepatic receptor for desialylated glycoproteins. The lack of effect of EDTA is also at variance with the observation that the receptor-mediated uptake of low-density lipoproteins in human fibroblasts depends on the presence of divalent cations.