Lipid polarity in brain capillary endothelial cells.

Abstract

Brain capillary endothelial cells (BCEC) represent an epithelial like cell type with continuous tight junctions and polar distributed proteins. In this paper we investigated whether cultured BCEC show a polar distribution of membrane lipids as this was demonstrated for many epithelial cell types. Therefore we applied a high yield membrane fractionation method to isolate pure fractions of the apical and the basolateral plasma membrane (PM) domains. Using a set of methods for lipid analysis we were able to determine the total lipid composition of the whole cells and the PM fractions. Both membrane domains showed a unique lipid composition with clear differences to each other and to the whole cell composition. Three lipid species were polar distributed between the two PM domains. Phosphatidylcholine was enriched in the apical membrane whereas sphingomyelin and glucosylceramide were enriched in the basolateral membrane. The possible function of this lipid polarity for the blood-brain barrier mechanism is the generation of a suitable lipid environment for polar distributed membrane proteins and the generation of two PM domains with different biophysical properties and permeabilities.