Content of dolichol and retinol in isolated rat non-parenchymal liver cells

The liver sinusoids, that are considered as a functional unit, harbour four types of sinusoidal cells (Ito, Kupffer, endothelial and pit cells). Dolichol content has been determined in many tissues and subcellular compartments, alteration has been reported in many types of liver injury, but until now no data are available on its content in every type of sinusoidal non-parenchymal liver cells. Dolichol and retinol metabolism might intersect in their traffic in biological membranes. Intercellular as well as intracellular exchange of retinoids is an essential element of important processes occurring in liver cells. It has been suggested that the role of dolichol, besides being a carrier of oligosaccharides in the biosynthesis of N-linked glycoproteins, may be to modify membrane fluidity and permeability, and facilitate fusion of membranes. Dolichol in the membrane is intercalated between the two-halves of the phospholipid bilayer, but its exact disposition is not known and the movement and distribution of retinoid in membranes may vary with the geometry of the membranes. Therefore the aim of this study is to obtain a global understanding of the sinusoidal system regarding dolichol and retinol content in each type of isolated rat liver sinusoidal cell, in normal conditions and after vitamin A administration. The information that can be drawn from the present results is that with normal vitamin A status of the animal, the dolichol content is almost uniform in all liver cells. After vitamin A supplementation, a great increase of dolichol, together with the known increase of retinol, can be measured only in a subpopulation of the Ito cells, the Ito-1 subfraction. Therefore in the cells that are present in the hepatic sinusoid, different pools of dolichol may have separate functions. Because retinol traffic among cells, membranes and plasma still remains to be fully understood, roles of dolichol in the exchange of vitamin A among sinusoidal liver cells are discussed.