Kinetics of appearance of lipoprotein particles in perisinusoidal cisternae of smooth endoplasmic reticulum of isolated rat livers perfused with free fatty acid.

Vesicles containing single lipoprotein particles are found in the perisinusoidal cytoplasm of rat hepatocytes in the proximity of particle-containing rough-smooth endoplasmic reticulum transition elements. these lipoprotein particle-containing smooth endoplasmic reticulum elements provide an alternative to Golgi apparatus as a supplier of very low density lipoprotein particles to the circulation. To test this possibility, the kinetics of appearance of lipoprotein particles in these elements was determined for isolated rat livers first depleted of particles and then perfused with free fatty acid to restore particles. The results show that elements of the smooth endoplasmic reticulum in the perisinusoidal cytoplasm acquire lipoprotein particles in advance of elements of the conventional Golgi apparatus and that the particles contained within the perisinusoidal elements of smooth endoplasmic reticulum are not products of endocytotic uptake of particles from the circulation.