STRUCTURE AND DYNAMICS OF THE FENESTRAE-ASSOCIATED CYTOSKELETON OF RAT-LIVER SINUSOIDAL ENDOTHELIAL-CELLS

This article describes the cytoskeleton associated with fenestrae and sieve plates of rat liver sinusoidal endothelial cells. Fenestrae cont rol the exchange between the blood and parenchymal cells. We present e vidence indicating that several agents that change the fenestrae and s ieve plates also cause changes in the cytoskeleton. Cultured liver end othelial cells (LECs) were slightly fixed and treated with cytoskeleto n extraction buffer. Detergent-extracted whole mounts of cultured cell s were prepared for either scanning electron microscopy (SEM) or trans mission electron microscopy (TEM). Extracted cells show an integral in tricate cytoskeleton; sieve plates and fenestrae are delineated by cyt oskeleton elements. Fenestrae are surrounded by a filamentous, fenestr ae-associated cytoskeleton with a mean filament thickness of 16 nm. Si eve plates are surrounded and delineated by microtubuli, which form a network together with additional branching cytoskeletal elements. The addition of ethanol to cultured cells enlarged the diameter for these fenestrae-associated cytoskeleton rings by 5%, whereas serotonin treat ment reduced the diameter by 20%. These observations indicate that the fenestrae-associated cytoskeleton probably changes the size of fenest rae after different treatments. After treatment with cytochalasin B th e number of fenestrae increased. However, cytochalasin B did not chang e the structure of the fenestrae-associated cytoskeleton ring, but dis perses the microtubuli. In conclusion, LECs have a cytoskeleton that d efines and supports sieve plates and fenestrae. Fenestrae-associated c ytoskeleton is a dynamic structure and plays a role in maintaining and regulating the size of fenestrae after different treatments. Therefor e, the fenestrae-associated cytoskeleton controls the important hepati c function of endothelial filtration.