A freeze-fracture study of the plasma membrane of the Ito cell in the normal rat liver.

The plasma membrane of the Ito cell in the normal rat liver was studied by freeze-fracture electron microscopy. Ito cells appeared to adhere to endothelial cells or to be embedded in the microvilli of hepatocytes. Ramified processes with a few microvilli of the cell extended along the endothelial cells. Caveolae were constantly seen on the plasma membrane, but their numbers varied among cells. Two different patterns of intramembranous particles were found on the plasma membrane of the Ito cells: most cells showed an even distribution of the particles, but the others, aggregates of them. Particle-free domains were seen on the plasma membrane in some Ito cells. Piles of concave or convex sheets were sometimes seen in the freeze-fractured lipid droplets.