Uptake of carbon and polystyrene particles by the sinusoidal endothelium of rabbit bone marrow and liver and rat bone marrow, with special reference to multiparticle-pinocytosis.

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Abstract
The endocytosis of tracer particles by sinusoidal endothelial cells was studied in the bone marrow and liver of the rabbit and in the bone marrow of the rat after i.v. injection. The tracer particles used included C particles and polystyrene particles of different sizes ranging from 0.11-5.7 .mu.m in diameter. The sinusoidal endothelial cells of the rabbit liver and rat bone marrow took up C through the formation of bristle-coated vesicles at the luminal surface, but they eventually failed to ingest polystyrene particles of 0.11 .mu.m or larger. The sinusoidal endothelial cells of the rabbit bone marrow took up C and polystyrene particles varying from 0.11-2.02 .mu.m in diameter. These endothelial cells were found to sequester circulating tracer particles in the cytoplasm through the the formation of 2 kinds of vesicles at the luminal surface: bristle-coated vesicles and multiparticle-pinocytotic vesicles. This special type of pinocytotic vesicle was larger in diameter than the bristle-coated vesicle and variable in size according to the size or amount of the particles to be sequestered. C and 0.11 .mu.m polystyrene partticles were taken up by means of both the bristle-coated vesicles and multiparticle-pinocytotic vesicles, whereas particles 0.30 .mu.m in diameter or larger were taken up by the vesicles similar in nature to multiparticle-pinocytotic vesicles. A sequence for the morphological events occurring in the formation of multiparticle-pinocytotic vesicles in the sinusoidal endothelial cells of rabbit bone marrow shall be suggested and discussed.