[The ultrastructure and possible role of the vacuolar component of hepatocyte nucleoli]

A study was made of the nucleolar vacuoles in guinea pig hepatocytes that are poorly investigated for animal cells. A comparison of ultrathin sections, contrasted by heavy metals, with those treated according to Bernhard allowed to reveal the following intravacuolar structures: 1) fibrils 10-15 nm and 20-30 nm thick similar to perinucleolar chromatin fibrils; 2) RNP-granules 15-20 nm in diameter resembling the granular component of the nucleolus; 3) RNP-fibrils 15-20 nm thick with high electron density. The latter were visualized for the first time, their function still remains obscure. Upon stimulation of hepatocytes with partial hepatectomy, the vacuolar component changed. In 2.5 and 5 hours after the operation the vacuoles became smaller, the number of RNP structures of two types increased. Further, in 9 hours, the enlarging of vacuoles was accompanied by a sharp decrease in the number of these RNP-structures. The results obtained allow to suppose that the vacuoles of nucleolonemic nucleoli may be functioning elements, linking intra- and perinucleolar chromatin fibrils. They are depots for the RNP synthesized in the nucleolus; the rRNP is transported through the vacuolar system.