Retinol transport in cultured stellate cells of rat liver: studies by light and electron microscope autoradiography.

The mechanisms of specific transport of retinoids into stellate cells (SC) of liver remain to be elucidated. In the present study, we have conducted experiments to observe the intracellular retinoid metabolism of cultured SC of rat liver using light and electron microscope autoradiography (LMARG and EMARG). After 72 h of culture, the cells were incubated in the medium containing 1.06 x 10(-6) or 6.36 x 10(-8) M of [3H]retinol for either 5 or 30 min. In some cases, incubation with the labeled retinol was followed by a medium containing nonlabeled 1 x 10(-6) M retinol for 90 min. First, the incorporation of labeled retinol (1.06 x 10(-6) M) into SC and hepatocytes was compared by LMARG. After 5 min, silver grains were already present on both cells. After 30 min, label was concentrated on the lipid droplets of SC. After the chase, the number of grains on hepatocytes decreased. On the other hand, grains on the lipid droplets of SC remained. Second, we studied the fine morphology and intracellular retinoid metabolism in SC using EMARG. The SC, which contained abundant multivesicular bodies (MVB) and lamellar bodies, were found to have a heavy accumulation of grains. Even in the medium containing a lower concentration of retinol (6.36 x 10(-8) M), SC also took up retinol. After 90 min of chase, many grains moved on the lipid droplets in SC. The labeled MVB were often accompanied by lamellar bodies and found near the lipid droplets. Sometimes we noticed small labeled lipid droplets bound by membranes in MVB. From the results of this study, we concluded that the MVB and lamellar bodies might be important organelles for retinyl ester formation and the initial storage of retinoid in the lipid droplets in SC.