Abstract
We have studied the mechanism for mobilization of retinol from stellate cells. Our data show that perisinusoidal stellate cells isolated from liver contained retinol-binding protein (RBP) mRNA. By Western blot analysis we found that cultivated liver stellate cells secreted RBP into the medium. Cultivated stellate cells loaded in vitro with [3H]retinyl ester mobilized radioactive retinol as a complex with RBP. Furthermore, exogenous RBP added to the medium of cultured stellate cells increased the secretion of retinol to the medium. These data suggest that liver stellate cells in vivo mobilize retinol directly to the blood and that a transfer to parenchymal cells for secretion as holo-RBP is not required. The direct mobilization of retinol from liver stellate cells as retinol-RBP to blood is indirectly supported by the demonstration of RBP mRNA production and RBP secretion by lung stellate cells. The data suggest that the same mechanism for retinol mobilization may exist in hepatic and extrahepatic stellate cells. This is, vitamin A-storing stellate cells in liver, lungs, and probably also in other organs may synthesize their own RBP (or alternatively use exogenous RBP) and mobilize holo-RBP directly to the blood.
Highlights
We have studied the mechanism for mobilization of that cultured parenchymal cells are able to synthesize and retinol from stellate cells
The data suggest that the plasma [12, 13]; ( b ) mRNA for plasma RBP has been the same mechanismfor retinol mobilizationmay exist detected in many extrahepatic tissues (14,15a)n; d (c) vitamin in hepatic and extrahepatic stellate cells
We have studied the mechanism for mobilization of retinol from liver stellate cells, the body's mainstorage site for retinol
Summary
Chemicals-Percoll and Nycodenz werepurchased from Pharmacia Fine Chemicals AB, Sweden and Nycomed A/S, Oslo, Norway, respectively.Collagenase (type IV, EC 3.4.24.3)and Pronase (typeXXI). Preparation of Liver Parenchymal Cells-Male Wistar rats (250300 g) and Chinchilla rabbits (2.5 kg) were fedan ordinary pellet diet (AREX, Mbllesentralen, Oslo, Norway). Total liver cell suspensions were prepared by a collagenase liver perfusion technique as described previously [17]. The parenchymal cell suspensions were contaminated with less than 0.1% endothelial cells, Kupffer cells, or stellate cells. Preparation of Liver Nonparenchymal Cells and Stellate CellsNonparenchymal cells were prepared from total liver cell suspensions by differential centrifugation [17], followed by centrifugation in 20% Nycodenz [19]to get rid of cell debris. The nonparenchymal cell suspensions contained about 72%endothelial cells, 17%Kupffer cells, and 8% stellate cells (mean of five preparations). Pure fractions of stellate cells were isolated from this cell suspension by density gradient centrifugation using Percoll as described previously [17].
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