We present a simple and improved method for in situ localization of albumin and collagen mRNAs in isolated mouse hepatocytes. The cells were isolated by collagenase perfusion, mincing, and differential centrifugation. Nick-translated 3H-labeled mouse albumin cDNA (pmalb-2) and chicken pro-a2(I) collagen cDNA (pCg45) probes were then hybridized with the cells in silane-treated microcentrifuge tubes. given time (9-12). Some studies suggest that differences in perfusion techniques may strongly influence the results (13). This is particularly relevant for albumin, the most abundant serum protein, because albumin from the bloodstream can readily crosscontaminate cells in liver tissue.Immunohistochemical methods are limited in that they do not provide information regarding the functional state of the protein synthesis machinery or the level of specific mRNA for a given protein in the cell. This information is important in evaluating the synthesis of proteins present at both high and low levels in cells. In contrast to albumin, collagen is a protein of relatively low abundance in the liver and is capable of being induced under certain pathophysiologic conditions. However, controversy exists as to whether collagen is actually synthesized by hepatocytes (14-20). To investigate this question and to evaluate the synthetic potential of hepatocytes for both albumin and collagen, we have employed in situ hybridization to detect the presence or absence of the specific mRNAs for these proteins. The present report describes a simplified method for in situ hybridization that permits accurate and sensitive localization of albumin and collagen mRNAs in hepatocytes isolated from mouse liver. (24), prepared by the same procedures, was used as a control.
MATERIALS AND METHODS
PreparationPreparation of Hepatocytes. Hepatocytes were isolated from CF1 mice (Charles River Breeding Laboratories). Livers were perfused in situ at 37°C by the technique of Elliott et al. (25) in a medium consisting of 137 mM NaCl, 5.3 mM KCI, 0.8 mM MgSO4, 0.4 mM Na2HPO4, 0.4 mM KH2PO4, 5.5 mM glucose, and 5 mM Hepes, pH 7.4, under continuous oxygenation while the pH was maintained constant. The liver was perfused in a noncirculating system for 2 min at a flow rate of 5 ml/min. The system was then set to recirculate at 5 ml/min for 5 min with the perfusate supplemented with 0.05% collagenase (Sigma type I) and 2.5 mM CaCl2. The liver was then removed, minced in the collagenase-containing buffer, and incubated for 5-10 min in a shaking water bath at 37°C. The suspension was passed through an 80-,tm nylon mesh and the cells were washed three times in the perfusate buffer without collagenase. The cells were then washed by a sedimentation-resuspension procedure utilizing a clinical centrifuge at 800 X g for 30 sec. The supernatant (containing Kupffer cells and damaged hepatocytes) was removed by aspiration. The pellet was suspended in the same buffer and passed through a 30-,Lm nylon mesh. Viability of isolated cells was determined by trypan blue dye e...