Importance of bicarbonate in bile salt independent fraction of bile flow.

The bile salt independent fraction (BSIF) of canalicular bile flow from the isolated rat liver perfused with bicarbonate-free perfusate is 50% of that from the liver perfused with bicarbonate-containing perfusate. HCO3-excretion is nearly eliminated and Na+ and Cl- excretion is reduced 50%. Replacement of HCO3- into perfusate increased bile flow by 0.3 microliter/g.min without changing bile acid excretion rate. 5.5-Dimethyl-2,4-oxazolidinedione (DMO) produced a similar effect. DMO was passively distributed between bile and plasma. The data indicate that a bicarbonate transport mechanism is responsible for production of up to 50% of the BSIF. Another weak acid, N-5[5-(2-methoxyethoxy)-2-pyrimidinyl]sulfamoylbenzene (glymidine), was rapidly excreted into bile and increased bile flow by over 2.0 microliter/g.min. Glymidine is probably excreted by an independent organic anion transport mechanism, and any effect on the bicarbonate transport mechanism is obscured. Canaliculus-enriched hepatocyte membrane fractions contained no HCO3-stimulated ATPase activity. Either this enzyme is unimportant in hepatocyte bicarbonate transport or transport occurs across membranes other than the bile canalicular membrane.     

A role of the heavy subfraction of the floating lipids in acute alcoholic fatty liver of rats

Two subfractions of floating lipids were studied to clarify the subcellular pathogenesis of ethanol-induced acute fatty liver in the rat. The main lipid in both the heavy and light subfraction was triglyceride, but the heavy subfraction was richer in phospholipids than the light subfraction. After ethanol-treatment of the animals, not only triglyceride but also phospholipids increased significantly in the light subfraction. The similarity of the phospholipid species in the two subfractions suggests a possible exchange of lipids between them. The heavy subfraction consisted of membrane-free lipid droplets of very low density lipoprotein (VLDL) size plus membrane-bound, vacuolated organelles; the light subfraction consisted of membrane-free lipid globules larger than 1000 nm in diameter. Occasionally adherent particles, 40 to 100 nm in diameter, were detected on the surface of the lipid globules. After ethanol treatment, the ratio of adherent particles to lipid globules increased significantly. These observations suggest that the biogenesis of acute alcoholic fatty liver in rats involves first the formation of membrane-free lipoproteins of VLDL size in the cytoplasm and subsequently their fusion to pre-existing lipid globules.     

A role of the heavy subfraction of the floating lipids in acute alcoholic fatty liver of rats.

Two subfractions of floating lipids were studied to clarify the subcellular pathogenesis of ethanol-induced acute fatty liver in the rat. The main lipid in both the heavy and light subfraction was triglyceride, but the heavy subfraction was richer in phospholipids than the light subfraction. After ethanol-treatment of the animals, not only triglyceride but also phospholipids increased significantly in the light subfraction. The similarity of the phospholipid species in the two subfractions suggests a possible exchange of lipids between them. The heavy subfraction consisted of membrane-free lipid droplets of very low density lipoprotein (VLDL) size plus membrane-bound, vacuolated organelles; the light subfraction consisted of membrane-free lipid globules larger than 1000 nm in diameter. Occasionally adherent particles, 40 to 100 nm in diameter, were detected on the surface of the lipid globules. After ethanol treatment, the ratio of adherent particles to lipid globules increased significantly. These observations suggest that the biogenesis of acute alcoholic fatty liver in rats involves first the formation of membrane-free lipoproteins of VLDL size in the cytoplasm and subsequently their fusion to pre-existing lipid globules.     

Bile canalicular membrane pathology in cytochalasin B-induced cholestasis.

The mechanism of cytochalasin B-induced intrahepatic cholestasis was examined using electron cytochemical techniques. Since previous studies suggested that the earliest lesions were in hepatic canaliculi, markers were used for three canalicular membrane components, namely ruthenium red for the glycoprotein-rich surface coat, the Mg2+-ATPase reaction as an example of a membrane-bound protein, and uranyl acetate en bloc and ruthenium red staining for the canalicular membrane-associated microfilaments. In rat liver infused in vivo with cytochalasin B, reduction in bile flow correlated with bile canalicular dilation, loss of the ruthenium red-positive surface coat from the canalicular membrane, and loss of demonstrable Mg2+-ATPase activity. In addition, structural alterations in microfilaments with widening of the ectoplasmic zone were noted. In isolated liver cells in vitro, identical changes were found. Bile canaliculi isolated from the in vivo cytochalasin B-infused rat liver lacked their normal investment of microfilaments. Detachment of the filaments from the bile canalicular membrane may be involved in the mechanism of cytochalasin B-induced cholestasis.     

Effects of chronic choleretic infusions of bile acids on the membrane of the bile canaliculus. A biochemical and morphologic study.

To determine whether choleretic infusions of bile acids modified the function or structure of the membrane of the bile canaliculus, sodium taurocholate (NaTc) or dehydrocholate (DHC) was infused into male rats at a rate of 80 mumoles per hour over an 18-hour period. Bile was collected by fistula and phospholipid and cholesterol content was measured in bile, liver homogenates, and isolated liver plasma membranes (LPM) enriched in bile canaliculi. Na+, K+-ATPase, Mg2+-ATPase, 5'-nucleotidase, and alkaline phosphatase activities were also measured in LPM. NaTc infusions enhanced cholesterol and phospholipid output in the bile in association with a significant increase in phospholipid in both LPM and liver homogenate. Although DHC infusions resulted in a comparable excretion of bile acid, phospholipid and cholesterol output in bile did not increase from control values and the concentration of these lipids in LPM and liver homogenate also did not change. However, LPM Na+, K+-ATPase significantly increased after DHC infusions compared to NaTc-infused animals or controls. Neither bile acid altered the activities of Mg2+-ATPase, 5'-nucleotidase, or alkaline phosphatase. Both bile acids increased the diameter of the lumen of the bile canaliculus as assessed by scanning electron microscopy and produced irregularities and outpouchings in the canalicular membrane. Diverticuli and loss of microvilli were most prominent with DHC infusions whereas canalicular side branching and the density of microvilli, either remained unchanged or increased following NaTc infusions. Although the morphologic findings are qualitative, the results of these studies indicate that chronic choleretic infusions of NaTc and DHC have divergent effects, not only on enzyme activities in liver plasma membrane, but on phospholipid composition and 3-dimensional structure. These findings suggest that bile acids may after biliary secretion not only through their osmotic effects, but by modifying lipids and enzymes in the membrane of the bile canaliculus.     

The isolation and characterization of a bile ductule cell population from normal and bile-duct ligated rat livers.

The separation of bile ductule cells from Kupffer and sinusoidal endothelial cells in a suspension of non-parenchymal cells has been attempted. Bile duct ligation was performed so that a four-fold increase in the total number of non-parenchymal cells isolated from rat liver was attained and the proportions of both Kupffer and bile ductule cells were elevated. Rate zonal centrifugation, through a Ficoll gradient, partially separated the cells into two populations: (1) small cells (4-6 micrometer diameter) probably originating from the sinusoidal endothelium and (2) larger bile ductule and Kupffer cells (8-12 micrometer diameter). A more successful separation was achieved by isopycnic centrifugation through a linear metrizamide gradient. Bile duct ligation (14 days) altered the distribution of cells on the gradient and the peak containing bile ductule and Kupffer cells partially subdivided into the separate cell types. Antiserum raised against the bile ductule fraction was shown to be compatible with that raised against common bile duct tissue. gamma-glutamyl transpeptidase and leucine aminopeptidase activity were preferentially located in the rate zonal fraction containing bile ductule cells. Their specific activity increased after bile duct ligation as did that of beta-glucuronidase, which was raised in all cells.     

Scanning electron microscopy of proliferating bile ductules.

Rats were subjected to ligation of the common bile duct to provoke bile ductular proliferation and were studied at intervals from 1 day to 6 weeks. After perfusion fixation with glutaraldehyde, and ethanol dehydration, blocks of liver were frozen in liquid nitrogen, fractured, and returned to ethanol prior to critical point drying. Examination with the scanning electron microscope showed a remarkable proliferation of bile ductules and preductules in addition to canalicular dilation. The ductules were surrounded by a longitudinal array of collagen fibers. The luminal surfaces contained many microvilli and cable-like structures, some identifiable as cilia by transmission electron microscopy. The present techniques offer the possibility for a reevaluation of obstructive jaundice and cholestasis.     

Vimentin expression of newly formed rat bile duct epithelial cells in secondary biliary fibrosis

Summary The intermediate filament profile and the growth fraction of hepatocytes and bile duct epithelial cells were studied in a rat model of biliary fibrosis secondary to common bile duct ligation and scission. Strong vimentin expression was observed in epithelial cells of newly formed bile ductules, while normal liver contained only few weakly positive bile duct epithelial cells. All epithelial cells reacted with a pan-cytokeratin antibody. A monoclonal antibody specific for human cytokeratin 7 selectively reacted with both normal and newly formed bile duct epithelial cells. The intermediate filament profile of hepatocytes was constant, showing no changes during proliferation or in periportal areas adjacent to excessive bile duct formations. The proliferation-associated antigen detected by the antibody Ki-67 was present in many hepatocytes, homogeneously distributed in the lobules, but was seen only in a small proportion of the epithelial cells of the newly formed bile ducts. We conclude that vimentin may serve as an indicator for cellular reorganization in the bile duct system, and that the epithelial cells of newly formed bile ductules in this particular model of secondary biliary fibrosis were most likely to be derived from an outgrowth of the biliary duct system and recruitment of preductular epithelial cells. No morphological or immunohistological evidence suggesting a derivation from hepatocytes by ductular metaplasia or from oval cells was obtained.     

Identification and characterization of the immunoprecipitating medium- and low-density tryptic fragments of bovine nasal cartilage proteoglycan

The fragments responsible for the immunodiffusion reactivity of middle- and low-density fractions of trypsin-digested bovine nasal cartilage proteoglycan have been identified and obtained in relatively homogeneous fractions. Glycosaminoglycan-bearing tryptic fragments were isolated from 4 M guanidinium chloride extracts of cartilage by ion-exchange chromatography and fractionated by dissociative equilibrium density gradient ultracentrifugation at a starting density of 1.50. Fragments in the middle fractions of the density gradient were digested with chondroitinase ABC and subfractionated by Sepharose 6B column chromatography. Middle-density subfractions contained fragments which were chemically and immunologically identical to those in high-density fragment subfractions of similar elution from Sepharose 6B. The middle-density subfractions contained two additional immunoprecipitating fragments. One, with alanine as N-terminal amino acid, was isolated by virtue of its retention by a column of concanavalin A-Sepharose 4B and its resistance to digestion with keratanase; the second was concentrated in a subfraction whose elution from concanavalin A-Sepharose 4B was retarded. The gradient fraction of lowest density contained fragments with the properties of the major tryptic fragments of the hyaluronic acid-binding segment of the proteoglycan monomer and the link proteins. These were recovered as a complex in the void volume upon Sepharose gel chromatography in saline-buffer and were resolved into relatively homogeneous fractions by column chromotography on CL-Sepharose 6B in 4 M guanidinium chloride. In all, tryptic digests of cartilage proteoglycan contain at least seven different immunoprecipitating fragments, some of which may not have been correctly identified previously.     

大鼠原位肝移植术后胆道并发症的影响因素

目的 研究大鼠原位肝移植术后胆道并发症的各种影响因素,为建立更稳定的大鼠原位肝移植模型提供实验依据.方法 雄性SD大鼠87只,完全随机法分组,其中移植组48只、非移植组36只、假手术组3只,实验共分胆管-胆管重建移植组、胆管-十二指肠重建移植组、胆管-胆管重建+肝动脉结扎非移植组、胆管-胆管重建非移植组、胆管-十二指肠重建+肝动脉结扎非移植组、胆管-十二指肠重建非移植组和假手术组7组.各手术处理组以出现明显胆道并发症或移植后14 d作为观察时间终点.通过肝脏大体标本肉眼观察、病理学检测和血清学分析等判断胆道并发症的发生率及其严重程度并进行各组间比较.结果 移植组总胆道并发症发生率为69.6%,明显高于非移植组(25.0%)和假手术组(0%),差异有统计学意义(均P<0.05).在移植组和非移植组中,胆管-十二指肠重建组的胆道并发症发生率明显高于胆管-胆管重建组(90.9%比50.0%,38.9%比11.1%,均P<0.05).非移植组中,结扎肝动脉组的胆道并发症高于不结扎肝动脉组(38.9%比11.1%,P<0.05).结论 经典"二袖套法"大鼠原位肝移植模型尚不完善,仍需进一步改进.就大鼠原位肝移植模型而言,胆管-十二指肠重建方式并非理想的选择.     

Characterization of a primary bile ductular cell culture from the livers of rats during extrahepatic cholestasis.

The establishment of novel bile ductular cell cultures was accomplished with the use of explants of a hyperplastic bile ductular tissue preparation obtained from rat livers at 10 to 15 weeks after bile duct ligation or a bile ductular cell fraction isolated from this tissue preparation by a procedure involving Percoll density gradient centrifugation. Observations made on these primary explant and monolayer bile ductular cell cultures were limited to the first 3 days of culture where the morphologic features of the bile ductular epithelium remained fairly well preserved, while fibroblast contamination was found to be very low. These cultured cells also retained over this period a high specific activity for the bile ductular cell marker enzyme gamma-glutamyl transpeptidase, as well as possessed measurable but decreasing specific activities for leucine aminopeptidase and alkaline phosphatase. Karyotypic analysis of the cultured monolayer cells further showed them to be diploid. In addition, preliminary transplantation studies demonstrated the presence of well-differentiated bile ductular-like structures following inoculation of the freshly isolated bile ductular cell fraction into the interscapular fat pads of recipient rats.     

The buoyant density of synaptic plasma membranes from the cerebral cortex of neonatal rats

Summary A fraction enriched in synaptic plasma membranes was prepared from neonatal (5–6 day old) rat cerebral cortex. The procedure was based on a method used to prepare synaptic plasma membranes from adult cerebral cortex. Critical steps were monitored by electron microscopy. Synaptic plasma membranes from neonatal cerebral cortex sedimented as a broad peak between 0.9 M and 1.1 M sucrose. In contrast, the majority of adult synaptic plasma membranes have been reported to sediment to 1.2 M sucrose. The activities of various enzyme markers were determined in subfractions of neonatal preparations in order to estimate contamination. The specific activities of these markers indicated substantial contamination of the neonatal synaptic plasma membrane fractions by microsomes and glia.     

Factors producing bile infarction and bile duct proliferation in biliary obstruction

To clarify the factors producing bile infarction and bile duct proliferation in obstructive jaundice, the incidence of the hepatic lesions and the serum levels of the bile constituents were examined in three rat models. (1) Ligation of the common bile duct induced bile infarction, bile duct proliferation, retention of bile in the liver, and elevation of the serum levels of total bilirubin and total bile acids. (2) The rats treated by choledochotomy had bile in the abdominal cavity, but there was no retention of bile in the liver. The degree of development of bile infarction was similar to that of the common bile duct ligation group, but bile duct proliferation was not found: the serum levels of total bilirubin and total bile acids were elevated. (3) In the rats subjected to partial bile duct ligation, bile infarction and bile duct proliferation were seen only in the lobes with ligation of the hepatic ducts: only slight or no elevation of the serum levels of total bilirubin and total bile acids was found. These data suggest that bile infarction is caused by the toxic action of bile constituents other than bilirubin and bile acids, absorbed into the blood from the obstructed biliary system, and that bile duct proliferation is due to mechanical factors following bile retention or direct actions of retained bile in the liver.     

Early effects of 1,1-dichloroethylene on canalicular and plasma membranes: ultrastructure and stereology

The pathogenesis of 1,1-dichloroethylene (1,1-DCE)-induced hepatotoxicity was investigated in fasted male rats by identifying the earliest morphological alterations in organelles. In situ perfusion-fixed liver tissue was examined by light and electron microscopy at 1, 2, or 3 hr after oral administration of 25, 50, and 100 mg 1,1-DCE/kg in mineral oil. The earliest morphological alterations, which occurred within 1 to 2 hr after 1,1-DCE administration, were dilation of bile canaliculi with an increase in the number of microvilli or membrane fragments in canaliculi and the formation of canalicular diverticuli in centrolobular hepatocytes. Subsequently, microvilli on sinusoidal surfaces were disrupted or lost. Membrane whorls were frequently found in bile canaliculi, the space of Disse, and between the lateral membranes of hepatocytes at early times. As injury progressed, centrolobular hepatocytes retracted from endothelial cells and sinusoidal plasma membranes invaginated to form cytoplasmic vacuoles. Stereological analysis of centrolobular hepatocytes at the 25 mg/kg dose showed a significant increase in canalicular volume density by 3 hr and no detectable alteration in mitochondrial volume density. These results indicate that changes in canalicular shape and microvilli configuration are the earliest morphological alterations following 1-DCE ingestion.     

Tauroursodeoxycholic acid inserts the bile salt export pump into canalicular membranes of cholestatic rat liver

Ursodeoxycholic acid exerts anticholestatic effects in chronic cholestatic liver disease in humans as well as in experimental animal models of cholestasis. Its taurine conjugate, TUDCA, was recently shown to stimulate insertion of the apical conjugate export pump, Mrp2 (ABCC2), into canalicular membranes of rat hepatocytes made cholestatic by exposure to taurolithocholic acid (TLCA). The aim of this immunoelectronmicroscopic study was to test whether TLCA and TUDCA modulate the canalicular density of the other key apical transporter, the bile salt export pump, Bsep (ABCB11), in a similar way. Immunoelectronmicroscopic analysis of Bsep density on canalicular membranes, microvilli, and pericanalicular area of hepatocytes was performed in rat liver tissue prepared after liver perfusion with bile acids or carrier medium only. TLCA (10 micromol/l for 50 min) decreased Bsep density in canalicular membranes to 31% of controls (P<0.05) when bile flow was reduced to 35% of controls (P<0.05). Concomitantly, Bsep density in a 1 microm pericanalicular zone increased to 202% (P<0.05) indicating effective retrieval of Bsep from the canalicular membrane induced by TLCA. Coadministration of TUDCA (25 micromol/l) led to a 3.2-fold increase of Bsep density in canalicular membranes equal to control liver (P<0.05 vs TLCA) in association with a 3.8-fold increase of bile flow (P<0.05 vs TLCA). Stimulation of apical membrane insertion of key transporters like the bile salt export pump, Bsep, and-as previously shown-the conjugate export pump, Mrp2, may contribute to the anticholestatic action of UDCA amides in cholestatic conditions.     

Immunochemical characterization of submicrosomal rat liver membranes

Rat liver microsomes were separated into three subfractions by means of ultracentrifugation through sucrose media of different densities and in the presence of different cations. Detergent extracts of these preparations were analysed by double diffusion in agar gel and immunoelectrophoresis with rabbit antisera against each of the subfractions.

One subfraction was derived from the `rough' and another from the `smooth' part of the endoplasmic reticulum of the liver parenchymal cells. Their extracts contained at least thirteen soluble antigens in common. However, fraction-specific antigens were also present. Thus, the extracts of the rough (R) membranes contained at least one typical antigen, not found in any of the other fractions. An antiserum against this component also precipitated a non-migrating antigen present only in the extracts of smooth (Sa) membranes. These two antigens may represent different molecular forms of a substance involved in binding of the ribosomes or in the assembly of membrane subunits.

At least eleven of the antigens common for the two fractions exhibited enzymatic activities when assayed after precipitation with antibody in the immunoelectrophoretic plates. Six immunologically and electrophoretically distinct antigens had esterase activity with α-naphthyl propionate as substrate. Two of these esterases also split indoxyl acetate. Three other antigens with acid phosphatase activity split both α-naphthyl acid phosphate and β-glycerophosphate. Three antigens had nucleoside diphosphatase activity when tested with uridine- or inosine-diphosphate. Preliminary experiments also suggested that two additional antigens possessed NADH-diaphorase activity and thus could belong to the microsomal electron transport systems.

The third subfraction consisted of electron-microscopically smooth membranes (Sb), enzymatically different from those of the endoplasmic reticulum. The antigens typical for the latter were either absent or present only in minor and variable concentrations. Its extracts contained at least two typical antigens. One of these was identified as contaminating ferritin. The nature and origin of the other antigen has not yet been established.

All antigens described in this paper were immunologically different from the common rat serum proteins.

     

Bile canalicular contraction and dilatation in primary culture of rat hepatocytes - possible involvement of two different types of plasma membrane Ca2+-Mg2+-ATPase and Ca2+-pump-ATPase

Increasing evidence has indicated that bile canalicular contraction is mediated by the nonmuscular Ca(2+)-calmodulin-actomyosin system, and the contraction facilitates canalicular bile flow. The aim of the present study was to examine, by electron cytochemistry, how the expression of two types of plasma membrane Ca(2+)-ATPase, i.e., Ca(2+)-Mg(2+)-ATPase and Ca(2+)-pump-ATPase, is related to the dynamic changes of bile canalicular contraction. Hepatocytes isolated from male Wistar rat liver by collagenase perfusion were cultured to form a primary monolayer. The canalicular dynamics in the couplets and triplets were analyzed by time-lapse cinematography. The Ca(2+)-Mg(2+)-ATPase activity was identified by the electron cytochemical method of Ando. Ultrastructural localization of Ca(2+)-pump-ATPase was examined by immunogold electron microscopy. We found that cytochemical reaction products showing the presence of Ca(2+)-Mg(2+)-ATPase activity were localized on the luminal side of the bile canalicular membranes. Immunogold particles, indicating the presence of Ca(2+)-pump-ATPase, were located mainly on the cytoplasmic side of the bile canalicular membranes. The expression of both Ca(2+)-ATPases on the canalicular membranes was enhanced during the contracting stage of bile canaliculi, whereas their expression was diminished in the dilating stage. We conclude that two different types of bile canalicular Ca(2+)-ATPase may be involved in the regulation of canalicular contractility to control the extrusion of intracytoplasmic free calcium ions into the canalicular lumen.     

Evidence for microfilament involvement in norethandrolone-induced intrahepatic cholestasis.

An experimental study of norethandrolone (NED)-induced intrahepatic cholestasis was made. NED was infused via a portal vein catheter into rat liver in vivo, and measurements were made of bile flow. Liver specimens were taken at intervals for light microscopy and for transmission and scanning electron microscopy. Bile-canalicular-rich membrane fractions were prepared. The effects of NED were also examined in isolated hepatocytes in suspension culture. NED infusion induced total cholestasis by 3 hours. Canalicular alterations commonly associated with cholestasis were found in in vivo infused liver and in isolated hepatocytes. Pericanalicular microfilament changes were also noted in both, with loss of filament structure and replacement by a granular zone. In isolated canalicular membrane fractions prepared from NED-treated animals, the normal investment of pericanalicular filaments was no longer present. Loss of the bile canalicular ruthenium red surface coat was also noted. In view of the identical findings in isolated hepatocytes and in in vivo liver, obstruction and mechanical factors can be excluded as possible causes. The results raise the possibility that the mechanism of NED-induced cholestasis may be related to disaggregation and/or detachment of microfilaments from the canalicular membranes.     

Improved isolation of small noradrenergic vesicles from rat seminal ducts following castration. A density gradient centrifugation and morphological study

Noradrenaline storage vesicles from nerve endings have been prepared by differential and density gradient centrifugation. Seminal ducts from castrated rats have been used as a source since fluorescence micrographs and electron microscopy demonstrated an increased concentration of sympathetic nerve endings in this tissue; probably as a result of muscle atrophy. The fractions obtained were analyzed biochemically and partly by electron microscopy.By centrifugation techniques, a density gradient fraction (at the density of 0.4–0.45m sucrose) was obtained in which noradrenaline was enriched about 10-fold from the homogenate. By using organs from castrated rats a further 4-fold increase was obtained in the noradrenaline/protein ratio of the density gradient fraction. This gradient fraction was studied by electron microscopy, after incubation with 5-hydroxydopamine as an exogenous marker, and was found to contain a high proportion of granular vesicle profiles. More than ? of all vesicles with a diameter below about 1000A?had an electron dense core. The vesicle preparation contained low activities of mitochondrial (cytochrome oxidase) and lysosomal (acid phosphatase) marker enzymes, while microsomes and plasma membrane fragments as indicated by NADH-cytochrome c reductase and adenosine triphosphatase had only been partially removed and probably constituted the main contaminants.The distribution of dopamine β-hydroxylase activity suggested that the small, light dense cored vesicles are deficient of this enzyme compared with the large, heavy dense cored vesicles, assumed to occur at the bottom of the gradient. The noradrenaline/adenosine 5'-triphosphate molar ratio was found to be 5.9 in the main noradrenaline fraction, but this fraction was not sufficiently pure to draw any definite conclusions about whether or not noradrenaline is stored together with adenosine 5'-triphosphate in small noradrenergic vesicles.     

Studies on the distribution of some histocompatibility antigens in mouse liver plasma membrane and microsomal fractions

The plasma membrane fraction, its two major derivative sub-fractions, and a smooth-surfaced microsomal fraction have been prepared from mouse liver tissue homogenates and their purity has been assessed by using enzymic markers. The antigenicity of the fractions was compared using a lymphocytotoxicity inhibition assay. The results indicate that the vesicular subfraction of the plasma membranes, known to be enriched in certain marker enzymes, was the most active preparation, whereas the microsomal fraction was the least active. An approximately two-fold increase in antigenicity was observed when the assay was performed on deoxycholate-treated fractions. The results suggest that the H-2 histocompatibility antigens may be present at higher concentrations in certain areas of the liver cell surface membrane.