Distribution of organelles and membranes between hepatocytes and nonhepatocytes in the rat liver parenchyma. A stereological study

Quantitative relationship between autophagy and proteolysis during graded amino acid deprivation in perfused rat liver

Fractional volumes of lysosomal-vacuolar elements and long lived protein degradation were quantitatively correlated in rat livers perfused in the single pass mode with varying levels of plasma amino acids. Volumes were determined stereologically; degradation was measured in a second stage cyclic perfusion from the linear accumulation of valine in the presence of cycloheximide and was corrected for loss of short lived proteins. Livers exhibited a high degree of amino acid responsiveness; total protein degradation decreased sharply from 4.5 to 1.5%/h (basal) over an amino acid range of 0-10 times (10X) normal plasma concentrations; near basal values were achieved at 1X. Vacuoles containing undegraded cytoplasm (AVi) appeared immediately following stringent deprivation and by 7.5 min were converted to degradative forms (AVd); both autophagic populations attained steady state volumes by 20 min. With amino acid additions, AVi formation virtually ceased and AVd regressed rapidly (0.087 min-1). Cytoplasmic turnover, calculated from this rate constant and the increases over basal in fractional volumes of either AVi or degradative components, agreed quantitatively with corresponding rates of protein turnover. Predictions from these findings, together with evidence for intralysosomal protein pools in both deprived and basal states, account fully for the accelerated proteolysis and suggest that cytoplasm is also internalized by lysosomes under basal conditions.

Relative contributions of parenchymal and non-parenchymal (sinusoidal) liver cells in the uptake of chylomicron remnants

The relative contributions of parenchymal cells and non-parenchymal (sinusoidal) cells to the in vivo hepatic uptake of chylomicron remnants was measured 30 min after intravenous injection into rats. The chylomicron remnants were labeled with [3H]leucine, which was almost exclusively present in apolipoprotein B. The isolated non-parenchymal cells (a mixture of Kupffer cells and endothelial cells) contained 6.7 times more apolipoprotein B radioactivity per mg cell protein than the isolated parenchymal cells. It was calculated that the contributions of non-parenchymal and parenchymal liver cells to the total hepatic uptake of chylomicron remnants are 35% and 65%, respectively.

Thyroid follicular cells: the resting membrane potential and the communication network

Intracellular recordings of membrane potentials, input resistance and time constant have been made in vitro from the follicular cells of the rat, rabbit and guinea-pig thyroid glands using glass microelectrodes. The passive permeability properties of these cells have been investigated by altering the concentration of one or more ions in the superfusing fluid. Investigations into the intercellular coupling characteristics of the thyroid gland were made by inserting two microelectrodes into neighbouring communicating cells. The mean transmembrane potentials were between - 60 and - 70 mV in all three species studied. The magnitude of the membrane potential in the rat was found to be dependent mainly upon the gradient for potassium (K+) across the membrane. Current-voltage relationships were investigated in all three species by injecting rectangular de- or hyperpolarizing current pulses through the recording microelectrode. Within a relatively wide range (- 20 to - 80 mV), there was an approximately linear relationship between injected current and change in membrane potential. The input resistance was about 11 Momega in all three species, while the time constant (tau) varied from 5-35 ms. Readmitting K to K-deprived rat thyroids during intracellular microelectrode recording caused a transient hyperpolarization which was unaccompanied by any change in input resistance. The transient hyperpolarization was abolished by ouabain. Addition of 10(-3) M ouabain to the resting cell caused an immediate depolarization of approximately 2 mV. Electrical coupling between neighbouring cells could only be observed if the distance between the tips of the two exploring microelectrodes was less than 15 micrometer. The coupling coefficient (V2/V1) was close to 1. Assuming uniform current spread within one follicle and electrical isolation of individual follicles from each other the specific membrane resistance of the rat thyroid follicular cells was calculated to be 4.9 komegacm2.

Analytical characterization and purification of plasma membrane from cultured hepatoma cells (HTC cells)

The plasma membrane of the hepatoma cell line, HTC cells, has been characterized and purified by cell fractionation techniques. In the absence of true 5'-nucleotidase in HTC cells, alkaline phosphodiesterase I has been used as a marker enzyme, following conclusions gained from differential and isopycnic centrifugation studies (Lopez-Saura, P., Trouet, A. and Tulkens, P. (1978) Biochim. Biophys. Acta 543, 430-449). To confirm this localization, HTC cells were exposed to anti-plasma membrane IgG at 4 degrees C and fractionated. Alkaline phosphodiesterase I and IgG showed superimposable distribution patterns in linear sucrose gradients. Alkaline phosphodiesterase I is, however, only poorly resolved from enzyme markers of other organelles, especially NADPH-cytochrome c reductase (endoplasmic reticulum) and galactosyltransferase (Golgi complex). Maximal purification from the homogenate is only 13-fold, on a protein basis, even when using a microsomal fraction (67 and 13% of alkaline phosphodiesterase I and protein, respectively) as the starting material. Improved resolution can be obtained after the addition of small quantities of digitonin (equimolar with respect to the cholesterol content). Digitonin increases the buoyant density of alkaline phosphodiesterase I by approx. 0.05 g/cm3, whereas the buoyant densities of galactosyltransferase and NADPH-cytochrome c reductase are increased only by 0.03 and 0.015 g/cm3, respectively. Accordingly, a procedure has been designed which yields a fraction containing 22.8% of alkaline phosphodiesterase I with a purification of 21-fold on a protein basis. The content of NADPH-cytochrome c reductase and galactosyltransferase is 1.2 and 2.1%, respectively. Electron microscopy shows smooth surface membrane elements and vesicles, with only occasional other recognizable elements.

The influence of soluble binding proteins on lipophile transport and metabolism in hepatocytes

A theory is presented that deals with the involvement of the intracellular binding proteins ligandin and aminoazodye-binding protein A (otherwise known as Z-protein or fatty-acid-binding protein) on the uptake and intracellular transport and metabolism of their ligands. Equations are derived that combine steady-state diffusional fluxes of small molecules that are (a) free in the aqueous phase of the cell, (b) bound to the two proteins and (c) partitioned into intracellular membranes, for model systems that resemble conditions in the rat hepatocyte. These equations are then combined with expressions for the enzyme-catalysed metabolic reactions undergone by these small molecules to assess the influence of diffusion rats on the overall metabolic rates. It is concluded that ligandin and protein A can enhance the rate of intracellular of their ligands by an order of magnitude or more and that this could make the hepatocyte several times more efficient in metabolizing these ligands. Various ways of testing this theory are discussed.

Effects of high-fat diets on hepatic fatty acid oxidation in the rat. Isolation of rat liver peroxisomes by vertical-rotor centrifugation by using a self-generated, iso-osmotic, Percoll gradient

1. Rat liver peroxisomal fractions were isolated in iso-osmotic Percoll gradients by using vertical-rotor centrifugation. The fractions obtained with rats given various dietary treatments were characterized. 2. The effect on peroxisomal beta-oxidation of feeding 15% by wt. of dietary fat for 3 weeks was investigated. High-fat diets caused induction of peroxisomal beta-oxidation, but diets rich in very-long-chain mono-unsaturated fatty acids produced a more marked induction. 3. Peroxisomal beta-oxidation induced by diets rich in very-long-chain mono-unsaturated fatty acids can oxidize such acids. Trans-isomers of mono-unsaturated fatty acids are oxidized at rates that are faster than, or similar to, those obtained with corresponding cis-isomers. 4. Rates of oxidation of [14-14C]erucic acid by isolated rat hepatocytes isolated from rats fed on high-fat diets increased with the time on those diets in a fashion very similar to that previously reported for peroxisomal beta-oxidation [see Neat, Thomassen & Osmundsen (1980) Biochem, J. 186, 369-371]. 5. Total liver capacities for peroxisomal beta-oxidation (expressed as acetyl groups produced per min) were estimated to range from 10 to 30% of mitochondrial capacities, depending on dietary treatment and fatty acid substrate. A role is proposed for peroxisomal beta-oxidation in relation to the metabolism of fatty acids that are poorly oxidized by mitochondrial beta-oxidation, and, in general, as regards oxidation of fatty acids during periods of sustained high hepatic influx of fatty acids.

A stereological analysis of capillaries in normal and hypertrophic muscle

A realistic model of the distribution of the partially orientated capillaries in skeletal muscles has been introduced for stereological analyses. Distributional parameters not previously estimated for capillary networks in muscles have been quantified. These include the lengths of capillary per unit volume of tissue ((L(v)) and a dimensionless index of orientation (omega). The present study demonstrates that surgical techniques for inducing skeletal muscle hypertrophy can be an effective stimulus for the proliferation of additional capillaries. In the hypertrophic muscles studied the capillaries become more highly orientated. This suggests that the growth of new capillaries occurs preferentially along the long axis of the muscle.

Circadian alterations in tubular structures on the outer mitochondrial membrane of rat hepatocytes

Subcellular structures of hepatocytes were examined at 11.00 h and 23.00 h (light cycle: 06.00 h-18.00 h) in four adult male Wistar rats (AF/Han) per time period. 1. The volume density of mitochondria in the cytoplasm of hepatocytes obtained from peripheral parts of liver lobules shows a statistically significant difference between the two time periods examined. 2. Tubular structures arising from the outer mitochondrial membrane are clearly demonstrated. Their cisternae are continuous with the interspaces between outer and inner mitochondrial membranes. 3. These tubular structures often open directly into the cisternae of rough or smooth-surfaced endoplasmic reticulum (rER and sER) and form a "bridge" between the endoplasmic reticulum and mitochondria. 4. At 11.00 h, the rER connected with the tubular structures often possesses very few ribosomes; at 23.00 h, the amount of ribosomes on the rER is substantially greater. Furthermore, at 23.00 h ribosomes are also occasionally found on the membranes of the tubular structures. 5. The incidence of tubular structures on the outer membrane of mitochondria varies significantly between the two time periods. 6. The changing pattern of the volume density of mitochondria in the cytoplasm parallels that of the incidence of the tubular structures, i.e., both are high during the active phase and low during the resting phase of the rat. 7. These results suggest that the tubular structures may play an important role in protein transport between the endoplasmic reticulum and mitochondria, and in the rearrangement of rER during a 24-h period.

Quantitation of catalase activity by microspectrophotometry after diaminobenzidine staining

The absorbance of the reaction product of catalase staining with diaminobenzidine is linearly proportional to enzyme activity. This is shown in semithin Epon sections of model systems containing serum albumin and catalase from bovine or guinea pig liver. Absorbance measurements were also performed on semithin sections of guinea pig liver, and from these, the activity of cytoplasmic (extraperoxisomal) catalase has been derived.

Fluid endocytosis by rat liver and spleen. Experiments with 125I-labelled poly(vinylpyrrolidone) in vivo

1. Rates of fluid endocytosis of rat liver, spleen, hepatocytes and sinusoidal liver cells have been determined, by using 125I-labelled poly(vinylpyrrolidone) as marker. Poly(vinylpyrrolidone) was injected intravenously into rats, and plasma clearance and uptake by liver and spleen were estimated. From these data, rates of fluid endocytosis of 1.2 and 1.8 ml of plasma/g of protein per day were calculated for liver and spleen respectively. Essentially the same results were found in nephrectomized rats. 2. Hepatocytes and sinusoidal cells were separately isolated by the collagenase/Pronase method, and sinusoidal cells were further fractionated by centrifugal elutriation. Hepatocytes, sinusoidal cells, Kupffer cells and endothelial cells showed rates of fluid endocytosis of 0.96, 9.0, 19 and 13 ml of plasma/g of cell protein per day respectively. Total-body X-irradiation did not influence uptake of poly(vinylpyrrolidone) by spleen, indicating that spleen lymphocytes are not significantly involved in fluid endocytosis. 3. For liver a rate constant of exocytosis of 5% per day was found, whereas for spleen no significant loss of accumulated label could be demonstrated during a 21-day period. 4. Distribution of label over a great number of organs and tissues was measured 9 days after the injection. Liver, skin, bone and muscle together contained about 70% of the label present in the carcass; only spleen and lymph nodes contained more label per g fresh weight of tissue than liver.

Studies on the rat liver following iron overload

Sprague-Dawley rats were given Jectofer injections to obtain iron overload in rat liver Kupffer and parenchymal cells. The release of iron was studied on the light and electron microscopical level by bleeding of the iron loaded animals and comparing the results with non bled controls. During the mobilization of iron. Kupffer cells showed a rapid and almost complete disappearance of electron dense iron containing particles (IP) while there was only limited decline of IPs in the parenchymal cells. Iron was demonstrated with X-ray microanalysis at the ultrastructural level, and presence of acid phosphatase was revealed using a histochemical method based on precipitation of lead phosphate at sites of enzyme activity in combination with X-ray microanalysis. It was demonstrated that all IP-containing cytoplasmic bodies also showed presence of acid phosphatase implying that all of them represented lysosomes. The mechanism of release of iron from Kupffer and parenchymal cells was discussed with special emphasis on the role of the lysosomes and the relationship between their contents and other cellular structures.

Cell types in long-term propagable cultures of rat liver

Under the conditions of this experiment, propagable hepatic epithelial cells in long-term culture were derived from a small, nonparenchymal precursor cell present in the liver in vivo. Progeny of the nonparenchymal precursor cell weakly expressed some hepatocyte-like properties in culture. Hepatocytes were not clonogenic under the conditions of this experiment. Propagable hepatic epithelial cells in long-term culture probably originate from hepatic stem cells in vivo. Terminal biliary ductular cells are facultative stem cells for hepatocytes.

Amino acid transport in plasma membrane vesicles from isolated rat liver parenchymal cells

Plasma membrane vesicles were prepared from isolated rat liver parenchymal cells. The transport of several amino acids was studied and found to be identical to that in membrane vesicles from whole liver tissue.

Uptake and degradation of rat and human very low density (remnant) apolipoprotein by parenchymal and non-parenchymal rat liver cells

1. The relative contribution of parenchymal and non-parenchymal cells to the in vivo hepatic uptake of serum apolipoproteins was measured 30 min after intravenous injection of radioiodinated rat very low density lipoprotein (VLDL) remnants, rat and human VLDL, low density lipoprotein (LDL) and high density lipoprotein (HDL). Using rat VLDL, VLDL-remnants, LDL and HDL, respectively, the non-parenchymal cells contain 4.7, 4.9, 6.1 and 5.3 times the amount of trichloroacetic acid-precipitable radioactivity per mg cell protein as compared to parenchymal cells. For human VLDL, LDL and HDL these values are 5.1, 12.0 and 5.9 respectively. 2. The abilities of homogenates of human liver, rat liver parenchymal cells and rat liver non-parenchymal cells to hydrolyze human and rat iodinated VLDL apoprotein were determined by measuring the amount of trichloroacetic acid-soluble (non-iodide) radioactivity liberated upon incubation at the optimal pH of 4.2. Non-parenchymal cells possess a 8--21-fold higher maximal capacity to degrade VLDL apoprotein per mg of cell protein than parenchymal cells. This factor is 5--6 for VLDL-remnant apoprotein degradation measured at low (suboptimal) apolipoprotein concentrations. 3. It is concluded that, in addition to parenchymal cells, the non-parenchymal cells play an important role in the hepatic uptake and possibly degradation of VLDL-(remnant) apoprotein.

An ultrastructural and morphometric study of the liver of normal and copper-poisoned sheep

In sheep given copper (Cu) at the level of 10 ml of a 0.2% solution of CuSO4.5H2O/kg body weight, the volume density of nuclei and cytoplasm of hepatocytes increased and the volume density of the sinusoids and the space of Disse decreased. These changes were interpreted as an indication of cellular swelling. There was a significant increase in volume density, number, and absolute volume of lysosomes when Cu was given. The greatest increase in number occurred during the pre-hemolytic period (mean = 48 days), and the highest increase in volume occurred thereafter. Thus, the most extensive proliferation of lysosomes occurred in livers of the pre-hemolytic sheep, and the hemolytic sheep had the largest and heaviest lysosomes. The liver necrosis in sheep undergoing hemolysis was possible caused by hydrolytic enzymes released by the rupture of the enclosing lysosomal membranes. The significant increase in volume density of mitochondria observed in livers of sheep given Cu was due to an increase in volume (swelling) rather than an increase in number.

Selective uptake of cadmium by the parenchyumal cells of liver

The uptake of cadmium in vivo into parenchymal and non-parenchymal (sinusoidal) cells of the liver was studied by a cell-separation technique. Liver parenchymal cells accumulate cadmium more readily than do non-parenchymal cells and synthesize metallothionein. It is proposed that cadmium uptake and metabolism from injected CdCl2, is restricted almost exclusively to the liver parenchymal cells.

Induction of peroxisomal beta-oxidation in rat liver by high-fat diets

Liver peroxisomes were prepared by using a Percoll gradient in a vertical rotor. beta-Oxidation was measured in peroxisomes isolated from livers of rats fed on either high-(15% by wt.) or low- (5% by wt.) fat diets. The feeding of high-fat diets gave a 1.4-2.4-fold increase in total liver peroxisomal beta-oxidation, and a similar increase in specific activity. A 1.5-4.5-fold increase was seen in the specific activity of purified peroxisomal preparations. The reasons for these increases are discussed.

Isolation of a lipocyte-rich fraction from rat liver nonparenchymal cells

A modified pronase digestion procedure is described for isolating nonparenchymal liver cells from vitamin A treated rats, which yielded a 15-23% population of lipocytes in the total cell suspension. The criteria for defining a lipocyte was the appearance of vitamin A containing cells as determined by fluorescent microscopy. Measurement of alcohol dehydrogenase and retinol dehydrogenase activities indicated that these enzyme activities were not present in the isolated nonparenchymal cells. A lipocyte-rich fraction of nonparenchymal cells was obtained by centrifugation of purified nonparenchymal cells in a linear Metrizamide gradient. Vitamin A fluorescence and chemical assay of vitamin A in the cell fractions indicated a four-fold enrichment of lipocytes in the cell fraction with d = 1.043 g/ml. Fractions high in vitamin A also had numerous cells with fat droplets as shown by transmission electron microscopy.

Fine structure of the liver in the larval lamprey, Petromyzon marinus L.; hepatocytes and sinusoids

The ultrastructure of hepatocytes, bile canaliculi, and hepatic sinusoids of the larval lamprey, Petromyzon marinus, was examined using thin-sectioned and freeze-fractured tissues. The liver is a "tubular gland" with hepatocytes arranged in a tubular fashion around large bile canaliculi. Hepatocytes are roughly conical in shape, with their tapered apices facing a bile canalicular lumen. They possess extensive rough and smooth endoplasmic reticulum, a well-developed Golgi complex, abundant mitochondria, and varying numbers of large secondary lysosomes. Both secondary lysosomes and the Golgi complex are concentrated in the apical or peribiliary cytoplasm, indicating a possible role in bile secretion. The apical surfaces of the hepatocytes bear numerous elongate microvilli and occasional cilia, which project into the bile canaliculi. The hepatocytes are joined, apically, by junctional complexes composed of zonulae occludentes and adhaerentes. In freeze-fracture, the zonulae occludentes are of variable apicobasal depth and consist of honeycomb-like meshworks of fibrils. Spaces of variable width frequently appear in the P-face grooves, indicating that the zonulae occludentes are "leaky." Numerous communicating (gap) junctions join the hepatocytes laterally. Varying numbers of lateral microvilli project into the intercellular spaces and, basally, the plasma membrane is deeply infolded, resulting in the formation of apparently interdigitating basal processes resting upon a thin basal lamina. Sinusoids are composed of both a heavily-fenestrated, continuous endothelium, and phagocytic reticulo-endothelial (Kupffer) cells. Depsite the difference in arrangement of their hepatocytes, the mammalian and lamprey livers show similar ultrastructural features.

Exoerythrocytic merozoites of Plasmodium berghei in rat hepatic Kupffer cells

Liver biopsies of white rates infected by Plasmodium berghei sporozoites were examined by electron microscopy. Intrahepatocytic schizont development was confirmed. In addition, at 60 and 70 h after sporozoite inoculation, exoerythrocytic merozoites were noted in Kupffer cells of liver sinusoids. Although it is theoretically possible that this observation may be of merozoite development in Kupffer cells, the authors suspect that this example of phagocytosis would be one of the host's natural defenses against sporozoite-transmitted malaria.

Basic stereological relationships for quantitative microscopical anatomy--a simple systematic approach

There exists in the literature a core of formulations regarded as 'the basic stereological principles' for quantifying cell and tissue morphology. They may be used to obtain information relating component volume, surface area, length and number to a specified containing volume (the so-called component densities in a volume: VV, SV, MV and NV). However, principles may also be formulated for relating these component dimensions to a containing surface (SS, MS and NS), containing length (MM and NM) and a containing number (NN). Methods for estimating these previously neglected stereological relations are presented. Possible biological applications of the principles are also discussed.

The rapid preparation of peroxisomes from rat liver by using a vertical rotor

A method is described for the rapid preparation of peroxisomes from rat liver by using sucrose-density-gradient centrifugation in a vertical rotor. The preparation, shown to be virtually free of mitochondrial and microsomal contamination, can be used to study fatty acid metabolism by isolated peroxisomes.

NADP-dependent dehydrogenases in rat liver parenchyma. II. Comparison of qualitative and quantitative G6PDH distribution patterns with particular reference to sex differences

Qualitative histochemical G6PDH distribution patterns obtained in the liver acinus of adult male and female rats with an improved method (Rieder et al., 1978) served as a basis for the isolation by microdissection of tissue samples of defined zonal affiliation. G6PDH activity was assayed quantitatively in tissue samples of zones 1 and 3 by a microfluorometric method, using the oil well technique and enzymatic cycling (Burch et al., 1963; Lowry and Passonneau, 1972). With the use of a correlation system further evidence could be presented for the validity of the recently described qualitative distribution patterns. From a total of 50 analyzed tissue samples the following G6PDH activities were calculated: 4.25 +/- 1.56 U/g dry weight in zone 1 and 2.08 +/- 0.46 U/g dry weight in zone 3 of male and 7.21 +/- 1.03 U/g dry weight in zone 1 and 11.10 +/- 2.56 U/g dry weight in zone 3 of female rats. These data were corrected for interference from the G6PDH activity of the Kupffer cells within zone 1 samples (approximately 80 U/g dry weight), so that the actual relative values for the parenchymal activity could be estimated for the first time: 2 U/g dry weight in zones 1 and 3 of male animals, 5 U/g dry weight in zone 1 and 11 U/g dry weight in zone 3 of female animals. In female livers G6PDH activity in zone 1 is therefore 2.5 times higher, and in zone 3 5 times higher than in the male. These zonal as well as sex-differences are clearly indicative of a heterogeneous functional organization of the liver acinus in terms of capacity for NADPH production, mainly in connection with reductive reactions in fatty acid synthesis.

Identification of G6PDH-active sinusoidal cells as Kupffer cells in the rat liver

The aim of this study was to identify the G6PDH-active sinusoidal cells in the rat liver described by Rieder et al. (1978). Because of their number and distribution in the liver parenchyma, endothelial cells and pit cells could be excluded. Fat-storing cells were specifically marked by vital staining with vitamin A and identified by fluorescence microscopy. Kupffer cells could be detected after vital staining with carmine. Both staining methods allowed a subsequent incubation for the demonstration of G6PDH activity in the same unfixed cryostat section. Whereas more than 80% of the fluorescent particles were found outside the enzyme-positive cells, all G6PDH-active cells contained carmine particles. After counting the G6PDH-active cells, an estimation of 0.217 x 10(8) cells/g liver tissue was obtained. The results indicate that high G6PDH activity is common to all Kupffer cells, and is therefore a highly specific marker enzyme for this class of sinusoidal liver cells.

Effects of hormones on changes in cytochrome P-450, prolyl hydroxylase, and glycerol phosphate acyltransferase in primary monolayer cultures of parenchymal cells from adult rat liver

Previous studies have shown that isolation and primary culture of rat hepatocytes in a standard, chemically defined medium is associated with selective changes in microsomal function. These changes were found to be selectively sensitive to addition of hormones to the culture medium. The concentration of cytochrome P-450 declined dramatically during the first 24 hours of incubation. However, cytochrome P(1)-450, a form of the hemoprotein induced by polycyclic aromatic hydrocarbons, was resistant to this change. Cytochrome P(1)-450 levels selectively rose during the first ten hours in culture and, thereafter, declined at a less rapid rate than did the cytochrome P-450 in normal hepatocytes or in cells prepared from phenobarbital pretreated animals. Addition of dexamethasone to the medium at the time of cell plating partially prevented the fall of cytochrome P-450 and of (14)C-heme in microsomes prepared from hepatocytes derived from rats given 5(14)[C]-δ-aminolevulinic acid. This suggests that the steroid decreases degradation of the hemoprotein. As compared to the loss of cytochrome P-450 in cultures of normal hepatocytes, the hemoprotein fell to lower levels in hepatocytes prepared from regenerated liver four days after partial hepatectomy. This result may be related to the accelerated formation of the monolayer in the cultures of regenerated hepatocytes. Both sn-glycerol-3-phosphate acyltransferase activity and glycerol kinase activity declined in the first 24 hours of culture. The fall in the latter enzyme was partially prevented by addition of estradiol. Collagen prolyl hydroxylase, a newly discovered microsomal constituent of the hepatocyte, rose slightly during the first 24 hours in culture. This change was augmented threefold by addition of insulin to the medium. We conclude that the present hepatocyte culture system with its attendant changes in functional phenotype may be useful in better defining the role of hormones in modulating metabolic processes in the liver.

Quantitative and qualitative changes in the mitochondria in hepatocytes during postnatal development of male rats

The volume density of mitochondria increases during postnatal development of the hepatocytes of male rats (test ages: 0 [birth], 1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 14th, 21st, 28th day and 2nd, 3rd, 4th, 5th and 6th month) from 0.165 at birth to 0.236 on the 14th day, after which it decreases to 0.139 until the 6th month. At the same time the absolute volume of the mitochondria of the hepatocytes increases from 728.8 micrometer 3 at birth to 1225.5 micrometer 3 on the 14th day and reaches a maximum of 2102.3 micrometer 3 at the end of the 2nd month. The number of mitochondria per hepatocyte is 204 at birth. It increases continuously and reaches 2199 at the end of the 6th month. The volume of the average mitochondrion on the other hand diminishes during postnatal development from 3.83 micrometer 3 at birth to 0.64 micrometer 3 towards the end of the 6th month. Transverse divisions of mitochondria, budding of parts of mitochondria, autophagocytotic processes and degenerative changes can be observed throughout this period.

Cell membrane potential and resistance in liver

1. Isolated segments of mouse liver were placed in a Perspex bath through which physiological saline solutions of varying composition were circulated. Two microelectrodes were inserted in different liver cells under microscopic control allowing measurement of distance between the two micro-electrode tips. Current pulses were injected through one of these electrodes, causing electrotonic potential changes in nearby cells by current spread through intercellular junctions. These electrotonic potential changes were recorded with the second micro-electrode. The spatial decrement of the amplitude of the electrotonzpotential changes and their dependence on extracellular ion concentrations were analysed by three-dimensional cable analysis, modified to account for the geometry of the tissue. 2. During exposure to control solution the mean resting cell membrane potential was -37 mV, the space constant for intracellular current spread (lambda3 = square root of Rm/chrRi) was 390 micron and Ri, a measure which includes the intracellular resistivity and the junctional resistances, was 1.4 komegacm. From these values, and an estimate of tissue cell membrane density (chi) obtained by others, the specific membrane resistance (Rm) was calculated to be 5.1 komegacm2. 3. Replacement of extracellular Na+ by K+ resulted in a large depolarization and a large decrease in the membrane resistance. Replacement of extracellular Na+ by choline resulted in a small transient hyperpolarization and a small increase in the membrane resistance. Replacement of extracellular Cl- by methylsulphate or sulphate or of NaCl by sucrose resulted in a small transient depolarization and a large increase in the membrane resistance. 4. Glucagon (10(-7) M) and adrenaline (10(-5) M) evoked membrane hyperpolarization and reduction of membrane resistance (Rm). 5. The resting membrane ion conductance can be considered to consist of three components, Cl conductance (GCl), GK and GNa. The results suggest that GCl greater than GK greater than GNa. Changes in extracellular ion concentrations specifically alter the permeability properties of the cell membrane. The glucagon action can be explained in part by an increase in GK.

Plasma clearance of glycoproteins with terminal mannose and N-acetylglucosamine by liver non-parenchymal cells. Studies with beta-glucuronidase, N-acetyl-beta-D-glucosaminidase, ribonuclease B and agalacto-orosomucoid

Glycoproteins having mannose and/or N-acetylglucosamine in the terminal non-reducing position [Stockert, Morell & Scheinberg (1976) Biochem. Biophys. Res. Commun. 68, 988--993], and various lysosomal enzymes [Stahl, Schlesinger, Rodman & Doebber (1976) Nature (London) 264, 86--8] are rapidly cleared from plasma by the liver after intravenous administration. A liver cell-separation technique was used to determine the cellular localization of 125I-labelled beta-glucuronidase, ribonuclease B, agalacto-orosomucoid and asialo-orosomucoid. On a specific readioactivity basis, all ligands except 125I-labelled asialo-orosomucoid were enriched in the non-parenchymal cell fraction. Isolated cells, fixed and stained for beta-glucuronidase or N-acetyl-beta-D-glucosaminidase activity after intravenous injection of the enzymes, showed enrichment in the non-parenchymal cell fraction (probably Kupffer cells). After uptake by the non-parenchymal cells, liver lysosomal beta-glucuronidase and N-acetyl-beta-D-glucosaminidase showed degradation half-times of 2.2 and 0.4 days respectively.

A quantitative analysis of hepatic ultrastructure in rats during enhanced bile secretion

The ultrastructural changes in hepatocytes of rats subjected to selective biliary obstruction (SBO), wherein the biliary system draining approximately two-thirds of the liver is obstructed, were evaluated by quantitative electron microscopy or stereology. The remaining unobstructed portion of the organ compensates for this loss of bile secretion by functioning in a hypersecretory mode. This animal model permits the comparison of hepatocellular fine structure associated with the conditions of nonsecretion and hypersecretion of bile with that found in normal secreting sham-operated rats. Since recent evidence suggests the presence of lobular gradients in hepatic structure and function, both centrolobular and periportal hepatocytes were examined. The low incidence of Golgi membrane profiles in high magnification electron micrographs results in a low confidence level of sampling and, thus, necessitates the application of a novel parameter for estimating the amount of Golgi complex, i.e., the Golgi-rich area. For the most part, the lobular variation in hepatic fine structure in the sham-operated animals was similar to that described by Loud ('68). However, the periportal parenchyma contained approximately twice the volume of Golgi-rich area as the centrolobular tissue. The amount of cytoplasmic lipid increased significantly in the SBO unobstructed lobes, although there were few or no changes in the other intracellular organelles or inclusions except those related to the Golgi complex. The volume of Golgi-rich area increased significantly in the centrolobular tissue of the SBO unobstructed (hypersecretory) lobes to the extent that both intralobular zones contained similar amounts of this component. These data suggest that the Golgi complex is a dynamic unit which responds to changes in hepatocellular activity and may be involved in bile secretion.