Presence of Chromatium vinosum chaperonins 10 and 60 in mitochondria and peroxisomes of rat hepatocytes

In the present study we report the occurrence of chaperonins, cpn10 and cpn60, in Chromatium vinosum and rat hepatocytes, using specific polyclonal antibodies in conjunction with the protein A-gold immunocytochemical technique. As demonstrated by quantitative evaluations, the immunolabeling for cpn10 and cpn60 in C vinosum cells was associated primarily with the bacterial cell envelope. In rat liver homogenates, Western immunoblotting analysis has shown that antibodies to cpn10 from C vinosum recognize an unique 25-kDa protein that remains to be further characterized. On the other hand, the antibody to cpn60 from C vinosum revealed the presence of a 60-kDa protein in the rat liver homogenates. Immunofluorescence on rat liver tissue revealed an intracellular granular labeling for both chaperonins. On the other hand, using the post-embedding immunoelectron microscopy technique cpn10 and cpn60 were localized specifically in liver mitochondria and peroxisomes. Interestingly, further analysis of the labeling distribution confirmed the association of both proteins with the mitochondrial inner membrane whereas in the peroxisomes the chaperonins appeared to be located in the matrix, away from the limiting peroxisomal membrane. The colocalization of both chaperonins suggests that, as in other bacteria as well as eukaryotic cells, they may act in tandem for the proper folding of particular proteins.

Involvement of molecular chaperones in the aberrant aggregation of secretory proteins in pancreatic acinar cells

Molecular chaperones have recently been shown to be accurately located along distinct cellular compartments of the secretory pathway of pancreatic acinar cells. Since the aberrant aggregation of secretory proteins leading to the formation of RER intracisternal crystals induced by DL-p-chlorophenylalanine methyl ester (CPME) comprises major changes in the sorting, selective transport, and/or posttranslational modifications of secretory proteins, we decided to investigate the possible involvement of chaperones in this phenomenon by applying the protein A-gold immunocytochemical approach. In addition to their presence in the cellular compartments of the secretory pathway, the chaperonins cpn10 and cpn60 were found to also be concentrated in the RER intracisternal crystals. In contrast, the hsp70 protein remained confined to the trans-Golgi network and was absent from the crystals. In both control and experimental conditions the three chaperones were present in mitochondria. Quantitative evaluations confirmed these observations and revealed an overall decrease in the labeling, particularly for hsp70 after CPME treatment. These labeling patterns suggest a participation of the chaperonins cpn10 and cpn60 but not of the hsp70 in the aberrant aggregation of secretory proteins leading to RER crystal formation. The role played by chaperones in this process, however, remains to be elucidated.

Endocrine cells in the rat pancreatic and bile duct system: alteration in diabetes

Endocrine cells of the pancreatic and bile duct system of the diabetic rat were characterized with reference to their influence on duct function. In streptozotocin-induced diabetic rats, the endocrine cells showed various changes in number and topographic distribution along the epithelial lining of the duct system. With the exception of insulin cells, which demonstrated a marked decrease, the number of duct endocrine cells generally increased in the duct system of the diabetic animal, particularly in the terminal portion of both the common hepatic and the accessory pancreatic ducts encompassed by the muscle sphincters. Among them, the cells secreting somatostatin, a potential peptide inducing contraction of the muscle sphincter, showed a remarkable increase in the opening portion of the common hepatic and the accessory pancreatic ducts of the diabetic animal. The duct cells producing glucagon and pancreatic polypeptide, the hormones exerting an inhibitory effect on exocrine secretion of duct and acinar cells, also increased significantly in the duct system of the diabetic animal. These results suggest that the duct endocrine cells are closely related, not only to functional properties of the duct system, but also to disorders of the pancreas and biliary tract in diabetes.

Molecular chaperones in pancreatic tissue: the presence of cpn10, cpn60 and hsp70 in distinct compartments along the secretory pathway of the acinar cells

Three chaperones, the chaperonins cpn10 and cpn60, and the hsp70 protein, were revealed by immunochemistry and cytochemistry in pancreatic rat acinar cells. Western immunoblotting analysis of rat pancreas homogenates has shown that antibodies against cpn10, cpn60 and hsp70 protein recognize single protein bands of 25 kDa, 60 kDa and 70 kDa, respectively. Single bands for the cpn10 and cpn60 were also detected in pancreatic juice. Immunofluorescence studies on rat pancreatic tissue revealed a strong positive signal in the apical region of the acinar cells for cpn10 and cpn60, while an immunoreaction was detected at the juxtanuclear Golgi region with the anti-hsp70 antibody. Immunocytochemical gold labeling confirmed the presence of these three chaperones in distinct cell compartments of pancreatic acinar cells. Chaperonin 10 and cpn60 were located in the endoplasmic reticulum, Golgi apparatus, condensing vacuoles and secretory granules. Interestingly, the labeling for both cpn10 and cpn60 followed the increasing concentration gradient of secretory proteins along the RER-Golgi-granule secretory pathway. On the contrary, the labeling for hsp70 was mainly concentrated in the endoplasmic reticulum and the Golgi apparatus. In the latter, the hsp70 was found to be primary located in the trans-most cisternae and to colocalize with acid phosphatase in the trans-Golgi network. The three chaperones were also present in mitochondria. In view of the role played by the chaperones in the proper folding, sorting and aggregation of proteins, we postulate that hsp70 assists the adequate sorting and packaging of proteins from the ER to the trans-Golgi network while cpn10 and cpn60 play key roles in the proper packaging and aggregation of secretory proteins as well as, most probably, in the prevention of early enzyme activation in secretory granules.

Biochemical and morpho-cytochemical evidence for the intestinal absorption of insulin in control and diabetic rats. Comparison between the effectiveness of duodenal and colon mucosa

A combined biochemical and morpho-cytochemical investigation was carried out in order to assess insulin absorption by the duodenal and colon epithelium. Insulin was introduced in the lumen of the rat duodenum or colon in combination with sodium cholate and aprotinin. Blood analysis made at several time points has demonstrated a rapid increase in circulating levels of insulin followed by significant and consistent decreases in blood glucose. This indicates that biologically active insulin is absorbed by the intestinal mucosa and transferred to the circulation. Because of the initial high blood glucose levels, the lowering of the glycaemic values was more significant in diabetic animals. Also, levels of circulating insulin remained higher for longer time when the administration was performed in the colon. The integrity of the intestinal wall after insulin administration, evaluated morphologically, was retained. Application of protein A-gold immunocytochemistry has established the pathway for insulin absorption. In both duodenal and colon epithelial cells the labelling for insulin was detected in the endosomal compartment, in the Golgi apparatus and in association with the baso-lateral plasma membrane interdigitations. Some labelling was also present in the interstitial space and in capillary endothelial plasmalemmal vesicles. Insulin introduced in the lumen of the rat duodenum and colon appears thus to be rapidly internalized by the epithelial cells and transferred through a transcytotic pathway to the interstitial space from which it reaches the blood circulation. This exogenous insulin then induces significant decreases in plasma glucose levels which lasts for several hours. The results obtained support the possibility for the clinical development of an oral preparation of insulin.

Compartmentalization of secretory proteins in pancreatic zymogen granules as revealed by immunolabeling on cryo-fixed and molecular distillation processed tissue

Immunogold labeling of amylase obtained over zymogen granules of rat pancreatic acinar cells processed through cryofixation, molecular distillation drying and embedding in resins was found to be of high intensity and displayed a particular pattern. Indeed, it was concentrated in certain areas of the granules leaving others devoid of gold particles. This pattern of labeling reflects a strong compartmentalization of the secretory proteins within each granule. In order to assess this phenomenon, we have compared the intensities and the pattern of distribution of the labelings in tissues processed through: chemical fixation with embedding in various resins, cryo-ultramicrotomy and cryo-fixation followed by molecular distillation drying. Serials sections and double labeling experiments were performed for further evaluation of the results and for assessing artefactual displacement of proteins during tissue preparation. The results obtained indicate that the secretory proteins are indeed segregated within the granule which appears thus as a well organized structure. Cryo-fixation combined with molecular distillation appears thus to be superior in terms of preservation of protein antigenicity and retention of cellular components close to their living state.

Intracisternal crystals in pancreatic acinar cells: failure in the distinct aggregation of secretory proteins

Mechanisms leading to the formation of crystalline inclusions in the cisternal space of the rough endoplasmic reticulum are poorly understood. This phenomenon was investigated in pancreatic acinar cells using two different experimental models: 1) Intraperitoneal injection of DL-p-chlorophenylalanine methyl ester, and 2) culture of isolated acinar cells within the Matrigel basement membrane in the presence of 2% dimethyl sulfoxide. Features and composition of induced crystals were analyzed by protein A-gold and lectin-gold cytochemistry, electron microscope autoradiography, electron energy loss spectroscopic imaging and energy dispersive X-ray analysis. Crystal formation occurred in ribosome partially free rough endoplasmic reticulum (RER) regions and was similar in both experimental protocols. The protein A-gold revealed the presence of nine major pancreatic enzymes in the crystals. However, the labeling intensities varied among enzymes with higher concentrations of amylase than chymotrypsinogen when compared to the secretory granules. Concanavalin A and Helix pomatia labelings were weak over the crystals and did not correspond to those of RER or secretory granules. Sulfur contents in crystals were lower than phosphorus and their ratio was opposite to the one found in secretory granules. Electron microscope autoradiography demonstrated incorporation of radiolabeled leucine and presence of newly synthesized proteins in the crystals. Furthermore, cells containing both crystals and secretory granules displayed silver grains in most of the cellular compartments involved in secretion. Thus, failure in the normal concentration and sorting process of secretory proteins leading to crystal formation includes changes in protein glycosylation and decrease of disulfide bond formation while retaining secretory capabilities.

Differentiation of pancreatic acinar cells into duct-like cells in vitro

BACKGROUND

Previous studies have shown that a combination of both the extracellular matrix and secretagogues plays critical roles in the maintenance of well-differentiated pancreatic acinar cells in culture. In the present study, we have shown that, upon proper stimulation, acinar cells change their growth pattern and morphologic appearance to a duct like phenotype.

EXPERIMENTAL DESIGN

Both rat and guinea pig acinar cells were cultured on or embedded into the Matrigel basement membrane, in the presence of differentiating agents such as dimethylsulfoxide (DMSO), hexamethyl-bis-acetamide, dimethylformamide, triiodothyronine, and butyric acid. The growth patterns, cell proliferation, ultrastructural appearance, intracellular contents, secretion and immunolocalization of amylase, as well as the expression of the ductal marker carbonic anhydrase II and lectin-binding specific sites were analyzed. Moreover, the effects of metabolic inhibitors such as cycloheximide and actinomycin D on the DMSO induced action were also examined.

RESULTS

Isolated acinar cells from both rat and guinea pig pancreas showed an important modification of their growth pattern and morphologic appearance when culture embedded into Matrigel in the presence of 2% DMSO. They reaggregate and form isolated branched tubular structures lined by a single cell layer. These tubules can be maintained in culture for over a period of 21 days. The cells lining the tubules were originally acinar cells that became elongated and progressively lost their secretory granules. They displayed a lower number of apical microvilli and established long junctional complexes with elaborated interdigitations. The immunocytochemical localization and biochemical determination of intracellular and secreted amylase revealed a progressive decrease reaching minimal values by the 12th day of culture. The cells further expressed the duct cell marker carbonic anhydrase II and lost the Helix pomatia lectin-binding affinity characteristic of acinar cells. Cell proliferation by modified cells as measured by thymidine incorporation and the autoradiographic labeling index, was significantly lower than in control cultured acinar cells. The DMSO differentiating action was mimicked, but to a lesser extent, by the other agents except butyric acid. Since cycloheximide and actinomycin D inhibited the DMSO-induced changes, protein synthesis and DNA transcription seem to be required.

CONCLUSIONS

Our results demonstrate that normal pancreatic acinar cells retain a morphogenetic plasticity and, upon particular stimulation, can change their differentiation commitment pattern toward that of the duct cell phenotype.

Development of the endocrine cells in the rat pancreatic and bile duct system

Morphological features of the endocrine cells in the duct system of the pancreas and the biliary tract have been recently characterized in the adult animal with respect to their physiological roles. In the present study, we have investigated their chronological appearance as well as their developmental progress at various stages of the rat fetal and postnatal life. On day 12 of gestation, glucagon and insulin, as well as CCK cells, were identified in the pancreatic primordium. On day 14, glucagon and CCK cells were first detected in the epithelial lining of the common hepatic and the hepatic ducts. These cells remained the dominant endocrine type in the duct system during the fetal period. Insulin and pancreatic polypeptide cells were first observed in the common hepatic duct only on days 16 and 18 of gestation respectively. In spite of their presence in the islets, somatostatin cells were not detected in the duct system during fetal life. They started to appear in the accessory pancreatic duct of the neonate, and subsequently in the common hepatic duct as well as in the small pancreatic ones on day 7 after birth. During postnatal development, the endocrine cells showed progressive or retrogressive changes in different portions of the duct system according to the cell type. In general, somatostatin, CCK and pancreatic polypeptide cells showed an increase, while glucagon and insulin cells gradually dwindled in number up to the adult stage. Somatostatin cells exhibited a significant increase in number, becoming the highest population among the duct endocrine cells in the adult. Throughout the developmental progress, the endocrine cells appear to be allocated in regions relevant to their possible influence modulating the exocrine secretion as well as the drainage of the pancreatic and bile fluid.

Ultrastructural localization of DNA in immune deposits of human lupus nephritis

DNA molecules were revealed in the glomerular wall of lupus nephritis patients by applying two specific colloidal gold cytochemical approaches at the electron microscope level: immunocytochemistry using a monoclonal anti-DNA antibody in conjunction with protein A-gold and enzyme-gold cytochemistry using DNAse-gold complexes. Application of both techniques has demonstrated that DNA molecules are preferentially located over the electron-dense deposits found in the glomerular basement membrane and mesangial matrix of SLE patients, as well as over the nuclei. Their distribution within the glomerular wall was correlated with electron-dense immune deposits revealed by anti-light chain antibodies. In normal control kidney, DNA labeling was restricted to the cell nuclei. Several control experiments have demonstrated the high specificity of the results. These data thus suggest a possible role for DNA as an antigenic component in the formation of immune complexes.

Absence of trypsinogen autoactivation and immunolocalization of pancreatic secretory trypsin inhibitor in acinar cells in vitro

To establish the significance of the addition of trypsin inhibitors to pancreatic acinar cells maintained in vitro, cells were cultured in the presence or absence of soybean trypsin inhibitor. Both cultures exhibited similar growth pattern, ultrastructural appearance, as well as secretory properties. Moreover, there was no evidence of trypsinogen activation in the culture medium. Using the immunocytochemical approach, pancreatic secretory trypsin inhibitor antigenic sites were revealed with specific polyclonal and monoclonal antibodies. The results obtained demonstrated that this trypsin inhibitor is in fact a typical pancreatic secretory protein being processed through the endoplasmic reticulum-Golgi-granule secretory pathway of the acinar cells in rat and human tissues. While the polyclonal antibody yield labelings of increasing intensities along the secretory pathway, the monoclonal one probably due to the molecular nature of its specific antigenic determinant, gave higher labelings in the endoplasmic reticulum. In conclusion the present study has shown that pancreatic acinar cells secrete a specific pancreatic trypsin inhibitor which most probably is involved in the mechanism to prevent trypsinogen activation.

Pathway of insulin in pancreatic tissue on its release by the B-cell

Insulin was revealed in the extracellular space and blood capillaries of the rat pancreas by applying protein A-gold immunocytochemistry. On the discharge by the B-cell, insulin diffuses in the extracellular space and interacts with the plasma membrane of all pancreatic cells. For the B-cell, the interstitial microvillar plasma membrane domain was preferentially labeled compared with the flat domain. In contrast, the digitations and flat domains of the basal plasma membrane of the acinar cells were equally labeled. In the endothelium, the labeling was superior in fenestrated areas than in the high cytoplasmic ones, the fenestrae, the luminal and abluminal plasma membranes being labeled. In the cytoplasmic areas the plasmalemmal vesicles were significantly labeled; the intercellular junctions were not. These results indicate that upon binding to the membrane, the transfer of insulin across the capillaries occurs through both the fenestrations and the vesicular system. The labeling of insulin in the subendothelial space and blood capillaries decreased significantly from the insular to the peri-insular and further to the teleinsular regions, demonstrating that insulin levels, high in insular tissue, decrease very rapidly as insulin circulates through and out of the pancreas. The pancreatic cells are thus exposed to very high levels of insulin that vary according to the regions, probably contributing to the topographical partition of the acinar parenchyma into peri-insular and teleinsular tissues.

Poly-L-lysine-gold probe for the detection of anionic sites in normal glomeruli and in idiopathic and experimentally-induced nephrosis. A comparative ultrastructural study

Anionic sites play a key role in the charge selectivity of glomerular filtration as well as in the maintenance of the structural integrity of the visceral epithelium and podocytes. Alterations in these sites are believed to be a major factor underlying human idiopathic nephrosis and puromycin-nephrosis in the rat. The poly-L-lysine-gold complex was used for the ultrastructural detection of anionic sites in renal glomeruli of patients with idiopathic nephrosis as well as of rats with puromycin-induced nephrosis, allowing for study of the changes occurring in the anionic sites during nephrosis and for the comparison between human disease and this experimental model. In both normal human and rat controls, the probe was detected on epithelial and endothelial cell surfaces and on the glomerular basement membrane, mainly in both laminae rarae. In proteinuric rats, a decrease in labeling intensity was noted on podocyte membranes and in the lamina rara externa, with a corresponding increase in the more central areas of the glomerular basement membrane. These changes were not as evident in proteinuric humans. Furthermore, a reduction in labeling density was noted in the glomerular basement membrane of proteinuric animals, although this could not be substantiated in human tissues. Poly-L-lysine-gold is a useful probe for anionic sites in fixed tissues, and allows for comparison between human disease and its experimental counterpart.

Hapten-tagged plasma proteins as immunocytochemical probes for the study of vascular permeability

Bovine serum albumin and transferrin were covalently coupled with fluorescein isothiocyanate and digoxigenin, respectively, and intravenously co-injected in equal amounts in mouse. The derivation of the two proteins induces minor alterations of their physicochemical properties as well as of their physiological functions. The two tracers were revealed within vascular and extravascular compartments of diaphragm by quantitative postembedding immunocytochemistry, using antibodies against each of the haptens in conjunction with the protein AG-gold complexes. The influence of different fixatives and embedding protocols on the immunodetectability of the hapten-tagged proteins was assessed. Both resist reasonably well to osmication and embedding in Epon. None of the haptens reacted with the heterologous antibody. At 30 minutes after injection, the tracers were detected in blood plasma, interstitium, and endothelial plasmalemmal vesicles. The presence of both proteins within the interendothelial clefts was inconspicuous. The ratios between the labeling densities found over endothelium, interstitial space, and vascular lumen were similar for both tracers. This suggests that the endothelium of mouse diaphragm capillaries might exhibit comparable permeabilities towards serum albumin and transferrin which are similar in size and charge. The study shows that hapten-tagged polypeptides are close to the corresponding native macromolecules, and represent interesting tools for the morphological study of dynamic processes such as transcytosis.

Differences in secretory granule content in pancreatic acinar cells from peri-insular and tele-insular regions

By applying morphometrical and quantitative double immunocytochemical techniques, differences in size and in amylase and chymotrypsinogen contents were found among pancreatic zymogen granules. These differences were present in granules of peri-insular and tele-insular acinar cells, the peri-insular ones displaying higher numbers of granules of smaller sizes. No correlation was found among enzyme contents in individual granules, nor was there a correlation between enzyme content and granule size. The results suggest that each individual secretory granule is formed in an independent way and that each enzyme is processed and packaged into granules independently. The differences among granules may be associated with nonparallel secretion, since this phenomenon has been reported in the intracellular processing of secretory enzymes. This hypothesis, however, remains to be demonstrated.

Immunocytochemical study of glomerular permeability to anionic, neutral and cationic albumins

The renal handling of albumin of various isoelectric points (pI) was studied in mice by high resolution quantitative immunocytochemistry. Bovine serum albumin (BSA) was tagged with dinitrophenol (DNP) and cationized to pI 6.5 to 7.5 and to pI over 8.5. These tracers, including the anionic BSA-DNP (pI 4.8) were injected in the iliac vein of mice and the post-embedding protein A-gold technique was used with antibodies against DNP to localize the different tracers in renal tissue. Morphometric analysis of the labeling over the glomerular wall has demonstrated variations in its distribution according to the pI of the markers. Anionic and neutral BSA molecules were detected on the endothelial side of the basement membrane, while labeling for cationic BSA was present mainly in the laminae rarae interna and externa known to display fixed polyanionic sites. Neutral and cationic BSA-DNP reached the urinary space and were detected within the endocytotic apparatus of the proximal tubule epithelium. Neutralization of the anionic sites of the basement membrane with cationic BSA resulted in an increase in the permeability towards anionic BSA-DNP. In addition to the demonstration of glomerular permeability properties towards various probes, the present study has demonstrated that dinitrophenylated albumin represents an excellent versatile tool for the quantitative morphological investigation of glomerular permeability.

Transendothelial transport of serum albumin: a quantitative immunocytochemical study

The steady-state distribution of endogenous albumin in mouse diaphragm was determined by quantitative postembedding protein A-gold immunocytochemistry using a specific anti-mouse albumin antibody. Labeling density was recorded over vascular lumen, endothelium, junctions, and subendothelial space. At equilibrium, the volume density of interstitial albumin was 18% of that in circulation. Despite this large difference in albumin concentration between capillary lumen and interstitium, plasmalemmal vesicles labeling was uniformly distributed across the endothelial profile. 68% of the junctions displayed labeling for albumin, which was however low and confined to the luminal and abluminal sides. The scarce labeling of the endothelial cell surface did not confirm the fiber matrix theory. The kinetics of albumin transcytosis was evaluated by injecting radioiodinated and DNP-tagged BSA. At 3, 10, 30, and 60 min, and 3, 5, and 24 h circulation time, blood radioactivity was measured and diaphragms were fixed and embedded. Anti-DNP antibodies were used to map the tracer in aforementioned compartments. A linear relationship between blood radioactivity and vascular labeling density was found, with a detection sensitivity approaching 1 gold particle per DNP-BSA molecule. Tracer presence over endothelial vesicles reached rapidly (10 min) a saturation value; initially localized near the luminal front, it evolved towards a uniform distribution across endothelium during the first hour. An hour was also needed to reach the saturation limit within the subendothelial space. Labeling of the junctions increased slowly, out of phase with the inferred transendothelial albumin fluxes. This suggests that they play little, if any, role in albumin transcytosis, which rather seems to proceed through the vesicular way.

Characterization of the endocrine cells in the pancreatic-bile duct system of the rat

Six types of endocrine cells showing immunolabelling against gut or pancreatic islet hormones were identified in the pancreatic-bile duct system of the normal adult rat at the light and electron microscopic levels. They were located within the epithelial lining of the duct system from the intercalated portion to its duodenal opening. However, the distribution and frequency of each endocrine cell varied along the length of the duct system. While insulin, glucagon, somatostatin, and pancreatic polypeptide cells were widely distributed along the entire duct system, small numbers of cholecystokinin and serotonin cells were confined to the terminal portion. A considerable number of somatostatin cells were concentrated in gland-like pouches of the terminal portion of the common pancreatic-bile duct. When the accessory pancreatic duct was present, insulin, glucagon, and somatostatin cells were also found in its epithelial lining. Electron microscopically, the specific content of the secretory granules of all endocrine cells was confirmed by immunolabelling or cytochemical staining. Further the characteristics of the secretory granules of each endocrine cell type corresponded to those present in the same kind of endocrine cells in gut or pancreatic islet. The duct endocrine cells displayed a particular ultrastructural appearance. The "open type cells" were highly polarized, with their apical cytoplasmic process reaching the duct lumen, whereas "closed type cells" showed long basal cytoplasmic processes with no connection with the duct lumen. In general, insulin, and somatostatin cells were of the "open type", while no morphological connection with the duct lumen was found for glucagon and pancreatic polypeptide cells. The presence of various duct endocrine cells with their particular ultrastructural appearance implies that they may take part in modulating the function of the duct system.

Association of secreted insulin with particular domains of the pancreatic B-cell plasma membrane: the actin-rich microvilli

Association of insulin with the plasma membrane of the pancreatic B-cell was revealed using the high-resolution protein A-gold immunocytochemical approach. The labeling was found to be heterogeneously distributed, the plasma membrane of the actin-rich microvilli being preferentially labeled. Morphometrical evaluation of labeling intensities confirmed the microvilli location of the insulin binding sites. This membrane domain, which also displays the glucose transporter, therefore appears to play important functional roles in the secretory activity of the B-cell. That the autocrine influence insulin exerts on its own secretion is receptor mediated through these insulin binding sites remains, however, to be determined.

Effect of temperature change on the permeability of eel rete capillaries

The changes in the permeability properties of the rete capillaries of the eel in response to temperature shifts were studied during countercurrent perfusion at constant flow and pressure. Tracers and oxygen were added to the arterial perfusate. From the ratio of end concentrations of arterial to venous capillaries divided by surface area, calculated from rete weight, a value for the ratio of permeability to flow, P/F, with dimensions in centimeters-2 was estimated. Because flow and surface area are constant, this provides an index of how permeability varies with time. A group of paracellular (albumin, sucrose, and sodium) and cellular (antipyrine, water, and oxygen) probes were used. When the temperature of the perfusate was raised abruptly from 25 degrees C to 35 degrees C, P/F values rose continuously and irreversibly from 0.042 +/- 0.009 to 0.281 +/- 0.112 cm-2 (mean +/- SEM) for 125I-albumin, from 0.082 +/- 0.006 to 1.74 +/- 0.070 cm-2 for [14C]sucrose, and from 0.32 +/- 0.06 to 2.78 +/- 0.62 cm-2 for 22Na, whereas they were not modified for [14C]antipyrine, [3H]water, and O2. Gradual increase of temperature was accompanied by a smaller rise in sucrose and sodium permeability and no change in albumin permeability; with decrease, the change was reversible.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelial cell protrusions in the rat aortic wall. Immunocytochemical evidence for an alternative transendothelial passage of plasma proteins

Focal morphological changes in the endothelial lining were observed in the aortic wall of control rats. They consisted of endothelial cytoplasmic projections and vacuolar structures protruding towards the luminal space and containing electron-dense material. Some of these structures were observed to open into the subendothelial space. Endogenous albumin was detected in these compartments by applying protein A-gold immunocytochemistry to thin tissue sections of glutaraldehyde-fixed, Lowicryl-embedded aortic segments. The labelling was mainly distributed along the plasma membrane of the projections as well as over the dense content of the endothelial protrusions. The presence of endogenous albumin in these endothelial structures, together with their opening into the subendothelial space, suggests a role for these structures in an alternative transendothelial transport of albumin.

Ultrastructural localization of endogenous albumin in human aortic tissue by protein A-gold immunocytochemistry

The presence of endogenous plasma albumin in human aortas was demonstrated by immunocytochemical procedures. The protein A-gold approach, combining high resolution and specificity, was applied at the light and electron microscope levels to determine the in situ cellular and extracellular localization of albumin on tissue sections derived from normal and atherosclerotic human aortas. The distribution of albumin across the aortic wall interstitium was found to be uneven, with low to moderate staining intensities in the aortic subendothelial space, low intensities in the media, and high intensities around the vasa vasorum in the adventitia. Albumin was associated with collagen fibers as well as with the electron-dense material bordering the elastic laminae in both normal and pathologic tissues. Extracellular multilamellar structures were found to be characteristic of the necrotic areas of atherosclerotic aortas. These structures were intensely labeled for albumin, with the labeling being closely associated with the membranes. Numerous smooth muscle cell-derived and monocyte-derived foam cells were present in pathologic tissues, and some of their lysosomal compartments were labeled for albumin, suggesting an internalization and degradation of interstitial albumin by these cells.

Contractile proteins in podocytes: immunocytochemical localization of actin and alpha-actinin in normal and nephrotic rat kidneys

Actin and alpha-actinin immunoreactive sites have been localized at the electron microscope level by the protein A-gold immunocytochemical technique in podocytes of normal and nephrotic rat renal tissues. In normal renal glomeruli, fibrillar networks located in the core of foot processes or bundles of microfilaments interconnecting them were found to be labelled for these two cytoskeletal proteins. On the other hand, in nephrotic renal glomeruli, concomitant with the loss of podocytic foot processes a reorganization of the podocytic cytoskeleton and a concentration of some of its elements into thick uniform bands was observed. Actin and alpha-actinin were revealed in these bands. Control experiments confirmed the specificity of the labelling obtained. Our results suggest that normal podocytes contain an actin-based contractile system that might contribute to the maintenance of the particular cell shape of these cells and that the rearrangement of the podocytic cytoskeleton occurring in the nephrotic syndrome might account for the changes in the foot processes and contribute to the alteration in glomerular function.