In vitro fusion of rabbit liver Golgi membranes with liposomes

Fusion of Golgi membranes isolated from rabbit liver with liposomes was studied by lipid mixing of fluorescent lipid analogues and internal content mixing and by electron microscopic observation of transfer of horseradish peroxidase from liposomes into Golgi membranes. A monoclonal antibody was used to confirm fusion of Golgi membranes but not other contaminating vesicles. Fusion was rapid and efficient, reaching about 20% of the maximum after a 5-min incubation using small or large unilamellar dioleoylphosphatidylcholine vesicles. The fusion was dependent on temperature, decreasing at lower temperatures, and becoming nearly zero below 10 degrees C. The addition of ATP, GTP, cytosolic factors, or N-ethylmaleimide did not affect fusion. Treatments of Golgi membranes with 0.1 M Na2CO3 or 1 M KCl did not cause any changes in fusion. However, treatment with proteases inhibited fusion. These results suggest that Golgi integral membrane protein(s) are involved in fusion. Changing the medium to an isoosmotic substance, sucrose, in place of KCl or NaCl inhibited fusion. The binding assay of fluorescent liposomes to Golgi membranes showed that lowering the temperature or replacing salts with sucrose did not affect binding. However, treatment of Golgi membranes with proteases inhibited binding. Addition of phosphatidylserine or phosphatidylethanolamine to dioleoylphosphatidylcholine liposomes caused a 2-fold increase in binding and fusion. Fusion between Golgi membranes by themselves did not occur. These results provide some information on the mechanism of intracellular vesicular transport.

Ultrastructure of the basement membrane and its precursor in developing rat submandibular gland as shown by alcian blue staining

The ultrastructure of the epithelial basement membrane and membrane precursor was studied in rat submandibular rudiment and a model system of the reconstructed basement membrane, by transmission electron microscopy following alcian blue staining. Directly beneath the epithelial plasma membrane, a meshwork layer was found to consist of anastomosing thin fibers arranged as a three-dimensional meshwork (100-400 nm in thickness). Straight strands (5-10 nm in diameter) could sometimes be seen to pass through the meshwork. Adjacent to this layer, a coarse network composed of threads (20-40 nm in diameter) connected the meshwork layer with collagen fibers of the underlying connective tissue. The earliest precursors recognized in the reconstruction-model system were part of the fine-meshwork structure, and showed this structure to be a fundamental component of the basement membrane.

Changes in cell polarity during mitosis in rat parotid acinar cells

We studied the ultrastructure and cytochemistry of mitotic parotid acinar cells in vivo after induction of mitosis by isoproterenol injection. With entrance of the cells into the division cycle, the Golgi apparatus lost its characteristic stacked structure and internal polarity among the cisternae, appearing as fragments distributed throughout the cytoplasm. These fragments consisted of electron-lucent vesiculotubular structures and electron-dense 70-nm vesicles; neither component showed thiamine pyrophosphatase activity, a marker for trans cisternae of the Golgi apparatus, but the 70-nm vesicles showed a positive reaction for osmium impregnation, indicating retention of the cis nature. The rough endoplasmic reticulum was dilated and fragmented. Recovery of the structure of Golgi apparatus and rearrangement of rough endoplasmic reticulum occurred in daughter cells during telophase. These changes were the same as those observed after drug-induced inhibition of protein transport. The secretory granules were not dispersed but were divided into two groups with which centrioles were closely associated. Both groups migrated with the centrioles as far as the next interphase. The distribution of 5'-nucleotidase on the luminal plasma membrane showed no change during the process of division, thus demonstrating that surface polarity was maintained during mitosis. These changes in organelle structure and distribution may be due to the conversion of cell function from a secretory to a mitotic action.

Reconstruction of the basement membrane in a cultured submandibular gland

In a rat submandibular rudiment on day 16, both laminin (LM) and type IV collagen (Col-IV) were found in all cases to colocalize not only in the basement membrane, but also in the rough endoplasmic reticulum of the epithelial cells, indicating that the synthesis of the components of basement membrane is greatly enhanced at this particular stage of extensive branch formation. Using the submandibular gland from a 16-day embryo, the model system was developed to determine the structural organization of the basement membrane. The pre-existing basement membrane was digested with collagenase and dispase, causing its complete disappearance. The subsequent gradual reconstruction of an authentic basement membrane was confirmed by electron microscopy and immunohistochemistry of LM and Col-IV. In the model system, this recovery started at 4 h of culture, and formation was complete by 8 h. During the recovery, thick bundles of actin filaments appeared transitionally in the basal cytoplasm. Electron microscopic analysis indicated two precursor structures, aggregated fuzzy fibers (type 1 extracellular matrix (ECM)) and 10-nm-thick strand piles (type 2 ECM), and an authentic basement membrane structure appeared during the course of membrane reconstruction. LM and Col-IV were always located together in these three structures. These observations clearly indicate that the precursors, containing LM, Col-IV and most likely heparan sulfate proteoglycan, appeared to form immediately following their secretion into the extracellular space, and assembled into the rigid structure of basement membrane within 8 h. The ultrastructural and immunohistochemical process of basement membrane reconstruction appeared to coincide closely with that of the glomerular basement membrane in developing kidney.(ABSTRACT TRUNCATED AT 250 WORDS)

Exocytosis in living salivary glands: direct visualization by video-enhanced microscopy and confocal laser microscopy

Although exocytosis is widely believed to involve granule movement, membrane fusion and the emptying of granule content, direct study of these processes has been difficult in living cells because of the limited resolution of conventional light microscopy. Using video-enhanced microscopy and confocal laser microscopy, we have now studied these processes in living rat parotid and submandibular gland acinar cells. Under a differential interference contrast (DIC) microscope equipped with a CCD camera and a high speed image processor, secretory granules were in general stationary even after secretory stimulation with isoproterenol (IPR). Following IPR stimulation, however, there were abrupt changes in light intensity of secretory granules, and many granules disappeared. Confocal microscopy was then performed to confirm whether the observed changes in granules were related to membrane fusion and content release. For this, cells were perfused with the fluid-phase tracer Lucifer Yellow; confocal images thus obtained clearly demonstrated the appearance of fluorescence in omega-shaped invaginations of the apical plasma membrane which corresponded to the sites at which changes were observed in DIC images. The time sequence analyses of confocal images showed that there was a repetitive appearance and disappearance of omega-shaped fluorescent foci at the apical plasma membrane until most of the granules were depleted. During this time, there did not appear to be any significant expansion of the apical plasma membrane and if endocytic uptake of the tracer occurred, it was below the limit of detection. These observations provide new insights into the exocytotic process in salivary glands and are at variance in some respects with previous interpretations made from electron microscopy.

Microtubule-disrupting drugs blocked delivery of endocytosed transferrin to the cytocenter, but did not affect return of transferrin to plasma membrane

The fluorescence of FL cells after endocytosis of rhodamine-labeled transferrin initially appeared as a dispersed punctate pattern over the whole cell and then accumulated in the cytocenter on further incubation. In nocodazole-treated cells, the punctate fluorescence appeared along the cell edges, and stayed there on further incubation but did not accumulate in the cytocenter. The localization of transferrin was examined at the electron microscopic level with horseradish peroxidase (HRP)-labeled transferrin. Nocodazole did not affect endosome formation but affected the distribution of the endosomes. Several types of endosomes (tubular, small spherical, and microvesicular endosomes) were observed in nocodazole-treated cells, as in control cells. The endosomes were in the Golgi area of the cytocenter and also in peripheral cytoplasm in control cells. In contrast, the endosomes were only in the periplasm, along the cell edges, in nocodazole-treated cells. The uptake and release of HRP-transferrin and the release of ferric ion into the cytoplasm in nocodazole-treated cells followed in the same time-course as those in control cells. The release of transferrin was the exponential with a half-time of 12 min. The activation energy of a rate-limiting step in the recycling was 5.5 kcal.mol-1 at around 37 degrees C and increased to 29 kcal.mol-1 below 25 degrees C. These results indicated that microtubule-dependent endosome transport was faster than the overall recycling process and was independent of the return event of transferrin to the plasma membrane.

Morphological effects of brefeldin A on the intracellular transport of secretory materials in parotid acinar cells

The morphological effects of Brefeldin A (BFA) on the parotid acinar cells of a rat were investigated at the stage of active resynthesis of secretory materials following administration of the secretogogue, isoproterenol. Incubation with BFA resulted in: a) marked dilation of the rough endoplasmic reticulum (RER), b) involution of the Golgi complex to rudimentary forms which disseminated throughout the cytoplasm, and c) agenesis of secretion granules. It appears that the primary action of BFA is inhibition of the export of secretory materials from the RER toward the Golgi complexes. Histochemical staining indicated the thiamine pyrophosphatase (TPPase) positive saccules of the Golgi stack to undergo degradation in autophagic vacuoles. In contrast, small vesicles showing the osmium reducing activity characteristic of cis elements, including osmium negative vesicles, continued to be present throughout a 4-h period of investigation, indicating the cis and, most likely, medial elements to be the components of the rudimentary Golgi complexes. On removal of the drug, a large number of transport vesicles appeared immediately from the RER and carried secretory materials to the rudimentary Golgi complex, so that the organelles were rapidly reconstructed within 30-60 min, followed by the reaccumulation of secretory granules by 90 min. It is thus indicated that the size and configuration of the Golgi complex is regulated by a dynamic equilibrium of the transport of secretory materials, and that the rudimentary Golgi complex containing cis and probably medial elements may function as the smallest units of the Golgi complex for full development as seen under normal conditions.

Roles of microfilaments in exocytosis: a new hypothesis

We observed the dynamic changes in the localization of microfilaments during the exocytic secretion of rat parotid and submandibular gland acinar cells, and obtained results which led us to propose a new concept of microfilament function in exocytosis. With the electron microscopy, NBD-Phallacidin (NBD-PL) fluorescence technique and immunohistochemistry for myosin, microfilaments consisting of F-actin and myosin were localized mainly underneath the luminal plasma membrane. Microfilaments were not detectable around the secretory granules which were stored in the cytoplasm, but were clearly observed around them whose membranes were continuous with the luminal plasma membrane. When viewed with NBD-PL and myosin fluorescence, the area of fused granule membranes revealed bright fluorescence in association with the luminal border, so that the luminal membrane undergoing exocytosis appeared like a 'bunch of grapes'. When excess exocytosis was stimulated by isoproterenol (IPR), the number of individual 'grapes' increased dramatically, indicating that the secretory granules are surrounded by microfilaments after the fusion with the luminal membrane. Microfilaments thus continuously undercoat the luminal membrane during exocytosis although the exocytic process involves the dilation and subsequent reduction of the luminal membrane due to the addition and removal of secretory granule membranes. This reduction of the dilated luminal membrane following exocytosis was, however, inhibited when the microfilaments were disrupted by cytochalasin D. Following this treatment, the lumina was expanded extraordinarily and the secretory products remained in the enlarged lumina, showing that the release of secretory products is inhibited when the microfilament function is disturbed. These results indicate that 1) microfilaments are localized mainly underneath the luminal plasma membrane and act as an obstacle to exocytosis when cells are at the resting phase and 2) at the secretory phase microfilaments allow exocytosis by disorganizing their barrier system and then, by encircling the discharged secretory granule membranes, provide forces for the extrusion of secretory products through the action of the acto-myosin contractile system.

Intracellular accumulation of basement membrane components during morphogenesis of rat submandibular gland

The distribution of two basement membrane (BM) components, laminin (LN) and type IV collagen (COLL IV), during acino-tubular morphogenesis of rat submandibular gland was examined immunohistochemically to determine the role of BM in the development of acino-tubular structures. On day 14 of gestation, LN could be found only in the BM separating an undifferentiated cell cluster of gland epithelium from surrounding mesenchyme. However, during a short period through days 15 to 17, LN was detected not only in the BM but also in intracellular vesicles of the cells of the terminal cluster. Immunoelectron microscopy showed the intracellular immunoreactive sites to be rough endoplasmic reticulum, indicating that active LN synthesis occurs in the cells of the terminal cluster. Intracellular immunostaining of LN disappeared completely on day 19 with the development of simple epithelium from the cell cluster, even though BM remained reactive. COLL IV also was accumulated in the intracellular vesicles of terminal cluster cells on day 16 of gestation but not on day 19. These results indicate that synthesis of certain BM components is transiently stimulated in gland epithelium before the formation of simple epithelial structure, and that these components are significantly involved in morphogenesis of the submandibular gland.

Biphasic accumulation of leukocytes in rat cardiac infarct tissue caused by leukotriene B4 and complement

An initial increase (3-12 hr) in the polymorphonuclear leukocytes (PMN) counts after ligation of the rat left main coronary artery was reduced by 49.4% (at 12 hr) by a 5-lipoxygenase inhibitor, AA-861 (80 mg/kg, p.o., 1 hr before ligation). Depletion of the complement components induced by cobra venoma factor (CVF) (i.v.), given one day before, resulted in significant reduction in the PMN accumulation after 12 hr (by 63.6% at 24 hr). The combined treatment (CVF+AA-861) suppressed the PMN accumulation by 69.7% (24 hr). The infarct size at 48 hr was also reduced by approximately 36% by either AA-861, CVF or combined treatments.

Mechanism for the removal of residual cytoplasm from spermatids during mouse spermiogenesis

During spermiogenesis, cytoplasmic processes of Sertoli cells invade spermatid cytoplasm to form a canal complex (Sakai et al., 1988). Thin tubules are formed from the canal complex and intertwine with each other to give rise to the "mixed body." In the present study, analysis of the changes undergone by the intertwining thin tubules indicated that they contribute to the removal of cell organelles from spermatid cytoplasm. Intertwining thin tubules were first detected at step 13. By step 15, their number had greatly increased. In the present study, the membranes of the intertwining thin tubules were clearly observed to be continuous with the spermatid plasma membranes. Thus, the mixed body possibly may be formed as a long pit of the spermatid plasma membrane situated close to the invading Sertoli cell process. With the progress of spermiogenesis, the lumens of the intertwining thin tubules gradually became swollen, and the intertwining swollen tubules fused with each other so that the spermatid cytoplasm enclosed by the intertwining swollen tubules isolated into fragments. This fragmented cytoplasm, which contained a large amount of endoplasmic reticulum, became spherical. Small branches of the invading Sertoli cell processes entered into the lumens of the intertwining swollen tubules and occupied their interior to the point that, finally, they completely engulfed the fragmented spermatid cytoplasm. Because the invading Sertoli cell processes were continuous with Sertoli cell bodies surrounding a spermatid at this step, it is possible for the fragmented cytoplasm to be transported into the latter by way of the invading Sertoli cell processes.

Monoclonal antibodies against rat T-kininogen: application to radioimmunoassay and immunohistochemistry

Monoclonal antibodies to rat T-kininogen were produced and 9 hybridomas were selected. Radioimmunoassay (RIA) was developed using 125I-labeled T-kininogen and cell walls of Staphylococcus aureus (Zysorbin) for the separation of bound from free ligand, when IgG2a and IgG2b were used. In the case of IgG1 monoclonals, a second antibody (goat anti-mouse IgG) and Zysorbin were used. By this RIA, 1-16 ng T-kininogen/tube showed a linear inhibition curve, and cross reactivities to rat purified LMW- and HMW-kininogens were less than 0.5%, respectively. These monoclonal antibodies were also used for the immunohistochemical staining of the liver to detect T-kininogen in hepatocytes. By using the RIA and immunohistochemical staining, the T-kininogen levels in rat plasma and liver following carrageenin-induced inflammation were estimated. At 3-5 h after the carrageenin injection, when the paw swelling was at its peak, the plasma level of T-kininogen and staining of the liver were slightly increased. T-Kininogen levels in plasma and liver peaked on the 2nd day, when the paw swelling had already decreased. The result indicates that the increase of T-kininogen level in the liver and plasma occurs with a time lag and T-kininogen is not directly involved in the increase of vascular permeability in carrageenin paw edema.

Dynamic changes in Sertoli cell processes invading spermatid cytoplasm during mouse spermiogenesis

Studies using thick sections stained by ATPase cytochemistry and scanning electron microscopy were carried out to determine three-dimensional ultrastructural alterations in Sertoli cell processes invading neighboring spermatids during mouse spermiogenesis. Sertoli cell processes start invading spermatid cytoplasm at the acrosomal phase of development and undergo considerable change at the maturation phase of development. At step 14, these processes elongate and begin to branch in the spermatid cytoplasm, and by step 15, they extend in various directions to form a complex of canals that the authors have designated the canal complex. The present observations also clarify that the complicated canal complex undergoes regional modification. At the late stages of maturation, the endoplasmic reticulum has gathered with other cell organelles to form aggregates of endoplasmic reticulum in the vicinity of which invading Sertoli cell processes extensively ramify further into thin tubules that intertwine with each other to form a region of thin tubules. In thin sections, each such region was a complex, consisting of small vesicles and endoplasmic reticulum, and corresponded to what has been defined as a mixed body by Morales and Clermont (Anat. Rec., 203:233-244, 1982). During the course of the formation of the region, the invading Sertoli cell processes are continuous at all times with the cell body of the surrounding Sertoli cell.

In vivo effects of tunicamycin on the secretory processes of rat parotid glands

The morphological and functional effects of tunicamycin were studied in rat parotid glands at the stage of the reformation of secretory granules following secretory stimulation by isoproterenol. Tunicamycin inhibited the incorporation of (3H)-mannose into the acid-insoluble fraction but had no effect on total protein synthesis as determined by the incorporation of (14C)-leucine. Thus the administration of tunicamycin in vivo inhibits the synthesis of mannose-rich glycoproteins in a manner similar to that in an in vitro system. The ultrastructure of the acinar cell showed little change following treatment with this drug, except that the number of reaccumulated secretory granules was greater than in the control. Amylase secretion stimulated by isoproterenol was inhibited in tunicamycin-treated cells, but did not decrease following treatment with N6,2'-O-dibutyryladenosine 3'-5'-cyclic monophosphate, a secretory stimulator bypassing the beta-receptor. A radio-receptor assay using (3H)-dihydroalprenolol and direct localization using the fluorescent beta-adrenergic blocker 9-amino-acridin-propranolol showed a marked reduction in the binding activity of beta-receptor following treatment with tunicamycin. Thus the inhibition of N-linked glycosylation appears to produce profound effects on the beta-adrenergic receptor-adenylate cyclase complex of acinar cells, although the steps of the transport and the exocytotic discharge of secretory materials are not affected.

A novel method for isolating specific endocytic vesicles using very fine ferrite particles coated with biological ligands and the high-gradient magnetic separation technique

We have developed a novel method for isolating specific endocytic vesicles using magnetic ligands and high-gradient magnetic separation. Ligands were prepared by coating extremely fine ferrite particles (10-20 nm) with bovine serum albumin and then conjugating asialoglycopeptides. These ligands were introduced into rat liver by perfusion at 16 or 37 degrees C, or by injection through the tail vein. The ligand particles were observed as electron-dense small grains in membrane-bound vesicles in Kupffer as well as parenchymal cells by electron microscopy. Livers were taken out, homogenized and lightly centrifuged. The supernatant was pumped into a separator glass tube filled with very fine ferritic stainless steel fibers and placed in a magnetic field of 0.9-2 T. Vesicles containing ferrite particles were collected with a high efficiency (ca. 70% of endocytosed magnetic ligands). About 70% of uptake appeared to be mediated by the asialoglycoprotein receptors. The captured vesicles were practically free from marker enzymes for plasma membranes, endoplasmic reticulum, and Golgi apparatus. Lysosomal enzyme activity of the vesicles increased with the time of perfusion at 37 degrees C but not at 16 degrees C. Protein composition of the captured vesicles was analyzed by one- and two-dimensional gel electrophoresis. The composition changed characteristically with time on perfusion at 16 and 37 degrees C. The present method provides a powerful tool to collect prelysosomal endocytic vesicles containing specific ligands and lysosomes fused with these specific endocytic vesicles.

Protection against cadmium toxicity by zinc: decrease in the Cd-high molecular weight protein fraction in rat liver and kidney on Zn pretreatment

The amounts of cadmium, associated with high molecular weight proteins, metallothionein and low molecular weight fractions obtained on Sephadex G-75 gel filtration, were determined in the liver and kidneys of rats treated with Cd. When rats were pretreated with zinc 24 h prior to the Cd injection, Cd associated with the high molecular weight proteins was decreased in both the liver and kidneys. Although the Cd concentration in the liver was increased, the liver showed less morphological damage in Zn-pretreated rats. The above results suggest that Cd-toxicity toward the liver and kidneys may be related to the accumulation of Cd in the high molecular weight proteins.

Immunocytochemical study on fibrous sheath formation in mouse spermiogenesis using a monoclonal antibody

One of the components of the fibrous sheath was localized in the spermatids by the immunocytochemical method using the monoclonal antibody, K32, against the fibrous sheath of mouse mature epididymal sperm. The K32 immunoreaction was first detected in the cytoplasm of spermatids at stage 14 and appeared to increase in intensity at stage 15. At this stage, the framework structure of the fibrous sheath was formed completely in the tail, but the positive reaction in the fibrous sheath was observed only in the proximal portion of the principal piece. This change in the antigenicity of the fibrous sheath proceeded in a proximal to distal direction, which was opposite to the mode of formation of the framework structure in the fibrous sheath. Finally, the entire fibrous sheath strongly reacted to the K32 antibody at stage 16, while the reaction in the cytoplasm ceased to occur. These observations indicate that the fibrous sheath matures with immunologically detectable changes in its components following formation of the framework structure. In consideration of the retrograde progression of the cytoplasmic reaction, the fibrous sheath components may possibly be transported from the spermatid cytoplasm into the principal piece.

Electron microscopic localization of 5'-nucleotidase in rat salivary glands. Comparative enzyme- and immunohistochemical studies

The localization of 5'-nucleotidase in rat parotid and submandibular glands was investigated at the electron microscope level by an immunohistochemical technique using a highly specific antibody, and the results were compared with those obtained using the newley developed cerium method for enzyme histochemistry. Both methods demonstrated that 5'-nucleotidase is located on the external surface of the luminal plasma membranes of acinar cells as well as on intercalated and striated ductal cells. In the basolateral membranes of these cells, the portions adjacent to myoepithelial cells exhibited intense reaction products, but the other areas of plasma membranes contained only trace amounts of the reaction products. Both cerium-based enzyme histochemistry and immunohistochemistry showed that myoepithelial cells retain the enzyme on their plasma membranes. Neither method produced reaction products in the intracytoplasmic structure of constitutive cells of the salivary glands. We discuss the usefulness of the cerium-ion method for the demonstration of 5'-nucleotidase activity and compare it with the traditional lead-ion method.

Acinar structure and membrane regionalization as a prerequisite for exocrine secretion in the rat submandibular gland

The significance of glandular organization in exocrine secretion was examined by analysing the functional and morphological features of the dissociated rat submandibular gland with special reference to the acinar structure and luminal specialization. The digestion of the gland with collagenase (C preparation) produced relatively large cellular masses having well-preserved acinar structures. When EGTA and the proteolytic enzyme Dispase were added to the C preparation (CED preparation), the gland was dissociated into small cellular aggregates in which the acinar structure disintegrated. Upon stimulation with either isoproterenol or dibutyryl cyclic AMP, a large amount of peroxidase, one of the secretory products of the rat submandibular gland, was released from C-treated cells, while discharged peroxidase was greatly reduced after the CED preparation was used. Measurements of dye exclusion, oxygen consumption, protein synthetic activity and receptor binding, as well as ultrastructural features and the absence of inhibitory effects of EGTA and Dispase, suggested that the reduced secretory response of CED-treated cells was not attributable to cellular death, denaturation of receptors or the inhibitory effects of EGTA and Dispase. When the localization of dipeptidyl aminopeptidase IV was surveyed by both enzyme histochemistry and immuno-histochemistry, the luminal plasma membrane was the exclusive site for the reaction in C-treated cells as well as intact acini, whereas the entire cell surface was reaction-positive in CED-treated cells. In addition, the luminal microfilament system and tight junctions, as revealed by nitrobenz-oxadiazole-phallacidin staining and freeze-replica studies, respectively, were well-preserved in the C-treated cells, but considerably disorganized in the CED-treated cells. All these results strongly suggest that: (1) luminal specialization plays an important role in exocrine secretion; and (2) normal acinar arrangement provides the luminal specialization.

Mobilization and aggregation of integral membrane proteins in erythrocytes induced by interaction with influenza virus at acidic pH

Effect of influenza virus on erythrocyte membranes was investigated by electron microscopy and fluorescence photobleaching recovery measurements. The virus induced mobilization of integral proteins in erythrocyte membrane at acidic pH, where it fused with the cell membrane to cause hemolysis and also cell fusions but not at neutral pH. At lower temperatures (e.g., 4 degrees C), the proteins aggregated in the membrane and, consequently, large protein-free lipid bilayer area was produced. At higher temperatures (e.g., 37 degrees C) the protein distribution became randomized. Spectrin meshwork underneath the erythrocyte membrane was also markedly modified by the virus at acidic pH. Diffuse fibril structure was converted into dense spots and the membrane area lacking the fibril structure was produced. Isolated hemagglutinin rosettes also caused mobilization and aggregation of the integral proteins at acidic pH but to smaller extent than that induced by virus. The membrane perturbation detected as the protein mobilization by the action of hemagglutinin was assigned to be the cause for envelope fusion.

Acceleration of rat liver phospholipid metabolism after long-term cadmium administration

Male Wistar rats, 6 weeks old, were allowed free access to water containing cadmium chloride at a concentration of 250 ppm as cadmium (Cd) for 6 and 12 months. The growth, as measured by body weight of Cd-treated rats, was significantly retarded. Electron microscopic studies revealed the appearance of small vacuoles in the cytoplasm, and involution of the rough endoplasmic reticulum (RER) in both the liver and whole kidney. When radioactive precursors of phospholipids, H3(32)PO4 and [1(3)-H]glycerol, were injected (ip) into cd-treated rats, the incorporation of 32P into phosphatidylcholine (PC) in the liver was increased 3.2- and 5.8-fold after 6- and 12-month Cd administration, respectively, and that of 3H into PC was also increased 2.3- and 2.2-fold after 6- and 12-month Cd administration, respectively. In the kidney, however, the incorporation rates of these radioactive precursors were little affected by long-term Cd administration. In the liver of rats treated with Cd for 6 and 12 months, the activity of CDP-choline:cholinephosphotransferase was increased by 20-30% over the control. It was shown that de novo synthesis of PC, which is a major constituent of biological membranes, was accelerated by long-term Cd administration in the liver but not in the kidney. These results suggest the possibility of regenerating the membranes in damaged hepatocytes after 6 and 12 months of Cd administration.

Infectious cell entry mechanism of influenza virus

Interaction between influenza virus WSN strain and MDCK cells was studied by using spin-labeled phospholipids and electron microscopy. Envelope fusion was negligibly small at neutral pH but greatly activated in acidic media in a narrow pH range around 5.0. The half-time was less than 1 min at 37 degrees C at pH 5.0. Virus binding was almost independent of the pH. Endocytosis occurred with a half-time of about 7 min at 37 degrees C at neutral pH, and about 50% of the initially bound virus was internalized after 1 h. Electron micrographs showed binding of virus particles in coated pits in the microvillous surface of plasma membrane and endocytosis into coated vesicles. Chloroquine inhibited virus replication. The inhibition occurred when the drug was added not later than 10 min after inoculation. Chloroquine caused an increase in the lysosomal pH 4.9 to 6.1. The drug did not affect virus binding, endocytosis, or envelope fusion at pH 5.0. Electron micrographs showed many virus particles remaining trapped inside vacuoles even after 30 min at 37 degrees C in the presence of drug, in contrast to only a few particles after 10 min in vacuoles and secondary lysosomes in its absence. Virus replication in an artificial condition, i.e., brief exposure of the inoculum to acidic medium followed by incubation in neutral pH in the presence of chloroquine, was also observed. These results are discussed to provide a strong support for the infection mechanism of influenza virus proposed previously: virus uptake by endocytosis, fusion of the endocytosed vesicles with lysosome, and fusion of the virus envelope with the surrounding vesicle membrane in the secondary lysosome because of the low pH. This allows the viral genome to enter the target cell cytoplasm.

Localization of 5'-nucleotidase activity in the parotid acinar cells of a rat treated with isoproterenol

Cytochemical localization of 5'-nucleotidase (AMPase) has been investigated in the parotid acinar cells of rats at various stages of exocytic secretion induced by an administration of isoproterenol (IPR). In the resting stage, the acinar cells show AMPase activity located on the baso-lateral and luminal plasmalemma, and in the earliest secretory stage the luminal plasma membranes are devoid of the enzymatic activity. However, these particular regions exhibit AMPase activity during the advanced stages of secretion, and the AMPase positive membranes become absorbed into the cytoplasm by endocytic activity. The absorbed membrane components then seem to be degraded by the action of lysosomes. The intracellular fate of the endocytic vacuoles has been examined by the aid of ferritin particles introduced retrogradely through ductal lumina. Ferritin containing vacuoles are distributed in the cytoplasm, and these droplets change into secondary lysosomes. No tracer particles are recognized in the internal space of the Golgi lamella and its associated vesicles. The results suggested that in the exocytic secretion of parotid acinar cells, AMPase originating from plasma membrane intermingles with the membranes derived from secretion granules, and is translocated into cytoplasm by an endocytic mechanism. The internalized membrane components are, at least partly, degraded by lysosome action.

Cytochemical studies on the localization of 5'-nucleotidase in the acinar cells of the rat salivary glands

The cytochemical localization of 5'-nucleotidase (5'-AMPase), and its validity, were investigated in parotid and submandibular acinar cells of a rat. Biochemical determinations showed that adequate treatment with glutaraldehyde could minimize the loss of enzymatic activity, and that 5'-AMPase and non-specific alkaline phosphatase (beta-GPase) possessed different pH optima. The cytochemical distribution of the reaction products from the 5'-AMPase activity was distinct from those of beta-GPase. 5'-AMPase activity was localized on the surface membranes of acinar, ductal and myoepithelial cells of both salivary glands. beta-GPase activity was evenly distributed on the entire plasma membranes of myoepithelial cells and on the basal plasmalemma of acinar cells. The reaction products, which appeared on the luminal and lateral plasma membranes of the acinar cells, were presumed to reflect the presence of 5'-AMPase, while those on the myoepithelial surface and basal plasma membranes of the acinar cells demonstrated both 5'-AMPase and beta-GPase. The results indicate that 5'-AMPase activity can be utilized as a reliable marker enzyme of plasma membranes in the salivary acinar cells.

Postnatal development of acinar cells in rat submandibular gland as revealed by electron microscopic staining for carbohydrates

The postnatal differentiation of acinar cells in rat submandibular gland was studied by staining with periodic acid-thiosemicarbazide-silver proteinate to identify carbohydrate-containing macromolecules in the electron microscope. This method revealed glycogen particles and internal substructure in the secretory granules of developing acinar cells. On the basis of morphologic and histochemical criteria three phases of acinar cell development were defined. In the pro-acinar phase, during the first week after birth, pro-acinar cells and terminal tubular cells were the main components of the terminal tubules in the rudimentary gland. The secretory granules of the pro-acinar cells contained speckled or rod-like substructures which stained intensively for carbohydrates and were digested by proteolytic enzymes. During the second to third week after birth, which is the immature-acinar-cell phase, thread-like substructures were seen in the secretory granules. These structures, which were not digested by proteolytic enzymes, disappeared gradually. The acinar cells of 4-week-old or older rats displayed no particular substructure in the secretion granules and represented the final, mature phase of development.

Development of endogenous peroxidase in fetal rat submandibular gland

The prenatal development of endogenous peroxidase activity in the submandibular gland of rat was investigated by means of the diaminobenzidine-H2O2 histochemical method. The submandibular gland of a 16-day-old fetus was composed of cords of uniform, undifferentiated cells which contained no secretory granules and revealed no peroxidase activity. Peroxidase activity first appeared at the 17th day of gestation in the cisternae of the rough endoplasmic reticulum and nuclear envelope in a few cells. At the 18th day of gestation cells which exhibited reaction products in the rough endoplasmic reticulum and nuclear envelope also contained secretory granules with a strong peroxidase activity. During the last days of gestation the number of peroxidase positive cells, which contained numerous secretory granules, increased. The peroxidase-containing cells are the immediate precursors of the proacinar cells of early postnatal stages. During the same time period, when the peroxidase-containing cells differentiated, a second cell type also differentiated in the cellular cords. The development of this cell type was marked by the appearance of secretory granules stainable with toluidine blue. Through the prenatal development, this cell type revealed no peroxidase activity and was identified with the terminal tubule cell of the newborn. The morphologic and cytochemical findings indicate that terminal tubule cells and proacinar cells are committed cells; the former differentiate toward 2nd order intercalated duct cells and the latter transform to mature acinar cells.

Localization of peroxidase activity in the developing submandibular gland of normal and isoproterenol-treated rats

The localization of peroxidase activity was studied in the developing submandibular gland of normal and isoproterenol-treated rats using a diaminobenzidine-H2O2 method. During postnatal development peroxidase activity was localized in the proacinar and acinar cells. The proacinar cells were characterized by the presence of polymorphic secretory granules that gave a strong peroxidase reaction, particularly in the glands of 1-day-old rats. In addition to the secretory granules, enzyme activity was demonstrated in the rough endoplasmic reticulum and nuclear envelope. The terminal tubule cells and duct cells were devoid of peroxidase activity. The secretory granules in the fully developed acinar cells revealed little or no enzyme activity. Isoproterenol stimulated the secretion of the peroxidase-positive granules from the proacinar cells. The stimulation was followed by a reaccumulation of peroxidase-positive secretory material. During this process enzyme activity was demonstrable in the Golgi complex. Isoproterenol had no effect on the terminal tubule cells. A less effective depletion of the secretory granules from the proacinar cells was seen after pilocarpine administration. Chronic administration of isoproterenol to 5-day-old rats led to an acceleration of the differentiation of acinar cells and to a hypertrophy of the gland, without significant change in the localization of peroxidase activity.