The Clara cell: a comparative ultrastructural study in mammals.

Clara cells in the terminal bronchoiles of mouse, rat, rabbit, calf and human were compared by light, transmission and scanning microscopy, and species-differences were clearly present. Mouse Clara cells were most numerous and mouse and rabbit Clara cells had large dense mitochondria. Rabbit and calf had glycogen in Clara cells and rat Clara cells had the most variability in secretory granules, some of which had a crystalline structure. Calf Clara cells had deeply indented nuclei. Human Clara cells had the most prominent nucleoli and lacked smooth endoplasmic reticulum, which was a prominent feature of most other species. No evidence of apical extrusion or apocrine secretion of Clara cell secretory granules was observed.     

Morphometric analysis of hepatocytes from rats subjected to compound 48/80-induced anaphylactic shock

Morphometric and biochemical techniques were used to analyze hepatic glycogen, endoplasmic reticulum, and mitochondrial matrix granules in rats treated with compound 48/80 to induce an anaphylactic-like state of shock. Thirty minutes after insult there was a significant decrease in glycogen and mitochondrial matrix granules, an increase in rough endoplasmic reticulum (RER), and no change in smooth endoplasmic reticulum (SER). Less glycogen in experimental rats substantiated a previously described glycogenolytic response to compound 48/80. The decrease in matrix granules implies a loss and/or shift in intramitochondrial calcium as occurs in epinephrine-induced glycogenolysis in the rat. Since other glycogenolytic agents, e.g. glucagon, and starvation stimulate an increase in SER presumably from RER, the present morphological data suggest the increase in RER may precede proliferation of SER from RER.     

The ultrastructure of hemocytes inDactylopius confusus (Cockerell), and the role of granulocytes in the synthesis of cochineal dye

Summary The ultrastructural study of free circulating hemocytes in the adult cochineal scale,Dactylopius confusus (Cockerell), demonstrated five cell types: prohemocytes, typical granulocytes (T-granulocytes), oenocytoids, plasmatocytes, and granulocytes with modified sub-cellular structure to perform a special synthetic and secretory function, which we refer to as modified granulocytes (M-granulocytes). Prohemocytes showed undifferentiated sub-cellular structure of the basic stem cell type (i.e., high cytoplasmic density with numerous ribosomes, centrally located large nucleus with a distinct nucleolus, and poorly developed endoplasmic reticulum). The commonly observed typical granulocytes (T-granulocytes) had several smooth endoplasmic reticulum (SER) with dilated cisternae and many SER-derived membrane bounded granules of different sizes and electron density. Oenocytoids were identified by the presence of many crystals, RER-originated fine secretory granules, and an eccentric nucleus. Plasmatocytes were easily characterized by their variable shapes and irregular outline with pseudopodia-like cytoplasmic extensions, possession of an elongated lobed nucleus, multivesicular bodies, RER-derived membrane bounded, electron-dense, lysosomelike vacuoles, well-developed SER cisternae, and numerous pinocytic and SER-originated vesicles of different sizes along the peripheral region. M-granulocytes comprised the largest proportion of hemocytes in all samples observed. M-granulocytes were distinguished not only by the presence of membrane bounded granules of different sizes and electron density, but by the possession of large nuclei with distinct nucleoli, many mitochondria, and a highly developed network of rough endoplasmic reticulum (RER). M-granulocytes had abundant, rosette-shaped, RER-derived chains of fine secretory granules, which accumulated in the cytoplasm and vacuoles, and were ultimately deposited into the hemolymph by exocytosis. These fine granules gave a positive result with periodic acid-Schiff (PAS) test. Based on RER-synthesized fine secretory granules (M-granulocytes), their ultimate deposition into hemolymph, the red pigmentation of hemolymph, positive PAS histochemical test of these granules, and the high population of these hemocytes, no such cell type has been described in previous studies in insects. The sub-cellular structure of the granulocyte in this insect has been modified to perform a special synthetic and secretory function (i.e., possibly the synthesis of the red pigment found in hemolymph, which has been the source of commercially important cochineal dye).Abbreviations EM electron microscope - ER endoplasmic reticulum - LM light microscopy - MVB multivesicular body - PAS periodic acid-Schiff - RER rough endoplasmic reticulum - SER smooth endoplasmic reticulum - SG secretory granules - TEM transmission electron microscopy - UA uranyl acetate     

Observations on the role of smooth endoplasmic reticulum in glucocorticoid-induced hepatic glycogen deposition

We have studied by quantitative electron microscopy the relationship of specific hepatic cellular organelles to glycogen synthesis using dexamethasone, a potent synthetic glucocorticoid, to induce glycogen deposition in livers of adrenalectomized rats. Chemical and ultrastructural glycogen determinations revealed that the livers of fasted adrenalectomized rats had very low glycogen levels. Dexamethasone caused a time-related increase in hepatic glycogen which was the result of increases in the number of hepatocytes depositing glycogen and the amount of glycogen in each cell. The surface density of smooth endoplasmic reticulum (SER) in centrilobular and periportal hepatocytes also increased after treatment with dexamethasone; this increase preceded glycogen deposition. The newly deposited glycogen was spatially associated with membranes of SER, and a continued increase in SER surface density was correlated temporally with the increasing glycogen volume density. In both centrilobular and periportal hepatocytes, the suface density of rough endoplasmic reticulum (RER) initially decreased after dexamethasone administration but later increased. These data support the hypothesis that dexamethasone-induced enhancement of SER is functionally associated with the increase in glycogen, and that although the initial increase in SER may occur through transformation of RER to SER, later increases in SER require synthesis of new membranes.     

Age-dependent changes in structure and function of the male labial gland in Bombus terrestris

The cephalic region of the labial gland in the buff-tailed bumblebee, Bombus terrestris, consists of numerous acini (formed by associated secretory cells and a central lumen) and connecting ducts. Age-dependent changes in secretion production (both qualitative and quantitative) are associated with changes in the amount of rough endoplasmic reticulum (RER), Golgi apparatus, and smooth endoplasmic reticulum (SER). The main secretory organelle is RER in the youngest individuals (pharate, and less-than-a-day old males), Golgi apparatus in 1-day-old males, and SER in males older than 2 days. Secretory cell death starts at 5 days of age, with maximal longevity to 10 days. Pheromone production starts immediately after eclosion, with pheromone quantities increasing until day 7. 2,3-dihydrofarnesol, the main component of the male-marking pheromone, appears in 1-day-old male glands, and reaches a maximum at 7 days of age, when its presence in the gland starts to decrease gradually. Older glands contain compounds not present in young ones. Variation in pheromone quantity and composition are reflected sensitively in the response of the queen antennae. Though queen antennae responded to gland extracts of all ages examined, maximum sensitivity was observed in response to extracts of glands 2-10 days old, while extracts of older glands gradually lose their effectiveness. Both major and minor components of the labial gland secretion extract elicited queen antennal responses suggesting that the pheromone is a multicomponent blend. Age-dependent changes in pheromone production, accumulation and tuning of pheromone activity are all synchronized approximately with male flight from the hive.     

Light and electron microscopy study of the salivary glands of the carnivorous opisthobranch Philinopsis depicta (Mollusca, Gastropoda)

Cephalaspideans are a group of opisthobranch gastropods that comprises carnivorous and herbivorous species, allowing an investigation of the relationship between these diets and the morphofunctional features of the salivary glands. In this study, the salivary glands of the carnivorous cephalaspidean Philinopsis depicta were observed by light and electron microscopy. The secretory epithelium of these ribbon-shaped glands is formed by ciliated cells, granular cells and cells with apical vacuole. In ciliated cells the nucleus and most cytoplasmic organelles are located in the wider apical region and a very thin stalk reaches the base of the epithelium. These cells possess significant amounts of glycogen. Granular cells are packed with electron-dense secretory granules and also contain several cisternae of rough endoplasmic reticulum and Golgi stacks. The other type of secretory cell is mainly characterized by the presence of a large apical vacuole containing secretion. These cells possess high amounts of rough endoplasmic reticulum cisternae and several Golgi stacks. Vesicles with peripheral electron-dense material are also abundant, and seem to fuse to form the apical vacuole. The available data point out to a significant difference between the salivary glands of carnivorous and herbivorous cephalaspidean opisthobranchs, with an intensification of protein secretion in carnivorous species.     

Ultrastructural immunolocalization of apolipoprotein B within human jejunal absorptive cells

Apolipoprotein B (apoB) was localized by electron microscopy within absorptive cells of human jejunal biopsy specimens taken fasting and after micellar fat infusion. Nakane's double antibody immunoperoxidase technique was used to label apoB near open cut surfaces of 60-Micrometers fixed tissue slices sectioned by a Ralph knife in a Vibratome. In fasting tissue, apoB label was found within structurally intact peri-mitochondrial rough endoplasmic reticulum (RER) and within Golgi cisternae of absorptive cells covering the tips of jejunal villi. After fat infusion, apoB label was found adjacent to very low density lipoproteins (VLDL) and chylomicrons within apical smooth endoplasmic reticulum (SER). Less label was seen within RER than in fasting absorptive cells, and RER-SER connections containing apoB label were occasionally seen. Expanded Golgi vesicles and cisternae contained VLDL, chylomicrons, and apoB label. Vesicles containing chylomicrons and apoB label were occasionally visualized bordering the lateral plasma membrane in a configuration suggesting exocytosis. Specific apoB label was regularly seen within intercellular spaces and capillaries, but the in vivo significance of this Localization was problematical. These observations suggest that apoB is synthesized in RER, transfers to SER where it is incorporated into new VLDL and chylomicrons, and moves to Golgi cisternae and vesicles to be prepared for exocytosis through the plasma membrane.     

Ultrastructure of the lateral organs in larvalArgas (Persicargas) arboreus (Ixodoidea: Argasidae)

The ultrastructure of lateral organs (LO) in the larval tickArgas (Persicargas) arboreus is described before and after feeding and up to the 1st day of moulting. Three pairs of LO are associated with three pedal nerves arising from the synganglion. In unfed ticks, each LO is ensheathed by a neural lamella and consists of 6–7 neuronal cell bodies; their cytoplasm is mostly occupied by cisternae of rough endoplasmic reticulm (RER). In fully engorged ticks, the enlarged neuronal cells contain vacuolar cisternae of smooth endoplasmic reticulum (SER), coated vesicles and mitochondria. Golgi bodies are involved in the formation of neurosecretory granules which dominate, with the SER vacuoles, the cell cytoplasm before moulting. The vacuoles, coated vesicles and neurosecretory granules are similar to those found in the vertebrate steroid-secreting cells. Condensing vacuoles may fuse with lysosome-like bodies to form larger ones; these are possibly responsible for the cell breakdown when secretory products are no longer required. Ultrastructural observations of LO suggest that they are neuroendocrine glands and that, in engorged larvae, they may secrete a hormone involved in the control of moulting.     

Fetal mouse lung in circumfusion system cultures.

Fetal mouse lungs were cultivated, using the dual-rotary circumfusion system for tissue culture, and their histotypic development was surveyed for 75 days by phase-contrast and electron microscopy. Alveoli, terminal bronchioles and alveolar macrophages were photographed periodically with still and time-lapse phase-contrast microscopy. Their histotypic appearance was confirmed by electron micrographs of the 1- and 2 1/2-month-old specimens. These revealed typical alveoli surrounded by a basal lamina and composed of types I and II pneumocytes containing various lamellar-body forms within the type II cells, the alveolar lumen, and the alveolar macrophages. There was a shift from almost all type II cells in the 1-month-old alveoli to the presence of frequent type I cells as constituents of the alveoli in the 2 1/2-month-old cultures. The terminal bronchioles were tubules consisting of ciliated cells with Clara cells interspersed between them. The ciliated cells contained as many as 30 cilia or basal bodies per section and numerous microvilli. They were attached to each other and to the Clara cells by junctional complexes and accessory desmosomes which were generally in the apical ends of the cells. The Clara cells typically had glycogen granules interspersed between lamellae of the endoplasmic reticulum, contained numerous well dispersed mitochondria, occasional lysosome-like granules and crystalloid bodies which appeared to be tubular. Some Clara cells presented a moderatley dense secretory granule in the center of the whorl of the endoplasmic reticulum.     

Immunohistochemical, electron microscopic and morphometric studies of estrogen-induced rat prolactinomas after bromocriptine treatment

To clarify the effects of bromocriptine on prolactinoma cells in vivo, immunohistochemical, ultrastructural and morphometrical analyses were applied to estrogen-induced rat prolactinoma cells 1 h and 6 h after injection of bromocriptine (3 mg/kg of body weight). One h after treatment, serum prolactin levels decreased markedly. Electron microscopy disclosed many secretory granules, slightly distorted rough endoplasmic reticulum, and partially dilated Golgi cisternae in the prolactinoma cells. Morphometric analysis revealed that the volume density of secretory granules increased, while the volume density of cytoplasmic microtubules decreased. These findings suggest that lowered serum prolactin levels in the early phase of bromocriptine treatment may result from an impaired secretion of prolactin due to decreasing numbers of cytoplasmic microtubules. At 6 h after injection, serum prolactin levels were still considerably lower than in controls. The prolactinoma cells at this time were well granulated, with vesiculated rough endoplasmic reticulum and markedly dilated Golgi cisternae. Electron microscopical immunohistochemistry revealed positive reaction products noted on the secretory granules, Golgi cisternae, and endoplasmic reticulum of the untreated rat prolactinoma cells. However, only secretory granules showed the positive reaction products for prolactin 6 h after bromocriptine treatment of the adenoma cells. An increase in the volume density of secretory granules and a decrease in the volume densities of rough endoplasmic reticulum and microtubules was determined by morphometric analysis, suggesting that bromocriptine inhibits protein synthesis as well as bringing about a disturbance of the prolactin secretion.     

Fetal mouse lung in circumfusion system cultures

Summary Fetal mouse lungs were cultivated, using the dual-rotary circumfusion system for tissue culture, and their histotypic development was surveyed for 75 days by phase-contrast and electron microscopy. Alveoli, terminal bronchioles and alveolar macrophages were photographed periodically with still and time-lapse phase-contrast microscopy. Their histotypic appearance was confirmed by electron micrographs of the 1- and 2 1/2-month-old specimens. These revealed typical alveoli surrounded by a basal lamina and composed of types I and II pneumocytes containing various lamellar-body forms within the type II cells, the alveolar lumen, and the alveolar macrophages. There was a shift from almost all type II cells in the 1-month-old alveoli to the presence of frequent type I cells as constituents of the alveoli in the 2 1/2-month-old cultures. The terminal bronchioles were tubules consisting of ciliated cells with Clara cells interspersed between them. The ciliated cells contained as many as 30 cilia or basal bodies per section and numerous microvilli. They were attached to each other and to the Clara cells by junctional complexes and accessory desmosomes which were generally in the apical ends of the cells. The Clara cells typically had glycogen granules interspersed between lamellae of the endoplasmic reticulum, contained numerous well dispersed mitochondria, occasional lysosome-like granules and crystalloid bodies which appeared to be tubular. Some Clara cells presented a moderately dense secretory granule in the center of the whorl of the endoplasmic reticulum. This work supported by Grant HL19684 from the National Heart and Lung Institute, National Institutes of Health. Pregnant Strong A mice were kindly supplied by Dr. Henry Browning of the Department of Anatomy.     

Mast cells of lymph hearts during ontogenesis of frogs Rana temporaria

Electron microscopic observations of the lymph hearts of tadpoles and yearling frogs of Rana temporaria showed that mast cells (MCs) were present not only between muscle fibers (population of resident MCs), but in the cavities of lymph heart (population of circulating MCs), too. There were some differences in the ultrastructure of the resident MCs at each studied stage of larval development. The first recognizable MCs were revealed in the lymph hearts at premetamorphosis (stages 39-41). MCs presented as mononuclear relatively small and slightly elongated cells with a few immature secretory granules and numerous free ribosomes, polysomes and short cisternae of rough endoplasmic reticulum (RER) in the cytoplasm. Chromatin of their nuclei was poorly condensed; the Golgi apparatus was moderately developed. At pro-metamorphosis (stages 44-45), we revealed MCs at different levels of their differentiation. Some MCs demonstrated an active process of granulogenesis in their cytoplasm. Among densely packed cytoplasmic organelles, immature secretory granules were closely associated with cisternae of RER and free ribosomes. Other MCs appeared as more differentiated cells. They were characterized by a predominantly heterochromatic nuclei and cytoplasm filled with polymorphic and heterogeneous granules. MCs also showed a reduction in the number of free ribosomes and cisternae of RER in the cytoplasm. On the contrary, the Golgi apparatus was well developed. Stacks of Golgi cisternae, detaching vacuoles, and progranules occupied the perinuclear region. The majority of the outlines above ultrastructural features of differentiated MCs were typical for MCs of yearling frogs. At metamorphic climax (stages 52-53), MCs often tightly contacted with macrophages. We did not reveal apoptotic MCs. However, some MCs exhibited morphological features typical for programmed necrosis-like death, which was characterized by mitochondria swelling, dilatation of cisternae of RER and nuclear envelope, plasma membrane rupture and subsequent loss of intracellular contents. Electron microscopical immunocytochemistry revealed the localization of atrial natriuretic peptide (ANP), substance S (SP) and heat shock protein (Hsp70) in the secretory granules of the resident and circulating MCs at different stages of tadpole development and in yearling frogs.     

Ultrastructural immunocytochemical localization of cyclic AMP-dependent protein kinase regulatory subunits in rat parotid acinar cells

Polyclonal antibodies to types I and II regulatory (R) subunits of cyclic AMP-dependent protein kinase (cA-PK) were utilized in a post-embedding immunogold-labeling procedure to localize these proteins in rat parotid acinar cells. Both RI and RII were present in the nuclei, cytoplasm, rough endoplasmic reticulum (RER), Golgi apparatus, and secretory granules. In the nuclei, gold particles were mainly associated with the heterochromatin. In the cytoplasm, the label was principally found in areas of RER. Most gold particles were located between adjacent RER cisternae or over their membranes and attached ribosomes; occasional particles were also present over the cisternal spaces. Labeling of the Golgi apparatus was significantly greater than background, although it was slightly lower than that over the RER cisternae. In secretory granules, gold particles were present over the granule content; no preferential localization to the granule membrane was observed. Morphometric analysis revealed equivalent labeling intensities for RI and RII in the cytoplasm-RER compartment. Labeling intensities for RII in the nuclei and secretory granules were about 50% greater than in the cytoplasm-RER, and 3 to 4-fold greater than values for RI in these two compartments. Electrophoresis and autoradiography of the postnuclear parotid-tissue fraction, the contents of purified secretory granules and saliva collected from the main excretory duct, after photoaffinity labeling with [32P]-8-azido-cyclic AMP, revealed the presence of R subunits. Predominantly RII was present in the granule contents and saliva, while both RII and RI were present in the cell extracts. Additionally, R subunits were purified from saliva by affinity chromatography on agarose-hexane-cyclic AMP. These findings confirm the localization of cA-PK in parotid cell nuclei and establish the acinar secretory granules as the source of the cyclic AMP-binding proteins in saliva.     

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.     

Development of secretory activity in the seminal vesicle of the male migratory grasshopper,Melanoplus sanguinipes (fabr.) (Orthoptera : Acrididae)

This paper describes the ultrastructure of the seminal vesicle and the isoelectric focusing patterns of its secretion during sexual maturation and after allatectomy in Melanoplus sanguinipes (Fabr.) (Orthoptera : Acrididae). In epithelia from seminal vesicles of newly fledged males, the rough endoplasmic reticulum is well developed, and Golgi complexes are elaborate, which indicates the gland is metabolically active. The cells also contain large glycogen deposits and the lumen microvilli are well differentiated. These ultrastructural features are more dominant in 24-hr-old adults where the cytoplasm is clearly differentiated into basal and apical regions. Basally, the cytoplasm is dominated by rough endoplasmic reticulum, large Golgi complexes, glycogen deposits and numerous mitochondria, while the apical cytoplasm is filled with large secretory and/or lysosomal vesicles. Between days 3 and 7, the ultrastructural features change little other than the rough endoplasmic reticulum cisternae, which become vesicular. Analysis by isoelectric focusing shows that the amount of secretory protein increases with age until day 3, at which time the gland contains its full complement of secretion. In seminal vesicles from allatectomized insects, ultrastructural features of cells and isoelectric focusing patterns of the secretion arc identical to those from normal males.     

Relationship between the golgi apparatus, gerl, and secretory granules in acinar cells of the rat exorbital lacrimal gland

The method of secretory granuleformation in the acinar cells of the rat exorbital lacrimal gland was studied by electron microscope morphological and cytochemical techniques. Immature secretory granules at the inner face of the Golgi apparatus were frequently attached to a narrow cisternal structure similar to GERL as described in neurons by Novikoff et al. (Novikoff, P. M., A. B. Novikoff, N. Quintana, and J.-J. Hauw. 1971. J. Cell Bio. 50:859-886). In the lacrimal gland. GERL was located adjacent to the inner Golgi saccule, or separated from it by a variable distance. Portions of GERL were often closely paralleled by modified cisternae of rough endoplasmic reticulum (RER), which lacked ribosomes on the surface adjacent to GERL. Diaminobenzidine reaction product of the secretory enzyme peroxidase was localized in the cisternae of the nuclear envelope, RER, peripheral Golgi vesicles, Golgi saccules, and immature and mature secretory granules. GERL was usually free of peroxidase reaction product or contained only a small amount. Thiamine pyrophosphatase reaction product was present in two to four inner Golgi saccules; occasionally, the innermost saccule was dilated and fenestrated, and contained less reaction product than the next adjacent saccule. Acid phosphatase (AcPase) reaction product was present in GERL, immature granules, and, rarely, in the innermost saccule, but not in the rest of the Golgi saccules. Thick sections of AcPase preparations viewed at 100 kV revealed that GERL consisted of cisternal, and fenestrated or tublular portions. The immature granules were attached to GERL by multiple connections to the tublular portions. These results suggest that, in the rat exorbital lacrimal gland, the Golgi saccules participate in the transport of secretory proteins, and that GERL is involved in the formation of secretory granules.     

Simultaneous apocrine and merocrine secretion in the rat coagulating gland

The coagulating gland of the rat synthesizes two prevalent secretory proteins (transglutaminase and 115 K) that are discharched in a different manner, one being secreted in an apocrine fashion (transglutaminase) and the other one in a merocrine way (115 K). Differences in the intra- cellular pathway and the release of either protein were studied using immunofluorescence on semithin sections, immunoelectron microscopy of preembedding-processed chopper sections and postembedding-processed ultrathin sections of rat coagulating gland. Immunohistochemical staining using an anti-transglutaminase antibody resulted in dense labeling of the cytoplasm of secretory cells and their apical blebs, whereas the cisternae of the rough endoplasmic reticulum and the Golgi apparatus were completely unlabeled. When, on the contrary, the anti-115 K antiserum was used, dense labeling of the cisternae of the rough endoplasmic reticulum, the Golgi apparatus, and the secretory granules was seen. Intraluminal secretion was also labeled, but the secretory blebs remained unlabeled. Our findings show that, in the coagulating gland of the male rat, the two secretory proteins studied are processed in parallel, but at completely different intracellular pathways. They are released via different extrusion mechanisms. Transglutaminase is synthesized outside the endoplasmic reticulum, reaches the apical cell pole by free flow in the cytoplasm, and is released via apocrine blebs, the membranes of which appear to be derived from the apical plasma membrane. The protein 115 K, on the other hand, follows the classic route, being synthesized within the cisternae of rough endoplasmic reticulum, subsequently glycosylated in the Golgi apparatus, and released in a merocrine fashion. The mutual exclusion of the two secretory pathways and the regulation of the alternative release mechanism are still unresolved issues.     

Immunocytochemical localization of amylase and chymotrypsinogen in the exocrine pancreatic cell with special attention to the Golgi complex

Affinity-purified, monospecific rabbit antibodies against rat pancreatic alpha-amylase and bovine pancreatic alpha-chymotrypsinogen were used for immunoferritin observations of ultrathin frozen sections of mildly fixed exocrine pancreatic tissue from secretion-stimulated (pilocarpine) rats and from overnight-fasted rats and guinea pigs. The labeling patterns for both antibodies were qualitatively alike: Labeling occurred in (a) the cisternae of the rough endoplasmic reticulum (RER) including the perinuclear cisterna, in (b) the peripheral area between the RER and cis-Golgi face, and (c) all Golgi cisternae, condensing vacuoles, and secretory granules. Labeling of cytoplasmic matrix was negligible. Structures that appeared to correspond to rigid lamellae were unlabeled. Differences in labeling intensities indicated that concentration of the zymogens starts at the boundary of the RER and cis-side of the Golgi complex. These data support the view that the Golgi cisternae are involved in protein processing in both stimulated and unstimulated cells and that Golgi cisternae and condensing vacuoles constitute a functional unit.     

Light and electron microscopic localization of ACTH and pro-opiomelanocortin-derived peptides in human developmental and neoplastic cells

Oncofetal aspects of ACTH and pro-opiomelanocortin (POMC)-derived peptides were studied immunohistochemically at the light and electron microscopic level in human fetal pituitary glands, pituitary adenomas, and small-cell carcinoma of the lung. ACTH, beta-endorphin, and gamma-MSH were localized in the same cells of both fetal and adult pituitary, as well as in the above-mentioned neoplastic tissues. However, alpha-MSH was observed only in the early fetal pituitary, its concentration decreasing with advancing gestational age. The adult pituitary contained only a few alpha-MSH-positive cells. By immunoelectron microscopy, ACTH in the adult pituitary was localized exclusively in the secretory granules. In fetal pituitary at 9 weeks' gestation, ACTH was localized in the perinuclear spaces (PNS), cisternae of rough endoplasmic reticulum (RER), Golgi saccules, and secretory granules. The staining pattern of ACTH in these organelles varied from cell to cell. In fetal pituitaries of greater gestational ages, ACTH was localized in secretory granules. The pituitary adenomas mimicked the staining characteristics of the adult pituitary, i.e., negative or only very occasional alpha-MSH staining and localization of ACTH in the secretory granules. The ectopic ACTH-producing tumors showed a staining pattern similar to that of the early fetal pituitary, i.e., positive staining for alpha-MSH and the presence of ACTH in PNS and cisternae of RER.     

Localization of apoVLDL-II,a major apoprotein in very low density lipoproteins,in the estrogen-treated cockerel liver by immunoelectron microscopy

Summary We have studied the sites of synthesis, assembly, and secretion of apoVLDL-II, a major apoprotein in very low density lipoproteins (VLDL), in the cockerel liver by immunoelectron microscopy. In the liver of the estrogen-treated cockerel, apoVLDL-II reaction products were localized in the cisternae of the nuclear envelope and the rough endoplasmic reticulum (RER). Such products were not observed in the smooth endoplasmic reticulum (SER). ApoVLDL-II reaction products were also located on the surface of lipid particles in the Golgi apparatus and secretory vesicles. Such lipid particles were not detected in the RER or SER. Some secretory vesicles containing the reaction products were seen during the process of fusion with the plasma membrane. Such fusion took place against the plasma membrane lining the space of Disse as well as the intercellular spaces. Reaction products also occurred in the sinusoids. These observations are compatible with the following sequence of events in the synthesis, assembly and secretion of apoproteins in VLDL in the cockerel liver: ApoVLDL-II is synthesized on bound ribosomes attached to the nuclear envelope and RER, and is discharged into their cisternae. The protein is probably transported to the Golgi apparatus where the assembly of this protein and its lipid components probably takes place. Secretory vesicles derived from the Golgi apparatus carry the VLDL particles to the plasma membrane where secretion of these particles takes place by exocytosis, and the VLDL are discharged into the sinusoid via both the space of Disse and intercellular spaces.This work was supported by Grants 78-1102 from the American Heart Association, and HL-16512 from the NIH