Studies of the secretory process in the mammalian exocrine pancreas. I. The condensing vacuoles

Phosphatase cytochemistry was used to distinguish between the Golgi apparatus and GERL (considered as a specialized region of endoplasmic reticulum [ER] at the inner [trans] aspect of the Golgi stack) in pancreatic exocrine cells of guinea pig, rat, rabbit, and hamster. The trans element of the Golgi stack exhibits thiamine pyrophosphatase (TPPase) but no acid phosphatase (AcPase) activity. In contrast, GERL shows AcPase but no TPPase activity. The nascent secretory granules, or condensing vacuoles, are expanded cisternal portions of GERL. Continuities of condensing vacuoles with rough ER are suggested, and it is proposed that some secretory components may have direct access to the condensing vacuoles from ER. Connections of Golgi apparatus with GERL were not seen.     

Ultrastructural study of GERL in beige mouse alveolar macrophages

Alveolar macrophages of the beige mouse mutant have a system of smooth- surfaced elements with the hallmarks of GERL. GERL also appears to produce residual bodies, and both organelles show cytochemically demonstrable acid phosphatase activity. When cells are exposed to colloidal silver, the tracer is endocytosed via pinocytic vacuoles to GERL.     

Fine structural localization of thiamine pyrophosphatase and acid phosphatase activities in the mouse pancreatic acinar cell

The fine structural localization of thiamine pyrophosphatase (TPPase) and acid phosphatase (AcPase) was examined in pancreatic acinar cells of fasting and fed mice. The results were not affected by these conditions. TPPase activity was positive in two and sometimes three cisternae of the inner Golgi lamellae as well as in the condensing vacuoles of the trans area, but negative in the rigid lamellae and small vesicles of the trans area. AcPase activity was demonstrated in two and sometimes three cisternae of inner Golgi lamellae, condensing vacuoles, rigid lamellae, lysosomes and smooth or coated vesicles in the trans area. The inner Golgi lamellae and the condensing vacuoles were positive for both enzyme activities. From these facts, the lysosome is considered to be formed not only in the GERL system but also through the rough endoplasmic reticulum-Golgi apparatus route. It is reasonable to consider that Novikoff's GERL is not independent from the Golgi apparatus but represents a part of this organelle.     

Fine structural localization of thiamine pyrophosphatase and acid phosphatase activities in the mouse pancreatic acinar cell

Summary The fine structural localization of thiamine pyrophosphatase (TPPase) and acid phosphatase (AcPase) was examined in pancreatic acinar cells of fasting and fed mice. The results were not affected by these conditions. TPPase activity was positive in two and sometimes three cisternae of the inner Golgi lamellae as well as in the condensing vacuoles of the trans area, but negative in the rigid lamellae and small vesicles of the trans area. AcPase activity was demonstrated in two and sometimes three cisternae of inner Golgi lamellae, condensing vacuoles, rigid lamellae, lysosomes and smooth or coated vesicles in the trans area. The inner Golgi lamellae and the condensing vacuoles were positive for both enzyme activities. From these facts, the lysosome is considered to be formed not only in the GERL system but also through the rough endoplasmic reticulum-Golgi apparatus route. It is reasonable to consider that Novikoff's GERL is not independent from the Golgi apparatus but represents a part of this organelle.This study was supported by a grant from the Japan Educational Ministry     

Effect of colchicine on the Golgi complex of rat pancreatic acinar cells

Colchicine administered to adult rats at a dosage of 0.5 mg/100 g of body weight effected a disorganization of the Golgi apparatus in pancreatic acinar cells. The results obtained after various periods of treatment (10 min to 6 h) showed (a) changes in all components of the Golgi complex, and (b) occurrence of large vacuoles that predominated in cytoplasmic areas outside the Golgi region. The alterations in Golgi stacks concerned elements of the proximal and distal side: (a) accumulation of transport vesicles, (b) formation of small, polymorphic secretion granules, and (c) alterations in the cytochemical localization of enzymes and reaction product after osmification. Transport vesicles accumulated and accompanied short, dilated cisternae, which lack mostly the reaction products of thiamine pyrophosphatase, inosine diphosphatase, and acid phosphatase, and osmium deposits after prolonged osmification. After 4 to 6 h of treatment, accumulated transport vesicles occupied extensive cellular areas; stacked cisternae were not demonstrable in these regions. The changes on the distal Golgi side included GERL elements: condensing vacuoles were diminished; they were substituted by small, polymorphic zymogen granules, which appeared to be formed by distal Golgi cisternae and by rigid lamellae. Unusually extended coated regions covered condensing vacuoles, rigid lamellae, and polymorphic secretion granules. A cytochemical distinction between Golgi components and GERL was possible neither in controls nor after colchicine treatment. The cytochemical alterations in Golgi components were demonstrable 20-30 min following administration of colchicine; at 45 min, initial morphological changes--augmentation of transport vesicles and formation of polymorphic zymogen granules--became apparent. 20 min after administration of colchicine, conspicuous groups of large vacuoles occurred. They were located mostly in distinct fields between cisternae of the endoplasmic reticulum, and were accompanied by small osmium--reactive vesicles. Stacked cisternae were not demonstrable in these fields. Vacuoles and vesicles were devoid of reaction products of thiamine pyrophosphatase, inosine diphosphatase, and acid phosphatase. The results provide evidence that formation of stacked Golgi cisternae is impaired after colchicine treatment. The colchicine--induced disintegration of the Golgi complex suggests a regulatory function of microtubules in the organization of the Golgi apparatus.     

The Golgi apparatus and lysosomes of rat pancreatic acinar cells following refeeding

Summary The short term effects of refeeding on the Golgi apparatus and lysosomes of the rat exocrine pancreas were evaluated by ultrastructural, morphometric and cytochemical methods. Ten minutes after refeeding, there was a significant enlargement of Golgi cisternae and a significant increase, compared with the controls, in the number of condensing vacuoles and lysosomes. These modifications were accompanied by the appearance of acid phosphatase activity in stacked Golgi cisternae (as well as GERL) of some cells. One hour after refeeding, there were about the same numbers of condensing vacuoles and lysosomes as in the control; Golgi cisternae were still significantly enlarged, compared with the controls, but they were no longer reactive for acid phosphatase. In both fasting and refed animals, acid phosphatase activity was demonstrable in tubular lysosomes.The data are interpreted in terms both of membrane disposal and recycling, leading to enhanced formation of zymogen granules, during physiologically stimulated secretion.     

Chromogranin B (secretogranin I), a neuroendocrine-regulated secretory protein, is sorted to exocrine secretory granules in transgenic mice.

Chromogranin B (CgB, secretogranin I) is a secretory granule matrix protein expressed in a wide variety of endocrine cells and neurons. Here we generated transgenic mice expressing CgB under the control of the human cytomegalovirus promoter. Northern and immunoblot analyses, in situ hybridization and immunocytochemistry revealed that the exocrine pancreas was the tissue with the highest level of ectopic CgB expression. Upon subcellular fractionation of the exocrine pancreas, the distribution of CgB in the various fractions was indistinguishable from that of amylase, an endogenous constituent of zymogen granules. Immunogold electron microscopy of pancreatic acinar cells showed co-localization of CgB with zymogens in Golgi cisternae, condensing vacuoles/immature granules and mature zymogen granules; the ratio of immunoreactivity of CgB to zymogens being highest in condensing vacuoles/immature granules. CgB isolated from zymogen granules of the pancreas of the transgenic mice aggregated in a mildly acidic (pH 5.5) milieu in vitro, suggesting that low pH-induced aggregation contributed to the observed concentration of CgB in condensing vacuoles. Our results show that a neuroendocrine-regulated secretory protein can be sorted to exocrine secretory granules in vivo, and imply that a key feature of CgB sorting in the trans-Golgi network of neuroendocrine cells, i.e. its aggregation-mediated concentration in the course of immature secretory granule formation, also occurs in exocrine cells although secretory protein sorting in these cells is thought to occur largely in the course of secretory granule maturation.     

Cytochemical studies of GERL and its role in secretory granule formation in exocrine cells

Synopsis the structure and cytochemistry of GERL was studied in several different exocrine secretory cells, including the exorbital lacrimal gland, parotid, lingual serous (von Ebner's), submandibular, and sublingual salivary glands, and exocrine pancreas of the rat; the lacrimal, parotid and pancreas of the guinea-pig; and the lacrimal gland of the monkey. GERL was morphologically and cytochemically similar in all cell types studied. It was located in the inner Golgi region and consisted of cisternal and tubular portions. Immature secretory granules were in continuity with GERL through multiple tubular connections. Modified cisternae of endoplasmic reticulum, with ribosomes only on one surface, closely paralleled parts of GERL. GERL and immature granules were intensely reactive for acid phosphatase activity, while the inner Golgi saccules were reactive for thiamine pyrophosphatase and nucleoside diphosphatase activities. In the rat exorbital lacrimal and parotid glands, reaction product for endogenous peroxidase, a secretory enzyme, was present in the endoplasmic reticulum, Golgi saccules, immature and mature secretory granules. GERL was usually free of reaction product or contained only a small amount. The widespread occurrence of GERL in secretory cells, and its intimate involvement with the formation of granules, suggest that it is an integral component of the secretory process.     

Cytochemical localization of acid phosphatase and trimetaphosphatase activities in exocrine acinar cells

Acid phosphatase activity, a lysosomal marker, is commonly demonstrated using the Gomori technique with cytidine 5'-monophosphate or beta-glycerophosphate as substrate. Using this lead capture method on mouse and rat exorbital lacrimal, parotid, and pancreatic acinar cells, reaction product was localized in GERL, forming secretory granules, and secondary lysosomes. However, a different cytochemical localization was observed for inorganic trimetaphosphatase, another lysosomal enzyme. When the technique for trimetaphosphatase activity, a metal chelation method, was applied to exocrine acinar cells, reaction produce was conspicuously absent from GERL and forming secretory granules, but was present in secondary lysosomes, occasionally in Golgi saccules, and in previously unreported basal elongated lysosomes. The differences in the localization of the two enzymatic activities emphasizes the importance of employing more than one substrate where possible, and raises questions concerning the mechanism of delivery of acid hydrolases to secondary lysosomes.     

豚鼠Clara细胞GERL及其在低氧下变化的细胞化学观察

本文对正常和模拟海拔5000米高度24、48和72小时后豚鼠Clara细胞GERL进行了超微结构和ACP活性的电镜酶细胞化学观察。结果表明Clara细胞具发达的GERL,包括ACP阳性的致密膜囊、致密囊泡、有衣小泡和细胞衣被覆区,Clara细胞GERL参与了分泌颗粒的形成。在低氧下GERL肥大,ACP阳性分泌颗粒增多,提示低氧导致GERL功能亢进,形成分泌颗粒的作用增强。     

Fine structural and histochemical studies on salivary glands of Peripatoides novae-zealandiae (Onychophora) with special reference to acid phosphatase distribution

The Onychophora feed on small arthropods and produce saliva when ingesting prey. Although saliva undoubtedly helps to liquefy the food its constituents have not yet been fully described. The salivary glands, two long tubes of glandular epithelium, are known to secrete a powerful protease, however, besides other enzymes and mucus. In Peripatoides novae-zealandiae there are protein-secreting cells of three types, referred to here as columnar, cuboidal and modified cells, and mucus cells. The anterior two-thirds of the gland show most cell diversity, while the posterior region consists mainly of columnar cells. These are the most numerous elements overall and they probably secrete salivary protease. In thick resin sections the granules of all protein-secreting cells stain strongly with methylene blue. Those of columnar cells are markedly uneven in size and accumulate distally, eventually filling the cytoplasm. More proximal Golgi regions may be discernible. Mucus cells are all of one type and their secretion droplets are stained lightly by methylene blue. The electron microscope shows that distal microvilli, desmosomes and septate junctions are common to all gland cells. In columnar cells, secretory material is contributed by Golgi complexes and by rough endoplasmic reticulum. Early secretory vacuoles containing dense material are seen in the concavity of Golgi regions. They are precursors to larger condensing vacuoles whose contents have a more flocculent appearance, and which may attain 3–4 μm in diameter. These evolve into secretory granules, usually of uneven texture, which are up to 2–5 μm in diameter. Histochemical tests for acid phosphatase show moderate amounts of enzyme throughout the gland. In whole mounts and sections the strongest reaction is in a band of cuboidal cells along the anterior median border. Columnar cells show a diffuse cytoplasmic reaction towards the base and sometimes distal to the nucleus, and mucus cells may also react strongly round the nucleus. Cytoplasm near the lumen shows little reaction. The secretory granules do not appear to contain active enzyme. Under the electron microscope a positive reaction for acid phosphatase is seen in lysosomal derivatives near the base and lateral periphery of gland cells. These bodies are probably autophagic vacuoles and they may contain membranous whorls and possibly old secretion granules. Acid phosphatase is involved also in the elaboration of new secretory granules in both columnar and mucus cells. Dense reaction product is found in a system of interconnected tubules and cisternae near the innermost face of the Golgi complex, which is interpreted as GERL. Acid phosphatase is present in the peripheral zone of adjacent early secretory vacuoles, and interconnections occur between GERL and secretory vacuoles. It is suggested that GERL tubules containing the enzyme may fuse with early secretory vacuoles and release acid phosphatase at their periphery. The acid phosphatase reaction is negative in large condensing vacuoles and most secretory granules. These findings are consistent with what is known from mammalian cells, including those of salivary glands.     

A histochemical study of variations in the localization of 5′-nucleotidase activity in the acinar cell of the rat exocrine pancreas over the twenty-four hour period

The circadian variation of 5'-nucleotidase (AMPase) activity was studied in rat pancreatic exocrine cells. The localization of this enzyme, often associated with the plasmalemma, was studied by ultracytochemical methods at six time points over the 24-h period. The localization of AMPase activity exhibited a clear-cut circadian variation. During the light span strong activity was observed on the luminal plasmalemma, negative or weak activity on the baso-lateral plasmalemma and clearly visible activity on intracellular structures such as cytoplasmic vacuoles (fragmentation-like vesicles), dilated rims of the Golgi cisternae (or cisternal ends of the Golgi stacks), condensing vacuoles and lysosomal bodies. During the dark span the activity was detectable only on the baso-lateral plasmalemma. The fact that AMPase activity could not be found on the luminal plasmalemma during the dark span suggests that the luminal membranes may be replaced by the membranes of secretory granules, which do not display AMPase activity. The intracellular localization of AMPase activity during the light span, especially at 08.00 h, includes all cytoplasmic compartments which have hitherto been associated with the intracellular pathway for membrane retrieval from the plasmalemma. Moreover, the appearance of the activity in the dilated rims of the Golgi stack and condensing vacuoles indicates that these compartments may constitute a functional unit.     

CONDENSING VACUOLE CONVERSION AND ZYMOGEN GRANULE DISCHARGE IN PANCREATIC EXOCRINE CELLS: METABOLIC STUDIES

We have examined, in the pancreatic exocrine cell, the metabolic requirements for the conversion of condensing vacuoles into zymogen granules and for the discharge of the contents of zymogen granules. To study condensing vacuole conversion, we pulse labeled guinea pig pancreatic slices for 4 min with leucine-³H and incubated them in chase medium for 20 min to allow labeled proteins to reach condensing vacuoles. Glycolytic and respiratory inhibitors were then added and incubation continued for 60 min to enable labeled proteins to reach granules in control slices. Electron microscope radioautography of cells or of zymogen granule pellets from treated slices showed that a large proportion of prelabeled condensing vacuoles underwent conversion in the presence of the combined inhibitors. Osmotic fragility studies on zymogen granule suspensions suggest that condensation may result from the aggregation of secretory proteins in an osmotically inactive form. Discharge was studied using an in vitro radioassay based on the finding that prelabeled zymogen granules can be induced to release their labeled contents to the incubation medium by carbamylcholine or pancreozymin. Induced discharge is not affected if protein synthesis is blocked by cycloheximide for up to 2 hr, but is strictly dependent on respiration. The data indicate that transport and discharge do not require the pari passu synthesis of secretory or nonsecretory proteins (e.g. membrane proteins), suggesting that the cell may reutilize its membranes during the secretory process. The energy requirements for zymogen discharge may be related to the fusion-fission of the granule membrane with the apical plasmalemma.     

Ultrastructural localization of anionic phospholipids in skeletal muscle plasma membrane

Summary A cytochemical study of acid phosphatase (AcPase) in the lateral prostate of the rat was performed to investigate whether AcP-ase in the secretory apparatus can be distinguished from AcP-ase in lysosomes and their related structures. Two types of AcP-ase were observed in the rat lateral prostate. One was found in the secretory apparatus (Golgi saccules and some Golgi vesicles, condensing and secretory vacuoles), and reacted well with naphthol AS-BI phosphate (N AS-BI P) as substrate; the other was found in the lysosomes and Golgi-associated endoplasmic-reticulum-lysosome system (GERL)-like structure, and reacted well with -glycerophosphate (GP) as substrate. Although the AcP-ase which reacted well with N AS-BI P was also observed in certain portions of pleomorphic lysosomes, it was concluded that it was the same as the AcP-ase found in the condensing and secretory vacuoles, since a lysosome engulfing a condensing vacuole was often observed. Therefore, it is concluded that the AcP-ase in the secretory apparatus in the rat lateral prostate is different from the AcP-ase in lysosomes. Condensing vacuoles appear to originate from particular portions of Golgi saccules, but not from the GERL or GERL-like structure, at least in the rat lateral prostate.     

Regulated secretion of mature cathepsin B from rat exocrine pancreatic cells.

By indirect immunofluorescence and immunogold electron microscopy with an antibody that recognizes specifically the two forms of native mature rat cathepsin B (31 kDa and 5:25 kDa) but not the proenzyme, we detected cathepsin B not only in lysosomes of adult rat exocrine pancreatic cells but also in the trans Golgi condensing vacuoles, the zymogen granules and the pancreatic juice in the intralobular ducts. In contrast, immunocytochemistry with an antibody specific for rat cathepsin D showed the latter to be present in the same cells only in lysosomal compartments as expected. The same pattern of labeling with these two antibodies was found in the first zymogen granules to form in 17-day-old fetal rat pancreas. Counts of the extent of immunogold labeling of cathepsin B in the adult exocrine cells showed that the concentration of the enzyme was only two-fold higher in the lysosomal compartments than in the zymogen granules. To confirm these observations, rat pancreatic postnuclear supernatant (PNS), a fraction enriched in zymogen granules and rat pancreatic juice obtained by catheterization of the pancreatic duct, were subjected to 2D gel electrophoresis followed by immunoblotting with the cathepsin B antibody. All three samples contained a 31 kDa protein recognized by the antibody with a pI of about 4.5, the single chain mature form of cathepsin B. We then radiolabeled pancreatic PNS and zymogen granule fractions with benzyloxycarbonyl-Tyr[125I]-Ala-CHN2, an affinity label that covalently binds to the active sites of mature forms of both cathepsin B and cathepsin L. In both PNS and zymogen granule fractions this reagent labeled cathepsin B. Immunoprecipitation experiments showed that the antibody to cathepsin B recognized specifically both the single chain and the double chain mature forms of cathepsin B in the native state. Finally, Northern blots with a cDNA of rat cathepsin B showed that the concentration of cathepsin B mRNA in total pancreatic RNA increased following in vivo stimulation of the exocrine pancreatic cells with optimal doses of cerulein, a cholecystokinin analogue. We conclude that significant amounts of mature cathepsin B are secreted from exocrine pancreatic cells via the apical regulated exocytotic pathway, and we discuss this in terms of models for sorting of proteins to the cores of dense cored secretory granules.     

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.     

Cytochemical contributions to differentiating GERL from the Golgi apparatus

Synopsis Recent studies from our laboratory are described which deal with endocrine cells (insulinoma, -cells of the pancreas, thyroid epithelial cells), pancreatic exocrine cells, and hepatocytes. These emphasize the importance of the hydrolase-rich specialized region of endoplasmic reticulum, known as GERL, in secretory cells. Also reviewed in this paper are the varied molecular transformations which apparently occur in GERL in different cell types, as reported from other laboratories as well as our own. Evidence of the continuity of GERL with rough endoplasmic reticulum is presented. Two hydrolytic enzyme activities in GERL, in addition to acid phosphatase activity, are recorded. Finally, the use of cytochemical staining procedures in the study of microperoxisomes is briefly described. The Histochemical Journal lecture 1976. Delivered to the Histochemistry and Cytochemistry Section of the Royal Microscopical Society on 14 September 1976     

Synthesis and secretion of the enamel matrix precursor by the kitten secretory ameloblast

Secretory ameloblasts in kitten molar tooth germs were examined with an electron microscope to analyze the synthesis and secretion processes of the enamel matrix precursor. The contents of the secretion granule were identified as fine granular material, which observed in both the rough endoplasmic reticulum and the Golgi cisterns, accumulated in the dilated margins of the innermost Golgi cistern and formed condensing vacuoles. The same kind of condensing vacuoles was also produced from the GERL cisterns. During the secretion granule maturation processes in the Golgi region, the contents accumulated densely and the granules grew smaller. In addition, granule-limiting membranes acquired fine, bristle coats. The mature secretion granules then migrated, along microtubules, into the surfaces of the Tomes processes and finally released their contents by a process of exocytosis at the type 1 face which faces the enamel growth region.     

Localization of acid phosphatase activity in collagen-secreting and collagen-resorbing fibroblasts

The ultrastructural localization of acid phosphatase (ACPase) activity was examined in cultured human gingival fibroblasts in the formative and resorptive phases. In the collagen-secreting fibroblasts, weak ACPase activity was demonstrated in the lysosomes, inner Golgi cisternae, and condensing vacuoles, and none was found in the Golgi-associated endoplasmic reticulum-lysosome system (GERL), presecretory granules, or secretory granules. On the contrary, collagen phagocytosis induced strong ACPase activity in the GERL, which was in addition to the weaker activity found in the same sites as those in the collagen-secreting cells. At the same time, collagen secretion was suppressed, and dense elongated secretory bodies associated with ACPase activity accumulated within the cells. When collagen fibrils had been interiorized in whole or in part within the phagosomes, primary lysosomes derived from the Golgi-GERL complex then fused with them to form phagolysosomes. Collagen degradation occurred within these bodies. The observations indicate significant differences in ACPase activity used as a marker for lysosomal enzyme activities in the different functional phases of fibroblasts. These results suggest that fibroblasts work only one way at a given time, viz., collagen synthesis or collagen degradation.     

Localization of acid phosphatase activity in collagen-secreting and collagen-resorbing fibroblasts

Summary The ultrastructural localization of acid phosphatase (ACPase) activity was examined in cultured human gingival fibroblasts in the formative and resorptive phases.In the collagen-secreting fibroblasts, weak ACPase activity was demonstrated in the lysosomes, inner Golgi cisternae, and condensing vacuoles, and none was found in the Golgi-associated endoplasmic reticulum-lysosome system (GERL), presecretory granules, or secretory granules. On the contrary, collagen phagocytosis induced strong ACPase activity in the GERL, which was in addition to the weaker activity found in the same sites as those in the collagen-secreting cells. At the same time, collagen secretion was suppressed, and dense elongated secretory bodies associated with ACPase activity accumulated within the cells. When collagen fibrils had been interiorized in whole or in part within the phagosomes, primary lysosome derived from the Golgi-GERL complex then fused with them to form phagolysosomes. Collagen degradation occurred within these bodies. the observations indicate significant differences in ACPase activity used as a marker for lysosomal enzyme activities in the different functional phases of fibroblasts.These results suggest that fibroblasts work only one way at a given time, viz., collagen synthesis or collagen degradation.