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Biomedical subjects

A Amsterdam

Publications and source records attributed to A Amsterdam.

151 records · Page 9Linked to original sources
PubMed1972

Structural and functional characterization of isolated pancreatic exocrine cells.

Viable isolated exocrine cells have been obtained from guinea-pig pancreas by a tissue dissociation procedure using crude collagenase (EC 3.4.4.19) and hyaluronidase (EC 3.2.1.35), chelation of divalent cations, and mild shearing forces. Cell yields are 50-60%, based on recovered DNA, and about 90% of the population consists of exocrine cells which, although rounded up, retain their in situ polarity with regard to regional distribution of zymogen granules and specialization of the former luminal plasmalemma. The isolated cells incorporate labeled amino acids into proteins at linear rates for at least 4 hr at levels comparable to pancreatic slices in vitro; more than 95% of the exocrine cell population is active in this process, as shown by autoradiography. In response to secretogogues at optimal doses (100 muM carbamylcholine; 0.1 muM pancreozymin, or 0.01 muM caerulein), the cells discharge up to 30% of their content of pulse-labeled secretory proteins to the medium over a 3-hr period; in the same time, the controls release about 5% of their content. The results indicate that isolated exocrine cells are capable of synthesizing the processing secretory proteins, and of responding directly to cholinergic and peptidic secretogogues.

Animals↗
PubMed1971

Epinephrine-induced vacuole formation in parotid gland cells and its independence of the secretory process.

Catecholamines cause rapid release of K(+) and formation of vacuoles in acinar gland cells. A high K(+) concentration in the medium bathing parotid gland slices prevents vacuole formation by epinephrine and facilitates the secretion of most of the exportable amylase. N(6)-monobutyryl 3':5'-cyclic AMP does not cause K(+) release and vacuole formation although it efficiently induces amylase secretion. It is suggested that the secretory process is independent of vacuole formation.

Amylases↗
PubMed1971

Concomitant synthesis of membrane protein and exportable protein of the secretory granule in rat parotid gland.

After enzyme secretion the membrane of the secretory granule, which had been fused to the cell membrane, was resorbed into the cell. Experiments were therefore carried out to test whether formation of new secretory granules involves reutilization of the resorbed membrane or synthesis of a new membrane, de novo, from amino acids. Incorporation of amino acids-(14)C into proteins of various cell fractions was measured in vivo, 30, 120, and. 300 min after labeling. At all times the specific radioactivity of the secretory granule membrane was about equal to that of the granule's exportable content. At 120 and 300 min the specific radioactivity of the granule membrane and of the granule content was much higher than that of any other subcellular fraction. It is therefore concluded that the protein of the membrane is synthesized de novo concomitantly with the exportable protein. The proteins of the granule membrane could be distinguished from those of the granule content by gel electrophoresis. All major bands were labeled proportionately to their staining intensity. The amino acid composition of the secretory granule membrane was markedly different from that of the granule's content and also from that of the mitochondrial membrane. The granule membrane showed a high proline content, 30 moles/100 moles amino acids. The analyses show that the radioactivity of the granule membrane is indeed inherent in its proteins and is not due to contamination by other fractions. The possibility is considered that the exportable protein leaves the endoplasmic reticulum already enveloped by the newly synthesized membrane.

Amino Acids↗
PubMed1969

Dynamic changes in the ultrastructure of the acinar cell of the rat parotid gland during the secretory cycle.

Synchronization of the secretory cycle in vivo was obtained by injecting isoprenaline as an inducer of secretion. A quantitative correlation between enzyme release, its subsequent reaccumulation, and the sequence of ultrastructural changes was found. At the ultrastructural level secretion was paralleled by depletion of zymogen granules through fusion of the granule membrane with the lumen membrane and discharge of the content. Each zymogen granule membrane, once connected with the lumen, acted as a lumen membrane. Fusion was thus sequential and resulted in a dramatic enlargement of the lumen space. During the entire process the passage between the lumen and the intercellular space remained blocked by the tight junctions, as shown by their impenetrability to ferritin. Reduction of the lumen size following enzyme discharge seemed to be achieved by withdrawal of lumen membrane in the form of small smooth vesicles which appeared mostly in the apical part of the cell. At the same time, the cell retracted towards the lumen, the whole process being completed within 2 hr from onset of secretion. Disappearance of the smooth vesicle followed, concomitant with formation of many condensing vacuoles and appearance of mature zymogen granules. The fate of the zymogen granule membrane, including its fusion with the lumen membrane, resorption in the form of small smooth vesicles, and its eventual reutilization mediated by the Golgi system, is discussed.

Amylases↗
PubMed1966

Rapid release of the zymogen granule protein by osmium tetroxide and its retention during fixation by glutaraldehyde.

Fixation by osmium tetroxide and glutaraldehyde of zymogen granules isolated from rat parotid and pancreas was investigated. Protein determinations showed that osmium tetroxide caused rapid release of most of the soluble protein of the granule during fixation in buffered isotonic sucrose. Such granules when examined in the electron microscope after shadow casting appeared quite flat, indicating that most of the contents had indeed been removed. Numerous damaged membranes of the granules were also observed. In contrast, zymogen granules fixed by glutaraldehyde and shadow cast essentially retained the spherical shape and the protein contents. The application of the shadow-casting technique in quantitative studies on the protein content of zymogen granules is discussed.

Aldehydes↗
PubMedDate not supplied

Steroid regulation during apoptosis of ovarian follicular cells.

In each estrous cycle, only one follicle, the dominant follicle, reaches full maturation while the other recruited follicles become atretic in a process characteristic of programmed cell death. Moreover, the old corpus luteum formed in a previous cycle undergoes luteolysis by a mechanism also characteristic of programmed cell death. Granulosa cells comprise the largest cell population of the ovarian follicle and are the main source of estradiol and progesterone in the ovary. Their cyclic nature of differentiation and death determines the cyclic secretion of female sex hormones and therefore serve as an excellent model for steroid regulation during apoptosis. The characteristics of granulosa cell apoptosis, as in other cell types, are cell membrane blebbing, DNA degradation and protease activation. In addition, there are specific characteristics of steroidogenic granulosa cell apoptosis, as follows: 1) The trigger for apoptosis may be exerted by different effectors and signal transduction mechanisms during follicle development. For example, tumor necrosis factor (TNF) may trigger granulosa cell apoptosis at early stage of follicular development, while cAMP/p53 signals may trigger this process only in mature preovulatory granulosa cells. 2) cross-talk between paracrine and endocrine signals, and between death genes and tumor suppressor genes, may determine the fate of the granulosa cell. 3) in the mature follicle the follicular basement membrane plays an important role in transmitting survival signals and in prevention of apoptosis. 4) during the initial steps of apoptosis, steroidogenesis may be increased due to clustering of the steroidogenic organelles in the perinuclear region and their exclusion from the apoptotic blebs. 5) Actin cytoskeleton reorganization plays an important role in this compartmentalization as well as in transmitting survival signals exerted by basement membrane, laminin and growth factors which activate tyrosine kinase receptors.

Animals↗