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At least 469 records · Page 26Linked to original sources
PubMed1983

Peroxidase secretion from rat lacrimal gland cells in vitro: II. The role of calcium in stimulus-secretion coupling.

The role of calcium in stimulus-secretion coupling in rat lacrimocytes was investigated. Monolayers of lacrimocytes released peroxidase into the incubation medium upon stimulation with calcium ionophore A 23187, L-norepinephrine, L-phenylephrine and tyramine. Our lacrimocyte preparation can be considered free of endogenous catecholamines, because lacrimocytes derived both from normal and from reserpinized rats responded to tyramine with respect to peroxidase secretion. Phenoxybenzamine, cocaine, verapamil and sodiumorthovanadate failed to inhibit the L-phenylephrine-evoked peroxidase secretion. The stimulatory effects of A 23187, L-norepinephrine and L-phenylephrine required extracellular Ca2+ and could be blocked by phentolamine. The action of tyramine was insensitive to all these measures. It is suggested that the stimulus-secretion of peroxidase from lacrimocytes may consist of a Ca2+-dependent phase for stimulants as A 23187, L-norepinephrine and L-phenylephrine and a Ca2+-independent phase for the non-specific tyramine action.

Animals↗
PubMed1987

Effect of hypophysectomy, adrenalectomy, pituitary hormone secretion and gastric acid secretion on neurotensin induced gastric protection against stress gastric lesions.

In previous studies we have established that intracisternal (i.c.) but not peripheral (intravenous) administration of neurotensin (NT), a brain and gastrointestinal tridecapeptide, totally prevents the development of gastric lesions produced by cold-restraint stress (CRS) with food-deprived rats. In this investigation, removal of the pituitary and adrenal gland, anterior pituitary hormone secretion and gastric acid secretion were evaluated independently as potential intermediates for NT's protective effect. NT (30 micrograms) produced a significant reduction of gastric lesions incidence and severity in intact and sham-operated controls. Adrenalectomy, but not hypophysectomy totally blocked the protective effect of i.c. NT. In addition, replacement therapy with s.c. prednisone (1 mg/kg) for 5 days following adrenalectomy did not restore the protective activity of central (i.c.) NT in adrenalectomized rats. A significant reduction of serum levels of TSH, PRL and GH following i.c. NT (30 micrograms) was observed after 2h of CRS. The gastrosecretory studies revealed that i.c. NT (30 micrograms) did not affect gastric acid secretion in pylorus ligated rats. However, blockade of peripheral (gut) cholinergic (muscarinic) receptors with i.p. atropine methylbromide (1 mg/kg) significantly raised gastric pH and reduced gastric acid concentration and output. In conclusion, the results of this study indicate that the acute protective effect of brain NT appears to be mediated, at least in part, by the sympathoadrenomedullary axis, and not by the pituitary gland or substances derived from the pituitary or by inhibition of gastric acid secretion.

Adrenalectomy↗
PubMed1987

Pathways of secretion in the exocrine pancreas: the status of resting secretion.

In the last decade the concept of two distinct pathways of secretion in the exocrine pancreas has slowly emerged. According to this concept, one pathway is involved in stimulated (regulated) conditions and another under resting (constitutive) conditions. This hypothesis was elaborated at first from the comparison of the specific radioactivities of secretory proteins released by the gland under resting and stimulated conditions. Analysis of the protein composition of the juice released under these two physiological conditions further supported that hypothesis. More recent studies compared the kinetic of accumulation of newly synthesized proteins in zymogen granule and their release in the gland lumen. The latter results are in agreement with a model in which secretory proteins are channelled in two separate pathways, one regulated, and one constitutive. Essentially, the constitutive pathway would correspond to a paragranular route in which the proteins would be immediately secreted instead of being stored in zymogen granules. In addition, some of the proteins released in the juice under "resting" conditions are associated to microvesicles. The term "microvesicular secretion" is used to designate that type of secretion.

Animals↗
PubMed1990

Somatostatin secretion and action in the regulation of growth hormone secretion.

The inhibition of growth hormone (GH) secretion by the hypothalamic peptide, somatostatin, is mediated by two critical factors: the concentration of the peptide in hypothalamic portal plasma and the number of somatostatin (SRIF) receptors on the somatotroph. The secretory patterns of SRIF and GH-releasing hormone (GRH) in portal blood of unanesthetized sheep is pulsatile and a close relationship of GRH pulses to those of GH secretion was documented, while those of SRIF appear to have more of a modulatory role on the responses to GRH. Peripheral infusion of SRIF at a rate to provide concentrations comparable to those in the portal system leads to a desensitization of SRIF effects on the somatotroph, likely mediated by down-regulation of SRIF receptors. These effects are believed to modulate the GH responses to GRH secretion in the generation of pulsatile GH secretion.

Animals↗
PubMed1987

A role of diacylglycerol kinase in stimulus-secretion coupling of human platelets. Dissociation of serotonin secretion from Ca2+ mobilization.

The addition of diacylglycerol kinase inhibitor, R 59 022 (6-[2-[4-[(4-fluorophenyl)phenylmethylene]-1-piperidinyl]-7-methyl - 5H-thiazolo[3,2-alpha]pyrimidin-5-one) resulted in a marked accumulation of diacylglycerol in thrombin-stimulated platelets. Release of arachidonic acid induced by thrombin was not affected by the inhibitor. In intact platelets, the conversion of exogenously added 1-oleoyl-2-acetylglycerol to 1-oleoyl-2-acetylphosphatidic acid also was inhibited by the inhibitor. We further investigated the effects of the inhibitor on serotonin secretion and Ca2+ mobilization in thrombin-activated platelets. R 59 022 potentiated serotonin secretion induced by thrombin or 1-oleoyl-2-acetylglycerol. On the other hand, the thrombin-induced increase in cytosolic free Ca2+ concentration measured with aequorin or Quin2 was found to be depressed by R 59 022. These results indicate that diacylglycerol kinase has an important role in regulation of serotonin secretion and that Ca2+ mobilization may not be tightly coupled to serotonin secretion.

Aminoquinolines↗
PubMed1982

Induction of 19S IgM secretion in a murine pre-B cell line, 70Z/3, by cell hybridization with non-secreting myeloma cells.

Somatic cell hybrids were prepared between the TK-deficient variant of murine pre-B cell line, 70Z/3, cells and the HGPRT-deficient variant of non-secreting myeloma cells. Several hybrid clones which secreted IgM but did not express surface IgM were isolated. LPS stimulation did not induce the expression of surface IgM. SDS-PAGE analysis indicated that the IgM secreted by one of the hybrid clones was a 19S pentamer and that the size of its mu-chains was the same as that of mu-chains from MOPC 104E myeloma IgM. Two-dimensional gel electrophoresis of biosynthetically labeled immunoglobulin showed that the same pattern was obtained with kappa-chains from two hybrid clones and from the LPS-induced 70Z/3 cells. The result showed that cell hybridization could induce L-chain synthesis in the pre-B cell line. Anti-idiotypic antibody against the secreted IgM was prepared and it was shown that the surface IgM expressed on all LPS-stimulated 70Z/3 cells bore the same idiotype. Those results indicated that the specificity commitment has already occurred in 70Z/3 cells.

Animals↗
PubMed1984

Mechanism of effector cell blockade--IV. Induction by monoclonal anti-mu or anti-idiotypic antibody, role of secreted IgM and mechanism of decreased secretion.

Effector cell blockade (ECB), the inhibition of antibody synthesis by antigen or antigen-antibody complexes, was shown to be induced by monoclonal anti-mu or anti-idiotypic antibodies. An initial event in the induction of blockade was demonstrated to be the build up on the cell surface of a complex of membrane Ig, and either antigen or anti-mu or anti-Id antibody, together with secreted IgM. Trapping of secreted IgM in this complex was not, however, sufficient to account for the overall reduction in antibody secretion. This reduction was not due to reduced translation of mu mRNA, but rather to blockade of the normal process of assembly of the IgM molecule which was followed by increased intracellular degradation of intermediate precursor molecules. These findings have shown ECB to be a rapidly induced negative feedback control of IgM secretion which, at least initially, could be reversed. ECB may act in vivo as a flexible first-line mechanism for prevention of overproduction of IgM antibodies.

Animals↗
PubMed1984

Intratesticular secretion of a factor(s) with major stimulatory effects on Leydig cell testosterone secretion in vitro.

As intratesticular communication between the Sertoli and Leydig cells must take place via testicular interstitial fluid (IF), we have tested whether this fluid contains a factor(s) which has effect on testosterone secretion by Percoll-purified Leydig cells in vitro. Addition of increasing concentrations of charcoal-stripped IF to Leydig cells caused dose-dependent stimulation of basal testosterone secretion and greatly enhanced the response to a maximally stimulating dose of hCG. These effects were first evident after 2 h of incubation and were progressive up to 24 h. Charcoal-stripped serum from the same donor animals also had some stimulatory effect on basal and, occasionally, on hCG-stimulated testosterone secretion, but the magnitude and pattern of this effect and its limited dose-dependence were very different from the effects seen with IF. The effects of IF and serum were not altered by the addition of an antiserum to LH. It is therefore concluded that testicular IF contains a factor(s), not derived from serum, which can alter Leydig cell testosterone responsiveness. This factor(s) was heat-sensitive with a MW of greater than 10 000 daltons. IF from the abdominal testes of adult rats which had been made unilaterally cryptorchid contained much higher levels of the stimulatory factor(s) compared to the contralateral scrotal testes, and this is of interest because of the well-documented alteration in Sertoli-Leydig cell interaction that occurs in this situation. These results provide the first direct evidence that one or more factors capable of altering testosterone secretion are produced within the testis of the normal adult rat, and raises the possibility that this factors(s) may be involved in the local regulation of the intratesticular testosterone levels.

Animals↗
PubMed1993

Actinobacillus pleuropneumoniae haemolysin II is secreted from Escherichia coli by A. pleuropneumoniae pleurotoxin secretion gene products.

Actinobacillus pleuropneumoniae serotype 2 secretes type II haemolysin and pleurotoxin activities. Here, the genes for type II haemolysin were cloned in Escherichia coli, but type II haemolysin antigen and haemolysin activity were only detected intracellularly and not exported to culture supernatant. It has been reported that the genes for type II haemolysin are not linked to functional secretion genes, while those for pleurotoxin are. In this report the means of secretion of type II haemolysin was examined by constructing a hybrid plasmid carrying the genes required for type II haemolysin expression, together with determinants which allow secretion of pleurotoxin and are linked to the pleurotoxin toxin genes. These genes facilitated the export of type II haemolysin from E. coli, and may perform this function in A. pleuropneumoniae.

Actinobacillus pleuropneumoniae↗
PubMed1993

Use of a gram- signal peptide for protein secretion by gram+ hosts: basic protease of Dichelobacter nodosus is produced and secreted by Bacillus subtilis.

The bprV gene, encoding the extracellular basic protease of the Gram- anaerobic bacterium Dichelobacter nodosus, was expressed and the protein secreted in Bacillus subtilis using the novel cloning/expression vector pNC3 [Wu et al., Gene 106 (1991) 103-107]. The pre- and pro-peptides were processed correctly in this heterologous system, and the 127-amino acid C-terminal extension region was also removed. The recombinant gene product was indistinguishable biochemically or immunochemically from the authentic protease and was able to form crystals upon dialysis, as was found for the authentic protease. This is the first example of the direct secretion of a Gram- extracellular enzyme in B. subtilis via its own signal peptide. The fact that this gene can be expressed and its product secreted in both Escherichia coli and B. subtilis provides a unique opportunity to study and compare the similarities and differences in protein secretion between Gram- and Gram+ organisms.

Amino Acid Sequence↗
PubMed1994

High-level secretion of correctly processed beta-lactamase from Saccharomyces cerevisiae using a high-copy-number secretion vector.

We have sought to obtain a convenient system for the high-level production of secreted proteins in yeast. With the aid of a secretion reporter cassette we examined the secretion of beta-lactamase (Bla) as a model protein and found the highest expression in Saccharomyces cerevisiae using a high-copy-number plasmid. We further developed the high-copy-number plasmid introducing a secretion cassette that has a convenient cloning site coinciding with the sequence encoding the KEX2 cleavage site. Large quantities of correctly-processed product can therefore be obtained. We show that 0.3 g/l of correctly processed beta-lactamase can be obtained in fed-batch cultures without the need for selective media or significant loss of the plasmid.

Amino Acid Sequence↗
PubMed2005

Minimization of aggregation of secreted bivalent anti-human T cell immunotoxin in Pichia pastoris bioreactor culture by optimizing culture conditions for protein secretion.

In a bioreactor culture of genetically engineered Pichia pastoris secreting a bivalent immunotoxin, 64% of the secreted immunotoxin was present in aggregate forms and this resulted in a loss of bioactivity. Biochemical analyses of the secreted immunotoxin and an in vitro aggregation study using purified monomeric immunotoxin suggested that aggregation was primarily an extracellular event. By employing limited methanol feeding at 0.75 mlmin(-1) per 10l initial medium, oxygen consumption was reduced, permitting a lowering of the bioreactor agitation speed from 800 to 400 rpm. By increasing the anti-foam reagent to 0.6 mll(-1), the thickness of the air/liquid interfacial foam layer was reduced by 80%. These steps reduced the immunotoxin aggregates from 64% to 5%. Consequently immunotoxin purification yield was increased from 53.0% to 73.8%. Simultaneously this methodology enhanced immunotoxin secretion to 120 mgl(-1) at 163 h of methanol induction in a toxin resistant production strain. We conclude that minimizing shearing force and reducing the air/liquid interfacial foam area are crucial factors in reducing hydrophobic protein aggregation upon secretory expression in yeast bioreactor cultures.

Bioreactors↗
PubMed2005

hCG Secretion in human choriocarcinoma JAR cells is MAPK but not Stat3 dependent: contributions of TNFalpha and IL-1beta to inflammation-induced hCG secretion.

Inflammatory mediators play critical physiologic roles throughout the course of normal pregnancy. At the same time, uncontrolled inflammation appears to have an adverse affect on pregnancy outcome. Thus, a crucial task of reproductive immunology is to define the mechanisms through which inflammation is controlled at the maternal-fetal interface. We examined the signaling pathways activated in the human choriocarcinoma cell line, JAR, in response to an in vitro model of an inflammatory challenge. We incubated JAR cells with medium from peripheral blood mononuclear cells (PBMC) that had been activated with either LPS or PHA. Conditioned medium from each experimental model induced MAP kinase and Stat3 phosphorylation as well as human chorionic gonadotropin (hCG) secretion from JAR cells. hCG secretion could be blocked by pharmacologic inhibition of MAP kinase but not by inhibition of Stat3 using an siRNA approach. The MAPK activators IL-1beta and TNFalpha both induced hCG secretion from JAR cells, but not the Stat3 activators IFN-gamma and IL-6. Furthermore, hCG secretion induced by conditioned media could be blocked by IL-1 receptor antagonist. We conclude that inflammation at the maternal-fetal interface may involve complex webs of regulatory and counter-regulatory mechanisms that involve multiple cytokines and at least two major, independent cell-signaling systems.

Cell Line, Tumor↗
PubMed2003

Patterns of secretion of mucins and non-mucin glycoproteins in human submandibular/sublingual secretion.

The present investigation has characterised the influence of gustatory stimulation and duration of stimulation on the secretion pattern of salivary mucins MG1 and MG2 and non-mucin glycoproteins in submandibular/sublingual secretion (SMSL). Resting SMSL was collected for three 2 min intervals and stimulated SMSL was collected for ten 1 min intervals from six healthy subjects. Flow rates and total protein were significantly different under the two conditions. The secretion patterns of these proteins under resting and stimulated conditions was examined on periodic acid-Schiff reagent (PAS)-stained polyacrylamide gels using a Kodak Digital-Science Image Station. Image analyses revealed that the level of MG1 increased and the level of MG2 remained nearly the same after stimulation. Six other major glycoproteins (designated Band 1-6) were identified on the basis of their electrophoretic mobilities and immuno-reactivity on Western blots. After stimulation the intensity of Band 1 (lactoferrin and peroxidase) and Band 2 (amylase) decreased whereas the intensity of Band 3 (carbonic anhydrase), Band 4 (proline-rich glycoprotein) and Bands 5 and 6 (basic glycosylated proline-rich proteins) increased. These patterns probably reflect secretion from preformed vesicles since de novo synthesis would be unexpected within the time frame of these experiments. The variable patterns observed suggest that mucins and non-mucin glycoproteins in SMSL derive from different subsets of secretory vesicles, some of which may originate in mucous and others in serous acini, as well as in ductal cells. Quantification of mucins was performed by image analysis technology using purified MG1 and MG2 standards. Finally, the present investigation has shown that the secretory patterns of mucins and non-mucin glycoproteins from submandibular/sublingual glands are complex and represent an important aspect of salivary gland physiology.

Adult↗
PubMed1998

Constitutive secretion of exogenous neurotransmitter by nonneuronal cells: implications for neuronal secretion.

Fibroblasts in cell culture were loaded with exogenous neurotransmitter acetylcholine (ACh). ACh secretion from loaded cells was detected by whole-cell patch clamp recordings from Xenopus myocytes manipulated into contact with ACh-loaded cells. Two different approaches were used for ACh loading. In the first approach, fibroblasts were incubated in the culture medium containing ACh. Recordings from myocytes revealed fast inward currents that resemble miniature endplate currents found at neuromuscular synapses. The currents observed in recordings from myocytes were due to exocytosis of ACh-containing vesicles. Although exogenous ACh penetrated through the plasma membrane of fibroblasts during incubation and was present in the cytoplasm at detectable levels, cytoplasmic ACh did not contribute to the quantal ACh secretion. In the second approach, exogenous ACh was loaded into the cytoplasm of fibroblasts by microinjection. Under these experimental conditions, fibroblasts also exhibited spontaneous quantal ACh secretion. Analysis of the exocytotic events in fibroblasts following two different protocols of ACh loading revealed that the vesicular compartments responsible for uptake of exogenous ACh are associated with the endocytic recycling pathway. Extrapolation of our results to neuronal cells suggest that in cholinergic neurons, in addition to genuine synaptic vesicles, ACh can be secreted by the vesicles participating in endosomal membrane recycling.

Acetylcholine↗
PubMed2000

alpha-fluoromethylhistidine depletes histamine from secreting but not from non-secreting rat stomach ECL cells.

Histamine in the oxyntic mucosa of the rat stomach occurs in mast cells (10%) and ECL cells (90%). Unlike the mast cells, the ECL cells operate under the control of gastrin. alpha-Fluoromethylhistidine, an irreversible inhibitor of the histamine-forming enzyme, histidine decarboxylase depletes ECL-cell but not mast-cell histamine. This report shows that the effectiveness by which histidine decarboxylase inhibition depletes ECL-cell histamine depends on the rate of histamine secretion. Rats received alpha-fluoromethylhistidine by continuous subcutaneous infusion for 24 h. Maximally effective doses (>/=3 mg/kg/h) inhibited histidine decarboxylase and reduced oxyntic mucosal histamine in fed rats by 80-90%. In fasted rats, the reduction was 50%. alpha-Fluoromethylhistidine greatly reduced the number of histamine-immunoreactive ECL cells (immunocytochemistry) and of secretory vesicles in the ECL cells (electron microscopy) in fed but not in fasted rats. The half-life of oxyntic mucosal histamine (determined upon histidine decarboxylase inhibition) was 2.6 h in fed rats and 19.4 h in fasted rats. The amount of histamine secreted in response to gastrin (monitored by gastric submucosal microdialysis) was greatly reduced by alpha-fluoromethylhistidine in fed rats but not in fasted rats. ECL cells were isolated from rat stomach by elutriation (80% purity). Their histamine content was determined after culture, with or without alpha-fluoromethylhistidine, in the presence of varying concentrations of gastrin. In a medium containing 10 nM gastrin, ECL cells responded to a maximally effective concentration of alpha-fluoromethylhistidine (0.1 nM) with 80% reduction in histamine content. In the absence of gastrin, ECL cells responded to alpha-fluoromethylhistidine with 45% reduction of histamine; the releasable histamine pool was unaffected. In conclusion, the combination of histidine decarboxylase inhibition and a high rate of histamine secretion will promptly exhaust the ECL-cell histamine pool, while histidine decarboxylase inhibition and a low secretion rate will affect the histamine pool much less.

Animals↗
PubMed1992

Pulsatile secretion of gonadotropins and prolactin during the follicular and luteal phases of the menstrual cycle: analysis of instantaneous secretion rate and secretory concomitance.

OBJECTIVE: To characterize the pulsatile secretions of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) during the menstrual cycle and to statistically evaluate their secretory concomitance. DESIGN: Pulsatility study performed during the midfollicular and midluteal phases of a same menstrual cycle, blood samples being collected every 10 minutes for 6 hours. SETTING: Participants investigated in the Division of Endocrinology, University Hospital. PARTICIPANTS: Nine healthy women (22 to 38 years) with regular menstrual cycles. MAIN OUTCOME MEASURES: Plasma LH, FSH, and PRL values were analyzed as raw and deconvoluted data, and the specific (nonrandom) secretory concomitance was evaluated statistically. RESULTS: The pulsatile secretion of LH was confirmed, and that of FSH and PRL was clearly established during both phases of the cycle by characterization of peak frequency, period, and amplitude. A specific secretory concomitance was assessed between LH and FSH in the follicular but not the luteal phase, and a tight concomitance between LH and PRL was demonstrated during both phases. CONCLUSIONS: These results are supportive of significant pulsatile secretions of the three hormones during the menstrual cycle, and they are demonstrative of a definite copulsatility of these hormones, suggestive of common regulatory factors in the complex temporal patterns of gonadotropin and PRL secretions along the cycle.

Adult↗
PubMed1995

Molecular analysis of an A-protein secretion mutant of Aeromonas salmonicida reveals a surface layer-specific protein secretion pathway.

The Aeromonas salmonicida Tn5 mutant, A449-TM1, is unable to secrete the surface layer protein (A-protein) through the outer membrane. Immunogold labeling of thin sections of A449-TM1, with polyclonal antisera against the A-protein, showed the accumulation of large quantities of A-protein in an enlarged periplasm. The majority of the labeled A-protein could be seen at the poles of the cells. The ability of A449-TM1 to secrete other extracellular proteins such as hemolysin and protease was not impaired by the Tn5 insertion, which indicates that the mutation in A449-TM1 interferes with a secretion pathway specifically for the translocation of the A-protein through the outer membrane. The mutant, A449-TM1, was shown to be avirulent for fish. A cosmid clone from a gene library of A449-TM1, which contains the Tn5 insertion from the chromosome, was used to identify a 1.4 kb SaII/ClaI fragment from immediately adjacent to the Tn5 insertion. This fragment was used to identify and clone a 4 kb HindIII fragment from a chromosomal DNA digest from the wild-type strain, A449. DNA sequence analysis of this clone identified an open reading frame (ORF) of 1656 bp. The deduced product of this ORF showed sequence similarity to a family of ATP-binding secretion proteins, but appeared to be phylogenetically distinct from these proteins, consistent with its participation in a secretory pathway specific for surface layer protein.

Aeromonas↗