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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The electrophysiological properties of gonadotrophs have been studied in vitro, using the ovine adenohypophyseal pars tuberalis as a naturally enriched source of this cell type. Trypsin-dispersed pars tuberalis cells maintained in primary tissue culture had a membrane potential of -72 +/- 4 mV (mean +/- SEM) and an input resistance of 314 +/- 38 M omega. Spontaneous action potentials were not observed; however, a single spike could be induced by depolarizing current injection. The hypophysiotrophic peptide gonadotrophin-releasing hormone (GnRH) increased membrane voltage fluctuations, but these fluctuations (+/- 5-10 mV) did not induce action potentials or changes in membrane potential or resistance. Power spectra obtained from analysis of this noise indicated that the fundamental event underlying GnRH action has a mean life-time of 38.4 +/- 4.5 ms. The observations that cells incubated in recording medium secreted luteinizing hormone in response to GnRH and that the GnRH-induced increase in voltage noise was inhibited by Ca2+ channel antagonists support the hypotheses (1) that gonadotrophin secretion is initiated by GnRH-induced Ca2+ channel activation and (2) that action potentials are not a prerequisite for gonadotrophin release.
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PMID:Electrophysiological recordings from gonadotrophs. Evidence for Ca2+ channels mediated by gonadotrophin-releasing hormone. 241 85

Osmium impregnation techniques have become useful for imparting conductivity to tissue specimens for SEM, thereby avoiding coating with gold or other metals. Such techniques have been developed to produce aesthetically pleasing images of mammalian (particularly human) chromosomes prepared by standard cytogenetical methods which use methanol-acetic acid fixation. The present study was designed: (1) to examine changes in the appearance of chromosomes as a result of preparation by osmium impregnation techniques; (2) to assess the function and importance of the various stages of chromosome preparation; and (3) to identify the chemical groups responsible for osmium binding. Methanol-acetic acid fixed chromosomes are known to have lost many proteins during fixation, and appear to be flattened down on the substrate. Osmium impregnation swells these flattened chromosomes to a variable extent, but the result is inevitably an artefact, albeit a useful one, and not a true representation of the chromosome in vivo. The size of chromatin fibres, for example, is the consequence of the degree of protein extraction during fixation, the loss of material during pre-treatments (e.g. trypsin), and the amount of osmium uptake during impregnation. Trypsin pre-treatment removes a surface coating of protein from the chromosomes as well as exposing chemical groups which can react with osmium. The principal reactive site appears to be amino groups, which bind glutaraldehyde, which in turn binds thiocarbohydrazide, to which the osmium becomes attached. Pre-treatments other than trypsin can be used to extract chromosomal material and to reveal different aspects of chromosome structure.
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PMID:Factors affecting preparation of chromosomes for scanning electron microscopy using osmium impregnation. 261 57

A simple and efficient method for the analysis of the affinity and number of functional transferrin receptors (TFR) on human tumor cells is described. The technique is designed to utilize microtitration equipment; and is suitable for easy comparison of up to 8 different cell preparations per assay. Using this technique, 5 established cell lines were evaluated for functional TFR expression. The control erythroleukemic cell line K562 possessed 3.28 X 10(5) functional TFR per cell (+/- 3.69 X 10(4), SEM) Kd = 9.0 X 10(-9) X M-1. Trypsin and heat-pretreated cells were compared to control erythroleukemic K562 cells from the same culture to determine both the effects of receptor removal and cell viability on the assay. Trypsin and heat pretreatment of these K562 cells severely decreased receptor function as indicated by Scatchard analysis as well as by time course and cold competition analysis respectively. Whereas the affinity of trypsin-treated receptors on cells was similar to control values, heat-killed cells displayed an altered cellular affinity for 125I-transferrin underscoring the importance of utilizing cells of high viability in receptor assays.
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PMID:A rapid and efficient microtechnique for the analysis of functional transferrin receptors on tumor cells. 298 58

Serum trypsin concentrations within the portal venous system have been measured in man during transhepatic portal venography in an attempt to determine its source. In eight experiments, mean serum trypsin concentration at the splenic hilum was 180 +/- 25 ng/ml (mean +/- SEM). Trypsin concentration in the rest of the splenic vein was not significantly different. The mean concentrations in the portal vein (210 +/- 32 ng/ml) and within the superior mesenteric vein (233 +/-- 29 ng/ml) were, however, significantly higher than at the hilum (P less than 0.05). Following cholecystokinin-pancreozymin (CCK-PZ) and secretin stimulation, marked increases in serum trypsin concentration were seen within the portal vein (two patients) and deep within the superior mesenteric (two out of three patients). We conclude that circulating serum trypsin is derived, at least in part, from intestinal reabsorption.
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PMID:Origin of circulating serum immunoreactive trypsin in man. 697 4

The retina cognin (a glycoprotein isolated from the surface membrane of neural retina cells of chick embryos and postulated to mediate self-recognition and histogenetic association of retina cells) has been visualized by SEM on the surface of embryonic retina cells in vitro following immunolabeling of the cells with antibodies to the purified cognin and with polystyrene latex microbeads. Trypsin dissociation of retina tissue into separated cells resulted in cognin depletion from the cell surface; following incubation at 37 degrees C the cells regenerated the cognin. Regeneration was fastest and most abundant on cells from the youngest retinas examined; it declined markedly with the embryonic age of the cells, suggesting an age-dependent decrease in cell capacity for cognin formation. Evidence is discussed that the rate and amount of cognin regeneration on the cell surface are temporally-causally correlated with the capacity of the cells to reaggregate into retinotypic tissue. The results support the suggested role of the cognin in the mechanism of self-affinity and morphogenetic association of embryonic neural retinal cells.
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PMID:Age-dependent differences in cognin regeneration on embryonic retina cells: immunolabeling and SEM studies. 699 94

In order to further characterize low density lipoprotein (LDL)-platelet interaction, we investigated the effect of protease pretreatment of human platelets on the subsequent binding of iodinated LDL (125I-LDL). Our results showed that the platelet LDL receptor had a proteolytic susceptibility different from that of both classical LDL receptors and the fibrinogen receptor. Platelet pretreatment with chymotrypsin, trypsin, and pronase (at 50 micrograms/mL) had no effect on 125I-LDL binding, whereas fibroblast 125I-LDL binding was markedly reduced. Mild proteolytic digestion, however (up to 1 mg/mL), was helpful in characterizing the platelet LDL receptor. Scatchard analysis showed that chymotrypsin did not modify LDL binding characteristics, whereas trypsin and pronase altered maximal number of binding sites (Bmax) without variation in dissociation constant. Trypsin increased Bmax approximately twofold (2156 +/- 327 binding sites on control platelets vs. 5246 +/- 296 on treated platelets, P < 0.001, mean +/- SEM, n = 5), but pronase decreased Bmax about 50% (2017 +/- 275 control vs. 1153 +/- 195 treated, P < 0.001). A minimum of 30 min preincubation was required to detect significant effects, and apparent equilibrium was reached by 60 min. Maximal increase in platelet LDL binding sites induced by trypsin was observed at a protein concentration of 1 mg/mL at 37 degrees C, whereas at 4 degrees C no effect was found. In contrast, maximal pronase-inhibitory effect also was observed at 37 degrees C but at higher protein concentration (10 mg/mL). Aprotinin, phenylmethylsulfonylfluoride, and soybean trypsin inhibitor were capable of fully blocking both the stimulation and the inhibition of platelet LDL binding induced by trypsin and pronase, respectively. Platelet pretreatment with both chymotrypsin and pronase (0.5 mg/mL) activated fibrinogen binding sites to a similar extent as ADP (100 microM). Furthermore, LDL (at a protein concentration of 0.3 mg/mL) increased by 81 +/- 6% the binding of fibrinogen to both protease- and ADP-stimulated platelets, but was unable to activate fibrinogen binding sites in unstimulated platelets. Overall, the results suggest that platelet LDL receptor presents a different proteolytic susceptibility in comparison with both "classical" LDL receptor and fibrinogen receptor.
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PMID:Proteolytic susceptibility of platelet low density lipoprotein receptor. 853 80

This study was conducted to determine whether early-passage cultures of bovine endometrial fibroblastic (Fb, n = 7 uteri) and epithelial (Ep, n = 3 uteri) cells produce endothelial mitogens in vitro and to begin characterization of these mitogens. Confluent cultures of Fb and Ep were incubated for 72 h in serum-free media, and the resulting conditioned media (CM) were evaluated for effects on proliferation of bovine aortic endothelial cells. CM from these Fb cultures (n = 8) and Ep cultures (n = 4) stimulated (147 +/- 10% (mean +/- SEM), p < 0.01, and 124 +/- 8%, p < 0.10, respectively) proliferation of endothelial cells compared with control (unconditioned) media. Most of the mitogenic activity of a sample of Fb CM and a sample of Ep CM from one individual uterus bound to heparin-agarose, and each exhibited two major peaks of activity that eluted at 0.9-1.0 and 1.7-1.8 M NaCl; the Fb CM also exhibited an additional heparin-binding peak eluting at 0-0.1 M NaCl. Pooled Fb CM (n = 8 cultures from 7 animals) also contained mitogenic activity for endothelial cells that bound to heparin-agarose, but exhibited three major peaks, eluting at 0.6, 1.1, and 1.8 M NaCl. Pooled Ep CM (n = 4 cultures from 3 animals) showed only one peak of mitogenic activity, which eluted at 0.9 M NaCl. Further characterization indicated that heat treatment reduced the activity of all heparin-binding Fb CM and Ep CM peaks, except the Fb CM peak eluting at 1.7 M NaCl. Trypsin reduced the activity of all peaks except one. Protein-A-purified antibody against fibroblast growth factor 1 (FGF-1) had no or only a slight effect on the mitogenic activity of the peaks. Mitogenic activity of the Fb CM peak eluting at 0.6 M NaCl was reduced by antibody against FGF-2. Activity of the Fb CM and Ep CM peaks that eluted at 1.7-1.8 M NaCl also was immunoneutralized by antibody to FGF-2. These data demonstrate that early passage cultures of endometrial Fb and Ep cells produce heparin-binding endothelial mitogens that appear to be immunologically related to FGF-2. These heparin-binding endothelial mitogens may influence endometrial vascular growth.
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PMID:Production of heparin-binding endothelial mitogens by bovine uterine fibroblastic and epithelial cells. 896 Apr 1

Protease-activated receptors (PARs) belong to the family of membrane receptors coupled to G-proteins; their presence is reported in a wide variety of cells. The object of this study was to demonstrate the presence of PAR-1 and PAR-2 in myenteric glia of the guinea pig, and to elucidate the cellular mechanisms that are triggered upon receptor activation. Thrombin and PAR-1 agonist peptide (PARP-1) activate PAR-1 with a maximum mean +/- SEM change in intracellular calcium concentration with respect to basal level (Delta[Ca2+]i) of 183 +/- 18 nm and 169 +/- 6 nm, respectively. Trypsin and PAR-2 agonist peptide (PARP-2) activate PAR-2 with a maximum Delta[Ca2+]i of 364 +/- 28 nm and 239 +/- 19 nm, respectively. Inhibition of phospholipase C by U73312 (1 microm) decreased the Delta[Ca2+]i due to PAR-1 activation from 167 +/- 10 nm to 87 +/- 6 nm. The PAR-2-mediated Delta[Ca2+]i decreased from 193 +/- 10 nm to 124 +/- 8 nm when phospholipase C activity was inhibited. Blockade of sphingosine kinase with dimethylsphingosine (1 microm) decreased the Delta[Ca2+]i due to PAR-2 activation from 149 +/- 19 nm to 67 +/- 1 nm, but did not influence the PAR-1-mediated Delta[Ca2+]i. PAR-1 and PAR-2 were localized in myenteric glia by immunolabeling. Our results indicate that PAR-1 and PAR-2 are present in myenteric glia of the guinea pig, and their activation leads to increases in intracellular calcium via different signal transduction mechanisms that involve activation of phospholipase C and sphingosine kinase.
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PMID:Presence of functionally active protease-activated receptors 1 and 2 in myenteric glia. 1239 May 17

Magnetic macroporous PGMA and PHEMA microspheres containing carboxyl groups are synthesized by multi-step swelling and polymerization followed by precipitation of iron oxide inside the pores. The microspheres are characterized by SEM, IR spectroscopy, AAS, and zeta-potential measurements. Their functional groups enable bioactive ligands of various sizes and chemical structures to couple covalently. The applicability of these monodisperse magnetic microspheres in biospecific catalysis and bioaffinity separation is confirmed by coupling with the enzyme trypsin and huIgG. Trypsin-modified magnetic PGMA-COOH and PHEMA-COOH microspheres are investigated in terms of their enzyme activity, operational and storage stability. The presence of IgG molecules on microspheres is confirmed.
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PMID:New monodisperse magnetic polymer microspheres biofunctionalized for enzyme catalysis and bioaffinity separations. 2241 61

The preparation of biocatalysts based on immobilized trypsin is of great importance for proteomic research, industrial applications and organic synthesis. Here in, we have developed a facile method to immobilize trypsin on magnetic nanoparticles. Fe3O4 nanoparticles were synthesized by co-precipitating Fe2+and Fe3+in an ammonia solution and then coated by silicon dioxides were developed by sol-gel method. The silica-coated Fe3O4 nanoparticles were further modified with 3-aminopropyltriethoxysilane, resulting in attaching of primary amine groups on the surface of the particles. Trypsin from porcine pancrease was then immobilized on the magnetic core-shell particles by using glutaraldehyde as a cross-linker. The synthesis steps and characterizations of immobilized trypsin were examined by FT-IR, XRD, TGA, EDX and SEM. The results showed that the enzyme immobilization increased the enzyme activity in different pHs and temperatures, without any changes in the optimum pH and temperature for enzyme activity. The Kinetic results showed that the enzyme immobilization decreased and increased Vmax and Km values, respectively. The stability results showed that the enzyme immobilization improved trypsin thermostability in the absence and presence of 10% (v/v) of the used solvents (DMF, THF, DMSO, ACN and 1, 4-Dioxane). The reusability results indicated that the immobilized enzyme maintained 85% of its activity after 6 periods of activity.
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PMID:Immobilization of trypsin onto Fe3O4@SiO2 -NH2 and study of its activity and stability. 2997 3


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