scholarly journals Contraction kinetics of intact and skinned frog muscle fibers and degree of activation. Effects of intracellular Ca2+ on unloaded shortening.

1985 ◽  
Vol 86 (4) ◽  
pp. 479-500 ◽  
Author(s):  
J Gulati ◽  
A Babu
Keyword(s):  
Experimental Conditions ◽  
Bathing Medium ◽  
Internal Load ◽  
Skinned Fiber ◽  
Fiber Properties ◽  
Partial Activation ◽  
A Minor ◽  
Kinetics Of ◽  
Speed Of Shortening

This study addresses a long-standing controversy on the effects of the degree of activation on cross-bridge kinetics in vivo, by utilizing isolated intact and skinned fiber preparations. Steady force levels ranging from 0.1 to 0.76 P0 were achieved at 0 degrees C with temperature-step stimulation of intact fibers by varying the amount of caffeine in the bathing medium. The speed of unloaded shortening (by slack test) was found to be practically constant, which suggests that intracellular Ca2+ in the intact preparation has relatively little effect on isotonic shortening. Along with the results on tetanically stimulated fibers (force, P0), we observed a minor but significant trend for the speed to decline with lowered force levels. This trend is explained by the presence of a constant internal load equaling approximately 1% P0. The effect of Ca2+ on the shortening behavior of skinned fibers was examined at 0 and 10 degrees C. At 0 degrees C, there was practically no effect of Ca2+ on the shortening response in slack tests. At 10 degrees C, there was also no Ca2+ effect during the first activation cycle, but in subsequent cycles the speed of shortening was reduced during partial activation, which indicates that there were permanent changes in the fiber properties under these experimental conditions. The latter result could be explained if the internal load had increased to approximately 5% P0 in the modified skinned fiber (compared with 1% P0 in intact fiber). These findings show that isotonic contraction of frog fibers is intrinsically unaffected by the variations in intracellular Ca2+ that modulated the force over a nearly complete range. The results provide support for the idea that Ca2+ influences the force development in vivo by on-off switching mechanisms.

Different mechanisms in the attachment of cells to native and denatured collagen

1979 ◽  
Vol 38 (1) ◽  
pp. 267-281
Author(s):  
S.L. Schor ◽  
J. Court
Keyword(s):  
Cell Attachment ◽  
Experimental Conditions ◽  
Cell Matrix ◽  
Matrix Interactions ◽  
Independent Mechanism ◽  
Cell Matrix Interactions ◽  
Serum Dependent ◽  
Kinetics Of ◽  
Dependent Mechanism

The attachment of cells to collagen has been reported previously to require the presence of serum and the particular serum protein involved in this process, variously known as CIG, CAP or fibronectin, has been isolated. This conclusion that cell attachment to collagen requires serum (or more precisely, fibronectin) is based on experiments measuring the kinetics of cell attachment to films of collagen. We have measured the kinetics of attachment of HeLa and attachment to films of collagen-containing substrata under a variety of experimental conditions and present evidence that the serum-dependent mechanism of cell attachment described by others is actually only the case for films of denatured collagen, while cell attachment to native collagen fibres occurs by a different, serum-independent, mechanism. The possible relevance of these findings to cell-matrix interactions in vivo is discussed.

scholarly journals Origin and kinetics of pulmonary macrophages during an inflammatory reaction induced by intravenous administration of heat-killed bacillus Calmette-Guérin.

1981 ◽  
Vol 154 (2) ◽  
pp. 235-252 ◽  
Author(s):  
A Blussé van Oud Alblas ◽  
B van der Linden-Schrever ◽  
R van Furth
Keyword(s):  
Inflammatory Reaction ◽  
Population Increase ◽  
Bacillus Calmette Guerin ◽  
Local Production ◽  
In Vivo Labeling ◽  
Pulmonary Macrophages ◽  
A Minor ◽  
Kinetics Of

This report gives a quantitative description of the kinetics of the pulmonary macrophages and their direct precursors during the acute inflammatory reaction in the lungs induced by intravenous injection of heat-killed bacillus Calmette-Guérin (BCG) into specific-pathogen-free mice. After BCG injection, the total number of pulmonary macrophages isolated by lavage and subsequent enzyme digestion of lung tissue increased to 225% of normal within 12 h and, after a minor decrease, rose to a maximum of 250% of normal at 96 h, followed by a decrease to 150% at 144 h, the end of the observation period. The number of circulating monocytes doubled in the first 48 h and stayed close to that level. In vivo and in vitro labeling with [3H]-thymidine showed that an influx of monocytes transforming into pulmonary macrophages was mainly responsible for the population increase. A temporary increase in the number of locally dividing pulmonary macrophages--manifested by an increased in vitro labeling index, reaching a maximum of 9.6% 72 h after BCG injection--made a minor contribution to the population increase. All pulmonary macrophages were classified according to morphological criteria as alveolar-macrophage-like (AML) or non-alveolar-macrophage-like (NAML), and their respective characteristics were established. The in vivo labeling data showed NAML to represent exudate macrophages derived from circulating monocytes entering the interstitial tissue, and these cells changed morphologically into AML upon entering the alveolar hypophase. This mechanism was confirmed by the finding that the interstitially deposited BCG were found first inside NAML and later in AML. The in vivo labeling data showed that local production was mainly a result of division of macrophages that were morphologically identical with normal alveolar macrophages. The former cells, however, derived most probably recently from the circulation, because the turnover of the total population was very high before local macrophage production became maximal. In mice treated with HC before the injection of BCG, this population increase was absent, because of virtual abolition of the initial monocyte influx and absence of the increased local production of macrophages. Calculations showed that the monocyte influx in the first 48 h amounted to approximately 4 x 10(6) cells, i.e., eight times that found in the normal steady state, and that the efflux of pulmonary macrophages in that period amounted to approximately 3.5 x 10(6) cells, i.e., seven times the normal efflux. The local production over the total period of 144 h was only three times that found normally. The results of these quantitative studies show that the increase of the pulmonary macrophage population during an acute inflammation is brought about mainly by monocyte influx and to a minor extent by a temporary increased local production of macrophages. Disposal of interstitially deposited BCG occurred by phagocytosis by local macrophages and the subsequent efflux of the latter.

scholarly journals Chemical Forms of Selenium in the Metal-Resistant Bacterium Ralstonia metallidurans CH34 Exposed to Selenite and Selenate

2005 ◽  
Vol 71 (5) ◽  
pp. 2331-2337 ◽  
Author(s):  
Géraldine Sarret ◽  
Laure Avoscan ◽  
Marie Carrière ◽  
Richard Collins ◽  
Nicolas Geoffroy ◽  
...  
Keyword(s):  
Transformation Product ◽  
Lag Phase ◽  
Elemental Selenium ◽  
Experimental Conditions ◽  
Phase Duration ◽  
Contact Exposure ◽  
Ralstonia Metallidurans ◽  
A Minor ◽  
X Ray Absorption ◽  
Kinetics Of

ABSTRACT Ralstonia metallidurans CH34, a soil bacterium resistant to a variety of metals, is known to reduce selenite to intracellular granules of elemental selenium (Se0). We have studied the kinetics of selenite (SeIV) and selenate (SeVI) accumulation and used X-ray absorption spectroscopy to identify the accumulated form of selenate, as well as possible chemical intermediates during the transformation of these two oxyanions. When introduced during the lag phase, the presence of selenite increased the duration of this phase, as previously observed. Selenite introduction was followed by a period of slow uptake, during which the bacteria contained Se0 and alkyl selenide in equivalent proportions. This suggests that two reactions with similar kinetics take place: an assimilatory pathway leading to alkyl selenide and a slow detoxification pathway leading to Se0. Subsequently, selenite uptake strongly increased (up to 340 mg Se per g of proteins) and Se0 was the predominant transformation product, suggesting an activation of selenite transport and reduction systems after several hours of contact. Exposure to selenate did not induce an increase in the lag phase duration, and the bacteria accumulated approximately 25-fold less Se than when exposed to selenite. SeIV was detected as a transient species in the first 12 h after selenate introduction, Se0 also occurred as a minor species, and the major accumulated form was alkyl selenide. Thus, in the present experimental conditions, selenate mostly follows an assimilatory pathway and the reduction pathway is not activated upon selenate exposure. These results show that R. metallidurans CH34 may be suitable for the remediation of selenite-, but not selenate-, contaminated environments.

Kinetics of Homologous Urea-soluble 131I-Fibrin and 125I-Fibrinogen in Rabbits

1975 ◽  
Author(s):  
G. Müller-Berghaus ◽  
I. Mahn ◽  
G. Kövecker
Keyword(s):  
Exponential Decay ◽  
Distribution Volume ◽  
Fibrinolytic System ◽  
Experimental Conditions ◽  
Soluble Fibrin ◽  
Kinetics Of ◽  
Deutsche Forschungsgemeinschaft

In order to study the in vivo behaviour of soluble fibrin, purified rabbit 13I-fibrinogen was clotted in the presence of EDTA (0.005 M) and aprotinin (100 units/ml), the generated clot dissolved in buffered urea (3.0 M, pH 7.4), and the formed ureasoluble 131I-fibrin injected into rabbits. The behaviour of homologous 125I-fibrinogen was simultaneously studied in the same animals. Results: The distribution volume of 131I-fibrin (44 ml/kg) as well as that of 125I-fibrinogen (45 ml/kf) was nearly identical indicating that the injected soluble fibrin was homogenously distributed in the circulation immediately after injection. The elimination of soluble fibrin from the circulating blood did not represent a monophasic exponential decay. 84% (range: 77–94%) of the injected soluble fibrin disappeared from the circulation during the first 24 hours after injection, whereas only 54% (range: 41–72%) of the injected fibrinogen disappeared during that interval. Under these experimental conditions, the T/2 of fibrinogen was 46 hours. The clearance of urea-soluble fibrin did not influence the kinetics of 13I-fibrinogen. The disappearance of soluble fibrin could not be influenced by treating the animals with aprotinin for fibrinolysis inhibition. The experiments demonstrate that soluble fibrin can be traced in the circulation and cleared from the blood by a mechanism independent of the fibrinolytic system.(Supported by the Deutsche Forschungsgemeinschaft, Bad Godesberg, Germany.)

Extracellular ATP regulates transcervical permeability by modulating two distinct paracellular pathways

1997 ◽  
Vol 272 (5) ◽  
pp. C1602-C1610 ◽  
Author(s):  
G. I. Gorodeski ◽  
J. Goldfarb
Keyword(s):  
Phase I ◽  
Phase Ii ◽  
Extracellular Atp ◽  
Acetoxymethyl Ester ◽  
Experimental Conditions ◽  
Mucus Production ◽  
Atp Regulation ◽  
Junctional Resistance ◽  
Kinetics Of

Extracellular ATP stimulates a biphasic change in transepithelial electrical resistance (RTE) across cultures of human cervical epithelial cells: an acute decrease (phase I), followed by a delayed increase in resistance (phase II). The objective of this study was to determine the contributions of changes in the lateral intercellular space resistance (RLIS) and the tight junctional resistance (RTJ) to the changes in RTE. Phase I and phase II effects were uncoupled by treatment with 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA)-acetoxymethyl ester, which blocks the ATP-induced increases in cytosolic Ca2+ and abolishes phase I. BAPTA-loaded cells differed from control cells in that 1) phase I began when ATP was added, in contrast to a delay of 1.5-3.5 min in phase II, 2) phase I decreases in RLIS followed a simple exponential pattern, in contrast to the complex kinetics of phase II, and 3) the magnitude of phase II varied between 20 and 100% for increases of RTJ in day 2-6 cultures; the phase I decrease of 50% in RLIS was unrelated to different experimental conditions. These results indicate that phase I and phase II are induced simultaneously and independently by ATP, and they contribute to the total changes in RTE. We conclude that ATP regulation of RLIS and RTJ may be important mechanisms of modulating cervical mucus production in vivo.

scholarly journals Kinetics of Enzymatic Mercury Methylation at Nanomolar Concentrations Catalyzed by HgcAB

2019 ◽  
Vol 85 (13) ◽  
Author(s):  
Swapneeta S. Date ◽  
Jerry M. Parks ◽  
Katherine W. Rush ◽  
Judy D. Wall ◽  
Stephen W. Ragsdale ◽  
...  
Keyword(s):  
Developmental Disorders ◽  
Anaerobic Bacteria ◽  
Significant Risk ◽  
Health Concern ◽  
Global Public Health ◽  
Microbial Conversion ◽  
Experimental Conditions ◽  
Cell Lysates ◽  
Kinetics Of

ABSTRACTMethylmercury (MeHg) is a potent bioaccumulative neurotoxin that is produced by certain anaerobic bacteria and archaea. Mercury (Hg) methylation has been linked to the gene pairhgcAB, which encodes a membrane-associated corrinoid protein and a ferredoxin. Although microbial Hg methylation has been characterizedin vivo, the cellular biochemistry and the specific roles of the gene products HgcA and HgcB in Hg methylation are not well understood. Here, we report the kinetics of Hg methylation in cell lysates ofDesulfovibrio desulfuricansND132 at nanomolar Hg concentrations. The enzymatic Hg methylation mediated by HgcAB is highly oxygen sensitive, irreversible, and follows Michaelis-Menten kinetics, with an apparentKmof 3.2 nM andVmaxof 19.7 fmol · min−1· mg−1total protein for the substrate Hg(II). Although the abundance of HgcAB in the cell lysates is extremely low, Hg(II) was quantitatively converted to MeHg at subnanomolar substrate concentrations. Interestingly, increasing thiol/Hg(II) ratios did not impact Hg methylation rates, which suggests that HgcAB-mediated Hg methylation effectively competes with cellular thiols for Hg(II), consistent with the low apparentKm. Supplementation of 5-methyltetrahydrofolate or pyruvate did not enhance MeHg production, while both ATP and a nonhydrolyzable ATP analog decreased Hg methylation rates in cell lysates under the experimental conditions. These studies provide insights into the biomolecular processes associated with Hg methylation in anaerobic bacteria.IMPORTANCEThe concentration of Hg in the biosphere has increased dramatically over the last century as a result of industrial activities. The microbial conversion of inorganic Hg to MeHg is a global public health concern due to bioaccumulation and biomagnification of MeHg in food webs. Exposure to neurotoxic MeHg through the consumption of fish represents a significant risk to human health and can result in neuropathies and developmental disorders. Anaerobic microbial communities in sediments and periphyton biofilms have been identified as sources of MeHg in aquatic systems, but the associated biomolecular mechanisms are not fully understood. In the present study, we investigate the biochemical mechanisms and kinetics of MeHg formation by HgcAB in sulfate-reducing bacteria. These findings advance our understanding of microbial MeHg production and may help inform strategies to limit the formation of MeHg in the environment.

Photochemie von Ribonucleinsäuren

1964 ◽  
Vol 19 (9) ◽  
pp. 815-830 ◽  
Author(s):  
Heinz Schuster
Keyword(s):  
Pyrimidine Ring ◽  
Alkaline Treatment ◽  
Neutral Solution ◽  
Experimental Conditions ◽  
Compound A ◽  
Dark Reaction ◽  
Ribose Phosphate ◽  
Minor Part ◽  
A Minor ◽  
Kinetics Of

Irradiation of uridylic acid (Up) in buffer (at 254 mµ or 280 mµ) yields the hydrated molecule (UpH2O), which on subsequent alkaline treatment decomposes to Up (65%) and a new compound A (35%) with the pyrimidine-ring opened. Irradiation in ice (254 mµ) leads to the formation ofthe uridylic acid dimer (Up/Up), which on re-irradiation reverts to Up (230 mµ, in neutral solution) or compound A, via Up and UpH2O) (254 mµ, in alkaline solution).Similarly the hydrated cytidylic acid (CpH2O) is formed by irradiation of cytidylic acid (Cp) in buffer (254 mµ). In a subsequent dark reaction most of the CpH2O-molecules revert to Cp, a minor part being deaminated to UpH2O. Alkaline treatment of an irradiated Cp-solution yields Cp, Up and compound A, the latter two arising by decomposition of UpH2O. Neither Cp nor Up dimers were found after irradiation of Cp in ice (254 mµ).All the photoproducts of Up and Cp, in which the pyrimidine-ring was still preserved, lost 1 - 3% of their phosphoric acid (Pi) under the experimental conditions.The alkaline decomposition of UpH2O is used as a method for the titration of hydrated uracil residues in irradiated ribonucleic acid (RNA). Following irradiation (254 mµ) the RNA is degraded by alkali completely to mononucleotides and three new photoproducts: compound A, ribose phosphate, and another compound B, which behaves like Up dimer. Form the amount of compound A found, the number of hydrated uracils originally formed can be calculated. Furthermore the kinetics of the formation of the photoproducts are studied.The biological implications of these studies are discussed.

scholarly journals KINETICS OF THROMBIN INACTIVATION AS INFLUENCED BY PHYSICAL CONDITIONS, TRYPSIN, AND SERUM

1940 ◽  
Vol 24 (2) ◽  
pp. 169-188 ◽  
Author(s):  
Anthony J. Glazko ◽  
John H. Ferguson
Keyword(s):  
Major Effect ◽  
Order Reaction ◽  
Minor Effect ◽  
Serum Tryptase ◽  
Experimental Conditions ◽  
First Order ◽  
Physical Conditions ◽  
A New Technique ◽  
A Minor ◽  
Kinetics Of

1. A new technique for studying the progressive inactivation of thrombin is described. 2. Thrombin inactivation follows the kinetics of a first order reaction. 3. The rate constant of the inactivation reaction increases with temperature and pH (5.0 → 10.0), and also with the presence of crystalline trypsin, or serum. The rate varies for different thrombin preparations, even under the same experimental conditions. 4. The temperature characteristics of the reaction indicate that thrombin is associated with protein. 5. Thrombin preparations are most stable at pH 4 to 5, even when trypsin or serum is added. 6. The progressive inactivation is believed to be due to two mechanisms: (1) a major effect, thought to be the action of a "serum-tryptase," which is usually present in the thrombin preparations, and (2) a minor effect, probably attributable to denaturation of thrombin-protein. 7. Sources of the thrombinolytic factor (serum-tryptase) and its implications in the general theory and practical problems of blood coagulation and antithrombic action are briefly discussed.

scholarly journals Posttranslational modifications of alpha tubulin: detyrosination and acetylation differentiate populations of interphase microtubules in cultured cells.

1988 ◽  
Vol 106 (4) ◽  
pp. 1213-1220 ◽  
Author(s):  
J C Bulinski ◽  
J E Richards ◽  
G Piperno
Keyword(s):  
Posttranslational Modifications ◽  
Cultured Cells ◽  
Cell Types ◽  
African Green Monkey Kidney ◽  
Alpha Tubulin ◽  
Acetylated Tubulin ◽  
Minor Population ◽  
A Minor ◽  
Kinetics Of

Subsets of microtubules enriched in posttranslationally detyrosinated (Gundersen, G. G., M. H. Kalnoski, and J. C. Bulinski. 1984. Cell. 38:779) or acetylated (Piperno, G., M. Le Dizet, and X. Chang. 1987. J. Cell Biol. 104:298), alpha tubulin have previously been described in interphase cultured cells. In this study an immunofluorescence comparison of these minor populations of microtubules revealed that, in African green monkey kidney epithelial cells (TC-7 line), the population of microtubules enriched in detyrosinated tubulin was virtually coincident with the population enriched in acetylated alpha tubulin. In some cell types, however, such as human HeLa or marsupial PtK-2 cells, only one posttranslationally modified form of tubulin, i.e., acetylated or detyrosinated, respectively, was detectable in microtubules. In TC-7 cells, although both modifications were present, dissimilar patterns and kinetics of reappearance of microtubules enriched in detyrosinated and acetylated tubulin were observed after recovery of cells from microtubule-depolymerizing treatments or from mitosis. Thus, a minor population of microtubules exists in cultured cells that contains an elevated level of tubulin modified in either one or two ways. While these two modifications occur primarily on the same subset of microtubules, they differ in their patterns of formation in vivo.

Absorption of Galactose by the Rat Small Intestine in Vivo: Proximal—Distal Kinetic Gradients and a New Method to Express Absorption Per Enterocyte

1976 ◽  
Vol 50 (6) ◽  
pp. 499-509 ◽  
Author(s):  
R. M. Batt ◽  
T. J. Peters
Keyword(s):  
Small Intestine ◽  
Absorptive Capacity ◽  
Proximal Jejunum ◽  
Rat Small Intestine ◽  
Experimental Conditions ◽  
Carrier Mediated Transport ◽  
Saturation Kinetics ◽  
Kinetics Of ◽  
Diffusive Component

1. The absorption in vivo of d-galactose by the rat small intestine has been examined in proximal jejunum and distal ileum by use of a recirculation—perfusion technique. 2. Multiple sequential perfusions over 4 h produced no subsequent functional or morphological damage in the perfused segments. 3. Absorption of galactose from 8 and 64 mmol/l solutions was found to be independent of flow rate over the range 1·0–6·5 ml/min. 4. Galactose absorption in both the jejunum and the ileum exhibited saturation kinetics of the Michaelis—Menten type, and phlorrhizin sensitivity. Sorbose was only absorbed minimally. These observations demonstrate that galactose is absorbed by carrier-mediated transport and that there is no significant passive diffusive component in vivo. 5. Under the stated experimental conditions, the maximum absorptive capacity was 4·5 times greater in the jejunum than in the ileum. The Michaelis constant for galactose was higher in the jejunum than in the ileum. 6. Enterocytes were isolated from perfused segments and quantified by DNA assay with a correction for yield. In this manner, the absorptive capacity per enterocyte was calculated. 7. The maximum absorptive capacity per enterocyte was 3·5 times greater in the jejunum than in the ileum.

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