Fast, But Not Slow, Effects of Olivocochlear Activation Are Resistant to Apamin

2001 ◽  
Vol 85 (1) ◽  
pp. 84-88 ◽  
Author(s):  
Naohiro Yoshida ◽  
M. Charles Liberman ◽  
M. Christian Brown ◽  
William F. Sewell
Keyword(s):  
Hair Cells ◽  
Auditory Nerve ◽  
Calcium Release ◽  
High Sensitivity ◽  
High Concentrations ◽  
Efferent Suppression ◽  
In Vivo Effects ◽  
Very High ◽  
Small Conductance

Olivocochlear (OC) efferent suppression of auditory-nerve responses comprises a fast effect lasting tens of milliseconds and a slow effect building and decaying over tens of seconds. Both fast and slow effects are mediated by activation of the same alpha 9 nicotinic receptor. We have hypothesized that fast effects are generated at the OC synapse, but that slow effects reflect activation of calcium-activated potassium (KCa) channels by calcium release from the subsurface cisternae on the basolateral wall of the hair cells. We measured in vivo effects of apamin, a blocker of small-conductance (SK) KCa channels, and charybdotoxin, a blocker of large-conductance KCa channels, perfused through scala tympani, on fast and slow effects evoked by electrical stimulation of the OC bundle in anesthetized guinea pigs. Apamin selectively and reversibly reduced slow-effect amplitude without altering fast effects or baseline amplitude of the auditory-nerve response, but only when perfused at concentrations of 100 μM. In contrast, the effects of charybdotoxin were noted at 30 nM, but were not specific, reducing both afferent and efferent responses. The very high concentrations of apamin needed to block efferent effects contrasts with the high sensitivity of isolated hair cells to apamin's block of acetylcholine's effects. The results suggest that in vivo fast OC effects are dominated by a conductance that is not apamin sensitive.

scholarly journals Overexpression of SK2 Channels Enhances Efferent Suppression of Cochlear Responses Without Enhancing Noise Resistance

2007 ◽  
Vol 97 (4) ◽  
pp. 2930-2936 ◽  
Author(s):  
Stéphane F. Maison ◽  
Lisan L. Parker ◽  
Lucy Young ◽  
John P. Adelman ◽  
Jian Zuo ◽  
...  
Keyword(s):  
Nicotinic Acetylcholine Receptors ◽  
Hair Cells ◽  
Otoacoustic Emissions ◽  
Outer Hair Cell ◽  
Outer Hair Cells ◽  
Sk Channels ◽  
Cochlear Function ◽  
Cochlear Hair Cells ◽  
Efferent Suppression

Cochlear hair cells express SK2, a small-conductance Ca2+-activated K+ channel thought to act in concert with Ca2+-permeable nicotinic acetylcholine receptors (nAChRs) α9 and α10 in mediating suppressive effects of the olivocochlear efferent innervation. To probe the in vivo role of SK2 channels in hearing, we examined gene expression, cochlear function, efferent suppression, and noise vulnerability in mice overexpressing SK2 channels. Cochlear thresholds, as measured by auditory brain stem responses and otoacoustic emissions, were normal in overexpressers as was overall cochlear morphology and the size, number, and distribution of efferent terminals on outer hair cells. Cochlear expression levels of SK2 channels were elevated eightfold without striking changes in other SK channels or in the α9/α10 nAChRs. Shock-evoked efferent suppression of cochlear responses was significantly enhanced in overexpresser mice as seen previously in α9 overexpresser mice; however, in contrast to α9 overexpressers, SK2 overexpressers were not protected from acoustic injury. Results suggest that efferent-mediated cochlear protection is mediated by other downstream effects of ACh-mediated Ca2+ entry different from those involving SK2-mediated hyperpolarization and the associated reduction in outer hair cell electromotility.

scholarly journals Elongated Flexuous Plant Virus-Derived Nanoparticles Functionalized for Autoantibody Detection

Nanomaterials ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1438 ◽  
Author(s):  
Yuste-Calvo ◽  
López-Santalla ◽  
Zurita ◽  
Cruz-Fernández ◽  
Sánchez ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Diagnostic Value ◽  
Turnip Mosaic Virus ◽  
Antibody Detection ◽  
Induction Phase ◽  
Proposed Model ◽  
Inflammatory Processes ◽  
Autoantibody Detection ◽  
Very High

Nanoparticles derived from the elongated flexuous capsids of Turnip mosaic virus (TuMV) have been shown to be efficient tools for antibody sensing with a very high sensitivity if adequately functionalized with the corresponding epitopes. Taking advantage of this possibility, TuMV virus-like particles (VLPs) have been genetically derivatized with a peptide from the chaperonin Hsp60, a protein described to be involved in inflammation processes and autoimmune diseases. Antibodies against the peptide have been previously shown to have a diagnostic value in at least one autoimmune disease, multiple sclerosis. The functionalized Hsp60-VLPs showed their significant increase in sensing potency when compared to monoclonal antibody detection of the peptide in a conventional immunoassay. Additionally, the developed Hsp60-VLPs allowed the detection of autoantibodies against the Hsp60 peptide in an in vivo mouse model of dextran sodium sulfate (DSS)-induced colitis. The detection of minute amounts of the autoantibodies allowed us to perform the analysis of their evolution during the progression of the disease. The anti-Hsp60 autoantibody levels in the sera of the inflamed mice went down during the induction phase of the disease. Increased levels of the anti-HSP60 autoantibodies were detected during the resolution phase of the disease. An extension of a previously proposed model for the involvement of Hsp60 in inflammatory processes is considered, incorporating a role for Hsp60 autoantibodies. This, and related models, can now be experimentally tested thanks to the autoantibody detection hypersensitivity provided by the functionalized VLPs.

scholarly journals Exceptional iron concentrations in larval lampreys (Geotria australis) and the activities of superoxide radical detoxifying enzymes

1988 ◽  
Vol 252 (1) ◽  
pp. 167-172 ◽  
Author(s):  
D J Macey ◽  
M H Cake ◽  
I C Potter
Keyword(s):  
Superoxide Dismutase ◽  
Detoxifying Enzymes ◽  
Geotria Australis ◽  
Measured Activity ◽  
The Mean ◽  
High Concentrations ◽  
Haem Iron ◽  
Very High ◽  
Iron Concentrations

This study aimed to elucidate the way in which larvae of the lamprey Geotria australis counteract the potential problems of the very high concentrations of non-haem iron they contain and thereby avoid the deleterious effects associated with iron overload in other vertebrates. Particular attention has been paid to ascertaining whether increasing concentrations of iron are accompanied by (i) change to a less readily available form of iron and (ii) an increase in the activity of those detoxifying enzymes responsible for minimizing the production of harmful hydroxyl radicals via the Haber-Weiss reaction. The mean concentrations of haemosiderin and ferritin in larval G. australis were each far higher in the nephric fold than in either the liver or intestine, but all these concentrations were much greater than those in rat liver. Since haemosiderin releases iron far more slowly than ferritin, the iron it contains is much less readily available to catalyse the Haber-Weiss reaction. It is thus relevant that (i) non-haem iron in the nephric fold occurred to a greater extent as large dense haemosiderin granules than as ferritin molecules and (ii) the proportion of iron in the form of haemosiderin rose with increasing concentration of total non-haem iron. A strong correlation was also recorded between the activity of superoxide dismutase in the nephric fold and the concentrations of total non-haem iron and its haemosiderin and ferritin components. This demonstrates that enzyme detoxification of O2.- rises with increasing amounts of iron. The exceptional iron concentrations in the nephric fold were not reflected by a greater measured activity of superoxide dismutase than that found in other tissues. However, the nephric fold was shown to contain an augmentation factor which is presumed to enhance the activity of this enzyme in vivo. The activity of catalase and glutathione peroxidase, which catalyse the breakdown of H2O2 to O2 and water, were each significantly correlated with the concentration of ferritin.

scholarly journals INFLUENCE OF ORGANIC PHOSPHATES ON THE ROOT EFFECT OF MULTIPLE FISH HAEMOGLOBINS

1990 ◽  
Vol 149 (1) ◽  
pp. 425-437 ◽  
Author(s):  
BERND PELSTER ◽  
ROY E. WEBER
Keyword(s):  
Root Effect ◽  
Organic Phosphates ◽  
High Concentrations ◽  
Ph Range ◽  
Oxygen Carrying Capacity ◽  
Very High ◽  
Vitro Data ◽  
In Vitro Data

The influence of organic phosphates on the reduction in oxygen-carrying capacity at low pH (Root effect) in multiple fish haemoglobins has been analysed spectrophotometrically. In stripped haemolysates of carp, trout and eel, the Root effect in the presence of ATP was manifested below pH7.0. In the absence of phosphates, it was only found in trout haemolysate In the pH range between 8.5 and 6.1 no Root effect could be induced in the cathodic component (Hbl) of either trout or eel haemoglobin, even in the presence of very high concentrations of ATP or GTP. This was also true for component II (Hbll) of trout. The anodic component (HblV) of both species, however, exhibited a strong Root effect potentiated by NTP. At the same NTP/Hb4 concentration ratio, GTP was much more effective than ATP in both species The involvement of different haemoglobin components in the generation of high oxygen tensions in the fish swimbladder is discussed by comparing in vivo Root effect data obtained with an eel swimbladder preparation with in vitro data measured in eel blood and haemoglobin.

Physiologically silent sodium channels in mammalian outer hair cells

1994 ◽  
Vol 72 (2) ◽  
pp. 1037-1040 ◽  
Author(s):  
C. M. Witt ◽  
H. Y. Hu ◽  
W. E. Brownell ◽  
D. Bertrand
Keyword(s):  
Sodium Channels ◽  
Hair Cells ◽  
Sodium Current ◽  
High Sensitivity ◽  
Outer Hair Cells ◽  
Inward Current ◽  
Cell Recording ◽  
Voltage Dependent

1. Voltage-dependent properties of isolated guinea pig outer hair cells (OHCs) were investigated using whole-cell recording. An inward current was detected in approximately 10% of the cells. This inward current was identified as belonging to the voltage-activated sodium current family on the basis of its high sensitivity to tetrodotoxin and the effect of substitution of impermeant ions. Although this is the first report of a sodium current in the mammalian cochlea, it differs from the classical neuronal sodium current by having a variable magnitude from cell to cell and an inactivation that is shifted to hyperpolarized potentials. The sensory processing role of hair cells in general and outer hair cells in particular could be disrupted by the presence of a regenerative voltage-dependent current. The functional role of the OHC sodium channels is puzzling, particularly as they may be silent in vivo.

Contrast Medium Induced Changes in Granulocyte Adherence in Vitro and during Angiography

1988 ◽  
Vol 29 (5) ◽  
pp. 585-588 ◽  
Author(s):  
E. V. Lang ◽  
E. C. Lasser
Keyword(s):  
Contrast Medium ◽  
Human Body ◽  
Indirect Effect ◽  
Femoral Vein ◽  
The Other ◽  
High Concentrations ◽  
Induced Changes ◽  
Very High

The effect of ioxaglate and diatrizoate on per cent granulocyte adherence to nylon fibers was investigated in blood to which contrast medium was added in vitro and in blood from patients undergoing angiography. Very high concentrations of contrast medium, added to blood in vitro, directly abolished granulocyte adherence to nylon fibers. Intraaortic bolus injections of ioxaglate, but not of saline, transiently increased granulocyte concentrations in the femoral vein. Fractional granulocyte adherence to nylon fibers increased significantly above the baseline when angiographic dosages of contrast medium were diluted by circulation within the human body. On the other hand, dilute concentrations of contrast medium had no effect on per cent granulocyte adherence when added to whole blood in vitro. This indicates that the increased adherence produced in vivo is an indirect effect, which, usually, cannot be simulated in vitro.

A Mitochondrially Targeted Nitroxide JP4-039 Protects and Mitigates against Total Body Irradiation Induced Hematopoietic Syndrome

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 4721-4721 ◽  
Author(s):  
Michael W Epperly ◽  
Joshua G Pierce ◽  
Tracy Dixon ◽  
Darcy Franicola ◽  
Suhua Nie ◽  
...  
Keyword(s):  
Total Body Irradiation ◽  
Fold Increase ◽  
Linear Quadratic ◽  
Mitochondrial Fractions ◽  
High Concentrations ◽  
Total Body ◽  
Induced Apoptosis ◽  
In Vivo Effects

Abstract Nitroxides are efficient scavengers of free radicals and have been proposed for use as radioprotective agents. To circumvent the need for high concentrations for in vivo effects, and to target drugs to the mitochondria to prevent ionizing irradiation-induced apoptosis, we tested a family of compounds based on combining a hemi-gramicidin linker to a nitroxide. One small molecule (JP4-039) produced a 32-fold increased mitochondrial nitroxide localization in 32D cl 3 cells in vitro after one hour incubation at 37°C compared to the unlinked nitroxide tempo at 10uM. The cells were lyzed by rapidly freezing then thawing, followed by centrifugation to yield the nuclear, cytoplasmic, and mitochondrial fractions. EPR was used to quantitate nitroxide in each JP4-039 or tempo treated cell fraction. There was a 32-fold increase in the nitroxide signal for JP4-039 accumulation in the mitochondria compared to the nitroxide tempo. Irradiation survival curves were performed by incubating 32D cl 3 murine hematopoietic progenitor cells in JP4-039 or tempo (1 μM) for one hour before irradiation or by addition immediately following irradiation. The cells were irradiated to doses ranging from 0 to 8 Gy, suspended in methylcellulose-containing media, incubated for seven days at 37°C and colonies of greater than 50 cells were scored. The data was analyzed using linear quadratic and single-hit, multi-target models. Incubation of 32D cl 3 cells in JP4-039 for one hour prior to irradiation resulted in a significant increase in Do to 2.25 ± 0.11 Gy compared to 1.19 ± 0.13 Gy for 32D cl 3 cells alone or 1.32 ± 0.09 Gy for 32D cl 3 cells incubated in tempo (p=0.0042 or 0.0073, respectively). Similar results were achieved giving JP4-039 after irradiation with a Do of 1.97 ± 0.01 Gy (p < 0.0001). To test effectiveness in vivo, C57BL/6NHsd female mice were injected intraperitoneally with JP4-039 or tempo (10 mg/kg) 10 minutes before (or four hours after) total body irradiation to the LD 75/30 dose of 9.75 Gy. Mice were monitored and those moribund from the hematopoietic syndrome were sacrificed. Mice injected with 10 mg/kg JP4-039 before irradiation had a significant increase in survival of 60% compared to 28% for control irradiated mice (p = 0.0005) or 44% for tempo treated mice (p = 0.2252). JP4-039 given after irradiation had a survival of 53% at 30 days after irradiation (p = 0.0474). Thus, JP4-039, a mitochondrial targeted nitroxide, is an effective radioprotector, and mitigator.

Interaction of Bacterial Endotoxin and Liquoid with Blood Platelets: Aggregation and Decrease in the Electrokinetic Charge

1969 ◽  
Vol 22 (01) ◽  
pp. 192-202 ◽  
Author(s):  
K. A Gröttum ◽  
P. F Hjort ◽  
M Jeremic
Keyword(s):  
Platelet Aggregation ◽  
Electrophoretic Mobility ◽  
Blood Platelets ◽  
Human Platelets ◽  
Dextran Sulphate ◽  
Rabbit Platelets ◽  
High Concentrations ◽  
Very High

SummaryThe effects of Endotoxin and Liquoid on the electrophoretic mobility of human platelets and erythrocytes in vitro and on rabbit platelets and erythrocytes in vivo and in vitro have been investigated.Liquoid reduced the electrophoretic mobility of human platelets to 74% of normal and rabbit platelets to 59% in vitro and to 68% of normal in vivo, while the erythrocytes were unchanged. Liquoid induced massive aggregation of both human and rabbit platelets. In very high concentrations, Liquoid increased the electrophoretic mobility of human platelets and did not induce aggregation.Endotoxin reduced the electrophoretic mobility of rabbit platelets to 83% of normal and aggregated the platelets, but had none of these effects on human platelets.The effects of Endotoxin and Liquoid were inhibited by EDTA, but not by ADPase, suggesting that aggregation was not mediated through ADP.We conclude that Liquoid has the same pattern of effects on the electrokinetic charge of platelets and platelet aggregation as the acid polymeric agents dextran sulphate and heparin. There was good correlation between reduction in the electrokinetic charge of the platelets and platelet aggregation. There were striking similarities between the effects of these agents and Endotoxin.

In vitro and in vivo effects of increased concentrations of free fatty acids on free thyroxin measurements as determined by five assays

1990 ◽  
Vol 36 (4) ◽  
pp. 611-613 ◽  
Author(s):  
R Sapin ◽  
J L Schlienger ◽  
F Grunenberger ◽  
F Gasser ◽  
J Chambron
Keyword(s):  
Fatty Acids ◽  
Free Fatty Acids ◽  
The Other ◽  
In Vitro Experiments ◽  
Fat Emulsion ◽  
Before And After ◽  
High Concentrations ◽  
In Vivo Effects

Abstract To compare in vitro and in vivo effects of increased concentrations of free fatty acids (FFA) on free thyroxin (FT4) values, we measured FT4 in three pooled sera supplemented with oleate and in serum from 18 euthyroid patients before and after an infusion of fat emulsion (Intralipid). We used five FT4 RIA kits: two two-step methods [Gammacoat, Baxter (GC); Ria-gnost, Behring (RG)], two analog RIAs [Amerlex-M, Amersham (AM); Coat-Ria, BioMérieux (CR)], and one kit with labeled antibodies [Amerlex-MAB*, Amersham (AA)]. In vitro, at the maximum oleate addition of 5 mmol/L, FT4 increased when measured by the GC and RG kits, decreased by the AM kit, and showed no significant change by the CR and AA kits. In vivo, post-Intralipid, FFA concentrations rose significantly and the FT4 changes agreed with the results of the in vitro experiments, except for the RG kit, for which FT4 increased in only nine patients. We conclude that in vitro oleate addition is useful to predict the in vivo effect of increased FFA on FT4 values; moreover, in serum from euthyroid subjects with high concentrations of FFA, FT4 analyzed with the CR or AA kits should better agree with normal results for thyrotropin than FT4 values measured with the other kits.

Kinetic analysis of Arabidopsis glucosyltransferase UGT74B1 illustrates a general mechanism by which enzymes can escape product inhibition

2013 ◽  
Vol 450 (1) ◽  
pp. 37-46 ◽  
Author(s):  
Jakub Kopycki ◽  
Elizabeth Wieduwild ◽  
Janine Kohlschmidt ◽  
Wolfgang Brandt ◽  
Anna N. Stepanova ◽  
...  
Keyword(s):  
Natural Products ◽  
Plant Defence ◽  
Product Inhibition ◽  
General Mechanism ◽  
Substrate Affinity ◽  
Knockout Mutants ◽  
High Concentrations ◽  
Very High

Plant genomes encode numerous small molecule glycosyltransferases which modulate the solubility, activity, immunogenicity and/or reactivity of hormones, xenobiotics and natural products. The products of these enzymes can accumulate to very high concentrations, yet somehow avoid inhibiting their own biosynthesis. Glucosyltransferase UGT74B1 (UDP-glycosyltransferase 74B1) catalyses the penultimate step in the core biosynthetic pathway of glucosinolates, a group of natural products with important functions in plant defence against pests and pathogens. We found that mutation of the highly conserved Ser284 to leucine [wei9-1 (weak ethylene insensitive)] caused only very mild morphological and metabolic phenotypes, in dramatic contrast with knockout mutants, indicating that steady state glucosinolate levels are actively regulated even in unchallenged plants. Analysis of the effects of the mutation via a structural modelling approach indicated that the affected serine interacts directly with UDP-glucose, but also predicted alterations in acceptor substrate affinity and the kcat value, sparking an interest in the kinetic behaviour of the wild-type enzyme. Initial velocity and inhibition studies revealed that UGT74B1 is not inhibited by its glycoside product. Together with the effects of the missense mutation, these findings are most consistent with a partial rapid equilibrium ordered mechanism. This model explains the lack of product inhibition observed both in vitro and in vivo, illustrating a general mechanism whereby enzymes can continue to function even at very high product/precursor ratios.

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