Silver Diamine Fluoride and Potassium Iodide Disruption of In Vitro Streptococcus mutans Biofilm

Purpose: The purpose of this study was to investigate the inhibitory in vitro effects of silver diamine fluoride (SDF) with and without a saturated solution of potassium iodide (SSKI) on established Streptococcus mutans biofilm.Methods: Fifty μl of an overnight S. mutans culture (10⁶ CFU per mL) in Tryptic Soy Broth (TSB) and three ml of fresh TSB supplemented with one percent sucrose (TSBS) were incubated for 24 hours to establish an S. mutans biofilm in six-well tissue culture plates. Four treatments (SDF, SSKI, SDF plus SSKI, and untreated control) were used to disrupt the biofilm. The biofilm groups were each treated with reagent and washed; the biofilm was collected, diluted, and spiral-plated onto blood agar plates; and an automated counting machine was used to determine the bacterial colony forming units (CFU).Results: The control had significantly more CFU than the SSKI, SDF, and SDF plus SSKI groups (P<.0001). The SSKI group had significantly more CFU than the SDF and SDF plus SSKI groups (P<.0001). The SDF group had significantly fewer CFU than the SDF plus SSKI group (P=.02). The reduction from the control was more than seven-fold for SDF, four-fold for SDF plus SSKI, and two-fold for SSKI.Conclusions: SDF alone, SDF plus SSKI, and SSKI disrupted an established S. mutans biofilm. SDF alone had the greatest overall disruption.

Fusion Stage of HIV-1 Entry Depends on Virus-Induced Cell Surface Exposure of Phosphatidylserine

HIV-1 entry into host cells starts with interactions between the viral envelope glycoprotein (Env) and cellular CD4 receptors and coreceptors. Previous work has suggested that efficient HIV entry also depends on intracellular signaling, but this remains controversial. Here we report that formation of the pre-fusion Env-CD4-coreceptor complexes triggers non-apoptotic cell surface exposure of the membrane lipid phosphatidylserine (PS). HIV-1-induced PS redistribution depends on Ca2+ signaling triggered by Env-coreceptor interactions and involves the lipid scramblase TMEM16F. Externalized PS strongly promotes Env-mediated membrane fusion and HIV-1 infection. Blocking externalized PS or suppressing TMEM16F inhibited Env-mediated fusion. Exogenously added PS promoted fusion, with fusion dependence on PS being especially strong for cells with low surface density of coreceptors. These findings suggest that cell-surface PS acts as an important cofactor that promotes the fusogenic restructuring of pre-fusion complexes and likely focuses the infection on cells conducive to PS signaling.

Trans-channel interactions in batrachotoxin-modified skeletal muscle sodium channels: voltage-dependent block by cytoplasmic amines, and the influence of mu-conotoxin GIIIA derivatives and permeant ions

External mu-conotoxins and internal amine blockers inhibit each other's block of voltage-gated sodium channels. We explore the basis of this interaction by measuring the shifts in voltage-dependence of channel inhibition by internal amines induced by two mu-conotoxin derivatives with different charge distributions and net charges. Charge changes on the toxin were made at residue 13, which is thought to penetrate most deeply into the channel, making it likely to have the strongest individual interaction with an internal charged ligand. When an R13Q or R13E molecule was bound to the channel, the voltage dependence of diethylammonium (DEA)-block shifted toward more depolarized potentials (23 mV for R13Q, and 16 mV for R13E). An electrostatic model of the repulsion between DEA and the toxin simulated these data, with a distance between residue 13 of the mu-conotoxin and the DEA-binding site of approximately 15 A. Surprisingly, for tetrapropylammonium, the shifts were only 9 mV for R13Q, and 7 mV for R13E. The smaller shifts associated with R13E, the toxin with a smaller net charge, are generally consistent with an electrostatic interaction. However, the smaller shifts observed for tetrapropylammonium than for DEA suggest that other factors must be involved. Two observations indicate that the coupling of permeant ion occupancy of the channel to blocker binding may contribute to the overall amine-toxin interaction: 1), R13Q binding decreases the apparent affinity of sodium for the conducting pore by approximately 4-fold; and 2), increasing external [Na(+)] decreases block by DEA at constant voltage. Thus, even though a number of studies suggest that sodium channels are occupied by no more than one ion most of the time, measurable coupling occurs between permeant ions and toxin or amine blockers. Such interactions likely determine, in part, the strength of trans-channel, amine-conotoxin interactions.

A napkin-associated outbreak of Burkholderia cenocepacia bacteraemia in haemodialysis patients

This article reports a catheter-related outbreak of bacteraemia involving 38 patients in two haemodialysis units in Verona. Burkholderia cepacia complex strains were isolated from human blood and from an individually wrapped disinfection napkin that was contained in a commercially available, sterile dressing kit used to handle central venous catheters. Micro-organisms isolated from blood cultures and from the napkin were identified by standard procedures and confirmed as B. cenocepacia (genomovar III) by molecular analysis. Using pulsed-field gel electrophoresis analysis, the clinical isolates were indistinguishable or closely related to the B. cenocepacia isolated from the napkin. In conclusion, this study found that a contaminated commercial napkin soaked in quaternary ammonium, even when quality certified, was the source of infection.

Effect of a new hepatoprotective agent, YH-439, on the hepatobiliary transport of organic cations (OCS): Selective inhibition of sinusoidal OCs uptake without influencing glucose uptake and canalicular OCs excretion

The effect of a new hepatoprotective agent, YH-439, on the hepatobiliary transport of a model organic cation (OC), TBuMA (tributylmethylammonium), was investigated. The area under the plasma concentration-time curve (AUC) from time zero to 4 h following iv administration of TBuMA (6.6 micromol/kg) was increased significantly when YH-439 in corn oil (300 mg/kg) was orally administered to rats 24 h prior to the experiment. Nevertheless, the cumulative biliary excretion of TBuMA remained unchanged. As a consequence, the apparent biliary clearance (CLb) of TBuMA was decreased significantly as a result of YH-439 pretreatment, consistent with the fact that the in vivo excretion clearance of TBuMA across the canalicular membrane (CLexc) was not changed by the pretreatment. The in vitro uptake of TBuMA into isolated hepatocytes was decreased by one half by the pretreatment, owing to a decrease in the apparent Vmax and CLlinear, but the Km for the process remained constant. Most interestingly, however, the sinusoidal uptake of glucose, a nutrient, into hepatocytes was not influenced by the pretreatment, suggesting the YH-439 pretreatment specifically impaired the sinusoidal uptake of OCs. Thus, the OC-specific inhibition of hepatic uptake, without influencing the uptake of glucose, a nutrient, appeared to be associated with the hepatoprotective activity of YH-439.

Community Level Analysis: Genetic and Biogeochemical Approaches to Investigate Community Composition and Function in Aerobic Ammonia Oxidation

Aerobic ammonia oxidation is the process that converts ammonium to nitrate and thus links the regeneration of organic nitrogen to fixed nitrogen loss by denitrification. It is performed by a phylogenetically restricted group of Proteobacteria (ammonia-oxidizing bacteria, AOB) that are autotrophic and obligately aerobic. This chapter describes methods for the measurement of ammonia oxidation in the environment, with a focus on seawater systems and stable isotopic tracer methods. It also summarizes the current state of molecular ecological approaches for detection of AOB in the environment and characterization of the composition of AOB assemblages.

Apamin inhibits NO-induced relaxation of the spontaneous contractile activity of the myometrium from non-pregnant women

There is now considerable evidence for the involvement of K+ channels in nitric oxide (NO) induced relaxation of smooth muscles including the myometrium. In order to assess whether apamin-sensitive K+ channels play a role in NO - induced relaxation of the human uterus, we have studied the effect of specific blockers of these channels on the relaxation of myometrium from non-pregnant women. In vitro isometric contractions were recorded in uterine tissues from non-pregnant premenopausal women who had undergone hysterectomy. Apamin (10 nM) and scyllatoxin (10 nM) did not alter spontaneous myometrial contractions. However, 15-min pretreatment of the myometrium strips with apamin completely inhibited relaxation caused by diethylamine-nitric oxide (DEA/NO). The pretreatment with scyllatoxin significantly reduced (about 2.6 times) maximum relaxation of the strips induced by DEA/NO (p < 0.05). These results strongly suggest that, beside Ca2+ and voltage dependent charybdotoxin-sensitive (CTX-sensitive) K+ channels, apamin-sensitive K+ channels are also present in the human non-pregnant myometrium. These channels offer an additional target in the development of new tocolytic agents.

Mechanisms of nitrite accumulation occurring in soilnitrification

Because low concentration of nitrite could be toxic to biological systems and high amounts of nitrite have been observed in a river of northern China since 1990, nitrite from agricultural soil sources should be investigated. In this paper, effects of levels of ammonium-N (NH4+-N), soil pH and nitrification inhibitors on NO2- accumulation, and duration of nitrite in soils were studied. Application of 11.2 mg of nitrapyrin kg(-1) soil or 11.2 mg of sodium azide kg(-1) soil dramatically suppressed nitrite occurrence. Within all incubation times and at all levels of ammonium-N input, we did not detect any measurable NO2-N accumulation in samples of Yellow-brown earth (pH 5.67), but observed huge accumulation in the 2 alkaline soils, Fluvo-aquic loam (pH 7.89) and Fluvo-aquic sand (pH 8.20). The concentrations of nitrite in both alkaline soils were related to ammonium-N levels. The effect of pH on nitrite accumulation was demonstrated by using slurries of Fluvo-aquic sand under continuous aeration and buffers of different pH. Data showed that nitrite concentration increased with the elevated pH, yet that ammonia oxidizers from the original soil (pH 8.2) could adapt to the new medium of low pH (pH 5.35). Dynamic changes of nitrite in soils amended with different rates of nitrite-N were also measured in 6 days. Thereby, we concluded that nitrite was unstable in acid soils, but durable in alkaline soils. The authors suggested that NO2- accumulation in field soils and its subsequent environmental impact should receive more attention.

A comparison of five rapid direct toxicity assessment methods to determine toxicity of pollutants to activated sludge

Five rapid direct toxicity assessment methods were used in three European partner countries to determine the toxicity of single toxicants, mixed toxicants and real industrial wastes. The final aim was to protect microbial degradation of organic wastes in biological treatment processes and hence enhance the quality of treated effluents to be discharged to the environment. Nitrification inhibition, Respirometry, Adenosine triphosphate luminescence and Enzyme inhibition were tested utilising activated sludge as the testing matrix. The Vibrio fischeri toxicity test was used as a surrogate to compare the various microbial bioassays. The IC50 (toxicant concentration eliciting a 50% inhibitory effect) was determined for a number of pollutants including single toxicants Cd, Cr, Cu, Zn, 3,5-dichlorophenol, toluene and linear alkylbenzenesulphonate (LAS); a standard mixture of metals and LAS; a standard mixture of organics and LAS, and 16 industrial effluents. The V. fischeri bioassay was also chosen in order to assess quality control of toxicant preparation during testing in the different laboratories of the partner countries. Comparisons of sensitivity, cost of implementation, cost per test, relevance, and ease of use were made. The most sensitive bioassays were V. fischeri and Nitrification inhibition, however, this depended in the main on the pollutant and mixtures tested. It is recommended that during assessment of wastewater toxicity a suite of tests be used rather than reliance on one particular test.

Characterization and regulation of ammonium transport systems in Citrus plants

We have investigated both the kinetics and regulation of 15NH4+ influx in roots of 3-month-old hydroponically grown Citrus (Citrus sinensis L. Osbeck x Poncirus trifoliata Blanco) seedlings. The 15NH4+ influx is saturable below an external ammonium concentration of 1 mM, indicating the action of a high-affinity transport system (HATS). The HATS is under feedback repression by the N status of the plant, being down-regulated in plants adequately supplied with N during growth, and up-regulated by N-starvation. When assayed between 1 and 50 mM [15NH4+]0, the 15NH4+ influx showed a linear response typical of a low-affinity transport system (LATS). The activity of the LATS increased in plants supplied with NH4+ as compared with plants grown on an N-free medium. Transfer of the plants to N-free solution resulted in a marked decrease in the LATS-mediated 15NH4+ influx. Accordingly, resupply of NH4+ after N-starvation triggered a dramatic stimulation of the activity of the LATS. These data provide evidence that in Citrus plants, the LATS or at least one of its components is inducible by NH4+. Even when up-regulated, both the HATS and the LATS displayed a limited capacity, as compared with that usually found in herbaceous species. The use of various metabolic uncouplers or inhibitors indicated that 15NH4+ influx mediated by the HATS is strongly dependent on energy metabolism and H+ transmembrane electrochemical gradient. By contrast, the LATS is not affected by protonophores or inhibitors of the H(+)-ATPase, suggesting that its activity is mostly driven by the NH4+/NH3 transmembrane gradient. In agreement with these hypotheses, the HATS-mediated 15NH4+ influx was strongly inhibited when the solution pH was raised from 4 to 7, whereas influx mediated by the LATS was slightly stimulated.

Ecological aspects of ntcA gene expression and its use as an indicator of the nitrogen status of marine Synechococcus spp

Nitrogen nutrition in cyanobacteria is regulated by NtcA, a transcriptional activator that is subject to negative control by ammonium. Using Synechococcus sp. strain WH7803 as a model organism, we show that ntcA expression was induced when cells were exposed to nitrogen stress but not when they were subjected to phosphorus or iron deprivation. Transcript levels accumulated in cells grown on a variety of inorganic and organic nitrogen sources, with the sole exception of ammonium. ntcA transcription was induced when ammonium levels dropped below 1 microM and reached maximal levels within 2 h. Furthermore, the addition of more than 1 microM ammonium led to a rapid decline in ntcA mRNA. The negative effect of ammonium was prevented by the addition of L-methionine-D,L-sulfoximine (MSX) and azaserine, inhibitors of ammonium assimilation. Thus, basal ntcA transcript levels are indicative of ammonium utilization. Conversely, the highest ntcA transcript levels were found in cells lacking a nitrogen source capable of supporting growth. Therefore, maximal ntcA expression would indicate nitrogen deprivation. This state of nitrogen deprivation was induced by a 1-h incubation with MSX. The rapid response of ntcA gene expression to the addition of ammonium and MSX was used to design a protocol for assessing relative ntcA transcript levels in field populations of cyanobacteria, from which their nitrogen status can be inferred. ntcA was basally expressed in Synechococcus at a nutrient-enriched site at the northern tip of the Gulf of Aqaba, Red Sea. Therefore, these cyanobacteria were not nitrogen stressed, and their nitrogen requirements were met by regenerated nitrogen in the form of ammonium.

Effects of adenosine A1-receptor activation on torsade de pointes in rabbits

PURPOSE

We tested whether the adenosine A1 receptor agonist, R-PIA, suppressed torsade de pointes (TdP) induced by the delayed rectifier potassium channel blocker clofilium. Furthermore, we studied the underlying mechanism: beta-adrenergic antagonism or ATP-sensitive K+ channel (IK-ATP) opening.

METHODS

In anesthetized rabbits, TdP was induced by simultaneous infusion of clofilium and the alpha1-adrenoceptor agonist methoxamine. Four groups were studied: (1) saline infusion after TdP induction; (2) R-PIA (1.3 mg/kg) infusion; (3) R-PIA infusion after propranolol (2 micromol/kg) pretreatment; (4) R-PIA infusion after glibenclamide (10 micromol/kg) pretreatment.

RESULTS

TdP suppression rate was 0% in group 1, 78% in group 2 (p<0.01 vs. group 1), 67% in group 3 (p<0.05 vs. group 1, p = NS vs. group 2), 33% in group 4 (p = NS vs. group 1, p = 0.08 vs. group 2). TdP induction coincided with increased QT/QTc duration and QT dispersion. TdP suppression coincided with reduced QT dispersion, but further QT/QTc lengthening.

CONCLUSIONS

R-PIA suppressed TdP, not by beta-adrenergic antagonism, but mostly by IK-ATP opening. QT dispersion correlated better with TdP induction/suppression than QT/QTc duration.

Staurosporine blocks evoked release of FM1-43 but not acetylcholine from frog motor nerve terminals

The protein kinase inhibitor staurosporine inhibited, and often abolished, activity-dependent destaining of frog motor nerve terminals that had been preloaded with the fluorescent dye FM1-43. Staurosporine did not, however, block synaptic transmission; staurosporine treated muscles twitched in response to nerve stimulation, and the amplitudes of evoked end plate potentials were reduced only slightly, and in some cases not at all. The blockade of FM1-43 destaining was not reversed by washing, although treatment with black widow spider venom caused complete destaining. Nerve terminal pretreated with staurosporine could subsequently be stained with FM1-43 (and then destained by black widow spider venom). Thus, staurosporine blocked destaining but not staining of nerve terminals. Staurosporine treatment had little effect on the ultra-structure of resting terminals, the main difference we noted being a somewhat closer packing of synaptic vesicles after exposure to staurosporine. However, staurosporine blocked completely the ultrastructural changes produced by prolonged nerve stimulation, such as depletion of synaptic vesicles, appearance of intraterminal cisternae, and the uptake of horseradish peroxidase. The effects of staurosporine were not mimicked by KN-62, H7, calmidozolium, or trifluoroperazine. These and other observations are consistent with, but do not prove the hypothesis that, after exposure to staurosporine, the exocytotic fusion pore behaved like a valve, letting FM1-43 in, but not out, as if staurosporine interfered with the postexocytotic collapse of synaptic vesicles into the surface membrane.

Intestinal ammonium transport by ammonium and hydrogen exchange

BACKGROUND

Ionized ammonia (NH3) transport in the intestine has not been previously established as a mechanism of acidosis in urinary intestinal diversion or hepatic failure.

STUDY DESIGN

The purpose of this study was to establish that ionized transport of ammonium (NH4) occurs in the intestine and to characterize the mechanism of its transport using the methodology of brush border membrane vesicles and acridine orange fluorescence.

RESULTS

An NH4/H exchange was demonstrated and found to be the dominant mechanism causing a pH change when NH4 is transported across the lumenal membrane. Ionized NH4 transport was demonstrated to occur against an NH3 concentration gradient. The Km was 1.02 mmol and the Vmax was 247 U/sec. The Hill coefficient was 0.97, indicating a single port. Ammonium hydrogen exchange could be inhibited by amiloride but not by bumetanide. Sodium, potassium or chloride, or both, did not effect the NH4/H exchanger.

CONCLUSIONS

This study establishes that ionized NH4 transport occurs across the small intestine brush border in exchange for a hydrogen ion.

Mechanism of ammonium transport: inhibition by potassium and barium

Elucidating the precise mechanism of intestinal ammonium transport is critical to the understanding of the acidosis associated with intestinal urinary diversion. Unfortunately, it is incompletely understood and controversial. Recently, we have shown that furosemide and Ba2+ significantly inhibit ammonium absorption in the ileum. On the basis of this and other data, we have suggested that ionized ammonium absorption occurs via K(+)-transport pathways. The present study examines intestinal ammonium absorption and its inhibition by K+ and Ba2+ utilizing a simplified in vivo system in rat distal ileum. Ammonium absorption demonstrates a tendency towards saturation at initial concentrations between 0 and 300 mM/l. Above 300 mM/l. there was a marked increase in ammonium absorption suggesting a possible biological effect of high NH4+ concentrations on the intestinal segment. Potassium inhibits ammonium absorption. K+ (50 mM/l.) significantly inhibited ammonium at an initial concentration of 100 mM/l. (p less than 0.05) and K+ (100 mM/l.) inhibited ammonium absorption at both 50 and 100 mM/l. (p less than 0.05 and p less than 0.01 respectively). Potassium inhibition of ammonium absorption was lost at concentrations above 200 mM/l. suggesting that K+ inhibition occurs via a competitive mechanism. Ba2+ (25 mM/l.) was shown to be a potent inhibitor of ammonium absorption. This significant inhibition persisted at high initial ammonium concentrations suggesting a complex, noncompetitive mechanism of inhibition. In conclusion, this study provides important data further suggesting that ammonium transport in the intestine occurs via K+ transport pathways, and suggests that the traditionally held mechanism of nonionic ammonium diffusion needs reevaluation.

The antagonism of tetracycline and ferric iron in vivo

To test the hypothesis that the in-vivo antibiotic action of tetracycline might be affected by ferric iron and the enhancement of infection by ferric iron by tetracycline, the actions of intraperitoneal antibiotic and local ferric ammonium citrate, given separately and together, were measured in the dorsal skin of guinea-pigs bearing lesions due to staphylococci, streptococci, a Proteus sp., an Erysipelothrix sp., Clostridium perfringens, Pseudomonas aeruginosa, Aeromonas hydrophila and Klebsiella pneumoniae. Tetracycline, given in two intraperitoneal doses of 25 mg/kg at 0 and 2 h after intracutaneous challenge, maintained plasma concentrations of 4-6 micrograms/ml for more than the first 4 h of infection, after which the local lesions had become largely insusceptible to the antibiotic. The intracutaneous injection of Fe 10 micrograms in a volume of 0.1 ml containing the bacteria was sufficient to enhance infection by those strains susceptible to this effect. The in-vivo efficacy of tetracycline was not always related to low MIC; a low MIC was sometimes associated with little action and a high MIC with moderate action. Sixteen organisms were tested. The iron diminished the tetracycline effect only feebly with one staphylococcal strain and the strain of E. rhusiopathiae. In only one case, with a strain of Proteus sp., was the tetracycline action grossly diminished. On the other hand, tetracycline diminished the enhancement effect of iron moderately with three strains of staphylococci and one strain each of K. pneumoniae, P. aeruginosa and C. perfringens, and strongly with two strains of staphylococci, a group-C streptococcus and one strain each of K. pneumoniae, E. rhusiopathiae and A. hydrophila. It is evident that the diminution of tetracycline action by moderate excess of readily available Fe , whether endogenous or administered, is an unlikely event (three instances among the 16 tested) whereas the diminution of the infection-enhancing effect of iron by tetracycline is much more likely (12 instances among the 16). Insofar as a decrease in iron available for enhancement of infection is valid evidence of a diminution of the iron available for necessary physiological processes of the subject treated, our results suggest that these processes might be affected by tetracycline.

Pharmacological study on sympathetic inhibition of the urinary bladder in dogs

The sympathetic inhibitory mechanism in dog urinary bladder studied. The bladder contractions induced by electrical stimulation of the pelvic nerve both proximal and distal to the pelvic plexus and by intraarterial administration of tetramethylammonium (TMA) were inhibited by stimulation of the hypogastric nerve and intraarterial injection of catecholamines. The inhibition by hypogastric nerve stimulation was more potent at the low frequency of pelvic nerve stimulation than at the high frequency. The inhibition of contraction induced by stimulation of the pre-plexal pelvic nerve was antagonized by phentolamine and propranolol, whereas the inhibition of contraction induced by stimulation of the post-plexal pelvic nerve and by TMA treatment were antagonized only by propranolol. It is concluded that inhibition by hypogastric nerve stimulation of bladder contraction induced by pelvic nerve stimulation is composed of two different components. One occurs at the ganglia in the pelvic plexus and is mediated by alpha-adrenoceptors. The other occurs at the post-plexal pelvic pathway, probably at the ganglia in the bladder wall or on the muscle cells, and is mediated by beta-adrenoceptors. Moreover, the alpha-adrenergic action facilitated the pelvic nerve excitation in its pathway from the ganglionic cell bodies to the muscle cells.

Atropine blockade of cholinergic drugs on rabbit stomach muscle

The competition between atropine and a full agonist, carbachol, was tested on dibenamine-pretreated smooth muscle of rabbit stomach. Even after extensive irreversible blockade by dibenamine, atropine blockade of the response to carbachol was still competitive and the atropine affinity constant was unchanged. This differed from the noncompetitive action of atropine in blocking the contractile effects of partial agonists such as pilocarpine or heptyl trimethylammonium. The results thus indicate that it is not possible to convert a full agonist into a partial agonist merely by reducing the number of available cholinergic receptors. The present study compares the competitive effect of atropine on the actions of the full agonist carbachol, under conditions of irreversible blockade, with the competitive effect of atropine on partial agonists such as pilocarpine or heptyl trimethylammonium.

Neutralization effect of some agents on the antimicrobial activity of ammoniacal silver nitrate

The effect of some agents on the antimicrobial activity of ammoniacal silver nitrate, an endodontic medicament, was tested with Streptococcus faecalis by the serial tube dilution method. Its results indicated that sodium hypochlorite, hydrogen peroxide, and blood had a marked inhibitory effect. However, the presence of dentin, necrotic tissue, saliva, and hydrogen sulfide gas liberated from protein decomposition showed no or little effect on the antibacterial properties of the chemical. Since antiseptics or antibiotics generally may be decomposed by necrotic tissues, these findings suggested that the use of ammoniacal silver nitrate not only may resolve the problem of recalcitrant cases in endodontic treatment but also may simplify the disinfecting procedure for root canals.

Effects of glutamate and sulphur containing amino acids on ammonia toxicity and methionine sulphoximine convulsions in mice

Arginine and large doses of glutamate (greater than 500 mg/kg) were found to reduce ammonia toxicity transiently in mice. Smaller doses of glutamate (greater than or equal to 200 mg/kg) were effective when administered with glucose. Cysteic acid, homocysteine and methionine, but not taurine reduced ammonia toxicity. All 4 amino acids reduced the number of convulsions induced by methionine sulphoximine. It is proposed that taurine has a general anticonvulsant action and that cysteic acid, homocysteine and methionine may have a specific effect on the action of ammonia on the central nervous system.

Influence of ammonium ions on mechanical and electrophysiological responses of skeletal muscle

Substitution of ammonium ions for sodium ion initially potentiated and then depressed twitch tension of the frog sartorius muscle. The extent of potentiation and the rate of depression of the twitch were dependent upon the concentration of ammonium ions. Ammonium ion depolarized individual muscle fibers in proportion to concentration. Maximum depolarization (33 mV) occurred in muscles equilibrated in 120 mM ammonium-Ringer for 30 min. At the higher concentration of ammonium (72--120 mM), the potentiation was quickly reversed and the tension response was eliminated completely. The gradual loss of twitch tension was accompanied by progressive decrease in the electrical excitability of individual muscle fibers. Raising the extracellular calcium concentration fivefold reduced the twitch-depressant effect of ammonium ions by maintaining excitability of the muscle fibers. Caffeine contractures (3 and 10 mM) in muscles preequilibrated in 72 mM ammonium-Ringer developed similar tensions to paired controls muscles, but the onset of tension was more rapid in the ammonium-treated muscle. It was concluded that the depression of tension could be accounted for by the loss of membrane excitability and that the evidence did not support the hypothesis that ammonium ions acted at other sites in the excitation contraction coupling.

Chloride-dependent restoration of coupling by oligomycin in rat liver mitochondria

In rat liver mitochondria suspended in KC1 medium, oligomycin interfered with the effect of uncouplers on energy conservation. It antagonized the effect of uncouplers that are weak acids (2,4-dinitrophenol etc.), but enhanced that of the lipid-penetrating cation NN-dimethyl-N'N'-dibenzylammonium. Oligomycin caused none of the above effects when Br- or NO-/3 was substituted for C1- as the major anionic species in the assay medium. The concentration of oligomycin that exerted the above-mentioned effects was lower than that necessary for the inhibition of energy transfer, but was in the range that induced C1- permeation through the cristae membrane. The possible connexion between the effect of oligomycin on C1- permeation and its interference with the action of uncouplers is discussed.

[Comparative study of some quaternary ammoniums neutralizing agents. Influence of the nature of the bacterial strains used]

The neutralising capacity of the anti-bacterial activity of a quaternary ammonium salt, depends on the nature of the bacterial strains used. Consequently, the choice of a neutralising agent of the bactericidal activity can only be made following a preliminary study on several bacterial species. Out of five products which we tested, we found the Tween-lecithin fresh egg mixture alone had satisfactory activity.

Ammonia intoxication in rats: protection by N-carbamoyl-L-glutamate plus L-arginine

Rats given a lethal dose (LD(99.9)) of ammonium acetate (10.8 mmol/kg of body weight) were protected to the extent of 85 and 76% when previously injected with N-carbamoyl glutamate or L-arginine, respectively, at a level of 4 mmol/kg of body weight. At a dose of 1 mmol/kg of body weight, L-arginine protected 24%, while N-carbamoyl-L-glutamate protected 61% of the animals. When a combination of N-carbamoyl-L-glutamate plus L-arginine (1 mmol each per kg of body weight) was injected, 100% of the rats were protected. The efficacy of N-carbamoyl-L-glutamate is related to its role as an activator of mitochondrial carbamoyl phosphate synthetase (EC 2.7.2.5) and its resistance to hydrolysis by tissue acylaminoacid acylase. N-Acetyl-L-glutamate, the naturally occurring and most effective activator of mitochondrial carbamoyl phosphate synthetase, was relatively ineffective in protection against lethal dose of ammonium acetate, because of its ready hydrolysis by acylaminoacid acylase. The findings reported provide a rational basis for the use of N-carbamoyl-L-glutamate plus L-arginine in the prevention and treatment of hyperammonemia in clinical conditions of liver disease and parental infusion of amino acids, and in feeding of urea supplements to ruminants.

The effect of ammonium salts on cerebral and hind-limb consumption of oxygen and glucose in the ventilated dog

1. Ammonium acetate (13 mmol) was injected intravenously over 10 min into fourteen dogs. This consistently caused a transient depression in both cerebral and limb oxygen consumption.

2. An equivalent dose of ammonium chloride given to five dogs caused a similar decrease but ammonium hydroxide caused a slight increase.

3. The decreased cerebral oxygen consumption and blood flow caused by ammonium acetate infusion was abolished by simultaneous intravenous administration of sodium bicarbonate (five dogs). Sodium chloride did not abolish it. Bicarbonate alone did not alter oxygen consumption or blood flow.

Differentiation between the actions of acetylcholine and tetramethylammonium on the isolated taenia of the guinea-pig caecum by hemicholinium-3

1. Contractions of the isolated taenia of the guinea-pig caecum produced by acetylcholine and TMA were examined in the presence of various antagonists and anticholinesterases.2. Hemicholinium-3 (HC-3) (50-400 mug/ml) inhibited contractions or relaxations produced by TMA but not contractions produced by acetylcholine. The inhibition was rapid in onset and readily reversible. Contractions produced by transmural stimulation were unaffected by HC-3 but responses produced by nicotine were inhibited.3. Low concentrations of hyoscine and benzhexol inhibited responses to acetylcholine to a greater extent than those to TMA.4. Morphine, raised concentrations of Mg(++) or reduced concentrations of Ca(++) inhibited contractions produced by TMA and by acetylcholine to a similar extent.5. Edrophonium, in concentrations which preferentially inhibit acetylcholinesterase, increased contractions produced by acetylcholine and converted responses to nicotine or transmural stimulation into contractions or biphasic responses with a marked contraction phase but did not increase contractions produced by TMA.6. Iso-OMPA, in concentrations which preferentially inhibit butyrylcholinesterase, had no effect on responses to acetylcholine, nicotine, transmural stimulation or TMA.7. HC-3 inhibited contractions produced by TMA in the presence of anticholinesterases but had little effect on contractions produced by acetylcholine.8. These results suggest that TMA produces contractions by acting directly on receptors of the smooth muscle. An analysis of possible reasons for HC-3 (in the concentrations used) acting as an antagonist of TMA but not of acetylcholine indicates that the findings do not necessarily contradict the interpretation that both agonists act on the same receptor.

Influence of polyvalent cations on the activation of muscle end plate receptors

The influence of polyvalent cations on the activation of end plate receptors has been studied in vitro on the sartorius muscle of the frog. In the absence of extracellular calcium, the sensitivity of the receptors to depolarizing quaternary ammonium salts was markedly reduced. Maximum receptor activation occurred in those fibers equilibrated in 1.8 mM calcium Ringer solution, with the response being reduced as the calcium concentration was raised or lowered. Magnesium was less efficient than calcium in regulating the sensitivity of the end plate receptors, the maximum receptor response occurring in those fibers equilibrated in 8 mM magnesium Ringer solution. In the presence of lanthanum the end plate response to carbamylcholine or acetylcholine was enhanced. Lanthanum increased the conductance change produced by carbamylcholine both in polarized and in potassium-depolarized fibers. The application of 10(-2) mM lanthanum to the end plate increased MEPP's amplitude, rise time, and half-fall time by 19, 54, and 45%, respectively. The results suggest that polyvalent cations influence postjunctional membrane receptor processes in addition to their well-documented prejunctional action.

Experimental conditions affecting ribonucleic acid polymerase in isolated rat liver nuclei. Effect of nucleoside triphosphate concentration, temperature, ammonium sulphate and heparin

1. The conditions affecting the activity of RNA polymerase in isolated rat liver nuclei were studied with Mg(2+) or Mn(2+) as activating ions. 2. The enzyme assayed with Mg(2+) and at low ionic strength is saturated by a lower concentration of nucleotide substrates than if assayed with Mn(2+) at low ionic strength or with either ion at high ionic strength. 3. At low and at high ionic strength the incorporation of AMP is affected in a similar way by variations in the temperature of incubation. Preincubation at 37 degrees impairs the AMP incorporation. 4. Heparin stimulates the RNA polymerase activity in the presence of Mn(2+). 5. Both ammonium sulphate and heparin ;restart' the reaction if added after 15min., the effect being more marked with ammonium sulphate than with heparin, and also more marked in the presence of Mn(2+) than of Mg(2+). 6. alpha-Amanitin abolishes the effect of ammonium sulphate and of heparin.