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D F Wilson

Publications and source records attributed to D F Wilson.

At least 145 records · Page 8Linked to original sources
PubMed1988

Imaging of phosphorescence: a novel method for measuring oxygen distribution in perfused tissue.

The imaging of phosphorescence provides a method for monitoring oxygen distribution within the vascular system of intact tissues. Isolated rat lives were perfused through the portal vein with media containing palladium coproporphyrin, which phosphoresced and was used to image the liver at various perfusion rates. Because oxygen is a powerful quenching agent for phosphors, the transition from well-perfused liver to anoxia (no flow of oxygen) resulted in large increases of phosphorescence. During stepwise restoration of oxygen flow, the phosphorescence images showed marked heterogeneous patterns of tissue reoxygenation, which indicated that there were regional inequalities in oxygen delivery.

Animals↗
PubMed1988

The oxygen dependence of mitochondrial oxidative phosphorylation measured by a new optical method for measuring oxygen concentration.

Oxygen-dependent quenching of phosphorescence has been used to measure the dependence of mitochondrial oxidative phosphorylation on oxygen concentration in suspensions of isolated rat liver mitochondria. An instrument has been designed which simultaneously monitors the phosphorescence lifetime of a fluorophor and the reduction of cytochrome c by dual wavelength spectrophotometry. The phosphorescence lifetime method gives very rapid (less than 100 ms) measure of the oxygen concentration (Vanderkooi, J. M., Maniara, G., Green, T. J., and Wilson, D. F. (1987) J. Biol. Chem. 262, 5476-5482) from concentrations characteristic of air-saturated media to as low as 2 x 10(-8) M. The results may be summarized as follows. For well coupled rat liver mitochondria at pH 7.0 and in the presence of ATP, as the oxygen concentration was lowered, increased cytochrome c reduction was observed to begin at oxygen concentrations greater than 20 microM. For mitochondria in the presence of uncoupler, cytochrome c reduction began at oxygen concentrations less than 1.0 microM. The oxygen dependence of reduction of cytochrome c in well coupled mitochondria treated with ATP was strongly dependent on the pH of the suspending medium. Reduction of cytochrome c began at higher oxygen concentrations as the pH was made more alkaline. The oxygen concentration for half-maximal respiratory rates was much larger for well coupled mitochondria treated with ATP (approximately 0.7 microM) than for mitochondria treated with uncoupler (less than 0.1 microM). It is concluded that the oxygen dependence of mitochondrial oxidative phosphorylation is such that mitochondria could function in their proposed role of tissue oxygen sensors for regulation of such diverse functions as local blood flow and electrical activity in the carotid body.

Adenosine Triphosphate↗
PubMed1988

Phosphorimeters for analysis of decay profiles and real time monitoring of exponential decay and oxygen concentrations.

A phosphorimeter which can be assembled at low cost from mainly commercially available components and which has better time resolution, data acquisition rate, sensitivity, and flexibility than commercially available instruments is described. As a phosphorescence analyzer the instrument can measure phosphorescence lifetimes ranging from approximately 30 microseconds to seconds from samples with variable intensity, excitation, and emission spectra and which may follow complex decay behavior. Configured as a phosphorescence monitor it is designed for fast, repetitive calculation of phosphorescence lifetime, assuming single-exponential decay, and can be used to calculate oxygen concentration in biological samples in real time.

Luminescent Measurements↗
PubMed1988

Myocardial metabolism and coronary flow: effects of endotoxemia.

The effects of sublethal endotoxemia on the regulation of coronary flow by myocardial metabolism were examined in the isolated perfused heart preparation. Fasted Sprague-Dawley rats were injected (ip) with either endotoxin (0.5 mg/kg of body wt) or 5% dextrose 12 h before heart perfusion. The efficacy of endotoxin treatment was determined by measurement of plasma [NH3] and [urea] and colonic temperature. During perfusion with buffer containing glucose-pyruvate, oxygen consumption and coronary flow were increased by 17 and 42%, respectively, in hearts from endotoxin-treated rats as compared with those from controls. In the hearts from endotoxemic animals, the mitochondrial [NAD+]/[NADH] was decreased by approximately 25%, and the active form of pyruvate dehydrogenase was increased by 36% as compared with control hearts. [ATP]f/[ADP]f[Pi] was unaltered. The enhanced metabolic rate was associated with comparable changes in peak systolic pressure development, maximal positive and negative dP/dt, and the tension-time index when measured in the isovolumetric preparation. In these hearts, stimulation of respiration by perfusion with an alternate source of fuel or inhibition by infusion of amytal elicited large, transient increases in the level of coronary flow that returned rapidly to prestimulus values. By contrast, in hearts from controls, the transient increase in flow was coupled to sustained vasodilation, i.e., approximately 30% rise in flow for either metabolic condition. In both groups, [ATP]f/[ADP]f[Pi] either increased or decreased with stimulation or inhibition of respiration, respectively. Adenosine (1.2 microM) produced a 35% increase in flow in the hearts from the control animals, whereas it was without significant effect in those from the endotoxin-treated animals. It is concluded that sublethal endotoxemia causes 1) an increased metabolic rate and enhanced mechanical activity in the heart and 2) an uncoupling of flow from regulation by cardiac metabolism.

Adenine Nucleotides↗
PubMed1988

Neuromuscular transmission changes associated with tolerance development after chronic exposure to diisopropylfluorophosphate.

Three groups of rats were used to examine the basis for tolerance development to chronic exposure to diisopropylfluorophosphate (DFP). One group was injected every 3 days with a low dose of DFP (referred to as DFP1); the second group was similarly injected with a higher dose of DFP (referred to as DFP2) and a third group that served as a control was injected with the diluent, arachis oil. Symptoms of intoxication were mild in DFP1 animals. DFP2 animals initially exhibited severe symptoms of DFP poisoning. However, by the fifth injection, symptoms were mild and it was concluded that the animals had become tolerant to DFP. Animals were sacrificed 24 hr after injection 1, 2 or 7. Acetylcholinesterase activity was depressed in both groups throughout the period of DFP administration. EPPs and MEPPs were recorded from the hemidiaphragm cut muscle preparation to monitor quantal release, binomial statistical parameters of release and spontaneous transmitter release. No significant changes in MEPP amplitude were observed. MEPP frequency was significantly depressed in both groups of DFP-treated animals. When stimulated at 50 Hz the second EPP of the train was significantly depressed relative to the first EPP in the DFP2-treated animals during the initial period of treatment. Quantal release and statistical release measurements were not affected by DFP treatment. The EPP duration was significantly increased in DFP1- and DFP2-treated animals. In DFP2-treated animals that had become tolerant to DFP, the EPP duration had shortened. It is concluded that tolerance development to chronic treatment with DFP is not associated with changes in presynaptic activity or changes in postsynaptic sensitivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholinesterase↗
PubMed1988

Amino acids modulate calcium permeability of the plasma membrane of human neuroblastoma cells.

Four different amino acids (kainate, N-methyl-D-aspartate, L-cysteine sulfinate and D,L-2-amino-5-phosphonovalerate) have been observed to stimulate uptake of 45Ca2+ into human neuroblastoma cells. This stimulation of uptake is specific and many amino acids which are structural analogs of the above compounds are without activity. The calcium movement is not inhibited by compounds which block voltage-dependent calcium channels. Biological specificity is observed in which some cell lines respond to the amino acids and others do not. It is concluded that these amino acids are acting on a class of receptors whose physiological role is modulation of neuronal metabolism by modulating the calcium permeability of the plasma membrane. The amino acids can substitute for the, as yet, unidentified natural agonists, albeit with low affinity.

2-Amino-5-phosphonovalerate↗
PubMed1988

Calcium dependent regulation of catecholamine and serotonin metabolism in human neuroblastoma cells.

Three human neuroblastoma cell lines were shown to have markedly different contents of catecholamines and serotonin. Two of the cell lines (CHP-134 and IMR-5) have higher levels of dopamine and its metabolites, while CHP-404 cells have higher levels of serotonin and its metabolites. Each cell line responded to the addition of D,L-2-amino-5-phosphonovalerate, an agent which increases plasma membrane permeability to Ca2+ (Pastuszko and Wilson, 1988; with striking changes in the metabolism of the neurotransmitters. These changes were dependent on the extracellular calcium concentration and include activation of dopamine synthesis (tyrosine hydroxylase), increased levels of dihydroxyphenylacetic acid and increased formation of N-methylated dopamine derivatives. Catabolism of serotonin to 5-hydroxyindole acetic acid was inhibited while that to 5-hydroxytryptophol was stimulated. These data clearly identify several important sites for regulation of neurotransmitter metabolism by calcium. The mechanisms, direct or indirect, by which the enzyme activities are modulated by calcium remain to be established.

2-Amino-5-phosphonovalerate↗
PubMed1987

Cysteine sulfinate modulated calcium permeability in synaptosomes from rat brain.

Cysteine sulfinate (CSA) was shown to increase 45Ca2+ permeability of plasma membrane of synaptosomes isolated from rat brain. The 45Ca2+ enter through a system which has properties different from those of voltage dependent Ca2+ channels or Na+/Ca2+ exchange. The effect of CSA appeared to be mediated by highly specific receptors saturable by ligand. The high concentrations of CSA required (mM) suggest this amino acid is not the physiological agonist for the receptors.

Amino Acids↗
PubMed1987

Regulation of calcium uptake in synaptosomes from rat brain by DL-2-amino-5-phosphonovaleric acid.

DL-2-Amino-5-phosphonovaleric acid stimulated calcium influx into synaptosomes isolated from rat brain. The increase in Ca2+ permeability of the synaptosomal membranes induced by this amino acid is not markedly dependent on the membrane potential or Na+ concentration. It is postulated that 2-amino-5-phosphonovaleric acid is an agonist for a receptor(s) which regulates intraneuronal free calcium concentrations by modulating a selective calcium channel. The observed stimulation of calcium uptake may provide an assay system for purification of the endogenous ligand for this receptor and for characterization of its physiological role in neuronal function.

2-Amino-5-phosphonovalerate↗
PubMed1987

An optical method for measurement of dioxygen concentration based upon quenching of phosphorescence.

An optical method for measuring oxygen concentrations in aqueous solutions is described. This method is based upon the oxygen-dependent quenching of phosphorescence. Phosphorescence excitation and emission spectra and lifetimes of some of the probe molecules suitable for measurement of oxygen in aqueous solutions are given. The probes include fluorescein derivatives, 4'5'-diiodofluorescein, eosin Y, 5(and 6)-carboxyeosin, erythrosin, and 5(and 6)-carboxyerythrosin as well as the Zn(II), Y(III), Sn(IV), Lu(III), and Pd(II) derivatives of meso-tetra-(4-sulfonatophenyl)-porphine, meso-tetra-(N-methyl-4-pyridyl)-porphine and coproporphyrin. The phosphorescence lifetimes of the given probes were found to depend upon the oxygen concentration by a simple Stern-Volmer relationship with a quenching constant of approximately 10(9) M-1 S-1. Binding of the molecules to bovine serum albumin decreased the quenching constant for oxygen by approximately an order of magnitude and also inhibited probe self-quenching, indicating that at the protein binding site the probes are somewhat protected from collision with quenchers. The use of this optical method for measuring oxygen is demonstrated for reactions catalyzed by glucose oxidase and by cytochrome c oxidase. It is shown that, using this method oxygen concentrations can be measured from approximately 250 microM (air saturation) down to the nanomolar range.

Animals↗
PubMed1987

A versatile and sensitive method for measuring oxygen.

Oxygen dependence of the lifetime of the excited triplet state of phosphorescent molecules can be used to measure the oxygen concentration in aqueous media. These measurements are insensitive to much of the optical interference that limits the usefulness of measurements based on the oxygen dependent quenching of luminescence intensity. The measurements also extend to significantly lower oxygen concentrations than are normally attainable using oxygen electrodes. The phosphorescence lifetimes can be accurately measured from a few microseconds to seconds, permitting a wide dynamic range of oxygen concentration measurements. With currently available probes, for example, it is possible to make continuous measurement of oxygen concentrations from 10(-4) M to 10(-8) M in a single experiment.

Animals↗
PubMed1987

Scanning electron microscopy of incinerated teeth.

The aim of the present scanning electron microscopy study was to document the nature of morphologic changes occurring in human enamel and dentin subjected in vitro to temperatures in the range of 200-1,000 degrees C for variable times. The results of the investigation confirm that human enamel and dentin remain microscopically identifiable after incineration at 1000 degrees C. Furthermore, these tissues remain identifiable after incineration at 1,000 degrees C for periods greater than 3 h. No consistent or reliable differences in morphology could be detected in enamel or mineralized dentin incinerated in the temperature range 200-600 degrees C. Temperature-dependent changes involving the predentin zone were observed. Following incineration at 800 degrees C for over 3 h and at 1,000 degrees C for 3 h, a metamorphosis of enamel and dentin into a globular form was observed.

Adult↗
PubMed1987

Ammonia-induced release of neurotransmitters from rat brain synaptosomes: differences between the effects on amines and amino acids.

The effect of NH4Cl on release of amine and amino acid transmitters from rat brain synaptosomes was investigated. Ammonia (0.1-10 mM) stimulated the secretion of dopamine and 5-hydroxytryptamine in a dose-dependent manner, in a process which was additive with the effect of 40 mM K+, almost unaffected by withdrawal of Ca2+, and markedly decreased by increasing [H+] in the medium. The NH4Cl-induced dopamine efflux, in contrast to that caused by high [K+]e, was inhibited by benztropine. The release of gamma-aminobutyric acid, aspartate, and glutamate was unaltered by [NH4Cl] less than 5 mM, but somewhat stimulated at higher levels. Transmembrane pH gradient, acid inside, was dissipated by NH4Cl in a concentration-dependent manner and the internal alkalinization correlated with the stimulation of the rate of dopamine efflux. Transmembrane electrical potential was unaffected by [ammonia] less than 5 mM, but a small depolarization was observed at higher levels. It is postulated that ammonia-induced alkalinization of the intrasynaptic storage granules causes extrusion of amines into the cytoplasm and their subsequent leakage into the medium through a reversal of the plasma membrane transporters. A lack of correlation between the release of amino acid neurotransmitters and the dissipation of the delta pH suggests that in rat brain intrasynaptic vesicles, acidic inside, are unlikely to store substantial amounts of gamma-aminobutyric acid, aspartate, or glutamate.

Amines↗
PubMed1987

Relationship of myocardial metabolism and coronary flow: dependence on extracellular calcium.

The hypothesis that extracellular [Ca2+] ([Ca2+]e) influences the transmission of vasoregulatory information from the heart to coronary smooth muscle was examined. The isolated, retrogradely perfused rat heart was used to evaluate vascular reactivity to transient infusion of either 0.88 mM Amytal (amobarbital), hypoxia (95% N2-5% CO2), or 12 microM adenosine in the presence and absence of 2.5 microM verapamil. Amytal alone enhanced coronary flow by 78% and lactate efflux by 10-fold, whereas it decreased O2 consumption by 40% and the ratio of the free cytosolic concentrations of ATP-to-ADP times the intracellular concentration of inorganic phosphate ([ATP]f/[ADP]f[Pi]) by 10-fold. These responses were attenuated by preperfusion with verapamil, i.e., flow and lactate efflux increased by 4% and fourfold, respectively, and O2 consumption and [ATP]f/[ADP]f/[Pi] decreased by 8% and threefold, respectively, as compared with values attained with verapamil at steady state. Washout of the calcium channel antagonist by perfusion for 55 min with a verapamil-free medium resulted in a return of metabolic variables to control levels. Subsequent infusion of Amytal induced metabolic changes that were similar to those obtained before exposure to the calcium antagonist, but flow rose only by 26%. Vascular responses to hypoxia were similarly modified, whereas those to adenosine were unaffected. Hearts perfused with media containing either low [Ca2+]e or 10 microM diltiazem and exposed to Amytal produced flow patterns analogous to those perfused with verapamil. These data, in part, distinguish changes in vascular resistance that occur in response to cardiac metabolism from those which result from agents with direct action on smooth muscle, in particular, adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1986

Glutamine metabolism in rat hepatocytes. Stimulation by a nonmetabolizable analog of leucine.

The metabolic effects of beta-(+/-)-2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid (BCH), a nonmetabolizable analog of leucine and known activator of glutamate dehydrogenase, were studied in hepatocytes isolated from fed and fasted rats. With glutamine as substrate, BCH stimulated in a concentration-dependent manner urea synthesis in both physiological states and glucose formation in hepatocytes from fasted rats. Despite the much higher rates of ureagenesis in the fasted animals, the degree of stimulation by BCH, over 2-fold, was similar. The effect of the drug was specific for glutamine since the rates of urea synthesis from NH4Cl, alanine, and asparagine were essentially unaltered. The stimulation of glutamine catabolism by BCH led to a decrease in the content of intracellular glutamine. The redox states of the mitochondrial and cytosolic nicotinamide adenine dinucleotides remained unaltered. In hepatocytes isolated from fasted rats and incubated with 5 mM glutamine the BCH-induced increases in urea, ammonia, and the amino acids, glutamate, aspartate, and alanine, accounted fully for the 2.4-fold rise in glutamine utilization. The stimulatory effects of BCH and glucagon on the formation of glucose, urea, and 14CO2 from [U-14C]glutamine were additive. Aminooxyacetate, and inhibitor of transaminases, neither blocked glutamine catabolism (as measured by the sum of urea, ammonia, and glutamate) nor prevented its activation by BCH. It is suggested that, in isolated hepatocytes, BCH-induced stimulation of glucose and urea formation from glutamine results from activation of glutaminase by a mechanism which is distinct from that of glucagon.

3-Hydroxybutyric Acid↗