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Biomedical subjects

J A Steele

Publications and source records attributed to J A Steele.

At least 37 records · Page 2Linked to original sources
PubMed1990

Chloride action potentials and currents in embryonic skeletal muscle of the chick.

Chloride-dependent action potentials were elicited from embryonic skeletal muscle fibers of the chick during the last week of in ovo development. The duration of the action potentials was extremely long (greater than 8 sec). The action potentials were reversibly blocked by the stilbene derivative, SITS, a specific blocker of chloride permeability. Using patch clamp pipettes, in which the intracellular chloride concentration was controlled and with other types of ion channels blocked, the membrane potential at the peak of the action potential closely coincided with the chloride equilibrium potential calculated from the Nernst equation. These data indicate that activation of a chloride-selective conductance underlies the long duration action potential. The occurrence of the chloride-dependent action potential was found to increase during embryonic development. The percentage of fibers that displayed the action potential increased from approximately 20% at embryonic day 13 to approximately 70% at hatching. Chloride-dependent action potentials were not found in adult fibers. The voltage and time-dependent currents underlying the action potential were recorded under voltage clamp using the whole-cell version of the patch pipette technique. The reversal potential of the currents was found to shift with the chloride concentration gradient in a manner predicted by the Nernst equation, and the currents were blocked by SITS. These data indicate that chloride ions were the charge carriers. The conductance was activated by depolarization and exhibited very slow activation and deactivation kinetics.

Action Potentials↗
PubMed1989

Voltage- and time-dependent chloride currents in chick skeletal muscle cells grown in tissue culture.

Membrane chloride currents in chick skeletal muscle cells grown in tissue culture were studied by use of the whole cell variation of the patch electrode voltage clamp technique. Small diameter myoballs were obtained by adding colchicine to the growth media. To isolate the currents through the chloride channels, the currents through the sodium, calcium and potassium channels were minimized. With symmetrical chloride concentrations bathing the membrane, inward currents were activated by depolarizations above -45 mV. Above 0 mV, the currents became outward. The reversal potential for the currents shifted with the chloride concentration gradient in a manner consistent with the Nernst relation, indicating that the currents were predominantly carried by chloride ions. The instantaneous current-voltage relation obtained from tail current data was linear. The relationship between conductance and membrane potential was sigmoid. The conductance activated above -45 mV, increased steeply between -45 and -10 mV and saturated above +20 mV. Over the range of potentials where the conductance was just beginning to activate, the conductance increased e-fold for a 7 mV depolarization. The currents activated with an exponential time course and did not decline during step depolarizations. Tail currents declined slowly as the sum of two exponential components. The currents were reversibly suppressed by 100 microM SITS and were irreversibly suppressed by 10 microM DIDS.

Animals↗
PubMed1989

Hydrogen sulfide in combination with taurine or cysteic acid reversibly abolishes sodium currents in neuroblastoma cells.

Patch clamp studies of neuroblastoma cells have shown that in the presence of sodium hydrogen sulfide (NaHS; the in vitro precursor of H2S), addition of the sulfonated amino acids, taurine or cysteic acid resulted in reversible abolition of the inward sodium currents. This effect could also be demonstrated by preincubating cells for 3-20 min with 5-10 mM NaHS followed by replacement of the solution with taurine or cysteic acid in sulfide-free saline. Neither NaHS, taurine nor cysteic acid alone had any effect. The sulfhydryl reagents, beta-mercaptoethanol and dithiothreitol, were also found to abolish reversibly the sodium currents. As the effects of the above treatments were nearly identical, the synergistic action of NaHS with taurine or cysteic acid may result from reduction of the disulfide bonds between subunits comprising the sodium channel. The responses to NaHS and taurine, a putative neurotransmitter/neuromodulator, suggest that reductions in sodium channel function may be the mechanism(s) responsible for loss of central respiratory drive during H2S poisoning.

Amino Acids, Sulfur↗
PubMed1984

Membrane electrical properties of developing fast-twitch and slow-tonic muscle fibres of the chick.

Isolated single fibres from the anterior (a.l.d.) and the posterior (p.l.d.) lattissimus dorsi muscles of embryonic and young chicks were used to study in vivo development of membrane electrical properties. Isolated fibres were obtained by an enzymatic dissociation procedure. Intracellular micro-electrode recordings from isolated fibres and from fibres in intact muscles showed that the dissociation procedure did not significantly alter resting membrane potentials, input resistances or membrane time constants (tau m). The 14 day embryonic fibres of a.l.d. and p.l.d. did not have a measurable resting conductance to Cl-. At hatching, about 70% of the resting conductance in p.l.d. fibres was due to Cl-. Membrane electrical properties were estimated from the analysis of voltage responses to intracellular injection of rectangular pulses of current. At 14 days in ovo, membrane resistance (Rm) was approximately 20 k omega cm2 and membrane capacitance (Cm) was 1-2 microF/cm2 for both a.l.d. and p.l.d. The mean membrane length constants (lambda) were 1.7 mm for a.l.d. and 1.5 mm for p.l.d. For p.l.d., the values of Rm, tau m and lambda decreased as development proceeded. For a.l.d., there was no change in these values by the time of hatching (21 days). The decreases in the electrical constants for p.l.d. fibres were partly explained by the appearance of a resting Cl- conductance during the last week of embryonic development.

Animals↗
PubMed1981

Lipid vesicle-mediated alterations of membrane cholesterol levels: effects on Na+ and K+ currents in squid axon.

We demonstrate that cholesterol can exchange from sonicated lipid vesicles to a perfused squid axon membrane and that vesicles with varying cholesterol/phospholipid (C/P) mole ratios can be used to achieve either net loading or net depletion of axon membrane cholesterol. Two types of evidence were obtained which show that net loading or depletion of cholesterol was achieved: (i) changes in the cholesterol/phospholipid (C/P) mole ratios of axons, and (ii) visualization of cholesterol depleted from the preparation by cholesterol-free vesicles by thin-layer chromatography. The C/P mole ratios indicate that cholesterol levels in the preparation were increased or decreased by 30-40%. Increasing or decreasing membrane cholesterol levels were ineffective in altering the Na+ or K+ occurrents in voltage-clamped axons. In addition, we determined that cholesterol "flip-flop" across the axonal membrane occurred with a t 1/2 of 7.3 to 15.3 min.

Animals↗
PubMed1978

The stimulation of coupling factor 1 ATPase by tentoxin.

Tentoxin at 10--1000 micrometer causes a marked species-selective stimulation of coupling factor 1 Ca2+-dependent ATPase activity (Ka 6.3 . 10(3) M-1). This effect decreases the Km for ATP to about 0.3 mM and increases V 2.75-fold. Above 1.6 micrometer tentoxin the rate of coupled electron transport was reduced to basal without uncoupling.

Adenosine Triphosphatases↗
PubMed1978

Tentoxin. An uncompetitive inhibitor of lettuce chloroplast coupling factor 1.

The interaction of tentoxin [cyclo-(-L-leucyl-N-methyl-(Z)-dehydrophenylalanyl-glycyl-N-methyl-L-alanyl-)] with solubilized lettuce chloroplast coupling factor 1 was characterized by direct binding studies, measurement of the time course of ATPase inhibition, and steady-state enzyme kinetics. Neither substrates, products or Ca2+ competed with the tentoxin binding site, nor did they induce any large change in tentoxin affinity. The inhibition of lettuce chloroplast coupling factor 1 ATPase was found to be the time dependent, and at equilibrium the affinities estimated by equilibrium ultrafiltration and enzyme inhibition were similar (1.8 . 10(8) M-1). The steady-state kinetics best fit an uncompetitive pattern suggesting that the inhibited steps follow an irreversible step occurring after ATP binding.

Adenosine Diphosphate↗
PubMed1978

Combining auditory and visual stimuli in the adaptive testing of speech discrimination.

This investigation determined the feasibility of using both auditory and visual stimuli in the adaptive testing of speech discrimination. Thirty-six adults with normal hearing and vision were subjects. Using the adaptive methodology known as the Doublet technique, speech-discrimination testing using monosyllabic word lists from the Northwestern University Auditory Test No. 6 (NU-6) (Tillman and Carhart, 1966) was performed at the target levels of 29.3 and 70.7% for both auditory-only and auditory-visual conditions. The results indicated that a specific discrimination score could be obtained under more adverse listening conditions with the addition of visual cues. The contribution of visual cues was constant for the two target scores. The adaptive technique at the 29.3 and 70.7% targets was reliable for both the auditory-only and auditory-visual conditions. Constant level testing showed good agreement with the adaptive technique for the auditory-visual condition. In conclusion, the use of standard error calculations is useful in determining measurement errors and the effects of an aural rehabilitation program.

Acoustic Stimulation↗
PubMed1977

Metabolism of zearalenone by Fusarium roseum.

Twenty products associated with the metabolism of zearalenone by Fusarium roseum were analyzed with respect to time and culture conditions. By statistical analysis a set of six metabolites possibly related to zearalenone were selected. These products were characterized by gas chromatography--mass spectrometry and other methods. The chemical structures of these six confirmed the statistical relationships, and evidence for the formation of these materials from zearalenone is presented. A suggested scheme of metabolism of zearalenone by F. roseum includes the formation of the two isomers of 8'-hydroxyzearalenone, 6',8'-dihydroxyzearalene, 6-(carboxypentyl)-beta-resorcyclic acid, and phenylacetic acid derivatives.

Fusarium↗
PubMed1976

Some effects of tentoxin on mature and developing chloroplasts.

Tentoxin affected chloroplasts of all stages of development; it caused chlorosis of expanded and developing bean and lettuce leaves when introduced through the stem or roots and inhibited greening of etiolated lettuce seedlings. Cotyledons from 6-day-old lettuce seedlings grown in 10 mug/ml tentoxin had 50-68% of the monogalactosyldiglyceride and digalactosyldiglyceride content of healthy tissue whereas the sulfolipid, phosphatidyl-glycerol, -ethanolamine, -choline and -inositol levels were unchanged. Toxin-treated tissue also showed selective increases in C-16 and C-18 saturated fatty acids.

Alternaria↗
PubMed1976

Estimation of protein-ligand binding parameters from contiuous ultrafiltration results.

A method of analyzing the result of continuous ultrafiltration experiments to obtain protein-ligand binding parameters is presented. This method employs a nonlinear least-squares regression algorithm coupled with a model of protein-ligand binding which alloww the computation of free ligand concentrations, and a second-order Runge-Kutta method to integrate free concentrations with respect to collected ultrafiltrate. The approach is general and effectively removes the constraints on maximum fraction size imposed by other methods.

Adenosine Triphosphatases↗
PubMed1976

Chloroplast coupling factor 1: A species-specific receptor for tentoxin.

Tentoxin, a cyclic tetrapeptide, induces chlorosis in certain plant species. It inactivated photophosphorylation and coupling factor 1 (CF(1)) ATPase in lettuce, a sensitive species. This effect was due to binding of tentoxin with CF(1) at a single site (affinity constant 1.3 to 20 x 10(7) M(-1)). Neither AMP nor adenyl-5'-yl imidodiphosphate appeared to bind to this site. In radish, an insensitive species, 20 times more tentoxin was required for 50% inhibition of photophosphorylation. In this species CF(1) ATPase was unaffected by tentoxin, and its CF(1) bound tentoxin only weakly (affinity constant less than 1 x 10(4) M(-1)). Sensitivity of photophosphorylation to tentoxin was correlated with chlorosis sensitivity in six other species examined.

Journal Article↗
PubMed1973

Effect of zinc, copper, and iron on ochratoxin A production.

The effect of zinc, copper, and iron levels on production of ochratoxin A by Aspergillus ochraceus Wilhelm in a synthetic medium in a shake culture was investigated. Optimal concentrations of ZnSO(4), CuSO(4), and FeCl(3) for ochratoxin A production were 0.055 to 2.2 mg/liter, 0.004 to 0.04 mg/liter, and 1.2 to 24 mg/liter, respectively. Zinc and copper levels greater than optimum reduced the rate of ochratoxin accumulation without altering either glutamate or sucrose utilization. Ochratoxin A production was correlated with rapid utilization of sucrose by the fungus and decreasing pH of the medium. Most of the glutamic acid was removed from the medium prior to ochratoxin production. There was no correlation between mycelial dry weight and ochratoxin A production.

Aspergillus↗
PubMed1972

Tenuazonic acid, a toxic produced by Alternaria alternata.

Fifty-seven of 87 isolates of Alternaria alternata (Fr) Keissler grown on autoclaved, moist corn-rice substrate and fed to rats were lethal. The major toxin produced was isolated and characterized as tenuazonic acid. Twenty of 23 toxigenic Alternaria isolates examined produced tenuazonic acid. No tenuazonic acid could be detected in either of the field samples of sorghum or blackeyed peas, which were heavily invaded by Alternaria.

Acetates↗