The preparation of xylulose 5-phosphate using transketolase.
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Barium↗
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The role of sodium and potassium ions in the generation of the electro-olfactogram.
In order to clarify whether or not the electronegative olfactory mucosal potentials (EOG) are generator potentials, the effects of changed ionic enviroment were studied. The EOG decreased in amplitude and in some cases nearly or completely disappeared, when Na(+) in the bathing Ringer solution was replaced by sucrose, Li(+), choline(+), tetraethylammonium(+) (TEA), or hydrazine. In the K(+)-free Ringer solution, the negative EOG's initially increased and then decreased in amplitude. In Ringer's solution with increased K(+), the negative EOG's increased in amplitude. When K(+) was increased in exchange for Na(+) in Ringer's solution, the negative EOG's decreased, disappeared, and then reversed their polarity (Fig. 6). Next, when the K(+) was replaced by equimolar sucrose, Li(+), choline(+), TEA(+), hydrazine, or Na(+), the reversed potentials recovered completely only in Na(+)-Ringer's solution, but never in the other solutions. Thus, the essential role of Na(+) and K(+) in the negative EOG's was demonstrated. Ba(++) was found to depress selectively the electropositive EOG, but it hardly decreased and never increased the negative EOG. Hence, it is concluded that Ba(++) interferes only with Cl(-) influx, and that the negative EOG's are elicited by an increase in permeability of the olfactory receptive membrane to Na(+) and K(+), but not to Cl(-). From the ionic mechanism it is inferred that the negative EOG's are in most cases composites of generator and positive potentials.
Animals↗
Life-term effects of mercury, methyl mercury, and nine other trace metals on mice.
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Aluminum↗
Voltage- and calcium-activated potassium currents in mouse neuroblastoma x rat glioma hybrid cells.
1. Membrane currents were recorded from voltage-clamped, microelectrode-impaled cells of the NG108-15 mouse neuroblastoma x rat glioma clonal cell line, differentiated with prostaglandin E1. 2. A slow outward tail current reversing at post-pulse potentials between -80 and -90 mV was evoked by depolarizing pre-pulses to near 0 mV. The tail current was inhibited by Cd2+ ions (0.2-1 mM) and hence attributed to activation of a Ca2+-dependent K+ current by a priming voltage-activated Ca2+ current. 3. Two components to this tail current could be distinguished pharmacologically: an early (less than or equal to 50 ms) component inhibited by 1-5 mM-tetraethylammonium (TEA), and a late component lasting several hundred milliseconds inhibited by apamin (0.1-0.4 microM) or d-tubocurarine (0.1-0.5 mM). 4. Ionophoretic injection of Ca2+ ions evoked a transient outward current with an apparent reversal potential (from ramped current-voltage curves) of -70 mV. This current was succeeded or sometimes replaced by an inward current with an apparent reversal potential between -20 and -10 mV. 5. The outward current induced by Ca2+ injections was unaffected or partly inhibited by TEA (1-5 mM), but was strongly inhibited by apamin or d-tubocurarine. 6. Hyperpolarizing voltage steps from between -30 and -40 mV induced inward current relaxations reversing at between -80 and -90 mV. These were considered to result from deactivation of the voltage-dependent sustained K+ current, IM. 7. Application of methacholine, muscarine or Ba2+ ions produced an inward current, reduced input conductance and reduced IM deactivation relaxations. 8. It is concluded that differentiated NG108-15 cells possess several of the K+ currents present in sympathetic neurones, including a delayed rectifier current, two species of Ca2+-activated K+ current and the M-current.
Action Potentials↗
Membrane current responses of NG108-15 mouse neuroblastoma x rat glioma hybrid cells to bradykinin.
1. Membrane current responses to focal application of bradykinin (BK) were recorded in voltage-clamped NG108-15 neuroblastoma x glioma hybrid cells. 2. BK produced sequential outward and inward currents at clamp potentials between -60 and -30 mV, designated IBK(out) and IBK(in), respectively. 3. The outward current IBK(out) was accompanied by an increased membrane conductance. Ramp current-voltage (I-V) curves yielded a reversal potential (VBK) of -80 +/- 5.6 mV (mean +/- S.D., n = 9) in 5.4 mM [K+]o. VBK showed a positive shift on raising [K+]o, compatible with a primary increase in K+ conductance. Subtracted I-V curves indicated that the underlying conductance was not strongly voltage dependent between -120 and -40 mV. 4. IBK(out) was inhibited by d-tubocurarine (dTC, 0.1-0.5 mM) but was insensitive to tetraethylammonium (TEA) below 5 mM. 5. The inward current IBK(in) was accompanied by a fall in membrane conductance. This was associated with the inhibition of a time- and voltage-dependent K+ current, IM. In consequence, IBK(in) was strongly voltage dependent and dissipated, usually without reversal, on hyperpolarizing the cell beyond -70 mV in 5.4 mM [K+]o. Reversal to an outward current negative to -40 mV could be obtained on raising [K+]o to 54 mM. 5. Both IBK(in) and IBK(out) persisted when ICa was blocked with Co2+ or Cd2+. IBK(out) slowly diminished in Ca2+-free, Mg2+-substituted solution. 6. The Ca2+ spike current ICa and the Ca2+-activated K+ current IAHP were inhibited during IBK(out) or after Ca2+ injections. BK did not affect the voltage-activated K+ current IK(V) recorded in Co2+ solution. 7. It is concluded that the dual response to BK results from opposing effects on two different species of K+ current. IBK(out) results from activation of a Ca2+-dependent, voltage-insensitive K+ conductance, probably mediated by a transient rise in intracellular Ca2+. It is suggested that the Ca2+ is released from an intracellular store. IBK(in) results primarily from inhibition of the Ca2+-independent, voltage-gated K+ current, IM. This effect is not replicated by a rise of intracellular Ca2+ and must therefore be generated by another mechanism.
Action Potentials↗
Cultured melanotrophs of the adult rat pituitary possess a voltage-activated fast transient outward current.
1. Whole-cell voltage-clamp recordings were made from cultured melanotrophs obtained from adult rats and maintained in vitro using conventional cell culture procedures. 2. The outward current recorded in the presence of Na+ and Ca2+ channel blockers was normally comprised of two components: a slowly activating, slowly inactivating current (IK(s] and a fast transient current (IK(f]. The selective blockade of IK(s) by 20 mM-tetraethylammonium (TEA+) allowed the properties of IK(f) to be analysed in isolation. 3. The activation threshold for IK(f) was normally between -20 and -10 mV and the current-voltage relationship was linear. At positive potentials the decay of IK(f) was well fitted by a single exponential having a time constant of 20-35 ms. At -70 mV recovery from inactivation was best described by a single-exponential function with a time constant of 20-40 ms. IK(f) was fully activatable at -60 mV and was fully inactivated at -10 mV; the half-inactivation potential was approximately -25 mV. 4. Since IK(f) was reduced by raising the external concentration of K+, was blocked by Ba2+ and Cs+, and persisted in Ca2+-free medium it is attributed to a voltage-activated K+ conductance. The amplitude of IK(f) was unaffected either by 5 mM-4-aminopyridine (4-AP) or 50 microM-quinidine. 5. The electrical properties of IK(f) suggest that by affecting the amplitude and/or duration of the action potential IK(f) may modulate Ca2+ influx and consequently hormone release.
4-Aminopyridine↗
Characterization of inhibition mediated by adenosine in the hippocampus of the rat in vitro.
1. Intracellular recordings with single-electrode voltage clamp were employed to study the mechanism of adenosine-elicited inhibition of CA1 neurones of the rat in vitro. 2. Adenosine elicits a steady-state outward current in association with an increase in conductance. The driving force varied with external potassium concentration as predicted by the Nernst equation for a change primarily in potassium permeability. 3. Adenosine current was blocked by high concentrations of 4-aminopyridine or barium. In the majority of neurones this current was voltage insensitive. In the remainder, the current was inwardly rectifying. The rectification was blocked by tetraethylammonium. 4. When the adenosine-elicited potassium current was blocked, slow inward currents, normally carried by calcium, were unaffected by adenosine. We conclude that this adenosine inhibition is mediated by an increase in a voltage- and calcium-insensitive potassium conductance in CA1 neurones.
4-Aminopyridine↗
An inward-rectifying K+ current in clonal rat pituitary cells and its modulation by thyrotrophin-releasing hormone.
1. Voltage-dependent K+ currents were recorded in cultured tumour-derived anterior pituitary cells of the rat (GH3 cells) with the patch clamp technique. An inward-rectifying current is described which is found to be carried by K+. 2. In isotonic KCl, whole-cell inward K+ currents were elicited by hyperpolarizing pulses from a holding potential of -40 mV. These inward K+ currents showed time- and voltage-dependent inactivation at potentials more negative than -60 mV. Inactivation was faster and more complete at larger hyperpolarizations. Recovery from inactivation was also time- and voltage-dependent. It was faster and more complete with more positive potentials. Time course of inactivation and of recovery from inactivation could be fitted by single exponentials. 3. Two results showed that a steady inward K+ current is present at -40 mV. The holding current at -40 mV was reduced following complete inactivation of the inward K+ current during strong hyperpolarizing pulses, and the amplitude of maximum inward K+ current elicited by hyperpolarization increased after depolarizing pre-pulses of 5 s. The resting conductance was estimated to be 20-30% of the maximum inward-rectifying conductance. 4. The inward K+ current was drastically reduced by Cs+ and Ba2+, but not by Ni2+ and Co2+. Quinidine, 4-aminopyridine and tetraethylammonium chloride blocked the current. In contrast, dendrotoxin was without effect. 5. Thyrotrophin-releasing hormone (TRH) which induces biphasic secretion of prolactin in GH3 cells consistently reduced the inward K+ current in the presence of internal Ca2+. This reduction was abolished if the pipette solution contained guanosine 5'-O-(2-thiodiphosphate) (GDP beta S; 400 microM), confirming the involvement of G-proteins in the signal transduction pathway. 6. TRH shifted the voltage-dependence of inward K+ current inactivation to less negative potentials resulting in pronounced K+ current inactivation in the range of the resting potential of these cells (-40 to -60 mV). 7. In intact cells, closing of K+ channels would result in a depolarization. The existence of an inward-rectifying K+ current in GH3 cells which is able to be reduced by TRH could readily explain the TRH-induced increase in action potential firing underlying the sustained second phase of secretion.
4-Aminopyridine↗
A mechanosensitive channel in whole cells and in membrane patches of the fungus Uromyces.
Bean leaf stomata provide a topographical signal that induces germlings of the phytopathogen Uromyces appendiculatus to develop specialized infection structures. Protoplasts from germ tubes of this fungus, when examined with patch-clamp electrodes, displayed the activities of a 600-picosiemen mechanosensitive ion channel. This channel passes a variety of cations, including Ca2+, and is blocked by Gd3+ at 50 micromolar. This channel could transduce the membrane stress induced by the leaf topography into an influx of ions, including Ca2+, that may trigger differentiation.
Barium↗
Comparison of Kaopectate with barium for negative and positive enteric contrast at MR imaging.
In an evaluation of safe, inexpensive, orally administered contrast agents for use at magnetic resonance imaging, different concentrations of the clay agents kaolin-pectate and attapulgite were compared in an in vitro phantom by performing spin-echo imaging with variable echo times to estimate T2 relaxation time. Additional phantoms containing from 0% to 100% attapulgite or barium preparations were compared by using spin-echo and spoiled-gradient-echo techniques to estimate T1, T2, and T2* relaxation times. In vivo spin-echo and gradient-echo images were obtained of 10 healthy volunteers and of five patients with pancreatic disease after oral administration of 12-16 oz of attapulgite preparation. T1 and T2 relaxation times obtained with use of attapulgite were slightly lower than those obtained with kaolin-pectate at both 50% and 25% concentrations. Compared with barium, attapulgite had shorter T1, T2, and T2* relaxation times, and concentration-dependent relaxivity was greater by nearly an order of magnitude. All subjects were able to drink the attapulgite, and the only complaints were of bad taste and mildly loose stools.
Barium Sulfate↗
Gastric clearance of radiopaque markers in non-ulcer dyspepsia patients.
BACKGROUND: The use of radiopaque markers has been proposed as an easy, non-invasive method for measuring gastric emptying. In this study we intended to evaluate the effectiveness of this test in determining the gastric motor function in patients with non-ulcer dyspepsia. METHODS: Simultaneous recording of scintigraphic solid gastric emptying and gastric clearance of radiopaque markers were conducted in 65 non-ulcer dyspepsia patients. RESULTS: Forty-two patients (64.4%) showed abnormal gastric clearance of radiopaque markers, and 38 patients (58.5%) showed delayed solid gastric emptying. There was no correlation between delayed solid gastric emptying and abnormal gastric clearance of radiopaque markers (p > 0.05). Although the frequency of abnormal gastric clearance of radiopaque markers was higher than that of delayed solid gastric emptying (64.6% versus 58.5%), it was not statistically significant. CONCLUSIONS: On the basis of the results of our study, gastric clearance of radiopaque markers may be used as an easy, non-invasive screening test for the purpose of detecting gastric motor dysfunction. However, this test is not superior to scintigraphic gastric emptying studies.
Adolescent↗
Quantitative cell culture biocompatibility testing of medical devices and correlation to animal tests.
The biocompatibility of a wide variety of biomaterials was quantitatively assessed, in a physiologically normal environment" as to cytotoxicity induced in WI-38 cells by cell culture medium extracts. Materials tested included PVC plastic, rubber, silicone rubber, polyethylene, polypropylene, acetal, polyurethane, Teflon, nylon, epoxy, and polystyrene. Cell culture test results were correlated to U.S.P. animal tests. Potential test artifacts, lead, barium, cadmium, and endotoxin were tested for cytotoxicity in WI-38 cells. Cell culture methods yielded more positive tests, particularly rubber, PVC plastic and silicone rubber compounds, than observed in U.S.P. animal tests. Positivity in animal tests did not correlate quantitatively to cytotoxic titers in cell culture. Discrepancies between cell cultures tests and animal tests, specifically rubber compounds, were attributable, in some instances, to differentials in elution efficiency between saline, cottonseed oil, and complete MEM cell culture medium. In other instances, particularly PVC plastics, differences between cell culture and animal test results were due to an inherent difference in the two indicator systems to respond to specific toxic moieties.
Acetals↗
[Hygienic aspects of the impact of solid waste disposal sites on the habitat].
The "Dmitrovsky" solid garbage (SG) ground is one of the largest enterprises of this kind in the Moscow Region. A total of 200,000-750,000 tons of solid garbage (91%) and industrial waste products (9%) annually come to the ground. A total of 5,500,000 tons of garbage and waste products have been accumulated since it was put into operation. From the accumulated SG deposits, iron, manganese, beryllium, titanium, barium, boron, petroleum products enter the surface and underground waters, methane, carbon oxide, ammonia, toluene, xylene, hydrogen sulfide, cresol, phenol come into the atmospheric air; the compounds of zinc, lead, cadmium, copper, nickel, magnesium, and cobalt do into the soil. The studies conducted in 1997-2002 make it possible to establish that the ground has a negative impact on the environment and to evaluate the efficiency of nature-conservation and hygienic measures, and to improve the technological process of SG utilization.
Environment↗
[Photoluminescence properties of A2SnO4 (A = Ca, Sr, Ba) : Eu nanocrystalline].
Nanosized A2SnO4 (A = Ca, Sr, Ba) : 1% Eu with diameters ranging from 50 to 100 nm were synthesized by complex sol-gel methods. The structures and spectral properties of A2SnO4 (A = Ca, Sr, Ba) : Eu were studied by using X-ray powder diffraction (XRD) and luminescence spectra. The experimental results show that Ca2SnO4 : 1% Eu exhibits bright red emission at about 615 nm under UV excitation, which makes it a possible good candidate for FED application. However Sr2SnO4 : 1% Eu and Ba2SnO4 : 1% Eu exhibit orange emission at about 590 nm because in these hosts Eu3+ ions occupy the symmetric sites.
Barium↗
The role of sulfhydryl groups in contraction of vascular smooth muscle.
While high concentrations (50 micronmol/l) of merurial sulfhydryl (SH) reagents p-chloromercuribenzoate (PCMB) and p-chloromercuriphenyl sulfate (PCMPS) caused a nonspecific inhibition of constrictor responses in isolated rabbit ear arteries, lower concentrations had selective effects. At a concentration of 10 micronmol/l both agents abolished responses to epinephrine and reduced responses to barium and calcium, but responses to caffeine were unaffected by PCMB and potentiated by PCMPS. Responses to histamine were little affected by PCMPS, but with PCMB, histamine responses were first reduced but later potentiated. In contrast, ethacrynic acid, a nonmercurial SH inhibitor which gains access to the intracellular space, failed to show any specificity of action and inhibited contractile responses to all these agonists. The results suggest that SH inhibitors whose actions are limited to the cell membrane exert both specific and nonspecific effects. The specific effect may be at SH groups associated with the alpha adrenoceptor while nonspecific effects may involve changes in membrane permeability.
4-Chloromercuribenzenesulfonate↗
Comparison of electrical responses of terminals, axons, and somata of a peptidergic neurosecretory system.
Spontaneous and evoked electrical activity was recorded intracellularly from somata, axons, and terminal dilatations of an isolated peptidergic neurosecretory system, the X-organ-sinus gland, of the crabs Cardisoma carnifex and Podophthalmus vigil in order to compare their electrical characteristics. Spontaneous impulse activity was present in most penetrations and included irregular and pacemaker-like firing, as well as patterned activity (bursting). Extracellular recording showed that spontaneous impulses and bursting originate in a proximal region of the axon tract. Somata vary from being electrically nonresponsive to having overshooting impulses with a relatively slow rate of rise. Overshooting impulses were consistently recorded from axons and terminals. Regional differences include (1) a longer action potential duration in terminals, (2) ability of axons and terminals but not somata to sustain repetitive firing, (3) presence of depolarizing afterpotentials in axons but of hyperpolarizing afterpotentials in somata and terminals, and (4) occurrence of impulse broadening during repetitive firing in some terminals but not in axons or somata. Somata and terminals sustained reduced and slowed, but regenerative impulses in nominally Na-free saline and showed alterations of waveform in nominally Ca-free salines, while axons showed no regenerative responses in Na-free saline and no change of impulse form in Ca-free saline. Terminal responses in the presence of tetraethylammonium chloride (TEA) (50 mM) or Ba (50 mM) exhibited long depolarized plateaus, while impulses of somata were much less prolonged. Bursts often took the form of impulses superimposed on a depolarized plateau. Bursts could be evoked by single stimuli applied to the axon tract but not by current passed intracellularly. After addition of TTX, axon tract stimulation evoked plateaus without superimposed impulses. Terminals exhibit specialization of their electrical responses by comparison to axons and somata in having long-duration action potentials attributable to participation of Ca, capability of sustained firing, impulse broadening, and channels supporting sustained inward currents, all of which might enhance the admission of Ca for initiation of peptide secretion.
Action Potentials↗
Characterization of voltage-activated currents in Hermissenda type B-photoreceptors.
Two distinct voltage-dependent K+ currents have been previously identified in the type B-photoreceptors of Hermissenda: an early, rapidly inactivating K+ current (IA), and a late, 4-AP- and TEA-resistant voltage and Ca(2+)-dependent current (IK(Ca)). Using conventional two-electrode voltage-clamp techniques, we have characterized two additional currents, a late voltage-dependent outward K+ current (IK(v)) and a voltage-dependent inward current identified as an inward rectifier (Iir). In addition, we have further studied the activation-inactivation kinetics of IA. In 0-Na+ ASW, Iir activates at a potential of > -50 mV, is steeply voltage-dependent and noninactivating, and reaches steady-state within 800 msec to 3 sec at -100 mV. In addition to the variability in activation kinetics, there was also considerable variability in Iir magnitude (-5 to -80 nA, at -100 mV). Iir was blocked by external 4-AP (5 mM), external and internal TEA, internal Cs+, but not external Ba2+. The major component of outward K+ current in type B-photoreceptors is IK(v), the delayed rectifier. IK(v) was isolated after removal of IA and IK(Ca). IK(v) activates at around -25 mV or more positive membrane potentials and its activation and inactivation are strongly voltage dependent. IK(v) inactivation to steady state is reached within 1.5-2.5 sec. The wide range of activation-inactivation rates suggests that there may be kinetic subtypes of IK(v). The proposed "slow" IK(v) peaked in 50-90 msec at +30 mV, and decayed with a single exponential component with an average tau off of 279 msec. Proposed "intermediate" and "fast" IK(v) subtypes peaked within 12-50 msec at +30 mV, and had a decay fitted by two exponentials, with an average tau 1 of 147 msec and tau 2 of 275 msec, respectively. IK(v) exhibited marked twin-pulse inactivation with a recovery time of 30-40 sec, and also exhibited time- and voltage-dependent cumulative inactivation to repeated depolarizing pulses. Both types of inactivation were quickly removed by a prepulse hyperpolarization. 4-AP (5 mM) produced partial to complete block of the inactivating component of IK(v), leaving only a residual sustained component. Complete block of the transient and sustained components of IK(v) was obtained by 100 mM TEA. Reliable voltage separation of IA from IK(v) was achieved by activating IA in the range of -50 to -20 mV, from a Vh of -80 mV. Voltage-dependent steady-state inactivation curves for IA were determined, yielding an average h0.5 value of -56 mV.(ABSTRACT TRUNCATED AT 250 WORDS)
4-Aminopyridine↗
[Extracellular photoreceptor potential of albino rats].
In this study methodically simple model of mammalian's total rods photoreceptor potential obtained by the known methods of outside electrical activity suppression by barium ions and sodium aspartate is offered. The farmacological analysis of that potential with using of ions-blockers of the potential-dependent conductances demonstrated that the offered potential consisted of the same components as the known intracellular responses.
Animals↗