Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Barium Compounds”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,261 records · Page 70Linked to original sources
PubMed1996

[Diagnostic accuracy and clinical significance of combined small bowel enema and scintigraphy with pure fractions of neutrophil granulocytes labeled with HMPAO-Tc99m in chronic intestinal inflammation].

Enema is the primary imaging method in the diagnosis of Crohn's disease in the small bowel, with clinical follow-up examinations performed by gastroenterologists as the gold standard. The information provided by small bowel enema, in addition to endoscopic findings, is usually sufficient for the gastroenterologist to make the definitive diagnosis and to plan the whole treatment. Scintigraphy with leukocytes labelled with HMPAO-Tc99m has several unique characteristics favoring its use as a diagnostic imaging method in Crohn's disease and ulcerative colitis. It is a noninvasive method requiring no bowel preparation and it is safe in severely ill patients in whom such conventional imaging methods as barium enema or colonscopy might be hazardous. In this study, the authors report the results of their experience with diagnostic small bowel enema and leukocyte scintigraphy with HMPAO-Tc99m in 28 patients with inflammatory bowel disease (Crohn's disease in 18 patients, ulcerative colitis in 7 and radiation-induced inflammatory stenosis of the sigma-rectum, bowel inflammation after appendicectomy and bladder surgery, respectively, in 1 patient each). Scintigraphy with autologous granulocytes with HMPAO-Tc99m was positive in 26 patients and negative in 2. Twenty-five patients were true positives and 1 was a false positive. Fifteen patients were also submitted to small bowel enema: 12 of them were positive (true positive) and 3 negative (1 false negative and 2 true negative). The results of granulocytes scintigraphy were compared with those of small bowel enema: the radionuclide study appeared superior in the assessment of bowel inflammation associated with Crohn's disease and ulcerative colitis. Indeed, scintigraphy depicted granulocyte uptake in the colon where enema had shown no major findings in 4 patients with Crohn's disease. In the author's opinion, the overall sensitivity, specificity and positive predictive value of combined leukocyte scintigraphy and small bowel enema play a major role in the early diagnosis of Crohn's disease and ulcerative colitis and in the assessment of disease extent and activity.

Adolescent↗
PubMed1994

Vitamin D3 analogs stimulate calcium currents in rat osteosarcoma cells.

1 alpha, 25-Dihydroxyvitamin D3 (1,25-D3) rapidly (within seconds) shifts the threshold for activation of inward calcium currents to more negative and physiological potentials. To determine whether the opening of calcium channels in bone cells is mediated by the cytosolic 1,25-dihydroxyvitamin D3 receptor (VDR), several natural metabolites 1,25-D3, 25-hydroxyvitamin D3, and 24R,25-dihydroxyvitamin D3 and synthetic analogs 25-hydroxy-16,23E-diene D3 (HO), 25-hydroxy-23-yne D3 (Y), and 1 alpha, 25-dihydroxy-16-ene-23-yne-26,27-F6 D3 (EO) were tested on dihydropyridine-sensitive inward barium currents. In order to probe the structural specificity at the 1 position of the steroid for stimulation of barium currents, we used several synthetic 1-(1'-hydroxyethyl) (NP, ON, NN, OP) and 1-(2'-hydroxyethyl)-25-hydroxyvitamin D3 analogs (14w-1 alpha and 14-w1 beta). Using the perforated patch-clamp technique, we found that the naturally occurring vitamin D3 analogs gave nearly the same rank order potency for stimulation of barium currents as their affinity for VDR with 1,25-D3 being the most potent analog. Using the synthetic analogs which have minimal affinity for VDR, we found that the compounds without 1-OH group but with additional double bonds in positions 16 and 23 or with a triple bond in position 23 retained high affinity for calcium channel activation. Furthermore, 1-hydroxyethyl-25-hydroxyvitamin D3R isomers at the 1' position had greater affinity than the S isomers at this position, and a beta oriented 2'-hydroxyethyl group gave the homolog greater affinity than did the alpha-oriented 2'-hydroxyethyl group. The fact that these synthetic analogs cause rapid effects on calcium channels and show pharmacological specificity different from the binding to the cytosolic vitamin D3 receptor suggests that calcium influx is mediated by a distinct signal transduction pathway. The high and physiological affinity of 1,25-D3 (50 pM) suggests that it is a biological regulator of calcium channels.

Animals↗
PubMed1981

The effects of the bradycardia-producing compound alinidine on action potentials and tension development in cardiac fibres.

Alinidine (ST 567, N-Allyl-Clonidine) exerted concentration-dependent negative chronotropic effects in isolated, spontaneously-beating sinus node cells and Purkinje fibres of guinea pigs and in ventricular strips of chick embryonic myocardium. Reduction of beat frequency by 30% was found after addition of 8.6 mumol/l alinidine in the former. A chronotropic effect was not seen during Ba2+-induced automaticity or triggered activity in guinea-pig papillary muscles and in enzymatically disaggregated cells of embryonic chick myocardium, which lose the beta-adrenoceptor responsiveness of the intact embryonic ventricle. In contrast to alinidine, D600 showed very pronounced and quinidine minor negative chronotropic effects in these latter experiments. Reduction of excitability, rate of rise of the action potential and velocity of repolarization as well as prolongation of the refractory period were seen after applications of very high concentrations of alinidine (285 mumol/l). In electrically-driven atria isometric peak tension was only slightly changed (increased by 85.5 mumol/l, decreased by 285 mumol/l) but it was reduced (to 36.8%) by alinidine (85.5 mumol/l) in papillary muscles. Both in atria and in papillary muscles, the maximum rate of rise of the action potential was unchanged by alinidine up to 85.5 mumol/l and the slight reduction following 285 mumol/l alinidine application was independent of the rate of stimulation. The present findings confirm the selectivity of the bradycardic effects of alinidine which has a main mode of action different to that of membrane stabilizing compounds or inhibitors of the slow inward current.

Action Potentials↗
PubMed1994

Use of cultured human neuroblastoma cells in rapid discovery of the voltage-gated potassium-channel blockers.

Depolarization of human neuroblastoma cells by high concentrations of extracellular potassium ions, leads to the activation of the voltage-gated potassium channels. The activity of such potassium channels can be effectively and rapidly monitored by tracking the efflux of 86Rb from pre-loaded target cells in response to the depolarizing stimulus. The inclusion of compounds with unknown activity in the assay medium, can result in the identification of novel blockers of the voltage-gated potassium channels. Since this functional assay is performed in 96-well microtitre plates, it represents a rapid and high-volume primary screening method for the detection and identification of the voltage-gated potassium-channel blockers, which may have therapeutic utility in several indications including memory degeneration and cardiac arrhythmias.

4-Aminopyridine↗
PubMed2004

Dinuclear barium(II) complexes based on a calix[4]arene scaffold as catalysts of acyl transfer.

Two novel regioisomeric calix[4]arene derivatives (2 and 3), decorated with two aza[18]crown-6 units at vicinal (1,2) or diagonal (1,3) positions of the upper rim, were synthesized. The catalytic activities of their dinuclear Ba2+ complexes were investigated in the ethanolysis of esters 8-11, endowed with a carboxylate anchoring group. Major results are as follows: 1) the two metal ions in the dinuclear catalysts work together in a cooperative fashion; 2) the vicinal calix[4]arene catalyst 2 is far superior to its diagonal regioisomer 3 in the reactions of all of the investigated esters; and 3) the distance between the carboxylate and ester carbonyl, which increases regularly from 8 to 11, influences reactivity of catalytic ester cleavage in a way that is decidedly suggestive of the importance of a good match between ester size and metal-to-metal distance. However, the superiority of the vicinal catalyst 2 relative to 3 cannot be explained on the basis of the putative match of ester size to intermetal distance, thus providing an indication that additional, still poorly understood effects may contribute significantly to catalytic efficiency.

Barium↗
PubMed1994

Implication that potassium flux and increase in intracellular calcium are necessary for the initiation of sperm motility in salmonid fishes.

Flux of K+ and changes in intracellular Ca2+ in the sperm of salmonid fishes were measured with spectrophotometry, ion electrode, microscopic fluorometry, and radioisotope accumulation. Release of K+ occurred at the initiation of sperm motility which is induced by decrease in external K+ and the K+ efflux and sperm motility were inhibited by K+ channel blockers. Intracellular Ca2+ increased within a short period in K(+)-free condition, and the accumulation of 45Ca in sperm cells was higher in motile sperm than that in immotile sperm. The efflux of K+ and the increase in intracellular Ca2+ were suppressed when external K+ concentration increased, i.e., sperm remained immotile. These results suggest that efflux of K+ through K+ channel and subsequent increase in intracellular Ca2+ are prerequisite for the initiation of sperm motility.

4-Aminopyridine↗
PubMed1991

Effects of Ca2+ removal and of tetraethylammonium on membrane currents induced by carbachol in isolated cells from the rat parotid gland.

In freshly dispersed rat parotid acinar cells, 10 microM carbachol increased outward currents at 0 mV and also inward currents at -70 mV recorded with the wholecell clamp method using patch pipettes containing 1 mM EGTA. When EGTA in the pipette was increased to 2.4 mM, carbachol increased only outward currents and a further increase of EGTA to 4 mM blocked the carbachol response. Effects of changes in external K+ and Cl- concentrations suggested that outward currents were carried by K+ and inward by Cl-. Effects of Ca2+ removal from the medium differed between experiments with 0 and 5 mM ATP in the patch pipettes. When pipettes contained no ATP, responses evoked by repeated applications of 10 microM carbachol (0.5-1 min) at 1.5-4 min intervals decreased only slowly after Ca2+ removal, outward currents being reduced to 90 +/- 6% and inward currents to 47 +/- 11% (n = 6) in 10 min. On the other hand, when 5 mM ATP was included in the electrodes, Ca2+ removal abolished the carbachol responses in about 5 min (n = 4). It was also found that tetraethylammonium (5 mM) strongly reduced both currents, by blocking muscarinic receptors, while Ba2+ (2.4 mM) inhibited only the outward K+ current.

Adenosine Triphosphate↗
PubMed1977

Effects of verapamil on excitation-contraction coupling in single crab muscle fibers.

The effects of verapamil and its optical isomers on the electrical and mechanical characteristics of single muscle fibers of Callinectes danae were studied. Verapamil (10-20 microng/ml) blocked the procaine- and TEA-induced spikes; the blockade was preceded by reduction in the rate of rise of the upstroke and increase in the duration of the action potentials. Inhibition of Ba-spikes required higher concentrations of verapamil (greater than 50 microng/ml). These concentrations reduced the amplitude of the normally occurring graded electrogenic membrane responses and reduced the rate of development of the current-induced tensions. With lower concentrations (10-30 microng/ml) verapamil enhanced the negative afterpotentials and the peak amplitude of the local contractions elicited by depolarizing current pulses, while the graded membrane responses were not markedly modified. Verapamil (1-100 microng/ml) did not affect the resting membrane potential but increased the effective membrane resistance. Determination of the cable characteristics by DC pulses indicated that verapamil (1-10 microng/ml) shortens the membrane length constant, increases the specific resistivity of the sarcoplasm and, in most cases, increases the membrane time constant. Verapamil (10 microng/ml) induced tension in these crab fibers. The contractions were potentiated in Na-deficient media, by increase in [Ca]0, and by membrane depolarization; "Ca-free" salines depressed, and procaine abolished these contractions. The results suggest that verapamil affects both Ca and K conductances and interferes with the Ca-sequestering mechanisms of these fibers. The (-)-isomer of verapamil was more effective than the (+)-isomer with respect to tension development, prolongation and subsequent blockade of procaine-spikes and enhancement of current-induced after-potentials and contractions.

Animals↗
PubMed1996

Further investigation of ionic diffusive properties and of NH4+ pathways in Xenopus laevis oocyte cell membrane.

To study the ionic diffusive properties and the NH4+ pathways in the Xenopus laevis oocyte cell membrane, we recorded the effects of various inhibitors on membrane potential (Vm) and membrane resistance (Rm); intracellular acidification was taken as an index of NH4+ influx from the bath to the cytoplasm. The following results were obtained: in the control state, barium and quinine (Q) ions depolarized Vm and raised Rm, consistent with inhibition of K+ conductance(s). Diphenylamine-2-carboxylic acid (DPC), 3',5'-dichlorodiphenylamine-2-carboxylic acid (DCDPC) and gadolinium ions hyperpolarized Vm and increased Rm, suggesting the inhibition of nonselective cationic conductance(s). In the presence of 20 mmol/l NH4Cl, Vm depolarized, Rm fell, and intracellular pH (pHi) decreased, consistent with an NH4+ influx. In the presence of DPC, the same manoeuvre induced a biphasic Vm change (i.e. a spike depolarization followed by a membrane hyperpolarization) and a fall of Rm; in most oocytes, intracellular acidification persisted and was reversible upon adding ouabain (Oua). These results indicate that a DPC-sensitive conductance is not the unique NH4+ pathway and that Na, K-ATPase may also mediate NH4+ influx. However, Oua did not prevent the Rm decrease, suggesting that ouabain-insensitive rheogenic pathway(s) are activated. Thus, we investigated the Vm change induced by NH4Cl addition in the presence of DPC: the spike depolarization followed by secondary hyperpolarization became a plateau depolarization when Q was added, suggesting involvement of Q-sensitive pathway(s) in the above described biphasic Vm change. In the presence of DPC, Q and Oua, intracellular acidification upon adding NH4Cl persisted consistent with further NH4+ influx through quinine-, DPC- and Oua-insensitive pathway(s).

Animals↗
PubMed1990

Action potentials and membrane currents of isolated single smooth muscle cells of cat and rabbit colon.

Membrane potentials, action potentials and macroscopic currents in enzymatically dispersed, single smooth muscle cells of the circular layer of cat and rabbit colon were investigated. The cells did not exhibit spontaneous depolarizations and repolarizations (slow waves) or spontaneous action potentials. Single action potentials of smooth muscle cells were evoked by depolarizing current pulses of 5 ms to 3 s duration. A repetitive action potential discharge and an increase in the duration of the action potential was observed in cells during long depolarizing current pulses by superfusion with tetraethylammonium (TEA) or 4-aminopyridine (4-AP). Tetrodotoxin (TTX) did not alter the configuration of the action potential. Voltage-clamp experiments revealed two major outward macroscopic currents: a quasi-instantaneous (time-independent) and a time-dependent outward current. Both currents were identified as potassium (K) currents due to their pharmacological sensitivity to K antagonists [TEA, 4-AP and cesium (Cs)] and due to the reversal potential of outward tail currents. Barium selectively blocked the time-independent current. A time-dependent outward K current in colon cells was observed which appeared to be dependent upon entry of calcium ions (Ca2+) through voltage-dependent Ca-channels, since it was blocked by cadmium and low concentrations of nifedipine. The majority of cells did not exhibit transient outward currents. Inward currents were exposed in some of the cells when the K currents were blocked by external TEA and by replacement of K by Cs and TEA in the recording pipette. Inward currents were presumably carried by Ca2+, since they were not altered by TTX, were sensitive to external Ca concentrations and were abolished by the Ca channel antagonist, nifedipine. Carbachol augmented the amplitude of the inward Ca current.

Action Potentials↗
PubMed1984

Effects of tetraethylammonium-chloride and divalent cations on the afterhyperpolarization following repetitive firing in leech neurons.

In leech Retzius cells, repetitive activity evoked a prolonged Ca2+-dependent after-hyperpolarization (PAH) (30-60 s) accompanied by an increase in input conductance. PAH persisted in Retzius cells, as well as in nociceptive (N) cells, when Sr2+ but not Mg2+ was substituted for Ca2+. In the presence of tetraethylammonium-chloride (TEA) or Ba2+, PAH was replaced by a Ca2+-dependent, Mg2+-blockable depolarization which was present in the order N greater than R. Careful study of the differences in such phenomena in identified cells may improve our understanding of the differential susceptibility of various neurons to hyperexcitability.

Animals↗
PubMed1992

Repulsion between tetraethylammonium ions in cloned voltage-gated potassium channels.

Tetraethylammonium ion (TEA+) blocks voltage-gated K+ channels by acting at two sites located at opposite ends of the aqueous pore. This allowed us to test two predictions made by models of ion permeation, namely that K+ channels can be simultaneously occupied by multiple ions and that the ions repel each other. We show that externally applied TEA+ antagonize block by internal TEA+ and vice versa. The antagonism is less than predicted for competitive binding, hence TEA+ may occupy both sites simultaneously. External TEA+ and internal TEA+ reduce each others affinity 4- to 5-fold. In addition, K+ antagonizes block by TEA+ at the opposite side of the membrane, and external TEA+ antagonizes is block by internal Ba2+. The antagonism between ions applied at opposite sides of the membrane may be common to all cations binding to K+ channels.

Animals↗
PubMed2005

Development of an inorganic cations retention model in ion chromatography by means of artificial neural networks with different two-phase training algorithms.

This paper describes development of artificial neural network (ANN) retention model, which can be used for method development in variety of ion chromatographic applications. By using developed retention model it is possible both to improve performance characteristic of developed method and to speed up new method development by reducing unnecessary experimentation. Multilayered feed forward neural network has been used to model retention behaviour of void peak, lithium, sodium, ammonium, potassium, magnesium, calcium, strontium and barium in relation with the eluent flow rate and concentration of methasulphonic acid (MSA) in eluent. The probability of finding the global minimum and fast convergence at the same time were enhanced by applying a two-phase training procedure. The developed two-phase training procedure consists of both first and second order training. Several training algorithms were applied and compared, namely: back propagation (BP), delta-bar-delta, quick propagation, conjugate gradient, quasi Newton and Levenberg-Marquardt. It is shown that the optimized two-phase training procedure enables fast convergence and avoids problems arisen from the fact that every new weight initialization can be regarded as a new starting position and yield irreproducible neural network if only second order training is applied. Activation function, number of hidden layer neurons and number of experimental data points used for training set were optimized in order to insure good predictive ability with respect to speeding up retention modelling procedure by reducing unnecessary experimental work. The predictive ability of optimized neural networks retention model was tested by using several statistical tests. This study shows that developed artificial neural network are very accurate and fast retention modelling tool applied to model varied inherent non-linear relationship of retention behaviour with respect to mobile phase parameters.

Algorithms↗
PubMed1982

Solvent substitution as a probe of channel gating in Myxicola. Effects of D2O on kinetic properties of drugs that occlude channels.

The effects of solvent substitution on the steady-state and kinetic properties of drugs (gallamine triethiodide) and ions (nonyltriethylammonium and Ba++) known to occlude Na+ and K+ channels have been examined and compared with the effects of D2O on unmodified channels. In general, we observed large isotope effects on the kinetics of occlusion at temperatures of 5 degrees C, but only minor effects at 15 degrees C, consistent with processes involving significant solvent interaction. Steady-state behavior was not affected. In the case of gallamine, where a dual effect on INa is evident, although both processes were D2O sensitive, only the occlusion phase had a significant temperature dependence.

Animals↗
PubMed1984

Detection of enteric-urinary fistulas with a noninvasive quantitative method.

The 51chromium test is an inexpensive, noninvasive test to evaluate patients for enteric-urinary fistulas. Of 11 patients studied the 51chromium test demonstrated correctly a fistula in 5 of 6 patients with fistulas and showed no lesion in all 5 without fistulas. Excretory urography, barium enemas, visible contrast medium, cystograms and upper gastrointestinal series failed to demonstrate the fistulas with similar accuracy. Cystoscopy suggested a possible lesion in 4 patients but was definite for a fistula in only 2 of those patients.

Adult↗
PubMed1975

Comparative responses of the isolated human testicular capsule to autonomic drugs.

The testicular capsule of the human has been prepared for the first time as an isolated tissue suitable for pharmacological investigation. Cholinergic and adrenergic agents caused a contraction of the isolated testicular capsule. In addition, periodic spontaneous contractions of the isolated testicular capsule had been observed in the absence of any added pharmacological agents. The present experiments have demonstrated that the testicular capsule contains smooth muscle, thereby offering a reasonable anatomical explanation for spontaneous and drug-induced contractions of the testicular capsule. Therefore, it appears likely that the rhythmic contractions and relaxations of the testicular capsule provide a pumping action capable of explaining the transport of non-motile sperm out of the testes into the epididymis where they can attain their motility.

Acetylcholine↗