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At least 1,099 records · Page 61Linked to original sources
PubMed1988

Effects of potassium channel-blocking agents on neurons in the inferior mesenteric ganglion in guinea-pig.

Intracellular recordings were made from neurons (n = 121) in the inferior mesenteric ganglion (IMG) in guinea-pig. The pharmacological actions of 4-aminopyridine (4-AP), barium ions (Ba2+) and tetraethylammonium ions (TEA) were studied on IMG cells which received an excitatory, cholinergic input from mechanosensory nerves in the gastrointestinal tract. 4-AP mediated an excitatory action which involved two separate effects. Firstly, 4-AP increased the incidence of spontaneously occurring, fast EPSPs which gave rise to a spontaneous discharge of action potentials. This indirect, excitatory effect was attributed to an increase in the spontaneous release of acetylcholine from excitatory nerves to the IMG. Secondly, 4-AP altered the excitability of IMG cells and brought about burst discharges and continuous discharges of action potentials. This direct, excitatory effect was not dependent on the spontaneous release of acetylcholine; instead, it was attributed to the blockade of a potassium current similar to the A-current (IA). The excitatory action of Ba2+ also involved two separate effects. Firstly, Ba2+ increased the incidence of spontaneously occurring, fast EPSPs which gave rise to a spontaneous discharge of action potentials. This indirect, excitatory effect was interpreted as Ba2+ mimicking the actions of Ca2+ to facilitate the spontaneous release of acetylcholine. Secondly, Ba2+ altered the excitability of IMG cells and brought about a continuous discharge of action potentials. This excitatory effect was attributed to the blockade of a potassium current similar to the M-current (IM). TEA exerted an excitatory, then inhibitory, action on IMG cells. Initially, TEA brought about the continuous discharge of action potentials; firing gradually arrested as IMG cells depolarized slowly and a depolarizing block of excitation (i.e. inhibition) developed. The block on excitation was relieved by first restoring the resting membrane potential of IMG cells with hyperpolarizing current-clamp. Thereafter, action potentials were elicited by anode-break excitation by temporarily removing the hyperpolarizing current-clamp. The durations of action potentials and afterspike hyperpolarizations were prolonged in the presence of TEA. The effect of TEA on the action potential of IMG cells was attributed to the blockade of the delayed rectifier (IK). The effect on the afterspike hyperpolarization was considered the indirect consequence of a blockade of IK; it allowed the development of an inward calcium current which enhanced the calcium-activated, potassium current (IKCa) mediating afterhyperpolarizations.

4-Aminopyridine↗
PubMed1996

Participation of NH4+ in total ammonia absorption across the rumen epithelium of sheep (Ovis aries).

1. Participation of NH4+ in total ammonia transport across sheep rumen wall was studied in vitro. 2. In Ussing-type chambers addition of NH4+ or K+ to the incubation solution on the mucosal side of the epithelium evoked positive short-circuit currents (ISC). 3. The K+ induced ISC but not the NH4+ induced ISC could be blocked by Ba2+ whereas both, K+ or NH4+ induced ISC were blocked by quinidine. 4. Transepithelial fluxes of ammonia were significantly reduced when quinidine was present in the incubation solution. 5. When the transepithelial potential difference was clamped to -25 mV (polarity on the serosal side) ammonia fluxes from the mucosal to the serosal side were significantly larger than fluxes of ammonia measured as a potential difference of +25 mV. 6. It is suggested that NH4+ takes part in ammonia transport across the rumen epithelium, most probably by using a K(+)-transport system.

Ammonia↗
PubMed1994

Evaluation of oral contrast agents for abdominal magnetic resonance imaging.

We evaluated the efficacy of six available oral contrast agents in improving visualization of bowel and surrounding structures on magnetic resonance imaging of the abdomen and pelvis. Five volunteers were examined without oral contrast (baseline) and, on separate occasions, after ingestion of 600-900 cc of two positive contrasts [12.5% weight-to-volume (w/v) corn oil emulsion (COE), Redi Cat (EZ-Em Corp., Westbury, NY) mixed with 1% ferric ammonium citrate (FAC)] and four negative contrasts [220%, 105%, 85%, 60% w/v barium sulfate (Liquid HD, Liquid Polybar Plus, HD 85, reconstituted EZ Pake; EZ-Em Corp., Westbury, NY)]. Spin-echo axial and coronal T1-weighted and axial T2-weighted images were obtained in the abdomen and pelvis. Three radiologists blindly graded the images for improved visualization of bowel and surrounding structures. Data were analyzed for statistical significance using the General Linear Models algorithm. In the upper abdomen (stomach, duodenum, liver, and pancreas), COE yielded the highest mean scores (p < .0001), followed by 220% w/v barium. For the lower abdomen (ileum, colon), 220% w/v barium yielded the highest scores (p < .0001) and COE was much worse. The higher density barium preparations (220% and 105% w/v) yielded higher scores than their lower density counterparts (85% and 60%). All contrasts improved visualization of the retroperitoneum and spleen, but no one agent was best. All agents tested are superior to no agent at all. For visualization of the upper abdomen, 12.5% COE performed best. For visualization of the lower abdomen, 220% w/v barium performed best. For concurrent evaluation of both areas with one agent, 220% w/v barium performed best.

Abdomen↗
PubMed2000

High-pressure synthesis of a new silicon clathrate superconductor, Ba8Si46.

A new silicon clathrate compound with a composition of Ba8Si46 was prepared under high-pressure and high-temperature conditions. The compound was isomorphous with Na8Si46 and became a superconductor with a transition temperature of 8.0 K. Barium atoms occupy all of the Si20 and Si24 cages of the clathrate structure. This is the first clathrate superconductor obtained as a bulk phase.

Journal Article↗
PubMed1985

Technetium 99m-labelled-sucralphate isotope scanning in the detection of peptic ulceration.

An isotope scan using sucralphate labelled with technetium-99m has been compared with barium meal in the detection of peptic ulceration in 18 patients with endoscopically proven upper gastrointestinal lesions and eight controls. Gastric (75%) and duodenal (67%) ulcers were detected with identical frequency by isotope scan and barium meal but both were inferior to endoscopy. Structural, non-ulcerated lesions, were not identified by isotope scanning. The scan has potential value in duodenal ulcer disease, the serial assessment of ulcer healing and in paediatric gastroenterology.

Barium Sulfate↗
PubMed1976

Effect of calcium ions on growth and metabolism of Saccharomyces carlsbergensis.

Addition of calcium ions increased 2- to 3-fold the growth of Saccharomyces carlsbergensis 2I in a minimal glucose-containing medium. The minimal concentration enhancing growth was 25 to 50 mug/ml CaCl2. Other divalent and trivalent cations tested, except for strontium ions, did not duplicate the calcium effect. Actively growing and dividing cells took up 45Ca2+, while resting yeast cells did not. The radiocalcium taken up was incorporated into newly synthesized structural material, presumably into the membrane protein.

Barium↗
PubMed2001

Staphylococcus aureus requires increased level of Ca(2+) or Mn(2+) to grow normally in a high-NaCl/low-Mg(2+) medium.

Mg2+-availability in Staphylococcus aureus cells decreased significantly with increasing NaCl concentration in growth media. Cells grew in a NaCl-free, Chelex resin-treated complex medium only if the medium was supplemented with 50 microM MgCl2, while, growth was limited when the medium was further supplemented with 1.0 M NaCl. Cells grown in such a high-NaCl/low-Mg2+ medium exhibited the morphologic abnormality of larger than normal cells. Both sufficient growth and normal cell morphology were restored by increasing Mg2+ concentration in a high-NaCl medium, or by supplementation with either CaCl2 or MnSO4 in a high-NaCl/low-Mg2+ medium. Supplementing with BaCl2, SrCl2 or FeSO4, however, had no effect. These results indicate that Ca2+ and Mn2+ might play some essential role in the growth of Staphylococcus aureus in a high-NaCl/low-Mg2+ environment.

Barium↗
PubMed1984

The time course of muscarinic depolarization of guinea-pig myenteric neurones.

Intracellular recordings were made from neurones in the myenteric plexus of the guinea-pig ileum in vitro. Muscarinic depolarizations were evoked by brief (1-500 ms) ionophoretic applications of acetylcholine (ACh) or other agonists. Nicotinic responses to ACh evoked by the same ionophoretic pulse had short latencies and rapid rise times, indicating close proximity of the ionophoretic pipette to the neurone membrane. The time course (duration several seconds) of the muscarinic depolarization was independent of the identity of the agonists applied (ACh, methacholine, carbachol, oxotremorine). Hyoscine and barium were ejected onto the neurones by brief (30 ms-1 s) pressure pulses applied to micropipettes. Hyoscine applied immediately after ACh, during the latency and rising phase of the muscarinic depolarization, did not antagonize the response to ACh. The same application of hyoscine immediately prior to ACh caused complete antagonism. Muscarinic depolarizations evoked by continuous application of ACh (by repeated ionophoresis or perfusion) were reversed by hyoscine. The time course of this reversal was similar to the decline of the muscarinic response following a single brief application of ACh. Barium caused a depolarization similar to that produced by muscarinic agonists in its latency, time course and temperature sensitivity, and having the same reversal potential (-90 mV). These barium potentials were not affected by hyoscine. It is suggested that neither diffusion of ACh to the receptors nor the kinetics of the agonist-receptor interaction contributes significantly to the latency and prolonged time course of the muscarinic depolarization.

Acetylcholine↗
PubMed1978

45Ca displacement related to pharmacologically induced prolonged action potentials in Nitella flexilis.

Nitella cells were loaded with 45Ca2+ to an activity of 2 X 10(5) cpm. Insertion of two glass-capillary electrodes into each of six cells released varying amounts of Ca2+ in the order of 1 mumol per cell, but hyperpolarizing and depolarizing pulses up to 500 ms in duration caused no measurable loss (less than 57 pmol) of Ca2+ even when the latter elicited action potentials. Addition of 10 mumol of Ba2+ or tetraethylammonium (TEA) caused losses up to 1200 pmol of Ca2+ from the cells and prolonged the action potentials by a factor of three or more. Subsequent addition of Ba2+ or TEA to treated cells caused no further losses of Ca. Because prolonged action potentials can apparently only be elicited after the chelation or displacement of Ca2+, we propose that, as in many animal cells, the K+ channels responsible for the normal brief repolarizing phase of the action potential are controlled by Ca2+ in these electrically excitable plant cells.

Action Potentials↗
PubMed1985

[Modulating action of barium and other ions on the sensory activity of frog labyrinth].

The effect of Ba2+, TEA, 4-AP and CoCl2 on the EPSP and spike discharges recorded from single fibres of the posterior nerve in the isolated frog labyrinth has been investigated. In Ca-free solution Ba2+ preserved, at low concentration (0.3 mM), the resting activity and at higher levels (up to 6 mM) it resulted in a pronounced facilitation of the EPSP and spike discharges. Facilitation increased on increasing Ba2+ concentration up to 4-5 mM and it was more evident in those units exhibiting a low resting spike firing. The effect of Ba2+ (1 mM) was completely antagonized by 10 mM Ca2+ X CoCl2 (3 mM) suppressed the resting rate at the normal external Ca2+ concentration; the Co2+ block was partially relieved by 1.8 mM Ba2+ X TEA (20 mM) evoked a clear-cut increase in the EPSP and spike discharges which, however, was less consistent than that produced by Ba2+. By comparing the effect of TEA on the spike frequency with that obtained at different Ba2+ levels, the Ba2+ capacity to carry the Ca2+ current was dissected. Such an effect is dose-dependent and it is more evident in low-frequency units. Conversely, 4-AP did not affect the resting discharge frequency. These results indicate that either the Ca2+ or the Ba2+ current sustain the transmitter release at the cyto-neural junction. The effect of TEA suggests that the Ca2+-dependent K+ current may play an important role in supporting the neurosecretory process by controlling the membrane potential of the hair cells.

4-Aminopyridine↗
PubMed1994

Inhibitor effects on the ionic exchanges through the human amniotic epithelial cell membranes.

Direct measurements of cell podocyte/or microvillous membrane ionic exchanges were performed on the membranes of isolated human amniotic epithelial cells. The ionic exchanges were determined from the measures of cellular input conductances. The effects of various inhibitors: ouabain, amiloride, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS), 4'4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), quinidine, barium, manganese were analyzed. This study shows that the ionic exchanges through the epithelial cells are regulated by the presence of Na+,K+,Cl- channels, Na+/H(+)-Cl-/HCO3- antiports, (Na-K)ATPase and Na+/Ca(2+)-Na+/Mg2+ exchangers on the 2 faces of the cells and of a Na(+)-K(+)-2Cl- cotransport on the membrane facing the amniotic cavity only.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1978

Dissolution of Barium-impaction ileus by Gastrografin.

Ileus caused by impaction of hardened residual barium stagnated in the colon-a rare complication of barium-meal examination-constitutes a particularly serious problem when it occurs following abdominal operations, leading to postoperative ileus. The administration of Gastrografin in such cases has proven efficacy in the dissolution of inspissated barium, refractory to routine means of evacuation. Four case reports provide an illustration of this problem. The satisfactory results obtained, and the hitherto reported lack of side effects of this compound, justify recommendation of Gastrografin as a safe, simple method for use in the management of these cases.

Aged↗