Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Potassium 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 559 records · Page 31Linked to original sources
PubMed1996

Bond strength and durability of porcelain bonding systems.

Because the most effective bonding system for ceramic restorations has not been documented, this study examined bond strength and durability of bonding systems joined to a feldspathic porcelain. Disks of porcelain specimens were fired on refractory investment materials and were air-abraded with alumina. The disks were then bonded with six combinations of five silane primers and six luting agents. Durability of the bond was evaluated by means of a thermocycling machine. Shear bond strengths were determined before and after thermocycling. The results showed that reduction in bond strengths after thermocycling was remarkable for five systems (p < 0.05). However, three systems exhibited shear bond strength greater than 20 MPa after 20,000 cycles.

Air↗
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↗
PubMed2000

Influence of time and adhesive system on the extrusion shear strength between feldspathic porcelain and bovine dentin.

OBJECTIVES: The behavior of dual-cure cements over time remains unclear. This study evaluated the extrusion shear strength of the bond between feldsphatic porcelain and bovine dentin at different time intervals, using three adhesive systems based on dual-cure cements and one based on a self-cure cement. METHODS: The adhesive systems evaluated included: C&B/One-Step, Enforce/Prime&Bond NT Dual-Cure, RelyX ARC/Single Bond and Variolink II/Syntac SC. Discs of bovine root dentin, 2.5 mm thick, had the root canal prepared with a standardized taper. Porcelain truncated cones etched with 4% hydrofluoric acid and silanized were bonded into the perforations. The extrusion shear test was performed after 15 min, 4 h, 12 h, 24 h, and 7 days. Data were analyzed using the Weibull distribution. The failure mode was accessed by stereomicroscope and SEM. RESULTS: Statistical differences were found between 15 min and 7 days for Variolink II/Syntac SC and RelyX ARC/Single Bond, and between 15 min and 24 h for Enforce/Prime&Bond NT Dual-Cure. For C&B/One-Step, difference was found between 15 min and 4 h. Between 24 h and 7 days, only the system RelyX ARC/Single Bond showed a significant increase in the characteristic strength. SEM analysis revealed that the failure involved the hybrid layer/dentin or the hybrid layer/adhesive interfaces, regardless of the time interval and adhesive system. SIGNIFICANCE: High characteristic strengths were observed after 15 min when dual-cure cements were used. In general, the values found at 24 h or 7 days were higher than at 15 min. However, there was always a considerable probability of bonding failure at low stress levels for all the systems tested.

Acid Etching, Dental↗
PubMed2000

gamma-aminobutyric acid type B receptors are expressed and functional in mammalian cardiomyocytes.

gamma-Hydroxybutyrate (GHB), an anesthetic adjuvant analog of gamma-aminobutyrate (GABA), depresses cell excitability in hippocampal neurons by inducing hyperpolarization through the activation of a prominent inwardly rectifying K(+) (Kir3) conductance. These GABA type B (GABA(B))-like effects are clearly shown at high concentrations of GHB corresponding to blood levels usually reached during anesthesia and are mimicked by the GABA(B) agonist baclofen. Recent studies of native GABA(B) receptors (GABA(B)Rs) have favored the concept that GHB is also a selective agonist. Furthermore, cloning has demonstrated that GABA(B)Rs assemble heteromeric complexes from the GABA(B)R1 and GABA(B)R2 subtypes and that these assemblies are activated by GHB. The surprisingly high tissue content, together with anti-ischemic and protective effects of GHB in the heart, raises the question of a possible influence of GABA(B) agonists on excitable cardiac cells. In the present study, we provide electrophysiological evidence that GHB activates an inwardly rectifying K(+) current in rat ventricular myocytes. This effect is mimicked by baclofen, reversibly inhibited by GABA(B) antagonists, and prevented by pertussis toxin pretreatment. Both GABA(B)R1 and GABA(B)R2 are detected in cardiomyocytes by Western blotting and are shown to coimmunoprecipitate. Laser scanning confocal microscopy discloses an even distribution of the two receptors in the sarcolemma and along the transverse tubular system. Hence, we conclude that GABA(B)Rs are distributed not only in neuronal tissues but also in the heart, where they can be activated and induce electrophysiological alterations through G-protein-coupled inward rectifier potassium channels.

Adjuvants, Anesthesia↗
PubMed1994

pH-metric log P. 4. Comparison of partition coefficients determined by HPLC and potentiometric methods to literature values.

The pKa and log P of 20 compounds, including six substituted phenols, two substituted quinolines, N-methylaniline, five barbiturate derivatives, two phenothiazines, and several other molecules of pharmaceutical interest, were determined by the potentiometric technique at 25 degrees C and ionic strength 0.1 M (KNO3). The log P values were determined also by partition HPLC. Three of the substances were of very low aqueous solubility, and for these the aqueous pKas were determined by extrapolation from methanol-water solutions using the Yasuda-Shedlovsky technique. Values of log P obtained both by potentiometry and by partition HPLC, which ranged from 0.3 to 5.4, were in very good acordance with literature values. The general applicability of the potentiometric technique to ionizable compounds of diversely varied structures was demonstrated by the study.

Chemical Phenomena↗
PubMed1990

Calcium antagonists and vasoconstrictor effects in intracerebral microarterioles.

The purpose of this work was to study the contractile activity of intracerebral microarterioles and their sensitivity to the calcium antagonist nimodipine. Potassium depolarization evoked contraction and rhythmic activity that was blocked by nimodipine (IC50 0.08 nM). High concentrations of noradrenaline and prostaglandin F2 alpha were needed to elicit a contractile response. Intracerebral microarterioles were very sensitive to endothelin (ED50, 0.2 nM). The contractions evoked by concentrations of endothelin lower than or equal to ED50 were relaxed by nimodipine, which also blocked the amplified response to potassium chloride depolarization occurring with subthreshold concentrations of endothelin. We discuss these observations in relation to brain ischemia.

Animals↗
PubMedDate not supplied

[Determination of electrical characteristics of synaptosomal membranes of the brain].

A correct method for evaluating the potential differences across plasma membranes of synaptosomes from the brain is presented. It takes into consideration the multicompartment synaptosome organization and is based on the accumulation of the radioactive permeant cation [3H]tetraphenylphosphonium. It is shown that upon potassium depolarization of the synaptosomes to about -5 mv there is a sharp decrease in the ion selectivity of the synaptic membranes.

Animals↗
PubMed1990

Cation transport by sweat ducts in primary culture. Ionic mechanism of cholinergically evoked current oscillations.

1. The coiled reabsorptive segment of human sweat ducts was cultured in vitro. Cells were then harvested and plated onto a dialysis membrane which was glued over a hole in a small disc. Cultures were maintained in a low serum, hormone-supplemented medium that allowed the cells to grow to confluency. The disc was then placed as a partition between two compartments of a miniature Ussing chamber. The chamber was mounted on the stage of an inverted microscope and intracellular potentials were recorded under transepithelial open-circuit or voltage clamp conditions. All values are given as means +/- S.E.M. and n refers to the number of preparations or duct cells. 2. Under control conditions, the cultured epithelia developed mucosa-negative transepithelial potentials (Vt) ranging from -2.5 to -38 mV (-13.5 +/- 1.5 mV, n = 36). The basolateral membrane potential (Vb) was -39.4 +/- 0.7 mV (n = 50 cells), and the apical membrane potential (Va) was linearly correlated with Vt:Va = 1.0 Vt -39.3 mV (r = -0.78, n = 50). 3. The epithelium generated inwardly directed short-circuit currents (Isc) of 12-95 microA cm-2 (45 +/- 4 microA cm-2, n = 36) with a steady-state intracellular potential. Vc = -31.1 +/- 0.6 mV and a fractional resistance of the apical membrane, fR = 0.59 +/- 0.01 (n = 115 cells). 4. The Na+ channel blocker amiloride (mucosal bath, 10 microM) abolished Isc -0.8 +/- 0.6 microA cm-2), the cells hyperpolarized to -61.0 +/- 1.2 mV, and fR increased to 0.85 +/- 0.01 (n = 44). These effects were fully reversible. 5. During initial stimulation with the cholinergic agonist, methacholine (serosa, 5 or 10 microM), the short-circuit current increased to 80 +/- 10 microA cm-2, the cells hyperpolarized to -55.8 +/- 1.2 mV, and fR increased to 0.82 +/- 0.01 (n = 35). 6. In short-circuited preparations stimulated with methacholine an increase in mucosal potassium concentration ([K+]m) from 5 to 25 mM had no significant effect, while a similar increase in the serosal K+ concentration ([K+]s) produced a change in Vc of 44 +/- 3 mV per log10[K+]s (n = 9). In non-stimulated preparations this change was only 16 +/- 2 mV per log10[K+]s (n = 13). After blocking the apical Na+ channels with amiloride the slope was 24 +/- 5 mV per log10[K+]s in unstimulated preparations.(ABSTRACT TRUNCATED AT 400 WORDS)

Amiloride↗
PubMed2006

Electrogenerated chemiluminescence of luminol on a gold-nanorod-modified gold electrode.

Electrogenerated chemiluminescence (ECL) of luminol on a gold-nanorod-modified gold electrode was studied, and five ECL peaks were obtained under conventional cyclic voltammetry in both neutral and alkaline solutions. Among them, four ECL peaks (ECL-1-4) were also observed on a gold-nanosphere-modified gold electrode, but the intensities of these ECL peaks were enhanced about 2-10-fold on a gold-nanorod-modified gold electrode in neutral solution. One new strong ECL peak (ECL-5) was obtained at -0.28 V (vs SCE) on a gold-nanorod-modified gold electrode in both neutral and alkaline solutions and enhanced with an increase in pH. In strong alkaline solutions, ECL-1 and ECL-2 on a gold-nanosphere-modified electrode were much stronger than those on a gold-nanorod-modified gold electrode, while ECL-3-5 appeared to only happen on a gold-nanorod-modified gold electrode. The emitter of all the ECL peaks was identified as 3-aminophthalate. The ECL peaks were found to depend on the scan direction, the electrolytes, the pH, and the presence of O(2) and N(2). The reaction pathways for ECL-4 have been further elucidated, and the mechanism of the new ECL peak (ECL-5) has been proposed. The results indicate that a gold-nanorod-modified gold electrode has a catalytic effect on luminol ECL different from that of a gold-nanosphere-modified gold electrode, revealing that the shape of the metal nanoparticles has an important effect on the luminol ECL behavior. The strong ECL of luminol in neutral solution obtained on a gold-nanorod-modified electrode may be used for the sensitive detection of biologically important compounds in physiological conditions.

Bromides↗
PubMed1975

Clinically available antischistosomal drugs.

The indications, the contraindications, and the characteristics of the antimonial and nonantimonial drugs clinically available for the treatment of human schistosomiasis are outlined. Of the antimonial compounds, antimony potassium tartrate or antimony sodium tartrate, both given by the intravenous route, are effective against Schistosoma japonicum, S. mansoni, and S. hematobium, but the production of severe side effects limits their use outside the treatment of individuals. Sodium antimonyl gluconate is less effective against S. mansoni and S. hemotobium and is also given intravenously. Of those antimonial compounds given intramuscularly, antimony dimercaptosuccinate is the most effective against all three common human schistosomes. Four available nonmetallic schistosomicides are considered. Niridazole, orally administered, is effective against all three common species of schistosome infecting man, but activity is maximal against S. hematobium. Many minor side effects have been described, but the major and most important side effects, neuropsychiatric symptoms and signs, are fortunately rare. Lucanthone hydrochloride, of moderate efficiency when given orally for S. hematobium or S. mansoni infections, is probably best used as a suppressant in small doses. Troublesome gastrointestinal toxicity limits its therapeutic use. Metrifonate, a cholinesterase-inhibiting organophosphorus compound, is effective only against S. hematobium. Clinical tolerance is very good. Hycanthone mesylate is highly effective against S. mansoni and S. hematobium but ineffective against S. japonicum. It is given as a single intramuscular dose. Many contraindications to its use exist, and acute hepatotoxicity has occurred infrequently. Its association with mutagenicity in certain experimental test systems has stimulated numerous ongoing studies to clarify the implications of its use in humans.

Antimony↗
PubMed1996

Recent advances in ceramics for dentistry.

For the last ten years, the application of high-technology processes to dental ceramics allowed for the development of new materials such as heat-pressed, injection-molded, and slip-cast ceramics and glass-ceramics. The purpose of the present paper is to review advances in new materials and processes available for making all-ceramic dental restorations. Concepts on the structure and strengthening mechanisms of dental ceramics are provided. Major developments in materials for all-ceramic restorations are addressed. These advances include improved processing techniques and greater mechanical properties. An overview of the processing techniques available for all-ceramic materials is given, including sintering, casting, machining, slip-casting, and heat-pressing. The most recent ceramic materials are reviewed with respect to their principal crystalline phases, including leucite, alumina, forsterite, zirconia, mica, hydroxyapatite, lithium disilicate, sanidine, and spinel. Finally, a summary of flexural strength data available for all-ceramic materials is included.

Aluminum Compounds↗
PubMed2005

Autoxidation of salvinorin A under basic conditions.

[reaction: see text] Treatment of salvinorin A (1a) with KOH in MeOH gave the enedione 3, for which the dienone structure 7 was recently proposed. Also isolated, after methylation, were the secotriesters 4a-c. A mechanism for this unusual series of autoxidations is proposed. Surprisingly, 4a showed weak affinity at the kappa-opioid receptor. Divinatorins A-C (2a-c) showed no affinity at opioid receptors. Attempted reduction of 3 to a novel salvinorin diol (9d) was unsuccessful, but careful deacetylation of salvinorin C (9a) provided a viable route to this compound. A general method for identifying salvinorin 8-epimers by TLC is also presented.

Diterpenes↗
PubMed2006

Design, synthesis, and pharmacological evaluation of R/S-3,4-dihydro-2,2-dimethyl- 6-halo-4-(phenylaminocarbonylamino)-2H-1-benzopyrans: toward tissue-selective pancreatic beta-cell KATP channel openers structurally related to (+/-)-cromakalim.

In the search of a novel series of benzopyrans structurally related to (+/-)-cromakalim and acting as pancreatic beta-cell potassium channel openers, several R/S-3,4-dihydro-2,2-dimethyl-6-halo-4-(phenylaminocarbonylamino)-2H-1-benzopyrans with or without a substituent on the phenyl ring in the 4-position were synthesized. Their activity on rat-insulin-secreting cells and rat aorta rings was compared to that of the K(ATP) channel activators (+/-)-cromakalim, diazoxide, (+/-)-pinacidil, and compound 4. Structure-activity relationships indicated that the most pronounced inhibitory activity on the pancreatic tissue was obtained by introducing a meta- or para-electron-withdrawing group (a chlorine atom) on the C-4 phenyl ring (drugs 37-42). Such molecules, unlike the parent compound (+/-)-cromakalim, also exhibited a high selectivity for the pancreatic tissue versus the vascular tissue. Radioisotopic and electrophysiological investigations performed with R/S-6-chloro-4-(3-chlorophenylaminocarbonylamino)-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran (38) confirmed that the drug activated pancreatic KATP channels.

Adenosine Triphosphate↗
PubMed1981

Effects of 2-chloroadenosine on electric potentials in brain synaptic membrane vesicles.

Isolated synaptic plasma membrane vesicles developed an internal negative membrane potential (delta psi) following loading with potassium succinate and incubation in NaCl, sodium succinate, or Tris succinate media. Membrane delta psi was monitored by measuring triphenyl[3H]methylphosphonium ion ([3H]TPMP+) accumulation by these vesicles. Estimates of delta psi ranged from --6.9 mV for vesicles incubated in sodium succinate to --28 mV for membranes incubated in NaCl. Intravesicular TPMP+ accumulation was strongly dependent on the K+ diffusion potential and was enhanced by the K+ ionophore valinomycin and by the adenosine analog 2-chloroadenosine (2-Cl-Ado). The stimulation of TPMP+ influx by 2-Cl-Ado was dependent on the concentration of this agent, independent of Cl- fluxes, and sensitive to inhibition by the methylxanthine theophylline. The increase of delta psi of the synaptic membrane vesicles caused by 2-Cl-Ado paralleled the hyperpolarization of neurons produced by adenosine and 2-Cl-Ado in physiological systems.

2-Chloroadenosine↗
PubMed1998

Depolarization of isolated brain nerve endings by nitric oxide donors: membrane mechanisms.

Nitric oxide (NO) is known to potentiate neurotransmitter release in several types of neuronal cells. In the present study, the influence of NO on the membrane potential of isolated nerve endings (synaptosomes) from rat brain was studied. NO donors--sodium nitroprusside (SNP), S-nitroso-L-cysteine (CysNO), and hydroxylamine (HA)--induced synaptosome depolarization monitored by decreasing accumulation of 86Rb+ and the lipophilic potential-sensitive probe [3H]tetraphenylphosphonium. SNP reduced plasma membrane potential by 3-5 mV with half-maximal effect at approximately 10 microM. More potent NO donors, CysNO and HA, led to significant depolarization of the plasma membrane at 10-100 microM concentrations and also induced depolarization of mitochondria at concentrations above 1 mM. At 10 microM-10 mM concentrations, NO donors inhibited potassium channels; CysNO and HA also suppressed the activity of the sodium pump. NO-induced depolarization was not blocked by guanylate cyclase inhibitor methylene blue and the permeable cGMP analog dibutyryl-cGMP did not affect the membrane potential. The effects of NO donors were mimicked by SH-modifying reagents including 5, 5'-dithio-bis(2-nitrobenzoic acid) (DTNB) and N-ethylmaleimide (NEM). Non-permeable SH-reagent DTNB caused small depolarization resembling SNP action in its magnitude and kinetics. Significant decrease of potential in the presence of NEM, which permeates through the plasma membrane, was similar to that of CysNO and HA. The data suggest that in the presynaptic nerve endings, NO-induced depolarization of the plasma and mitochondrial membranes involves modification of protein SH-groups. The plasma membrane depolarization is due to the decreased potassium permeability and inhibition of the sodium pump.

Animals↗