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At least 1,009 records · Page 56Linked to original sources
PubMed1985

Electrophysiologic effects of AHR 10718 on isolated cardiac tissues.

We used microelectrode and blood superfusion techniques to study the electrophysiologic effects of a new antiarrhythmic compound, AHR 10718 (N'-(2-(diethylamino)ethyl)-N-(1-methylethyl)-N-(2-(phenylsulfonyl )ethyl)urea,(Z)-butanedioate) on the electrophysiologic properties of canine Purkinje fibers and papillary muscles. AHR 10718 (greater than or equal to 5 X 10(-6) M) induced a use-dependent decrease in Vmax and significantly decreased Purkinje fiber conduction velocity and action potential duration. In addition, membrane responsiveness was depressed and the effective refractory period shortened. The effects of AHR 10718 were not highly dependent on [K+]0. Vmax of ventricular muscle action potentials also was reduced. However, in contrast to Purkinje fibers, ventricular muscle action potentials were significantly prolonged by AHR 10718 (greater than or equal to 5 X 10(-6) M). AHR 10718 had no effect on slow response action potentials induced by isoproterenol and high [K+]0. AHR 10718 significantly decreased normal automaticity, catecholamine-enhanced automaticity, and abnormal automaticity induced by barium or myocardial infarction. It also suppressed triggered activity and reduced delayed afterdepolarization amplitude in ouabain-treated Purkinje fibers and infarcted myocardium. These studies suggest that AHR 10718 may be effective against arrhythmias resulting from conduction disturbances and certain forms of abnormal impulse initiation.

Action Potentials↗
PubMed1986

TPP+ accumulation in rat brain synaptosomes as a probe for Na+ channels.

Tetraphenylphosphonium (TPP+) accumulation in rat brain synaptosomes was measured in the presence of various stimuli. TPP+ accumulation was sensitive to an increase of extracellular K+ or to the presence of Na+ channel neurotoxins. Examination of the effects of drugs with different physico-chemical properties on TPP+ accumulation showed that there was no effect under low and high K+ conditions; pimozide, flunarizine and buterizine were active in the presence of veratridine or scorpion venom. These results were compared to data obtained for the specific binding of [3H]BTX-B, a selective marker for the Na+ channel. It can be concluded that certain drugs, although active on [3H]BTX-B binding, are not necessarily identified when TPP+ is used as probe.

Animals↗
PubMed1989

The action of organic mercury compounds on the function of isolated mammalian heart muscle.

The effects of four organic mercury compounds (methylmercuric chloride; bromomercurihydroypropane, BMHP; chlormerodrin; p-chloromercuribenzoic acid, PCMB) on mechanical and electrical functions of guinea-pig papillary muscles were investigated. An initial decline in contraction force was followed by a transient positive inotropic response. The first was accompanied by a shortening of the action-potential duration and by a reduction of the depolarization velocity and the duration of the Ca2+-dependent slow response. The latter was characterized by an indirect component (release of noradrenaline) and by a direct component, which was dependent on the stimulation rate and on the extracellular concentration of Na+ and K+. The direct positive effect, therefore, was likely to have resulted from inhibition of the sarcolemmal Na+ + K+-ATPase. This notion was confirmed by experiments with isolated membrane particles. The prevalence of the negative or positive inotropic action of these compounds could be ascribed to their lipophilic or hydrophilic properties, respectively.

Action Potentials↗
PubMed1993

Cholecystokinin-8 increases K(+)-evoked [3H] gamma-aminobutyric acid release in slices from various brain areas.

[3H] gamma-Aminobutyric acid (GABA) release was studied in rat brain slices in the absence or presence of cholecystokinin-8 (CCK-8). [3H]GABA release under the conditions used was Ca(2+)-dependent and insensitive to the presence of the glial uptake blocker beta-alanine. While the basal release of [3H]GABA was not affected by CCK-8, the K(+)-stimulated release of [3H]GABA was significantly enhanced by 300 nM of CCK-8 in the caudate putamen, the substantia nigra, the hippocampal formation and the parietofrontal cortex. In the cerebral cortex the CCK-8 enhancement of [3H]GABA release was concentration-dependent and abolished by the CCKB receptor antagonists PD135,158 (1.0 nM) and L-365,260 (100 nM). A significant counteraction of the CCK-8 action was also found with the CCKA receptor antagonist L-364,718 (100 nM) but only in concentrations at which both CCKA and CCKB receptors are blocked. No CCK-8 effects on [3H]GABA release were observed when tetrodotoxin was superfused 5 min before the K(+)-induced [3H]GABA release. It is suggested that the enhancing actions of CCK-8 on K(+)-stimulated [3H]GABA release is mainly related to an activation of CCKB receptors.

Animals↗
PubMed1994

A new glibenclamide-insensitive neuroselective hyperpolarizing agent.

We describe a novel compound, (-)-N-(2-ethoxyphenyl)-N'-(1,2,3-trimethylpropyl)-2-nitroethene-1, 1-diamine), Bay x9227, that demonstrates dose-dependent hyperpolarizing activity of remarkable potency (EC50 3 picomolar) and selectivity for CNS neurons and clonal neurotypic cells compared to smooth muscle cells. Single cell membrane potential measurements were obtained in physiologic buffer using the fluorescent probe, bisoxonol. Unlike K+ATP-channel activators including its (+)-enantiomer (Hoffman et al., 1993, Biochem. Biophys. Res. Commun. 190(2), 551), this activity was insensitive to glibenclamide antagonism. These data suggest a novel pharmacologic site for effecting neuroselective hyperpolarization.

Animals↗
PubMed1995

Differential effects of the BKCa channel openers NS004 and NS1608 in porcine coronary arterial cells.

The effects of newly claimed BKCa channel openers NS004 (5-trifluoromethyl-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidazo le-2- one) and NS1608 (N-(3-(trifluoromethyl)phenyl)-N'-(2-hydroxy-5-chlorophenyl)urea) were investigated on whole-cell K+ current (IK) in enzymatically isolated porcine coronary arterial cells using patch-clamp technique with a double holding potential protocol. When cells were held at 0 mV, IK was augmented by NS004 in a concentration-dependent manner. With a holding potential of -60 mV, however, IK was moderately inhibited by NS004 between 0.5 and 10 microM, but robustly stimulated by 50 microM NS004 at highly depolarized potentials. The effects of NS1608 on IK did not differ due to change in holding potential. At -60 mV and 0 mV, NS1608 activated IK with bell-shaped concentration-response curves peaked between 5 and 10 microM. The differential mode of action of the two compounds suggested an involvement of mechanism(s) other than an opening of BKCa channel.

Animals↗
PubMed1985

Acylation of adenovirus type 12 early region 1b 18-kDa protein. Further evidence for its localisation in the cell membrane.

The 18-kDa E1b protein in Ad 12-transformed rat cells and in Ad 12-infected human cells binds lipid strongly. The lipid is not removed by boiling in the presence of SDS or by extraction with methanol/chloroform. It is, however, dissociated from the protein by treatment with methanolic KOH suggesting that attachment is through an ester linkage. The acylated 18-kDa protein is detected only in the membrane fraction. Labelling cell surface proteins on Ad 12-transformed cells with [125I]iodosulphanilic acid shows that some of the Ad 12 18-kDa E1b protein is present on the outside of the cell. It is concluded that this protein is responsible for cell surface T-antigen activity.

Acylation↗
PubMed1988

Simple graphical methods for use with complex ligand-binding and enzyme mechanisms.

Simple graphical plots in distribution-free space are shown to provide estimates of mechanism and kinetic parameters for complex steady-state processes. The methods were tested using simulated 1:1, 1:2, 2:2, 2:3 and 3:3 functions, and real data from polyol dehydrogenase, NADPH oxidation in the presence of DL-glyceraldehyde, and NADPH oxidation in the presence of an NADPH-binding protein. Estimates of mechanism and parameters agreed closely with those found from non-linear regression by computer.

Aldehyde Reductase↗
PubMed1989

Synthesis and evaluation of optically pure [3H]-(+)-pentazocine, a highly potent and selective radioligand for sigma receptors.

Tritium-labeled (+)-pentazocine ([3H]-1b) of specific activity 26.6 Ci/mmol was synthesized in 3 steps starting with (+)-normetazocine (2) of defined optical purity. [3H]-1b has been characterized as a highly selective ligand for labeling of sigma receptors. Competition data revealed that [3H]-1b could be displaced from guinea pig brain membrane preparations with a number of commonly used sigma receptor ligands. [3H]-1b exhibited saturable, enantioselective binding with a Kd of 5.13 +/- 0.97 nM and a Bmax of 1146 +/- 122 fmol/mg protein. Phencyclidine (PCP) displaced [3H]-1b with low affinity while MK-801 was inactive, thus indicating insignificant activity at the PCP-binding site; apomorphine failed to displace [3H]-1b indicating lack of dopamine receptor cross-reactivity. Since the affinity of [3H]-1b is about 6 times that of the two commonly employed sigma ligands ((+)-3-[3H]PPP and [3H]DTG) and since it is more selective for sigma receptors than the benzomorphan [3H]SKF-10,047, it represents the first example of a highly selective benzomorphan based sigma receptor ligand. [3H]-1b should prove useful for further study of the structure and function of sigma receptors.

Animals↗
PubMed1990

Differential movement of ions in artificial phospholipid vesicles.

Pyranine was incorporated into sonicated unilamellar vesicles of soybean phosphatidylcholine to monitor changes in the internal pH of the vesicles. Dilution of soybean phosphatidylcholine vesicles loaded with 0.3 M KCl, KNO3 or K2SO4 into salt-free buffer resulted in rapid exchange of K+ and protons. A pseudoequilibrium distribution of ions was achieved, since addition of valinomycin, uncoupler or nigericin now caused a rapid alkalinization of the vesicle interior. Dilution into buffer containing NaCl gave a further exchange of Na+ and protons following the initial K+/proton exchange. Na+ permeation was slower than that of K+. A stable membrane potential was not generated by the ion movements. It is proposed that aqueous channels are formed through the phospholipid bilayers and that K+ and Na+ permeate through these channels as the hydrated ions.

Arylsulfonates↗
PubMed1983

The short term hormonal control of cytoplasmic protein phosphorylation in hepatocytes from fed rats.

Exposure of 32P-prelabelled isolated hepatocytes to vasopressin affected the phosphorylation of nine of the 26 phosphoproteins resolved by sodium dodecyl sulphate gel electrophoresis. Glucagon (2 nM) or cyclic AMP elicited significant changes in the phosphorylation of only four phosphoproteins. A very high concentration of glucagon (1000 nM) affected additional phosphoproteins. Insulin alone significantly increased the phosphorylation of a single protein. Vasopressin, A23187, glucagon and cyclic AMP all induced the dephosphorylation of a single phosphoprotein of mol. wt 20,000. The significance of these results with respect to the short-term control of hepatic metabolism is discussed.

Animals↗
PubMed1983

3-hydroxy-3-methylglutaryl-CoA reductase from neonatal chick.

The optimal conditions for identification of mevalonic acid as the product of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase are described, as well as the effect of different buffer constituents on the enzyme activity. Under the chosen assay conditions, reductase activity from neonatal chick liver increased with the incubation time up to 60 min and was proportional to the amounts of protein added in a range of 0.1-0.5 mg. The specific activity was maximal in brain and liver and lower in intestine of 6-day-old chicks. Thermostability of hepatic reductase was studied. When microsomal preparations were maintained at 4 degrees C, reductase activity remained unchanged for 6 hr and decreased afterwards. Addition of 50 mM KF to the homogenization medium had no effect on the reductase activity. Similarly, preincubation of microsomal preparations with 105,000 g supernatants in the presence or absence of KF did not significantly increase the reductase activity. These results suggest that HMG-CoA reductase was isolated from neonatal chick in the fully activated form.

Animals↗
PubMed1987

Ferrous iron uptake by Bifidobacterium bifidum var. pennsylvanicus: the effect of metals and metabolic inhibitors.

Ferrous iron uptake studies in Bifidobacterium bifidum var. pennsylvanicus were carried out in a well-defined salt solution termed "modified Hanks solution" at both high iron concentrations (LAFIUS conditions) and low concentrations (HAFIUS conditions). Various divalent metals, Mn2+, Zn2+, Ni2+ and Cu2+, inhibited iron uptake under HAFIUS conditions in a non-competitive manner, and in a pseudo-competitive manner under LAFIUS conditions. Cr2+ had no effect. Co2+ inhibited iron uptake competitively under HAFIUS conditions. Metabolic affectors that inhibited iron uptake both under HAFIUS and LAFIUS conditions were: tetraphenylphosphonium chloride, diethylstilbesterol, vanadate, carbonylcyanide-m-chlorophenyl-hydrazone, and a mixture of valinomycin and nigericin. Substances that stimulated iron uptake were KCl, valinomycin, and nigericin. Iron uptake under LAFIUS conditions in piperazine-buffered modified Hanks solution was higher than that in the acetate-buffered solution, and acetate inhibited iron uptake in the piperazine buffer. HAFIUS showed no difference. It is concluded that iron uptake in bifidobacteria is driven by an ATPase-dependent proton-motive force and that both the pH gradient and membrane potential are involved in this process. Mn2+, Zn2+, Ni2+, and Cu2+ may be transported via LAFIUS, but not HAFIUS. HAFIUS may transport only Co2+ in addition to Fe2+.

Bifidobacterium↗
PubMed1989

Phosphorylation of 6-phosphofructokinase in rat lung.

1. 6-Phosphofructokinase of both fetal and adult rat lung consists of L, M and C subunits in a ratio of 65:25:10. 2. 6-Phosphofructokinase was purified to homogeneity from adult rat lung and subjected to phosphorylation in vitro by the catalytic subunit of cyclic AMP-dependent protein kinase. 3. This resulted in phosphorylation of the L and M subunit of 6-phosphofructokinase. 4. The C subunit was not phosphorylated. 5. However, if the phosphorylation of 6-phosphofructokinase was studied in the cytosol fraction of either fetal or adult lung using endogenous protein kinase(s), only the L subunit was phosphorylated. 6. This phosphorylation was dependent on cyclic AMP. 7. No influence of calcium, calmodulin or phosphatidylserine/diolein on the phosphorylation was observed. 8. It is concluded that although both L and M subunits of rat lung 6-phosphofructokinase are potential substrates for cyclic AMP-dependent protein kinase, their phosphorylation in situ is differentially regulated.

Aging↗