The antidepressant-like effect of Hypericum caprifoliatum Cham & Schlecht (Guttiferae) on forced swimming test results from an inhibition of neuronal monoamine uptake

A crude (ECH) and a purified cyclohexane extract (HCP) of Hypericum caprifoliatum and their main phloroglucinol derivative (HC1) were evaluated regarding their action on monoaminergic systems, more precisely on dopamine. In rats and mice forced swimming test, ECH and HCP dose-dependently reduced the immobility time. The effect of the highest dose was prevented by a prior administration of either sulpiride or SCH 23390 (D₂ and D₁ dopamine receptor antagonist, respectively). HCP (360 mg/kg) decreased the locomotor activity of mice. ECH (90 mg/kg) caused hypothermia and potentiated apomorphine-induced (16 mg/kg) hypothermia in mice. HCP and HC1 inhibited, in a concentration-dependent and monophasic manner, the [³H]-DA, [³H]-NA and [³H]-5HT synaptosomal uptakes, but did not prevent the binding of specific ligands to the monoamine transporters. Moreover, when tested at the concentrations corresponding to its IC₅₀ on [³H]-DA uptake, HC1 did not induce a significant [³H]-DA release, while at a higher concentration (200 ng/ml) it enhanced significantly (by 12%) the synaptosomal DA release. These data suggest that the antidepressant-like effect of H. caprifoliatum on the forced swimming test is due to an increase in monoaminergic transmission, resulting from monoamine uptake inhibition, more potently of dopamine, which may be related to their phloroglucinol contents.     

Role of potassium channels in the antidepressant-like effect of folic acid in the forced swimming test in mice

Potassium (K⁺) channels have been implicated in depressive disorders and in the mechanism of action of antidepressants. Considering that several studies have indicated that folic acid plays an important role in the pathophysiology of depression, the present study investigated the involvement of potassium channels in the antidepressant-like effect of this vitamin. For this aim, the effect of the combined administration of different types of K⁺ channel blockers and folic acid in the forced swimming test (FST) was investigated. Treatment of mice by intracerebroventricular (i.c.v.) route with subactive doses of glibenclamide (an ATP-sensitive K⁺ channels blocker, 0.5 pg/site), charybdotoxin (a large- and intermediate-conductance calcium-activated K⁺ channel blocker, 25 pg/site) or apamin (a small-conductance calcium-activated K⁺ channel blocker, 10 pg/site), augmented the effect of folic acid (10 mg/kg, p.o., subeffective dose) in the FST. Additionally, the administration of folic acid and the K⁺ channel blockers, alone or in combination, did not affect locomotion in the open-field test. Moreover, the reduction in the immobility time in the FST elicited by folic acid administered at a higher dose (50 mg/kg, p.o.) was prevented by the pretreatment of mice with the K⁺ channel opener cromakalim (10 μg/site, i.c.v.), without affecting locomotor activity. The results of this study indicate that the antidepressant-like effect of folic acid in the FST may be at least partly due to its modulatory effects on neuronal excitability, via inhibition of K⁺ channels.     

Quabain: Temporal relationship between the inotropic effect and the in vitro binding to,and dissociation from, (Na++K+)-activated ATPase

Summary The time course of the inotropic response to ouabain in Langendorff preparations was compared with that of the in vitro ATP-dependent (³H)-ouabain binding to cardiac (Na⁺+K⁺)-activated ATPase preparations, and subsequent dissociation, to determine the temporal relationship between the inotropic response and (Na⁺+K⁺)-activated ATPase inhibition.Species differences were minimal either in the onset of inotropic response or the (³H)-ouabain binding. The rates of both loss of the inotropic response to ouabain during washout and the dissociation of the ouabain-enzyme complex, however, were rapid in guinea pig and rabbit (relatively ouabain-insensitive species) and slow in cat and dog (ouabain-sensitive species). The half-time of the loss of the inotropic response was similar to the half-time of the dissociation of the ouabain-enzyme complex in each species.Since ATP-dependent binding of cardiac glycosides has been related to enzyme inhibition, it was concluded that the time course of the inotropic response to ouabain parallels the time course of (Na⁺+K⁺)-activated ATPase inhibition, and that the dissociation of ouabain from the enzyme may terminate the inotropic response.A part of this study was presented at the Fifth Annual Meeting of the International Study Group for Research in Cardiac Metabolism, Winnipeg, Manitoba, June, 1972.     

Dehydro-digitoxosides of digitoxigenin and digoxigenin: Binding to beef heart (Na++K+)-ATPase in relation to unchanged digitoxosides

Summary Dehydro-digitoxosides are metabolites of digitalis glycosides. In order to study their possible biological activity their affinity to (Na⁺+K⁺)-activated ATPase was determined and compared with unchanged glycosides. Based on the dissociation constants of glycoside-enzyme-complexes, the affinity of the dehydro-digitoxosides ranged in the same order of magnitude as that of the native glycosides. Comparing mono-, bis-, and tris-digitoxosides of digitoxigenin (dt-1, dt-2, dt-3) and of digoxin (dg-1, dg-2, dg-3) with the corresponding dehydrodigitoxosides (3-dehydro-dt-1, 9-dehydro-dt-2, 15-dehydro-dt-3, 3-dehydro-dg-1 and 9-dehydro-dg-2, respectively) the dehydro-digitoxosides had lower affinities to the enzyme. The highest dissociation constants (K _D)were found for 3-dehydro-dt-1 and 3-dehydro-dg-1. The half maximal inhibition of (Na⁺+K⁺)-ATPase activity (I₅₀) corresponded to affinity measurements in all but two cases: dehydro-dt-3 and dehydro-dt-2 showed very low I₅₀ values.     

Anti-ulcer activity of newly synthesized acylquinoline derivatives

Anti-ulcer activity of newly synthesized acylquinoline derivatives was investigated. For the in vitro screening, the effects of the compounds on gastric H+/K+ ATPase isolated from hog and rabbit were examined. Among them, AU-090, AU-091, AU-254, AU-413 and AU-466 exhibited good in vitro activity on both enzymes. To correlate the in vitro activity with in vivo action, the effects of the compounds on the basal gastric acid secretion were studied. Some derivatives showed considerable anti-secretory activities, and AU-413 was selected for further studies. AU-413 protected gastric damage induced by either ethanol or NaOH dose dependently when given orally. ED50 values of 12 mg/kg, p.o. (ethanol) and 41 mg/kg, p.o. (NaOH) were obtained. In addition, histamine-stimulated gastric secretion was reduced upon AU-413 administration. Taken together, newly synthesized acylquinoline derivatives, especially AU-413, is worthy of further investigation to be developed as an anti-ulcer agent.     

Antinociceptive activity of Paederosidic Acid Methyl Ester (PAME) from the n-butanol fraction of Paederia scandens in mice

Antinociceptive activity of Paederosidic Acid Methyl Ester (PAME), a chemical compound isolated from the n-butanol fraction of Paederia scandens, was evaluated in mice using chemical and thermal models of nociception. PAME given by intraperitoneal injection at doses of 20, 40 and 60 mg/kg produced significant inhibitions on chemical nociception induced by intraperitoneal acetic acid, subplantar formalin or capsaicin injections and on thermal nociception in the tail-flick test and the hot plate test. In the pentobarbital sodium-induced sleep time test and the open-field test, PAME neither significantly enhanced the pentobarbital sodium-induced sleep time nor impaired the motor performance, indicating that the observed antinociceptive activity of PAME was unlikely due to sedation or motor abnormality. Core body temperature measurement showed that PAME did not affect temperature within a 2-h period. Moreover, PAME-induced antinociception in the hot plate test was insensitive to naloxone or nimodipine but significantly antagonized by L-NAME (N (G)-nitro-l-arginine methyl ester), methylene blue and glibenclamide. These results suggested that PAME-produced antinociception was possibly related to the pathway of NO-cGMP-ATP sensitive K⁺ channels, which merited further studies regarding the precise site and mechanisms of action.     

Epigallocatechin-3-gallate is an inhibitor of Na,K-ATPase by favoring the E1 conformation

Four catechins, epigallocatechin-3-gallate, epigallocatechin, epicatechin-3-gallate, and epicatechin, inhibited activity of the Na⁺,K⁺-ATPase. The two galloyl-type catechins were more potent inhibitors, with IC₅₀ values of about 1 μM, than were the other two catechins. Inhibition by epigallocatechin-3-gallate was noncompetitive with respect to ATP. Epigallocatechin-3-gallate reduced the affinity of vanadate, shifted the equilibrium of E₁P and E₂P toward E₁P, and reduced the rate of the E₁P to E₂P transition. Epigallocatechin-3-gallate potently inhibited membrane-embedded P-type ATPases (gastric H⁺,K⁺-ATPase and sarcoplasmic reticulum Ca²⁺-ATPase) as well as the Na⁺,K⁺-ATPase, whereas soluble ATPases (bacterial F₁-ATPase and myosin ATPase) were weakly inhibited. Solubilization of the Na⁺,K⁺-ATPase with a nonionic detergent reduced sensitivity to epigallocatechin-3-gallate with an elevation of IC₅₀ to 10 μM. These results suggest that epigallocatechin-3-gallate exerts its inhibitory effect through interaction with plasma membrane phospholipid.     

Opposite modulation of glutamate uptake by nicotine in cultured astrocytes with/without cAMP treatment

Cultured cerebellar astrocytes were exposed to nicotine with or without dibutyryl cAMP (dBcAMP) for 2 to 10 days in situ in order to determine the effects of nicotine exposure on glutamate uptake in differently conditioned astrocytes. After acute nicotine exposure, glutamate uptake was lower and higher in the naive and the preconditioned astrocytes, respectively. After subacute nicotine exposure, the inhibitory effect of L-trans-pyrollidine-2,4-dicarboxylic acid (PDC) on the glutamate uptake in the naive and the conditioned cells was decreased and increased, and the IC50's for PDC were higher and lower, respectively. In addition, glutamine synthetase activity after subacute nicotine exposure was lower in the naive and higher in the conditioned astrocytes; the change in Na+/K+ ATPase activity was the opposite to that in glutamine synthetase activity. These results suggest that nicotine modulates the characteristics of glial glutamate transporters and glutamine synthetase activity in astrocytes. Furthermore, nicotine might differently affect the state of glial cells during development.     

Effect of nitric oxide on the sinusoidal uptake of organic cations and anions by isolated hepatocytes

The issue of whether or not the presence NOx (NO and oxidized metabolites) in the hepatocytes at pathological levels affects the functional activity of transport systems within the sinusoidal membrane was investigated. For this purpose, the effect of the pretreatment of isolated hepatocytes with sodium nitroprusside (SNP), a spontaneous NO donor, on the sinusoidal uptake of tributylmethylammonium (TBuMA) and triethylmethyl ammonium (TEMA), representative substrates of the organic cation transporter (OCT), and taurocholate, a representative substrate of the Na+/taurocholate cotransporting polypeptide (NTCP), was measured. The uptake of TBuMA and TEMA was not affected by the pretreatment, as demonstrated by the nearly identical kinetic parameters for the uptake (i.e., Vmax, Km and CL(linear)). The uptake of mannitol into hepatocytes was not affected, demonstrating that the membrane integrity remained constant, irregardless of the SNP pretreatment. On the contrary, the uptake of taurocholate was significantly inhibited by the pretreatment, resulting in a significant decrease in Vmax, thus providing a clear demonstration that NOx preferentially affects the function of NTCP rather than OCT on the sinusoidal membrane. A direct interaction between NOx and NTCP or a decrease in Na+/K+ ATPase activity as the result of SNP pretreatment might be responsible for this selective effect of NOx.     

Comparative studies of the influence of various K+ concentration on the action of K-strophthidin, digitoxin and strophanthidin-3-bromoacetate on papillary muscle and on membrane-ATPSA of guinea pig hearts

The influence of increasing K⁺ concentrations (5, 16, and 50 mM) on the effects of different cardenolides — digitoxin (DIG), k-strophanthidin (STR) and strophanthidin-3-bromoacetate (SBA) — on the contractile force of isolated electrically stimulated papillary muscles and on the activity of the Na⁺, K⁺-activated ATPase of guinea pig hearts was studied under comparable experimental conditions.     

Role of Na+-K+ ATPase enzyme in vascular response of goat ruminal artery

Objective:

To study the role of Na⁺, K⁺- ATPase enzyme in the vascular response of goat ruminal artery.

Materials and Methods:

Ruminal artery was obtained in chilled aerated modified Krebs-Henseleit solution (KHS) from a local slaughterhouse and transported in ice for further processing. The endothelium intact arterial ring was mounted in a thermostatically controlled (37 ± 0.5°C) organ bath containing 20 ml of modified KHS (pH 7.4) bubbled with oxygen (95%) and CO₂ (5%) under 2g tension. An equilibration of 90 min was allowed before addition of drugs into the bath. The responses were recorded isometrically in an automatic organ bath connected to PowerLab data acquisition system. In order to examine intact functional endothelium, ACh (10 μM) was added on the 5-HT (1.0 μM) - induced sustained contractile response. Similarly, functional characterization of Na⁺, K⁺-ATPase activity was done by K⁺-induced relaxation (10 μM-10 mM) in the absence and presence of ouabain (0.1 μM/ 0.1 mM), digoxin (0.1 μM) and barium (30 μM).

Results:

ACh (10⁻⁵ M) did not produce any relaxing effect on 5-HT-induced sustained contractile response suggesting that vascular endothelium has no significant influence on the activation of sodium pump by extracellular K⁺ in ruminal artery. Low concentration of Ba²⁺ (30 μM) (IC₅₀: 0.479 mM) inhibited K⁺-induced relaxation suggesting K_ir (inward rectifier) channel in part had role in K⁺-induced vasodilatation in ruminal artery. Vasorelaxant effect of KCl (10 μM-10 mM) in K⁺-free medium is also blocked by ouabain (0.1 μM and 0.1 mM) (IC₅₀:0.398 mM and IC₃₅: 1.36 mM), but not by digoxin (0.1 μM) (IC₅₀ 0.234 mM) suggesting that ouabain sensitive Na⁺, K⁺-ATPase isoform is present in the ruminal artery.

Conclusion:

In the goat ruminal artery functional regulation of sodium pump is partly mediated by K⁺ channel and ouabain sensitive Na⁺, K⁺ ATPase.     

Effects of monovalent cations on cardiac Na+, K+-ATPase activity and on contractile force

Summary The relationship between Na⁺, K⁺-ATPase inhibition by monovalent cations and their inotropic effect was studied in guinea pig hearts. The activity of partially purified cardiac enzyme was assayed in the presence of 5.8 mM KCl and either 20 or 150 mM NaCl. Rb⁺ and Tl⁺ inhibited Na⁺, K⁺-ATPase activity, the magnitude of the inhibition by these cations being greater in the assay media containing lower Na⁺ concentrations. Tl⁺ produced a dose-dependent inhibition of Na⁺, K⁺-ATPase activity in the presence of 20 mM Na⁺ and 75 mM K⁺, a cationic condition similar to that of intracellular fluid. Other monovalent cations such as K⁺, Cs⁺, NH₄ ⁺, Na⁺ or Li⁺ produced essentially no effect on the Na⁺, K⁺-ATPase activity or slightly stimulated it. In left atrial strips stimulated with field electrodes and bathed in Krebs-Henseleit solution (5.8 mM K⁺ and 145 mM Na⁺), addition of Cs⁺ failed to alter the isometric contractile force significantly. NH₄ ⁺ and K⁺ caused a transient positive inotropic effect which was partially blocked by propranolol. The positive inotropic response to K⁺ was followed by a negative inotropic response. Rb⁺ produced a sustained, dose-dependent inotropic response reaching a plateau at 1–2 min, whereas Tl⁺ produced a dose-dependent positive inotropic effect which developed slowly over a 30-min period. The positive inotropic effects produced by Rb⁺ and Tl⁺ were insensitive to propranolol pretreatment. Concentrations of Tl⁺ and cardiac glycosides which produce similar inotropic effects appear to cause the same degree of Na⁺-pump inhibition. The onset of the positive inotropic response to Rb⁺ or Tl⁺ was not dependent on the number of contractions which is in contrast to the cardiac glycoside-induced inotropic response. Substitution of 20 mM LiCl for an equimolar amount of NaCl in Krebs-Henseleit solution produced a significantly greater inotropic response than that observed when sucrose was substituted for NaCl. It appears that, among monovalent cations, only sodium pump inhibitors produce a sustained positive inotropic response.     

Activation of K+ channels and Na+/K+ ATPase prevents aortic endothelial dysfunction in 7-day lead-treated rats

Seven day exposure to a low concentration of lead acetate increases nitric oxide bioavailability suggesting a putative role of K⁺ channels affecting vascular reactivity. This could be an adaptive mechanism at the initial stages of toxicity from lead exposure due to oxidative stress. We evaluated whether lead alters the participation of K⁺ channels and Na⁺/K⁺-ATPase (NKA) on vascular function. Wistar rats were treated with lead (1st dose 4 μg/100 g, subsequent doses 0.05 μg/100 g, im, 7 days) or vehicle. Lead treatment reduced the contractile response of aortic rings to phenylephrine (PHE) without changing the vasodilator response to acetylcholine (ACh) or sodium nitroprusside (SNP). Furthermore, this treatment increased basal O₂⁻ production, and apocynin (0.3 μM), superoxide dismutase (150 U/mL) and catalase (1000 U/mL) reduced the response to PHE only in the treated group. Lead also increased aortic functional NKA activity evaluated by K⁺-induced relaxation curves. Ouabain (100 μM) plus L-NAME (100 μM), aminoguanidine (50 μM) or tetraethylammonium (TEA, 2 mM) reduced the K⁺-induced relaxation only in lead-treated rats. When aortic rings were precontracted with KCl (60 mM/L) or preincubated with TEA (2 mM), 4-aminopyridine (4-AP, 5 mM), iberiotoxin (IbTX, 30 nM), apamin (0.5 μM) or charybdotoxin (0.1 μM), the ACh-induced relaxation was more reduced in the lead-treated rats. Additionally, 4-AP and IbTX reduced the relaxation elicited by SNP more in the lead-treated rats. Results suggest that lead treatment promoted NKA and K⁺ channels activation and these effects might contribute to the preservation of aortic endothelial function against oxidative stress.     

Neutralization of endogenous digitalis-like compounds alters catecholamines metabolism in the brain and elicits anti-depressive behavior

Depressive disorders are among the world's greatest public health problems. Na⁺, K⁺-ATPase is the established receptor for the steroidal digitalis-like compounds (DLC). Alteration in brain Na⁺, K⁺-ATPase and DLC have been detected in depressive disorders raising the hypothesis of their involvement in these pathology. The present study was designed to further elaborate this hypothesis by investigating the behavioral and biochemical consequences of neutralization in brain DLC activity attained by anti-ouabain antibodies administrations, in normal Sprague-Dawley (SD) and in the Flinders Sensitive Line (FSL) of genetically depressed rats. Chronic i.c.v. administration of anti-ouabain antibodies to FSL rats elicited anti-depressive behavior. Administration of anti-ouabain antibodies intracerebroventriculary (i.c.v.) to SD rats significantly changed the levels of catecholamines and their metabolites in the hippocampus, ventral tegmentum and nucleus accumbence. These results are in accordance with the notion that endogenous DLC may be involved in the manifestation of depressive disorders and suggests that alteration in their levels may be of significant therapeutic value.     

Comparative effects of aluminum and ouabain on synaptosomal choline uptake, acetylcholine release and (Na+/K+)ATPase

Closing the gap between adverse health effects of aluminum and its mechanisms of action still represents a huge challenge. Cholinergic dysfunction has been implicated in neuronal injury induced by aluminum. Previously reported data also indicate that in vivo and in vitro exposure to aluminum inhibits the mammalian (Na(+)/K(+))ATPase, an ubiquitous plasma membrane pump. This study was undertaken with the specific aim of determining whether in vitro exposure to AlCl(3) and ouabain, the foremost utilized selective inhibitor of (Na(+)/K(+))ATPase, induce similar functional modifications of cholinergic presynaptic nerve terminals, by comparing their effects on choline uptake, acetylcholine release and (Na(+)/K(+))ATPase activity, on subcellular fractions enriched in synaptic nerve endings isolated from rat brain, cuttlefish optic lobe and torpedo electric organ. Results obtained show that choline uptake by rat synaptosomes was inhibited by submillimolar AlCl(3), whereas the amount of choline taken up by synaptosomes isolated from cuttlefish and torpedo remained unchanged. Conversely, choline uptake was reduced by ouabain to a large extent in all synaptosomal preparations analyzed. In contrast to ouabain, which modified the K(+) depolarization evoked release of acetylcholine by rat, cuttlefish and torpedo synaptosomal fractions, AlCl(3) induced reduction of stimulated acetylcholine release was only observed when rat synaptosomes were challenged. Finally, it was observed that the aluminum effect on cuttlefish and torpedo synaptosomal (Na(+)/K(+))ATPase activity was slight when compared to its inhibitory action on mammalian (Na(+)/K(+))ATPase. In conclusion, inhibition of (Na(+)/K(+))ATPase by AlCl(3) and ouabain jeopardized the high-affinity (Na(+)-dependent, hemicholinium-3 sensitive) uptake of choline and the Ca(2+)-dependent, K(+) depolarization evoked release of acetylcholine by rat, cuttlefish and torpedo synaptosomal fractions. The effects of submillimolar AlCl(3) on choline uptake and acetylcholine release only resembled those of ouabain when rat synaptosomes were assayed. Therefore, important differences were found between the species regarding the cholinotoxic action of aluminum. The variability of (Na(+)/K(+))ATPase sensitivity to aluminum of cholinergic neurons might contribute to their differential susceptibility to this neurotoxic agent.     

AMP-activated protein kinase (AMPK)-dependent and -independent pathways regulate hypoxic inhibition of transepithelial Na(+) transport across human airway epithelial cells

BACKGROUND AND PURPOSE

Pulmonary transepithelial Na⁺ transport is reduced by hypoxia, but in the airway the regulatory mechanisms remain unclear. We investigated the role of AMPK and ROS in the hypoxic regulation of apical amiloride-sensitive Na⁺ channels and basolateral Na⁺K⁺ ATPase activity.

EXPERIMENTAL APPROACH

H441 human airway epithelial cells were used to examine the effects of hypoxia on Na⁺ transport, AMP : ATP ratio and AMPK activity. Lentiviral constructs were used to modify cellular AMPK abundance and activity; pharmacological agents were used to modify cellular ROS.

KEY RESULTS

AMPK was activated by exposure to 3% or 0.2% O₂ for 60 min in cells grown in submerged culture or when fluid (0.1 mL·cm⁻²) was added to the apical surface of cells grown at the air–liquid interface. Only 0.2% O₂ activated AMPK in cells grown at the air–liquid interface. AMPK activation was associated with elevation of cellular AMP : ATP ratio and activity of the upstream kinase LKB1. Hypoxia inhibited basolateral ouabain-sensitive I_sc (I_ouabain) and apical amiloride-sensitive Na⁺ conductance (G_Na+). Modification of AMPK activity prevented the effect of hypoxia on I_ouabain (Na⁺K⁺ ATPase) but not apical G_Na+. Scavenging of superoxide and inhibition of NADPH oxidase prevented the effect of hypoxia on apical G_Na+ (epithelial Na⁺ channels).

CONCLUSIONS AND IMPLICATIONS

Hypoxia activates AMPK-dependent and -independent pathways in airway epithelial cells. Importantly, these pathways differentially regulate apical Na⁺ channels and basolateral Na⁺K⁺ ATPase activity to decrease transepithelial Na⁺ transport. Luminal fluid potentiated the effect of hypoxia and activated AMPK, which could have important consequences in lung disease conditions.     

Antibacterial activity of six novel peptides from Tityus discrepans scorpion venom. A fluorescent probe study of microbial membrane Na permeability changes

Six novel peptides (named bactridines) were isolated from Tityus discrepans scorpion venom. From mass spectrometry molecular masses were 6916, 7362, 7226, 7011, 7101 and 7173 Da (bactridines 1–6). Bactridines 1 and 2 were sequenced by Edman degradation. The sequences and in silico analysis, indicated that they are positively charged polypeptides comprised of 61 and 64 amino acids (AA), respectively, bactridine 1 and bactridine 2 containing 4 disulfide bridges. Bactridine 1 was only toxic to cockroaches and crabs, and bactridine 2–6 were only toxic to mice. Bactridine 1 has a 78% sequence identity with ardiscretin. Ardisctretin is an insect specific sodium toxin which also produces a small depolarization and induces repetitive firing in squid axons resembling those of DDT [1,10(pchlorobenzyl) 2-trichloretane] in its ability to slow down action potential, to induce repetitive firing. Measured as the minimal inhibitory concentration, bactridines had high antibacterial activity against a wide range of Gram positive and Gram negative bacteria. Complete bacterial growth inhibition occurred at concentrations from 20 to 80 μM depending on the bacteria and peptide tested. Effects on membrane Na⁺ permeability induced by bactridines were observed on Yersinia enterocolitica loaded with 1 μM CoroNa™ Red. CoroNa™ Red fluorescence leakage from bacteria was observed after exposure to 0.3 μM of any bactridine tested, indicating that they modified Na⁺ membrane permeability. This effect was blocked by 10 μM amiloride and by 25 μM mibefradil drugs that affect Na⁺ and Ca²⁺ channels respectively. We found no evidence of changes of K⁺ or Ca²⁺ concentrations neither inside nor outside the bacteria in experiments using the fluorescent dyes Fluo 4AM (10 μM) and PBFI (20 μM).     

Diphenyl ditelluride impairs short-term memory and alters neurochemical parameters in young rats

The aim of this study was to investigate if maternal exposure to 0.03 mg/kg of diphenyl ditelluride (PhTe)₂ during the first 14 days of lactational period in Wistar rats alters recognition memory and neurochemical parameters in young rats. Object recognition memory task, evaluation of synaptosomal [³H]glutamate uptake and release as well as cerebral Na⁺/K⁺ATPase activity were evaluated in 4 week-old rats. There were no significant specific overt signs of maternal intoxication. The body weight gain of rats was similar among groups. (PhTe)₂-exposed group showed a significantly lower time exploring the novel object when compared to the performance of the control group in short-term memory (STM) test. In addition, (PhTe)₂ significantly inhibited synaptosomal [³H]glutamate uptake and cerebral Na⁺/K⁺ATPase activity in animals. The synaptosomal [³H]glutamate release was similar between (PhTe)₂ and control groups. In conclusion, the present study establishes that young rats presented cognitive impairment after exposure to (PhTe)₂ via maternal milk, demonstrated by the performance of animals in object recognition memory task. The possible mechanism involved in (PhTe)₂ action in memory of recognition might involve inhibition of cerebral Na⁺/K⁺ATPase activity and synaptosomal [³H]glutamate uptake.     

Hemolytic and genotoxic evaluation of organochalcogens in human blood cells in vitro

This study investigated the hemolytic and genotoxic effect of different organoselenium and organotellurium compounds in human blood cells, as simple tests for screening the toxicity of organochalcogenides. For osmotic fragility (OF) test, samples of total blood were incubated with the organochalcogens at 4, 8, 50, 75 and 100 μM or vehicle (DMSO) for 90 min at 37 °C. The EC₅₀ values for hemolysis were significantly increased in erythrocytes exposed to diphenyl selenide (II), diphenyl diselenide (III), diphenyl telluride (IV), diphenyl ditelluride (V), (S)-2-amino-1-diselenide-3-methylpropanyl (IX), butyl(styryl)telluride (XIII) and 2-(butyltellurium)furan (XIV) at higher concentrations tested. The exposure of erythrocytes to organochalcogens diphenyl diselenide (II) and butyl(styryl)telluride (XIII), which had greater hemolytic effect, did not modify catalase activity, reactive oxygen species (ROS) production and -SH content. On the other hand, Na⁺/K⁺ ATPase activity of erythrocyte ghosts was significantly inhibited by the compounds diphenyl diselenide (II) and butyl(styryl)telluride (XIII) (P < 0.05) in a concentration-dependent manner. The inhibition of Na⁺/K⁺ ATPase activity was completely reversed by dithiothreitol (DTT); indicating reaction of these organochalcogens with thiol groups of the enzyme. The thiol oxidase activity of the compounds II and XIII was supported by the fact that the rate of DTT oxidation was increased significantly by both chalcogens. In the higher concentrations, the compounds (II) and (XIII) were strongly genotoxic and cytotoxic to human leukocytes cells, as verified by the DNA damage and cell viability evaluation. Our results suggest that at relatively high concentration organochalcogenides exhibit hemolytic and genotoxic action in human blood cells, which are probably linked to their thiol oxidase activity and preferential interaction with sulfhydryl groups critical to enzymes.     

Reduction of the equilibrium binding of cardiac glycosides and related compounds to Na+, K+-ATPase as a possible mechanism for the potassium-induced reversal of their toxicity

Summary The influence of potassium ions on the equilibrium state of the binding of cardiac glycosides and their derivatives to partially purified dog heart and rat brain enzyme preparations was studied in vitro. The addition of potassium to the incubation mixture containing enzyme preparation, ³H-ouabain, Na⁺, Mg²⁺ and ATP, at the time when the binding reaction is close to equilibrium, caused an immediate reduction of the bound drug concentration; the concentration apparently shifting toward a lower equilibrium state. The degree of the potassium-induced reduction in bound drug concentration was dependent on the potassium concentration and on the chemical structure of the compound. The binding of aglycones, pentacetyl-gitoxin and cassaine was affected to a greater extent than that of the glycosides. These data suggest that one of the mechanisms by which potassium antagonizes the toxic actions of digitalis on the heart is to reduce the drug binding to cardiac Na⁺, K⁺-ATPase.This work was supported by a U.S. Public Health Service Grant, HL-16052