Phenylacetonitrile (C6H5CH2CN) Ionic Liquid Blends as Alternative Electrolytes for Safe and High-Performance Supercapacitors.

The increasing need in the development of storage devices is calling for the formulation of alternative electrolytes, electrochemically stable and safe over a wide range of conditions. To achieve this goal, electrolyte chemistry must be explored to propose alternative solvents and salts to the current acetonitrile (ACN) and tetraethylammonium tetrafluoroborate (Et4NBF4) benchmarks, respectively. Herein, phenylacetonitrile (Ph-ACN) has been proposed as a novel alternative solvent to ACN in supercapacitors. To establish the main advantages and drawbacks of such a substitution, Ph-ACN + Et4NBF4 blends were formulated and characterized prior to being compared with the benchmark electrolyte and another alternative electrolyte based on adiponitrile (ADN). While promising results were obtained, the low Et4NBF4 solubility in Ph-ACN seems to be the main limiting factor. To solve such an issue, an ionic liquid (IL), namely 1-ethyl-3-methylimidazolium bis [(trifluoromethyl)sulfonyl] imide (EmimTFSI), was proposed to replace Et4NBF4. Unsurprisingly, the Ph-ACN + EmimTFSI blend was found to be fully miscible over the whole range of composition giving thus the flexibility to optimize the electrolyte formulation over a large range of IL concentrations up to 4.0 M. The electrolyte containing 2.7 M of EmimTFSI in Ph-ACN was identified as the optimized blend thanks to its interesting transport properties. Furthermore, this blend possesses also the prerequisites of a safe electrolyte, with an operating liquid range from at least -60 °C to +130 °C, and operating window of 3.0 V and more importantly, a flash point of 125 °C. Finally, excellent electrochemical performances were observed by using this electrolyte in a symmetric supercapacitor configuration, showing another advantage of mixing an ionic liquid with Ph-ACN. We also supported key structural descriptors by density functional theory (DFT) and COnductor-like Screening Model for Real Solvents (COSMO-RS) calculations, which can be associated to physical and electrochemical properties of the resultant electrolytes.

Simultaneous recording of fluorescence and electrical signals by photometric patch electrode in deep brain regions in vivo.

Despite its widespread use, high-resolution imaging with multiphoton microscopy to record neuronal signals in vivo is limited to the surface of brain tissue because of limited light penetration. Moreover, most imaging studies do not simultaneously record electrical neural activity, which is, however, crucial to understanding brain function. Accordingly, we developed a photometric patch electrode (PME) to overcome the depth limitation of optical measurements and also enable the simultaneous recording of neural electrical responses in deep brain regions. The PME recoding system uses a patch electrode to excite a fluorescent dye and to measure the fluorescence signal as a light guide, to record electrical signal, and to apply chemicals to the recorded cells locally. The optical signal was analyzed by either a spectrometer of high light sensitivity or a photomultiplier tube depending on the kinetics of the responses. We used the PME in Oregon Green BAPTA-1 AM-loaded avian auditory nuclei in vivo to monitor calcium signals and electrical responses. We demonstrated distinct response patterns in three different nuclei of the ascending auditory pathway. On acoustic stimulation, a robust calcium fluorescence response occurred in auditory cortex (field L) neurons that outlasted the electrical response. In the auditory midbrain (inferior colliculus), both responses were transient. In the brain-stem cochlear nucleus magnocellularis, calcium response seemed to be effectively suppressed by the activity of metabotropic glutamate receptors. In conclusion, the PME provides a powerful tool to study brain function in vivo at a tissue depth inaccessible to conventional imaging devices.

Differences in vascular nitric oxide and endothelium-derived hyperpolarizing factor bioavailability in blacks and whites.

OBJECTIVE: Abnormalities in nitric oxide (NO) bioavailability have been reported in blacks. Whether there are differences in endothelium-derived hyperpolarizing factor (EDHF) in addition to NO between blacks and whites and how these affect physiological vasodilation remain unknown. We hypothesized that the bioavailability of vascular NO and EDHF, at rest and with pharmacological and physiological vasodilation, varies between whites and blacks. APPROACH AND RESULTS: In 74 white and 86 black subjects without known cardiovascular disease risk factors, forearm blood flow was measured using plethysmography at rest and during inhibition of NO with N(G)-monomethyl-L-arginine and of K(+) Ca channels (EDHF) with tetraethylammonium. The reduction in resting forearm blood flow was greater with N(G)-monomethyl-L-arginine (P=0.019) and similar with tetraethylammonium in whites compared with blacks. Vasodilation with bradykinin, acetylcholine, and sodium nitroprusside was lower in blacks compared with whites (all P<0.0001). Inhibition with N(G)-monomethyl-L-arginine was greater in whites compared with blacks with bradykinin, acetylcholine, and exercise. Inhibition with tetraethylammonium was lower in blacks with bradykinin, but greater during exercise and with acetylcholine. CONCLUSIONS: The contribution to both resting and stimulus-mediated vasodilator tone of NO is greater in whites compared with blacks. EDHF partly compensates for the reduced NO release in exercise and acetylcholine-mediated vasodilation in blacks. Preserved EDHF but reduced NO bioavailability and sensitivity characterizes the vasculature in healthy blacks. CLINICAL TRIAL REGISTRATION URL: http://clinicaltrials.gov/. Unique identifier: NCT00166166.

Disease and region-related cardiac fibroblast potassium current variations and potential functional significance.

AIMS: Fibroblasts, which play an important role in cardiac function/dysfunction, including arrhythmogenesis, have voltage-dependent (Kv) currents of unknown importance. Here, we assessed the differential expression of Kv currents between atrial and ventricular fibroblasts from control dogs and dogs with an atrial arrhythmogenic substrate caused by congestive heart failure (CHF). METHODS AND RESULTS: Left atrial (LA) and ventricular (LV) fibroblasts were freshly isolated from control and CHF dogs (2-week ventricular tachypacing, 240 bpm). Kv currents were measured with whole-cell voltage-clamp, mRNA by quantitative polymerase chain reaction (qPCR) and fibroblast proliferation by (3)H-thymidine incorporation. Robust voltage-dependent tetraethylammonium (TEA)-sensitive K(+) currents (IC50 ∼1 mM) were recorded. The morphologies and TEA responses of LA and LV fibroblast Kv currents were similar. LV fibroblast Kv-current densities were significantly greater than LA, and Kv-current densities were significantly less in CHF than control. The mRNA expression of Kv-channel subunits Kv1.5 and Kv4.3 was less in LA vs. LV fibroblasts and was down-regulated in CHF, consistent with K(+)-current recordings. Ca(2+)-dependent K(+)-channel subunit (KCa1.1) mRNA and currents were less expressed in LV vs. LA fibroblasts. Inhibiting LA fibroblast K(+) current with 1 mmol/L of TEA or KCa1.1 current with paxilline increased proliferation. CONCLUSIONS: Fibroblast Kv-current expression is smaller in CHF vs. control, as well as LA vs. LV. KCa1.1 current is greater in LA vs. LV. Suppressing Kv current with TEA enhances fibroblast proliferation, suggesting that Kv current might act to check fibroblast proliferation and that reduced Kv current in CHF may contribute to fibrosis. Fibroblast Kv-current remodelling may play a role in the atrial fibrillation (AF) substrate; modulating fibroblast K(+) channels may present a novel strategy to prevent fibrosis and AF.

Glutamate transporter type 3 regulates mouse hippocampal GluR1 trafficking.

BACKGROUND: Rapid trafficking of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) to the plasma membrane is considered a fundamental biological process for learning and memory. GluR1 is an AMPAR subunit. We have shown that mice with knockout of excitatory amino acid transporter type 3 (EAAT3), a neuronal glutamate transporter, have impaired learning and memory. The mechanisms for this impairment are not known and may be via regulation of AMPAR trafficking. METHODS: Freshly prepared 300µm coronal hippocampal slices from wild-type or EAAT3 knockout mice were incubated with or without 25mM tetraethylammonium for 10min. The trafficking of GluR1, an AMPAR subunit, to the plasma membrane and its phosphorylation were measured. RESULTS: Tetraethylammonium increased the trafficking of GluR1 and EAAT3 to the plasma membrane in the wild-type mouse hippocampal slices but did not cause GluR1 trafficking in the EAAT3 knockout mice. Tetraethylammonium also increased the phosphorylation of GluR1 at S845, a protein kinase A (PKA) site, in the wild-type mice but not in the EAAT3 knockout mice. The PKA antagonist KT5720 attenuated tetraethylammonium-induced GluR1 phosphorylation and trafficking in the wild-type mice. The PKA agonist 6-BNz-cAMP caused GluR1 trafficking to the plasma membrane in the EAAT3 knockout mice. In addition, EAAT3 was co-immunoprecipitated with PKA. CONCLUSIONS: These results suggest that EAAT3 is upstream of PKA in a pathway to regulate GluR1 trafficking. GENERAL SIGNIFICANCE: Our results provide initial evidence for the involvement of EAAT3 in the biochemical cascade of learning and memory.

Non-specific inhibitors of aquaporin-4 stimulate S100B secretion in acute hippocampal slices of rats.

Aquaporin-4 (AQP-4) is the principal brain water channel and is predominantly expressed in astrocytes suggesting its dynamic involvement in water homeostasis in brain tissue. Due to the co-localization of AQP-4 and inward rectifier K(+) channels Kir 4.1, a functional coupling between these proteins has been proposed. AQP-4 has a putative role in the physiopathology of brain disorders including epilepsy and trauma. S100B is a calcium-binding protein expressed and secreted by astrocytes, and commonly used as a parameter of astroglial activation. Here, we investigate a possible link between AQP-4 activity (and Kir 4.1) and S100B secretion in hippocampal slices of rats of different ages using non-specific inhibitors of AQP-4 (AZA, acetazolamide and TEA, tetraethylammonium) and Kir 4.1 (barium chloride). We found that blockade of AQP-4 with TEA and AZA produced an increase in S100B secretion in young rats, compatible with an astroglial activation observed in many conditions of brain injury. On the other hand, BaCl(2) induced Kir 4.1 inhibition caused a decrease in S100B secretion. Both channels, AQP-4 and Kir 4.1, exhibited a similar ontogenetic profile, in spite of the functional uncoupling, in relation to S100B secretion. Moreover, we found a significant increase in the S100B secretion basal levels with the increasing of animal age and the incubation with high levels of potassium resulted in a decrease of S100B secretion in 30 and 90-day old rats. These data, together with previous observations from gap junctions and glutamate transport of astrocytes, contribute to characterize the operational system involving astroglial activation, particularly on S100B secretion, in brain disorders.

Magnetic alignment and quadrupolar/paramagnetic cross-correlation in complexes of Na with LnDOTP5-.

The observation of a double-quantum filtered signal of quadrupolar nuclei (e.g. (23)Na) in solution has been traditionally interpreted as a sign for anisotropic reorientational motion. Ling and Jerschow (2007) have found that a (23)Na double-quantum signal is observed also in solutions of TmDOTPNa(5). Interference effects between the quadrupolar and the paramagnetic interactions have been reported to lead to the appearance of double-quantum coherences even in the absence of a residual quadrupolar interaction. In addition, such processes lead to differential linebroadening effects between the satellite transitions, akin to effects that are well known for dipolar-CSA cross-correlation. Here, we report experiments on sodium in the presence of LnDOTP compounds, where it is shown that these cross-correlation effects correlate well with the pseudo-contact shift. In addition, anisotropic g-values of the lanthanide compounds in question, can also lead to alignment within the magnetic field, and consequently to the appearance of line splitting and double-quantum coherences. The two competing effects are demonstrated and it is concluded that both cross-correlated relaxation and alignment in the magnetic field must be at work in the systems described here.

[The role of fast and slow potassium currents in electrical activity of amphibian myelinated nerve fibres].

The paper reviews the information about the role of fast and slow potassium currents in electrical activity of amphibian myelinated nerve fibres. It demonstrates the importance of discovering of fast and slow potassium currents and their following pharmacological separation (by potassium channels blockers 4-aminopyridine and tetraethylammonium) in investigation of mechanisms of biological potentials generation. The information about the existence of fast and slow potassium channels in the nerve membrane and about the properties of 4-aminopyridine and tetraethylammonium action served as a base for determination the nature of biological potentials and discovering the mechanism of potential-dependent action of 4-aminopyridine that for tens of years suffered from the lack of adequate explanation.

Pharmacology of currents underlying the different firing patterns of spinal sensory neurons and interneurons identified in vivo using multivariate analysis.

The operation of neuronal networks depends on the firing patterns of the network's neurons. When sustained current is injected, some neurons in the central nervous system fire a single action potential and others fire repetitively. For example, in Xenopus laevis tadpoles, primary-sensory Rohon-Beard (RB) neurons fired a single action potential in response to 300-ms rheobase current injections, whereas dorsolateral (DL) interneurons fired repetitively at 10-20 Hz. To investigate the basis for these differences in vivo, we examined drug-induced changes in the firing patterns of Xenopus spinal neurons using whole cell current-clamp recordings. Neuron types were initially separated through cluster analysis, and we compared results produced using different clustering algorithms. We used these results to develop a predictive function to classify subsequently recorded neurons. The potassium channel blocker tetraethylammonium (TEA) converted single-firing RB neurons to low-frequency repetitive firing but reduced the firing frequency of repetitive-firing DL interneurons. Firing frequency in DL interneurons was also reduced by the potassium channel blockers 4-aminopyridine (4-AP), catechol, and margatoxin; 4-AP had the greatest effect. The calcium channel blockers amiloride and nimodipine had few effects on firing in either neuron type but reduced action potential duration in DL interneurons. Muscarine, which blocks M-currents, did not affect RB neurons but reduced firing frequency in DL interneurons. These results suggest that potassium currents may control neuron firing patterns: a TEA-sensitive current prevents repetitive firing in RB neurons, whereas a 4-AP-sensitive current underlies repetitive firing in DL interneurons. The cluster and discriminant analysis described could help to classify neurons in other systems.

Characterization of ionic currents and electrophysiological properties of goldfish somatotropes in primary culture.

Growth hormone release in goldfish is partly dependent on voltage-sensitive Ca(2+) channels but somatotrope electrophysiological events affecting such channel activities have not been elucidated in this system. The electrophysiological properties of goldfish somatotropes in primary culture were studied using the whole-cell and amphotericin B-perforated patch-clamp techniques. Intracellular Ca(2+) concentration ([Ca(2+)]i) of identified somatotropes was measured using Fura-2/AM dye. Goldfish somatotropes had an average resting membrane potential of -78.4 ± 4.6 mV and membrane input resistance of 6.2 ± 0.2 GΩ. Voltage steps from a holding potential of -90 mV elicited a non-inactivating outward current and transient inward currents at potentials more positive than 0 and -30 mV, respectively. Isolated current recordings indicate the presence of 4-aminopyridine- and tetraethylammonium (TEA)-sensitive K(+), tetrodotoxin (TTX)-sensitive Na(+), and nifedipine (L-type)- and ω-conotoxin GVIA (N-type)-sensitive Ca(2+) channels. Goldfish somatotropes rarely fire action potentials (APs) spontaneously, but single APs can be induced at the start of a depolarizing current step; this single AP was abolished by TTX and significantly reduced by nifedipine and ω-conotoxin GVIA. TEA increased AP duration and triggered repetitive AP firing resulting in an increase in [Ca(2+)]i, whereas TTX, nifedipine and ω-conotoxin GVIA inhibited TEA-induced [Ca(2+)]i pulses. These results indicate that in goldfish somatotropes, TEA-sensitive K(+) channels regulate excitability while TTX-sensitive Na(+) channels together with N- and L-type Ca channels mediates the depolarization phase of APs. Opening of voltage-sensitive Ca(2+) channels during AP firing leads to increases in [Ca(2+)]i.

Glial cell-derived neurotrophic factor enhances synaptic communication and 5-hydroxytryptamine 3a receptor expression in enteric neurons.

BACKGROUND & AIMS: Glial cell-derived neurotrophic factor (GDNF) is essential for the development of the enteric nervous system during embryogenesis. We have observed the presence of Gdnf transcripts in the gastrointestinal tract of adult mice, and its early up-regulation after inflammation. We therefore investigated the effects of GDNF on enteric neuronal function in vitro. METHODS: Primary neuronal cultures were established from isolated myenteric plexi, and characterized by immunostaining and Ca(2+) imaging. Gene expression of several ion channels was analyzed by quantitative polymerase chain reaction (PCR) and the electrophysiologic properties of the neurons were studied by patch clamp. RESULTS: GDNF enhanced synaptogenesis and intercellular communication in primary myenteric neuronal cultures. Expression profiling revealed that GDNF exposure results in an up-regulation of Htr3a expression in the cultures and a similar increase was observed in inflamed colonic tissue where Gdnf expression was also increased. The increased Htr3a expression was accompanied by a functional increase in the response of neurons to acute challenge with 5-hydroxytryptamine (5-HT). GDNF treatment also caused inhibition of delayed rectifying voltage-gated potassium (Kv) currents, which correlated with the up-regulation of Htr3a and 5-HT-induced responses. Furthermore, pharmacologic blockade of Kv channels mimicked the effect of GDNF by increasing Htr3a expression as well as enhancing 5-HT-induced responses in the cultured myenteric neurons. CONCLUSIONS: GDNF promotes synaptic communication in cultured myenteric neurons. It also up-regulates 5-HT(3a)-receptor expression via modulation of Kv channel activity. Up-regulation of Gdnf after gastrointestinal inflammation might play an important role in the pathophysiology of gastrointestinal diseases.

Age-related differences in the beta-adrenergic vasodilator response in rat aortic rings.

Mechanisms underlying age-dependent changes in vasodilator responses to beta-adrenergic drugs are poorly understood. The aim of the current study was to compare responses to isoproterenol (a non-selective beta-adrenergic receptor agonist) in phenylephrine or KCl precontracted aortic rings from 3 week and 3 month old male Wistar rats. Both the mechanism and the subtype of beta-adrenergic receptor underlying the response to isoproterenol in the both age groups were examined. Endothelial removal, pre-contraction with KCl (40 mM), pre-treatment with tetraethylammonium or with N(omega)-Nitro-L-arginine methyl ester inhibited the vasodilator response to isoproterenol only in aortic rings from older rats. The inhibition was total when TEA and L-NAME were administered together. In both age groups the response to isoproterenol was unaffected by the beta1-adrenergic antagonist CGP20712A, but was significantly inhibited by ICI 118551 (a beta2-adrenergic-antagonist) and to a greater extent by SR 59230A (a non-selective beta 3-adrenergic antagonist), the inhibition being more evident in the older rats. Unlike younger rats, in older animals the response to isoproterenol was partially dependent on endothelial nitric oxide and on K+ channels. In both age groups, beta2- and beta3-, but not beta1-adrenergic receptors were involved. The degree of relative participation of beta2 and beta3 adrenergic receptors may change with age and explain the differences in response to isoproterenol.

Protein kinase inhibition differentially regulates organic cation transport.

Previous studies showed that amantadine transport increased while tetraethylammonium (TEA) transport decreased in kidney tissue from diabetic rats. Changes in transport activity were reversed by exogenous insulin. We hypothesized that this difference in transport regulation is due to differential regulation of different transport systems. Native human embryonic kidney cortex cells (HEK293 cell line) and rat organic cation transporter (rOCT)-transfected cells were used to test the hypothesis. In support of differential regulation, short-term glucose starvation stimulated amantadine transport and inhibited TEA transport, but the effect was bicarbonate-modulated only for amantadine. cAMP analogues inhibited TEA transport while stimulating amantadine transport. This effect was additive to the effect of insulin, and the presence of bicarbonate affected the extent of the change. Our findings indicated that regulation of rOCT 1 and 2 was mediated by transmembrane adenylyl cyclase, and regulation of amantadine transport was mediated by soluble adenylyl cyclase, suggesting that intracellular microdomains of cAMP may be important in determining overall cellular transport for organic cations. Soluble adenylyl cyclase activity is known to be modulated by bicarbonate and lactate. These observations support our hypothesis and reconcile our previous studies demonstrating increased transport affinity for amantadine in the presence of bicarbonate and decreased transport affinity in the presence of lactate.

Low-voltage-activated potassium channels underlie the regulation of intrinsic firing properties of rat vestibular ganglion cells.

Individual primary vestibular afferents exhibit spontaneous activity the regularity of which can vary from regular to irregular. Different aspects of vestibular responsiveness have been associated with this dimension of regularity of resting discharge. Isolated rat vestibular ganglion cells (VGCs) showed heterogeneous intrinsic firing properties during sustained membrane depolarization: some neurons exhibited a strong adaptation generating just a single or a few spikes (phasic type), whereas other neurons showed moderate adaptation or tonic firing (tonic type). Tonic discharging VGCs were rare at postnatal days 5-7 and increased up to approximately 60% of neurons during postnatal 2-3 wk. To explore the major factors responsible for the discharge regularity of primary vestibular afferents, we investigated the contribution of K+ channels to the firing properties of isolated rat VGCs. Phasic firing became tonic firing in the presence of 4-aminopyridine or alpha-dendrotoxin, indicating that Kv1 potassium channels control the firing pattern of the phasic VGCs. Tetraethylammonium decreased the number of spikes during step current stimuli in all types. Blockade of Ca2+-activated K+ channels decreased the number of spikes in tonic VGCs. Our results suggest that Kv1 channels are critical both in determining the pattern of spike discharge in rat vestibular ganglion neurons and in their proportional change during maturation.

Chemical method to enhance transungual transport and iontophoresis efficiency.

Transungual transport is hindered by the inherent small effective pore size of the nail even when it is fully hydrated. The objectives of this study were to determine the effects of chemical enhancers thioglycolic acid (TGA), glycolic acid (GA), and urea (UR) on transungual transport and iontophoresis efficiency. In vitro passive and iontophoretic transport experiments of model permeants mannitol (MA), UR, and tetraethylammonium (TEA) ion across the fully hydrated, enhancer-treated and untreated human nail plates were performed in phosphate-buffered saline. The transport experiments consisted of several stages, alternating between passive and anodal iontophoretic transport at 0.1mA. Nail water uptake experiments were conducted to determine the water content of the enhancer-treated nails. The effects of the enhancers on transungual electroosmosis were also evaluated. Nails treated with GA and UR did not show any transport enhancement. Treatment with TGA at 0.5M enhanced passive and iontophoretic transungual transport of MA, UR, and TEA. Increasing the TGA concentration to 1.8M did not further increase TEA iontophoresis efficiency. The effect of TGA on the nail plates was irreversible. The present study shows the possibility of using a chemical enhancer to reduce transport hindrance in the nail plate and thus enhance passive and iontophoretic transungual transport.

Transungual iontophoretic transport of polar neutral and positively charged model permeants: effects of electrophoresis and electroosmosis.

Transungual iontophoretic transport of model neutral permeants mannitol (MA), urea (UR), and positively charged permeant tetraethylammonium ion (TEA) across fully hydrated human nail plates at pH 7.4 were investigated in vitro. Four protocols were involved in the transport experiments with each protocol divided into stages including passive and iontophoresis transport of 0.1 and 0.3 mA. Water and permeant uptake experiments of nail clippings were also conducted to characterize the hydration and binding effects of the permeants to the nails. Iontophoresis enhanced the transport of MA and UR from anode to cathode, but this effect (electroosmosis) was marginal. The transport of TEA was significantly enhanced by anodal iontophoresis and the experimental enhancement factors were consistent with the Nernst-Planck theory predictions. Hindered transport was also observed and believed to be critical in transungual delivery. The barrier of the nail plates was stable over the time course of the study, and no significant electric field-induced alteration of the barrier was observed. The present results with hydrated nail plates are consistent with electrophoresis-dominant (the direct field effect) transungual iontophoretic transport of small ionic permeants with small contribution from electroosmosis.

4-aminopyridine-induced contracture in frog ventricle is due to calcium released from intracellular stores.

The aim of the study is to demonstrate the presence of intracellular calcium store in frog ventricle based on contractures induced by 4-aminopyridine in calcium-free media. Frog-ventricular strips were subjected to field stimulation at 0.2 Hz and the force of contraction was recorded after stabilization. The preparation was then kept quiescent for some time in solutions with different sodium concentrations, containing 0 or 1 mmol/L calcium. Caffeine, 4-aminopyridine (4-AP), or tetraethylammonium chloride was then added. Frog skeletal muscle preparations were used as positive controls for the caffeine experiments. Frog ventricular preparations did not develop contractures (sustained contractions) in the presence of caffeine (25 mmol/L), while frog skeletal muscle preparations developed caffeine-induced contractures. However, 4-AP (16 mmol/L) was able to induce contractures in quiescent frog ventricular preparations, even when they were superfused with calcium-free solution. 4-AP contractures in frog ventricle were seen in the presence of nifedipine also. Amplitude of 4-AP evoked contractures in frog ventricle were much larger in low sodium (30 mmol/L) and sodium-free (sodium substituted by lithium) solutions than in normal sodium solution, suggesting that the route of extrusion of the cytosolic calcium (released from intracellular stores by 4-AP) is the sodium calcium exchanger, which gets reversed in low sodium solutions. Tetraethylammonium chloride (TEA) was not able to induce contractures in frog ventricle suggesting that the contracture evoked by 4-AP is not due to its potassium channel blocking effect. In quiescent frog skeletal muscle preparations, caffeine as well as 4-AP induced contractures in calcium-free solutions. We therefore conclude that there is a caffeine-insensitive, 4-AP sensitive intracellular calcium store in the frog ventricle.

Separation of beta-receptor blockers and analogs by capillary liquid chromatography (CLC) and pressurized capillary electrochromatography (pCEC) using a vancomycin chiral stationary phase column.

Enantiomeric separation of chiral pharmaceuticals was carried out by means of in capillary liquid chromatography (CLC) and pressurized capillary electrochromatography (pCEC) using a vancomycin chiral stationary phase (CSP). A 100 microm I.D. fused-silica capillary was packed with 5 microm diameter silica particles modified with vancomycin. Enantiomeric resolution of fifteen beta3-receptor blockers and analogs was studied by polar organic CLC mode and reversed-phase pCEC mode using mobile phases containing methanol-isopropanol-acetic acid-triethylamine and TEAA buffer-methanol, respectively. Several factors affecting chiral separation were investigated in both CLC and pCEC mode. Good enantiomeric resolution was achieved by CLC mode for propranolol, celiprolol, esmolol, bisoprolol, atenolol, metoprolol and carteolol using methanol-isopropanol-acetic acid-triethylamine (70:30:0.05:0.05, v/v/v/v) as mobile phase and for clenbuterol, bambuterol, terbutaline, and salbutamol using methanol-isopropanol-acetic acid-triethylamine (50:50:0.05:005 or 50:50: 0.025:0.05, v/v/v/v) as mobile phase. The baseline was achieved by pCEC mode for the separation of esmolol, bisoprolol, atenolol, metoprolol, carteolol in the mobile phase containing MeOH-0.05%TEAA (pH 7.0) (90:10, v/v) (-10 kV), and that of propranolol and celiprolol in the mobile phase containing MeOH-0.025%TEAA (pH 7.0) (90:10, v/v)(-10 kV). Comparative enantioseparations performed in polar organic CLC and reversed phase pCEC mode revealed significant difference.

Influence of estrogen and xenoestrogens on basolateral uptake of tetraethylammonium by opossum kidney cells in culture.

The sex steroid hormone estrogen down-regulates renal organic cation (OC) transport in animals, and it may contribute to sex-related differences in xenobiotic accumulation and excretion. Also, the presence of various endocrine-disrupting chemicals, i.e., environmental chemicals that possess estrogenic activity (e.g., xenoestrogens) may down-regulate various transporters involved in renal accumulation and excretion of xenobiotics. The present study characterizes the mechanism by which long-term (6-day) incubation with physiological concentrations of 17beta-estradiol (E(2)) or the xenoestrogens diethylstilbestrol (DES) and bisphenol A (BPA) regulates the basolateral membrane transport of the OC tetraethylammonium (TEA) in opossum kidney (OK) cell renal cultures. Both 17beta-E(2) and the xenoestrogen DES produced a dose- and time-dependent inhibition of basolateral TEA uptake in OK cell cultures, whereas the weakly estrogenic BPA had no effect on TEA uptake. Treatment for 6 days with either 1 nM 17beta-E(2) or DES reduced TEA uptake by approximately 30 and 40%, respectively. These effects were blocked completely by the estrogen receptor antagonist ICI 182780 (Faslodex, fulvestrant), suggesting that these estrogens regulate OC transport through the estrogen receptor, which was detected (estrogen receptor alpha) in OK cell cultures by reverse transcription-polymerase chain reaction. The J(max) value for TEA uptake in 17beta-E(2)- and DES-treated OK cell cultures was approximately 40 to 50% lower than for ethanol-treated cultures, whereas K(t) was unaffected. This reduction in transport capacity was correlated with a reduction in OC transporter OCT1 protein expression following treatment with both agents.

Role of BK channels in testosterone-induced relaxation of the aorta in spontaneously hypertensive rats.

The previous data indicated that the testosterone (Tes)-induced relaxation of thoracic aorta is greater in spontaneously hypertensive rats (SHR) than in normotensive rats (Wistar-Kyoto rats; WKY) and that there were differences between SHR and WKY in the functions of K(ATP), K(v), and K(Ca) channels. The present study was carried out to ascertain the mechanisms of the Tes-induced relaxation. Indomethacin (30 muM) pretreatment suppressed the Tes-induced relaxation. Following noradrenalin (NA)-induced vasoconstriction, the relaxation induced by Tes was significantly attenuated by endothelium removal in SHR (not in WKY), but the dilatory effect of Tes following KCl-induced vasoconstriction was not attenuated by endothelium removal. After tetraethylammonium (K(Ca) channel inhibitor) or iberiotoxin (large conductance, Ca(2+) activated BK channel inhibitor) pretreatment, the Tes-induced relaxation was attenuated in SHR, but not in WKY. This attenuation in SHR was not observed after endothelium removal. The above results suggest that the relaxation induced by Tes following NA-induced vasoconstriction in SHR results from hyperpolarization due to BK channel opening.