Presence Of Tetraethylammonium Chloride Research Articles

A high-spin alkylperoxo-iron(iii) complex with cis-anionic ligands: implications for the superoxide reductase mechanism.

The N3O macrocycle of the 12-TMCO ligand stabilizes a high spin (S = 5/2) [FeIII(12-TMCO)(OOtBu)Cl]+ (3-Cl) species in the reaction of [FeII(12-TMCO)(OTf)2] (1-(OTf)2) with tert-butylhydroperoxide (tBuOOH) in the presence of tetraethylammonium chloride (NEt4Cl) in acetonitrile at -20 °C. In the absence of NEt4Cl the oxo-iron(iv) complex 2 [FeIV(12-TMCO)(O)(CH3CN)]2+ is formed, which can be further converted to 3-Cl by adding NEt4Cl and tBuOOH. The role of the cis-chloride ligand in the stabilization of the FeIII-OOtBu moiety can be extended to other anions including the thiolate ligand relevant to the enzyme superoxide reductase (SOR). The present study underlines the importance of subtle electronic changes and secondary interactions in the stability of the biologically relevant metal-dioxygen intermediates. It also provides some rationale for the dramatically different outcomes of the chemistry of iron(iii)peroxy intermediates formed in the catalytic cycles of SOR (Fe-O cleavage) and cytochrome P450 (O-O bond lysis) in similar N4S coordination environments.

Potassium homeostasis and signaling as a determinant of Echinacea species tolerance to salinity stress

Salt tolerant is strongly related to potassium (K+) retention in plant tissues under salt stress conditions. However, it is unclear for different Echinacea species. So, mechanistic basis of four Echinacea species (i.e. Echinacea purpurea, Echinacea angustifolia, Echinacea pallida, and Echinacea sanguinea) to salinity stress tolerance, and K+ retention were assessed in the present study. Non-invasive microelectrode ion flux measuring, dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) activities, and pharmacological measurements were performed based on the standard methods. Ion flux measurements revealed higher K+ efflux in E. pallida and E. sanguinea species compared to the E. purpurea and E. angustifolia species in the elongation zone. Higher salinity-induced H+ efflux was found in the elongation zone than mature zone. However, E. angustifolia and E. purpurea had more Ca2+ influx compared to E. pallida and E. sanguinea species. Net K+ efflux decreased (> 90 %) in the presence of tetraethylammonium chloride (TEA) and GdCl3. Increasing of Ca2+ uptake and K+ loss in four Echinacea species roots were found in the presence of 0.3 mM Cu/Ascorbate (Cu/Asc). The significant role of H+-ATPase in H+ efflux was demonstrated by sodium orthovanadate. Ultimately, the physiological properties of Echinacea species have a critical role in salinity-resistant/sensitive differences. Future scientific understanding of Echinacea species physiognomies may be necessary for better understanding of the plant behavior to salinity stress.

Experimental study and thermodynamic modeling of the stability conditions of methane clathrate hydrate in the presence of TEACl and/or BMIM-BF4 in aqueous solution

In this work, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) and tetra ethyl-ammonium chloride (TEACl) were investigated to study their effects on thermodynamic stability conditions of methane clathrate hydrate. Different BMIM-BF4 and TEACl aqueous solutions (4.77 wt% (0.57 mol%) TEACl + 4.85 wt% (0.43 mol%) BMIM-BF4, 9.15 wt% (0.20 mol%) TEACl + 9.38 wt% (0.90 mol%) BMIM-BF4 and 11.82 wt% (1.63 mol%) TEACl + 11.82 wt% (1.20 mol%) BMIM-BF4) were used as thermodynamic inhibitors which have not been reported in literature. The experiments were conducted at constant volume from 274.6 K to 283.4 K and 3.18 MPa to 7.93 MPa. Moreover, methane hydrate phase equilibria in the aforementioned ioinic liquids (ILs) aqueous solutions were modeled. For this purpose, the chemical potential of water in hydrate phase is calculated using the van der Waals–Platteeuw (vdWP) theory. The Peng-Robinson (PR) equation of state (EoS) is used for calculation of fugacity in the gas phase. Water activity in the aqueous phase is determined by the NRTL activity coefficient model. Successful comparison of the experimental data with the modeling results confirms the model accuracy. It can also be observed that mixtures of the two aforementioned ionic liquids can inhibit methane hydrate formation more than each of single ILs. Furthermore, the studied ILs inhibit methane hydrate formation more at higher pressures.

Influence of tetraalkylammonium halides on analytical properties of universal acid-base indicator paper

Properties of three types of universal acid-base indicator paper (IP) obtained by means of noncovalent immobilization of five indicators (methyl yellow, methyl red, phenolphthalein, thymol blue, bromothymol blue) in the presence of tetraethylammonium chloride (TEAC) or tetrabutylammonium bromide (TBAB) and in the absence of salts were compared. It was proved that IP-TBAB has advantages in time stability of paper color, reliability of indicators retention in sorbent phase, and accuracy of visual determination of pH values using color scale. Values of acidity constants of indicators were determined by spectrophotometric method in water-ethanol solutions (mass fraction of ethanol is 50%) in the presence and absence of TBAB salt. It was found that modifying action of TBAB on properties of indicators in water-ethanol solutions and on paper is similar to influence of cationic surfactants. Examples of application of the indicator paper are given.

Naringenin inhibits pacemaking activity in interstitial cells of Cajal from murine small intestine

BackgroundNaringenin (NRG) is a common dietary polyphenolic constituent of fruits. NRG has diverse pharmacological activities, and is used in traditional medicine to treat various diseases including gastrointestinal (GI) disorders. Interstitial cells of Cajal (ICCs) are pacemaker cells of the GI tract. In this study, the authors investigated the effects of NRG on ICCs and on GI motility in vitro and in vivo. MethodsICCs were dissociated from mouse small intestines by enzymatic digestion. The whole-cell patch clamp configuration was used to record pacemaker potentials in cultured ICC clusters. The effects of NRG on GI motility were investigated by calculating percent intestinal transit rates (ITR) using Evans blue in normal mice. ResultsNRG inhibited ICC pacemaker potentials in a dose-dependent manner. In the presence of tetraethylammonium chloride or iberiotoxin, NRG had no effect on pacemaker potentials, but it continued to block pacemaker potentials in the presence of glibenclamide. Preincubation with SQ-22536 had no effect on pacemaker potentials or on their inhibition by NRG. However, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one blocked pacemaker potential inhibition by NRG. In addition, L-NG-nitroarginine methyl ester blocked pacemaker potential inhibition by NRG. Furthermore, NRG significantly suppressed murine ITR enhancement by neostigmine in vivo. ConclusionThis study shows NRG dose-dependently inhibits ICC pacemaker potentials via a cyclic guanosine monophosphate/nitric oxide-dependent pathway and Ca2+-activated K+ channels in vitro. In addition, NRG suppressed neostigmine enhancement of ITR in vivo.

Optimization of the hybridization-based method for purification of thermostable tRNAs in the presence of tetraalkylammonium salts

We found that both tetramethylammonium chloride (TMA-Cl) and tetra-ethylammonium chloride (TEA-Cl), which are used as monovalent cations for northern hybridization, drastically destabilized the tertiary structures of tRNAs and enhanced the formation of tRNA•oligoDNA hybrids. These effects are of great advantage for the hybridization-based method for purification of specific tRNAs from unfractionated tRNA mixtures through the use of an immobilized oligoDNA complementary to the target tRNA. Replacement of NaCl by TMA-Cl or TEA-Cl in the hybridization buffer greatly improved the recovery of a specific tRNA, even from unfractionated tRNAs derived from a thermophile. Since TEA-Cl destabilized tRNAs more strongly than TMA-Cl, it was necessary to lower the hybridization temperature at the sacrifice of the purity of the recovered tRNA when using TEA-Cl. Therefore, we propose two alternative protocols, depending on the desired properties of the tRNA to be purified. When the total recovery of the tRNA is important, hybridization should be carried out in the presence of TEA-Cl. However, if the purity of the recovered tRNA is important, TMA-Cl should be used for the hybridization. In principle, this procedure for tRNA purification should be applicable to any small-size RNA whose gene sequence is already known.

Electrochemical synthesis and characterization of tantalum alkoxides

Tantalum(V) propoxide (Ta(OPr n) 5), isopropoxide (Ta(OPr i) 5) and butoxide(Ta(OBu n) 5) were synthesized by electrochemical reactions of corresponding alcohol at sacrificial tantalum anode in the presence of tetraethylammonium chloride as a conductive additive. The pure products were isolated by reduced pressure distillation under 5 kPa. The crystal of Ta(OPr i) 5 was obtained by recrystallization from hexane at −10 °C. These samples were characterized by Fourier transform infrared spectra (FT-IR), Raman spectra, nuclear magnetic resonance spectra (NMR), TG/DTA and ICP-MS. The results show that direct electrochemical synthesis of metal alkoxides has a high current efficiency and electrolysis yield. These alkoxides have a high purity of 99.97% and can be directly used as the precursor of Ta 2O 5 films.

Phospholipase C-independent effects of 3M3FBS in murine colon

The muscarinic receptor subtype M 3 is coupled to Gq/11 proteins. Muscarinic receptor agonists such as carbachol stimulate these receptors that result in activation of phospholipase C (PLC) which hydrolyzes phosphatidylinositol 4,5-bisphosphate into diacylglycerol and Ins(1,4,5) P 3 . This pathway leads to excitation and smooth muscle contraction. In this study the PLC agonist, 2, 4, 6-trimethyl-N-(meta-3-trifluoromethyl-phenyl)-benezenesulfonamide ( m-3M3FBS), was used to investigate whether direct PLC activation mimics carbachol-induced excitation. We examined the effects of m-3M3FBS and 2, 4, 6-trimethyl-N-(ortho-3-trifluoromethyl-phenyl)-benzenesulfonamide ( o-3M3FBS), on murine colonic smooth muscle tissue and cells by performing conventional microelectrode recordings, isometric force measurements and patch clamp experiments. Application of m-3M3FBS decreased spontaneous contractility in murine colonic smooth muscle without affecting the resting membrane potential. Patch clamp studies revealed that delayed rectifier K + channels were reversibly inhibited by m-3M3FBS and o-3M3FBS. The PLC inhibitor, 1-(6-((17b-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122), did not prevent this inhibition by m-3M3FBS. Both m-3M3FBS and o-3M3FBS decreased two components of delayed rectifier K + currents in the presence of tetraethylammonium chloride or 4-aminopyridine. Ca 2+ currents were significantly suppressed by m-3M3FBS and o-3M3FBS with a simultaneous increase in intracellular Ca 2+. Pretreatment with U73122 did not prevent the decrease in Ca 2+ currents upon m-3M3FBS application. In conclusion, both m-3M3FBS and o-3M3FBS inhibit inward and outward currents via mechanisms independent of PLC acting in an antagonistic manner. In contrast, both compounds also caused an increase in [Ca 2+] i in an agonistic manner. Therefore caution must be employed when interpreting their effects at the tissue and cellular level.

Towards Convenient Precursors for α -Phosphonylated Aziridinium Ions

Mixtures of the respective 2-(N,N-dibenzylamino)-1-chloro- and 1-(N,N-dibenzylamino)-2-chlorophosphonates were obtained after mesylation of dimethyl (1R,2S)-2-(N,N-dibenzylamino)-1-hydroxy-3-methylbutylphosphonate and diethyl (1R,2S)-2-(N,N-dibenzylamino)-1-hydroxy-3-phenylpropylphosphonate with mesyl chloride in the presence of tetraethylammonium chloride. These mixtures are considered as useful precursors to α -phosphonylated aziridinium ions.

Electrochemically-driven conformational shift in mono- and di-copper constrained macrotricyclic cyclen receptors

An electrochemical study of mono- and di-copper constrained cyclen macrotricycles is presented. Electrochemical data in DMF solution indicate that the reduction of dinuclear complexes occurs in two steps in the -0.4 to -0.8 V vs.AgCl/Ag potential range yielding CuII CuI and CuI CuI species further reduced to Cu metal at highly negative potentials. Mononuclear complexes are reduced in two steps to CuI and Cu metal. Electrochemical data suggest that reduction of both mononuclear and dinuclear complexes approach a square scheme involving electrochemically-driven conformational shifts for metal ions. The presence of endo- and exo-forms of the complexes are revealed by changes in the electrochemical response of the complexes in the presence of tetraethylammonium chloride, 1-azabicyclo[2.2.2]octane and diazabicyclo[2.2.2]octane competing ligands.

A highly efficient synthesis of (Z)‐1‐aryl‐2‐silyl‐1‐ stannylethenes and their conversion to (E)‐2‐ arylethenyl‐, (Z)‐2‐(2‐pyridyl)ethenyl‐ and allenyl‐silanes

AbstractA Pd(dba)2–P(OEt)3 combination allowed the silastannation of arylacetylenes, 1‐hexyne or propargyl alcohols with tributyl(trimethylsilyl)stannane to take place at room temperature, producing (Z)‐2‐silyl‐1‐stannyl‐1‐substituted ethenes in high yields. Novel silyl(stannyl)ethenes were fully characterized by 1H‐, 13C‐, 29Si‐ and 119Sn‐NMR as well as infrared and mass analyses. Treatment of a series of (Z)‐1‐aryl‐2‐silyl‐1‐stannylethenes and (Z)‐1‐(3‐pyridyl)‐2‐silyl‐1‐stannylethene with hydrochloric acid or hydroiodic acid in the presence of tetraethylammonium chloride (TEACl) or tetrabutylammonium iodide (TBAI) led to the exclusive formation of (E)‐trimethyl(2‐arylethenyl)silanes with high stereoselectivity. A similar reaction of (Z)‐1‐(2‐anisyl)‐2‐silyl‐1‐stannylethene also produced E‐type trimethyl[2‐(2‐anisyl)ethenyl]silane, while (Z)‐trimethyl [2‐(2‐pyridyl)ethenyl]silane was produced exclusively from (Z)‐1‐(2‐pyridyl)‐2‐silyl‐1‐stannylethene. Protodestannylation of (Z)‐1‐[hydroxy(phenyl)methyl]‐2‐silyl‐1‐stannylethene with trifluoroacetic acid took place via the β‐elimination of hydroxystannane, providing trimethyl(3‐phenylpropa‐1,2‐dienyl)silane quite easily. The destannylation products were also fully characterized. Copyright © 2007 John Wiley & Sons, Ltd.

Intra- and Intermolecular Hydroamination of Alkynes Catalyzed by ortho-Metalated Iridium Complexes

Reaction of o-(diphenylphosphino)(N-benzylidene)aniline (P∼N) with [Ir(COD)Cl]2 affords the substitution product [(P∼N)Ir(COD)Cl] (1). Treatment of 1 with AgBF4 yields the cyclometalated iridium hydride complex [P,N,C-(P∼N)Ir(COD)H]BF4 (2). On the other hand, under atmospheric pressure of CO, carrying out the substitution of [Ir(COD)Cl]2 with P∼N results in the formation of [P,N,C-(P∼N)Ir(CO)HCl] (5). Conversion of 4 into 5 can be achieved by the reaction of 4 with CO in the presence of tetraethylammonium chloride. Both 4 and 5 are characterized by spectroscopic and X-ray structural analyses. All iridium complexes are not good catalysts for hydroamination. However, the combination of 5 with NaB[3,5-C6H3(CF3)2]4 (denoted as NaBArF4) provides a potent catalytic system for both intra- and intermolecular hydroamination of alkynes. Intramolecular reaction of o-(2-phenylethynyl)anilines produces the corresponding indoles in good yields. Furthermore, intermolecular hydroamination takes place smoothly to generate...

Concentration and Thermodynamic Stability Constants of Magnesium(II) and Calcium(II) Tartrate Complexes in Aqueous Solutions

The formation of calcium and magnesium tartrate complexes was studied by potentiometric titration at ionic strengths of 0.1 and 0.3 (in the presence of tetraethylammonium chloride) at a temperature of 298.15 K. The composition and the stability constants of the complexes formed in the system were determined. The known stability constants were used to optimize the conditions of calorimetric determination of the heats of formation of calcium and magnesium tartrates in an aqueous solution.

Acid‐dependent selective formation of trans‐aryl(germyl)ethenes or 1‐aryl‐1‐germylethenes by the protodestannylation of (Z)‐germyl(stannyl)ethenes

AbstractProtodemetallation of (Z)‐1‐aryl‐2‐germyl‐1‐stannylethenes using hydrochloric acid in the presence of tetraethylammonium chloride (TEACl) proceeds at 0 °C with retention of configuration to afford trans‐1‐aryl‐2‐germylethenes with high yields. In contrast, the reaction using hydroiodic acid in the presence of tetrabutylammonium iodide (TBAI) brings about a novel 1,2‐germyl migration accompanying the destannylation to form 1‐aryl‐1‐germylethenes. These 1,2‐germyl migration products result with especially high selectivity from adducts bearing a substituent at the ortho‐ or para‐position on the aromatic ring in the adduct. However, the germyl(stannyl)ethenes bearing a substituent at the meta position on the ring produce a regioisomeric mixture of a trans‐germylethene and a 1‐aryl‐1‐germylethene. Copyright © 2005 John Wiley & Sons, Ltd.

Adjuvant effect of benzalkonium chloride on the allergen-specific IgE, IgG1 and IgG2a antibody formation in BALB/cJ mice.

The quaternary ammonium compounds, of which benzalkonium chloride is the most frequently used, are cationic surfactants used e.g. as antiseptics, disinfectants, detergents and preservatives (Purohit et al. 2000). Quaternary ammonium compounds may possess adverse effect on the immune system. Thus, atopic sensitization, defined as increased IgE levels to common aeroallergens, occurred more frequently in pig farmers who used disinfectants containing these compounds – an effect which the authors suggested could be due to an adjuvant effect of the used compounds (Preller et al. 1996; Vogelzang et al. 1997). In itself, benzalkonium chloride seldomly causes allergic airway diseases (Purohit et al. 2000). The adjuvant effects on antibody production of several quaternary ammonium compounds have been revealed in a guinea pig study (Gall 1966), however not differentiated in antibody isotypes. Sparse information is available about the adjuvant effect of benzalkonium chloride. The present study investigates the effect of benzalkonium chloride on the murine type 1 helper cells (Th1) and Th2-dependent antibody levels. The Th1 response elicits IgG2a antibodies, whereas the Th2 response promotes formation of IgE and IgG1 (Corry & Kheradmand 1999). The activity of one of the most potent quaternary ammonium compound adjuvants, dioctadecyldimethylammonium bromide (DDA), has been shown in several studies to be influenced by other substances (Hilgers & Snippe 1992). As commercial quaternary ammonium compound-based products may contain a mixture of many quaternary ammonium compounds, we studied a possible interaction between benzalkonium chloride and tetraethylammonium bromide, a quaternary ammonium compound, which not per se possesses adjuvant properties as it contains short al-

Depolarization of membrane potential and the smooth muscle contraction by isothiocyanatobenzyl imidazoline in guinea-pig stomach circular muscle

Isothiocyanatobenzyl imidazoline (IBI) produces characteristic slowly developing contraction of many smooth muscle preparations including the circular smooth muscle of the guinea-pig stomach. Changes in the membrane potential were recorded intracellularly, and the muscle contraction induced by IBI was investigated. IBI at 100 micromol/l slowly produced a sustained depolarization of the membrane with a maximum change of approximately 15 mV. This depolarization could not be blocked by 1-hyoscyamine, 100 nmol/l. An imidazoline analogue, oxymetazoline at 1 micromol/l, did not change the resting membrane potential as observed after IBI. Significant membrane depolarization after IBI still occurred in Ca2+-free medium. During IBI-induced depolarization, sudden reduction of Na+ to 30 mmol/l in the medium reduced the depolarization slightly. IBI-induced depolarization was additive with that produced by 20 mmol/l K+ in the medium. In the presence of tetraethylammonium chloride or levcromakalim or nifedipine, IBI continued to depolarize the membrane although functional pharmacological experiments showed that the contractile effects of IBI were significantly inhibited by 30 micromol/l levcromakalim and abolished by 100 nmol/l nifedipine. At 100 micromol/l phentolamine (reported by others as an inhibitor of ATP-sensitive potassium channels) completely blocked IBI-induced contraction. Phentolamine (30 micromol/l) blocked the contractile effects of IBI by 50%. On the other hand, S(-)-Bay K 8644, a voltage-dependent calcium channel activator, was additive with the contractile response of IBI. These results indicated that IBI produced membrane depolarization and contraction of the guinea-pig stomach circular muscle, by a mechanism not involving muscarinic receptors or alpha-adrenoceptors. Even though levcromakalim, an ATP-sensitive potassium channel opener, could not inhibit IBI-induced depolarization, the ATP-sensitive potassium channel and the voltage-dependent calcium channel may be intrinsically linked with the action of IBI.

Relaxant effects of propofol on human omental arteries and veins

We have investigated the relaxant effects of propofol on smooth muscle tension in human omental arteries and veins to determine if endothelium-related mechanisms are involved. Isolated vessel segments were precontracted with endothelin-1 and propofol was added cumulatively (10(-7)-10(-4) mol litre-1). In both artery and vein segments, propofol induced relaxation, which was not dependent on an intact endothelium. Relaxation was reduced when the extracellular K+ concentration was increased and in the presence of tetraethylammonium chloride (TEA). In intact segments, N-nitro-L-arginine methyl ester (L-NAME), indomethacin, glibenclamide, 4-aminopyridine, clotrimazole and atropine did not affect the concentration-response curve of propofol. This indicates that propofol relaxes human omental arteries and veins in an endothelium independent manner, and that hyperpolarization caused by activation of the K+ channel, BKCa, may be involved.

Action potential propagation into the presynaptic dendrites of rat mitral cells

1. Dendritic patch-clamp recordings were obtained from mitral cells in rat olfactory bulb slices, up to 350 microns from the soma. Simultaneous dendritic and somatic whole-cell recordings indicated that action potentials (APs) evoked by somatic or dendritic current injection were initiated near the soma. Both the large amplitude (100.7 +/- 1.1 mV) and the short duration (1.38 +/- 0.07 ms) of the AP were maintained as the AP propagated back into the primary mitral cell dendrites. 2. Outside-out patches isolated from mitral cell dendrites contained voltage-gated Na+ channels (peak conductance density, 90 pS micron-2 at -10 mV). When an AP was used as a somatic voltage-clamp command in the presence of 1 microM tetrodotoxin (TTX), the amplitude of the dendritic potential was attenuated to 48 +/- 14 mV. This shows that dendritic Na+ channels support the active back-propagation of APs. 3. Dendritic patches contained voltage-gated K+ channels with high density (conductance density, 513 pS micron-2 at 30 mV). Dendritic K+ currents were reduced to 35% by 1 mM external tetraethylammonium chloride (TEACl). When an AP was used as a somatic voltage-clamp command in the presence of TEACl, the dendritic potential was markedly prolonged. This indicates that dendritic K+ channels mediate the fast repolarization of dendritic APs. 4. We conclude that voltage-gated Na+ and K+ channels support dendritic APs with large amplitudes and short durations that may trigger fast transmitter release at dendrodendritic synapses in the olfactory bulb.

3-Isobutyl-1-methylxanthine (IBMX) affects potassium permeability in rat sensory neurones via pathways that are sensitive and insensitive to [Ca2+]in.

The effects of externally applied 3-isobutyl-1-methylxanthine (IBMX), in millimolar concentrations, on the membrane currents in dorsal root ganglia (DRG) neurones isolated from newborn rats were investigated using the amphotericin-based "perforated" patch-clamp technique. In some experiments, simultaneous measurements of intracellular Ca2+ concentration ([Ca2+]in) were performed using fura-2 microfluorimetry. Applications of IBMX induced elevation of [Ca2+]in resulting from Ca2+ release from caffeine-ryanodine-sensitive internal stores. In addition to Ca2+ release, IBMX produced a biphasic membrane current response comprised of an inward current transiently interrupted by outward current. The onset of the inward current slightly preceded the onset of the [Ca2+]in transient, while the interrupting outward current developed synchronously with the [Ca2+]in rise. The development of IBMX-induced outward current ultimately needed the [Ca2+]in elevation. After the depletion of Ca2+ stores by IBMX or caffeine exposure, the subsequent IBMX challenge failed to produce both the [Ca2+]in transient and outward membrane current, although the inward current remained unchanged. Both components of the IBMX-induced membrane current response had a reversal potential close to the K+ equilibrium potential and the IBMX-induced membrane current response disappeared while dialysing the cell interior with K(+)-free, Cs(+)-containing solutions suggesting their association with K+ channel activity. External administration of 10 mM tetraethylammonium chloride (TEA-Cl) evoked an inward current similar to that observed in response to IBMX; in the presence of TEA-Cl, IBMX application was almost unable to induce additional inward current. IBMX (5 mM) effectively (approximately 50%) inhibited K+ currents evoked by step depolarizations of membrane potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of Ca2+ oscillations by vasopressin in the presence of tetraethylammonium chloride in cultured vascular smooth muscle cells.

The change of cytosolic Ca2+ concentration ([Ca2+]i) caused by vasopressin was examined in indo-1-loaded A7r5 smooth muscle cells by use of the high-performance laser cytometer and ratiometric fluorescence method. Vasopressin (100 nM) caused an initial rapid rise and a delayed increase in [Ca2+]i (n = 6). However, in the presence of tetraethylammonium chloride (10 mM), vasopressin consistently triggered sustained Ca2+ oscillations which were preceded by a large peak of [Ca2+]i. The latency for the development of this huge increase in [Ca2+]i prior to the occurrence of sustained Ca2+ oscillations was always the same. The frequency and amplitude of this type of Ca2+ oscillation varied depending upon the extracellular Ca2+ concentration. Ca(2+)-free solution did not completely suppress the sustained Ca2+ oscillations, but caffeine (20 mM) effectively abolished them. The present findings indicate that in A7r5 smooth muscle cells, the sustained Ca2+ oscillations triggered by vasopressin in the presence of tetraethylammonium chloride were mainly due to Ca2+ release from IP3-sensitive Ca2+ stores and Ca2+ influx from extracellular space, and did not require the pacemaker activity derived from the surface membrane. Moreover, the vasopressin-induced change in [Ca2+]i appeared to be linked to pertussis toxin-insensitive GTP-binding protein(s).