Stationary Concentration Research Articles

Deconvolution of electrokinetic and chromatographic contributions to solute migration in stereoselective ion‐exchange capillary electrochromatography on monolithic silica capillary columns

A monolithic silica stationary phase functionalized with an enantioselective strong cation exchanger based on an aminosulfonic acid derivative was used for chiral separations of basic test solutes by nonaqueous CEC and capillary LC. The effects of the applied electric field as well as the ionic strength in the eluent on electrokinetic and chromatographic contributions to the overall separation performance in the electrically driven mode were investigated. Hence, under the utilized experimental conditions, i. e., at an electric field strength in the range of approximately 120-720 V/cm (applied voltages 4-24 kV) and an ionic strength of the counterion between 5 and 25 mM (at constant acid-to-base, i. e., co- to counterion ratio of 2:1), no deviations from the expected linearity of the EOF were observed. This led to the conclusion that an occurrence of the so-called electrokinetic effects of the second kind resulting from electric double layer overlap inside the mesopores of the monolithic stationary phase and concentration polarization phenomena were largely negligible. Additional support to this conclusion was inferred from the observed independence of CEC retention factors on the electric field strength across the investigated ionic strength range of the BGE. As a consequence, a simple framework allowing for calculation of the CEC mobilities from the individual separation contributions, viz. electroosmotic and electrophoretic mobilities as well as retention factors, could be applied to model CEC migration. There was a reasonable agreement between calculated and experimental CEC mobility data with deviations typically below 5%. The deconvolution of the individual contributions to CEC migration and separation is of particular value for the understanding of the separation processes in which electrophoretic migration of ionic sample constituents plays a significant role like in ion-exchange CEC and may aid the optimization procedure of the BGE and other experimental conditions such as the optimization of the surface chemistry of the stationary phase. In combination with the remarkable column performance evident from the low theoretical plate heights observed under CEC conditions for all test solutes (3.5-7.5 microm in the flow rate range of 0.4-1.2 mm/s, corresponding to (130,000-300,000 plates per meter), the presented framework provides an attractive tool as the basis for the assessment of chromatographic selectivities in a miniaturized CEC screening of new selectors and chiral stationary phases (CSPs), respectively, from experimental CEC data and known CE mobilities.

The Major/Minor Concept: Dependence of the Selectivity of Homogeneously Catalyzed Reactions on Reactivity Ratio and Concentration Ratio of the Intermediates

The homogeneously catalyzed asymmetric hydrogenation of prochiral olefins with cationic Rh(I) complexes is one of the best-understood selection processes. For some of the catalyst/substrate complexes, experimental proof points out the validation of the major/minor principle; the concentration-deficient minor substrate complex, which has very high reactivity, yields the excess enantiomer. As exemplified by the reaction system of [Rh(dipamp)(MeOH)2]+/methyl (Z)-alpha-acetamidocinnamate (dipamp=1,2-bis((o-methoxyphenyl)phenylphosphino)ethane), all six of the characteristic reaction rate constants have been previously identified. Recently, it was found that the major substrate complex can also yield the major enantiomer (lock-and-key principle). The differential equation system that results from the reaction sequence can be solved numerically for different hydrogen partial pressures by including the known equilibrium constants. The result displays the concentration-time dependence of all species that exist in the catalytic cycle. On the basis of the known constants as well as further experimental evidence, this work focuses on the examination of all principal possibilities resulting from the reaction sequence and leading to different results for the stereochemical outcome. From the simulation, the following conclusions can be drawn: 1) When an intermediate has extreme reactivity, its stationary concentration can become so small that it can no longer be the source of product selectivity; 2) in principle, the major/minor and lock-and-key principles can coexist depending on the applied pressure; 3) thermodynamically determined intermediate ratios can be completely converted under reaction conditions for a selection process; and 4) the increase in enantioselectivity with increasing hydrogen partial pressure, a phenomenon that is experimentally proven but theoretically far from being well-understood, can be explained by applying both the lock-and-key as well as the major/minor principle.

Biological Monitoring as a Useful Tool for the Detection of a Coal-Tar Contamination in Bitumen-Exposed Workers

In our research project entitled “Chemical irritative and/or genotoxic effect of fumes of bitumen under high processing temperatures on the airways,” 73 mastic asphalt workers exposed to fumes of bitumen and 49 construction nonexposed workers were analyzed and compared with respect to polycyclic aromatic hydrocarbons (PAHs) exposure and exposure-related health effects. In order to assess the internal exposure the monohydroxylated metabolites of pyrene, 1- hydroxypyrene (1-OHP), and phenanthrene, 1-, 2- and 9-, and 3- and 4-hydroxyphenanthrene (OHPH) were determined in pre- and post-shift urinary samples. Significantly higher concentrations 1-OHP and OHPH were detected in the post-shift urine samples of 7 mastic asphalt workers working on the same construction site compared to the reference workers and all other 66 mastic asphalt workers. The adjusted mean OHPH in the reference, 66 mastic worker, and 7 worker subgroups was 1022, 1544, and 12919 ng/g creatinine (crn) respectively, indicating a marked rise in the 7 worker subgroup. In addition, there was a more than 12-fold increase of PAH metabolites from pre- to post-shift in these 7 workers, whereas in the other mastic asphalt workers there was only a twofold rise in PAH-metabolite concentration between pre- and post-shift values. The analysis of a drilling core from the construction site of the seven workers led to the detection of the source for this marked PAH exposure during the working shift as being coal tar plates, which were, without knowledge of the workers and coordinators, the underground material of the mastic asphalt layer. The evaluation of the stationary workplace concentration showed enhanced levels of phenanthrene, pyrene, fluorene, anthracene, and acenaphthene during working shifts at the construction site of these seven workers. Our study shows that biological monitoring is also a useful tool for the detection of unrecognized sources with high PAH concentrations.

Taylor’s regime of an autocatalytic reaction front in a pulsative periodic flow

Autocatalytic reaction fronts between reacted and unreacted species may propagate as solitary waves, that is, at a constant front velocity and with a stationary concentration profile, which result from a balance between molecular diffusion and chemical reaction. A velocity field in the supporting medium may affect the propagation of such fronts through different phenomena: advection, diffusion enhancement, front shape changes, etc. Here, we report on an experimental study and lattice Bhatnagar–Gross–Krook numerical simulations of the effect of an oscillating flow on the autocatalytic reaction between iodate and arsenous acid in a Hele–Shaw cell. In the low frequency range covered by the experiments, the front behavior is controlled by the flow across the gap and is reproduced with two-dimensional numerical simulations. It is shown that the front velocity oscillates at the frequency of the flow, whereas the front width oscillates at twice that frequency. Moreover, the Taylor regime in the presence of a Poiseuille flow is fully investigated: The description obtained in the case of a stationary flow provides an analytical prediction for the sinusoidal flow. The range of parameters, for which the prediction applies, is delineated and discussed.

Validation of a model for growth of Lactococcus lactis and Listeria innocua in a structured gel system: Effect of monopotassium phosphate

The effect of monopotassium phosphate (KH 2PO 4) on the chemical environment and on growth of Listeria innocua and Lactococcus lactis in coculture were investigated in a liquid and in a gelled microbiological medium at 12 °C and an initial pH of 6.2. As expected, addition of KH 2PO 4 to both the liquid and gelled media resulted in an increase in buffering capacity. This effect on buffering capacity changed the profiles of lactic acid dissociation and pH evolution. At all gelatin concentrations studied, addition of KH 2PO 4 increased the growth rate and the stationary cell concentration of L. lactis. In addition, the growth rate of L. innocua slightly increased but, in contrast, the stationary cell concentration remained unchanged. A new class of predictive models developed previously in our research team to quantify the effect of food model gel structure on microbial growth [Antwi, M., Bernaerts, K., Van Impe, J. F., Geeraerd, A. H., 2007. Modelling the combined effect of food model system and lactic acid on L. innocua and L. lactis growth in mono- and coculture. International Journal of Food Microbiology 120, 71–84] was applied. Our analysis indicate that KH 2PO 4 influenced the parameters of the chemical and microbiological subprocesses of the model. Nonetheless, the growth model satisfactorily predicted the stationary cell concentration when (i) the undissociated lactic acid concentrations at which L. innocua and L. lactis growth cease were chosen as previously reported, and (ii) all other parameters of the chemical and microbiological subprocesses were computed for each medium. This confirms that the undissociated lactic acid concentrations at which growth ceases is a unique property of a bacterium and does not, within our case study, depend on growth medium. The study indicates that microbial growth depends on the interplay between the individual food components which affect the physicochemical properties of the food, such as the buffering capacity. Towards future research, it can be concluded that mathematical models which embody the effect of buffering capacity are needed for accurate predictions of microbial growth in food systems.

Simultaneous Application of Glucose Oxidases and Peroxidases in Bleaching Processes

AbstractPeroxidases (POD) are used in textile decoloration and bleaching processes, but these enzymes are unfortunately inactivated rapidly at high hydrogen peroxide concentrations. A new concept has therefore been developed, which is based on a simultaneous application of glucose oxidase and peroxidase. Starting with glucose as a substrate for glucose oxidase (GOD), hydrogen peroxide was generated in situ. The freshly formed substrate H2O2 was immediately used by the POD oxidizing colored compounds in dyeing baths. For example, 20 mg of the dyestuff Sirius Supra Blue®FGG 200 % could be decolorized using 125 mg glucose which corresponds to 24 mg hydrogen peroxide. These experiments show that the enzyme cascade works in principle in homogeneous decoloration processes. The enzymes were not degraded by the oxidant, because under these conditions the stationary peroxide concentration is nearly zero over the whole reaction time. Moreover, experiments were carried out to check if this combined system with GOD, glucose and POD could be used even in heterogeneous systems such as the textile bleaching of natural cotton fibers. Starting from 55, a significant higher degree of whiteness (according to Berger) up to 66 could be obtained.

Fourier Analysis To Measure Diffusion Coefficients and Resolve Mixtures on a Continuous Electrophoresis Chip

We report a method to measure diffusion coefficients of fluorescent solutes in the 10(2)-10(6) Da molecular mass range in a glass-PDMS chip. Upon applying a permanent electric field, the solute is introduced through a narrow channel into a wide analysis chamber where it migrates along the injection axis and diffuses in two dimensions. The diffusion coefficient is extracted after 1D Fourier transform of the resulting stationary concentration pattern. Analysis is straightforward, requiring no numerical integration or velocity field simulation. The diffusion coefficients measured for fluorescein, rhodamine green-labeled oligonucleotides, and YOYO-1-stained dsDNA fragments agree with the literature values and with our own fluorescence correlation spectroscopy measurements. As shown for 151 and 1257 base pair dsDNA mixtures, the present method allows us to rely on diffusion to quantitatively characterize the nature and the composition of binary mixtures. In particular, we implement a DNA hybridization assay to illustrate the efficiency of the proposed protocol for library screening.

Measurements of carbon dioxide and oxygen concentrations in a diffusion respirator on the basis of track membranes

Concentrations of CO2 and O2 in the breathing hose and inside the mask of the diffusion respirator have been measured using an atomic emission spectrometer. The gas exchange system of this respirator efficiently, within 1 min, restores oxygen concentration in the inhaled air from 18.5 vol % to its atmospheric concentration (21 vol %) and carbon dioxide concentration from 2.9 vol % to a stationary concentration of ∼0.12 vol %. In the optimal configuration of the respirator, CO2 concentration inside the mask during breath is 0.23 vol %. The time resolution of the method is 200 ms and the CO2 detection limit is 0.08 vol %.

Stationary concentration of a binary solution in a growing drop and the time of its establishment

In the general case, the problem of describing the growth of a drop of a binary solution in a mixture of vapors of its constituent substances and a passive gas is quite difficult to solve. To solve this problem, even in the relatively simple case of diffusion-controlled drop growth, it is usually assumed [1, 2] that the solution concentration in the drop rapidly reaches a stationary value. To confirm this assumption, the time dependence of the concentration of an ideal binary solution in drops at various initial compositions was numerically calculated [2]. However, these numerical calculation results [2] show that the stationary solution concentration in a drop may be reached over quite a long time. It has recently been studied [3] how the stationary concentration of an ideal binary solution in a drop growing under diffusion control is reached, but neither has the value of this stationary solution concentration been found nor has the law under which the stationary concentration is reached with time been explicitly determined. In this work, we will study the case where the number density of molecules of each component in a twocomponent mixture of vapors that have condensed to form a drop noticeably exceeds the number density of molecules of each component in a two-component mixture of vapors being in equilibrium with this drop. In this interesting case, each of the two components of the vapor mixture intensely condenses to the drop. For diffusion-controlled drop growth, we will obtain expressions for the time dependence of the drop radius and the numbers of molecules of the substances that have condensed to the drop from the vapor mixture. We will find the time in which these expressions and the diffusioncontrolled mode of drop growth become valid after drop nucleation. We will find the stationary solution concentration in the drop growing under diffusion control and also will derive the power law under which the stationary solution concentration is reached with time. We will show that the stationary solution concentration in the growing drop is reached with time rather rapidly in comparison with the relatively slow drop growth. Unlike recent works [1‐3], we will need no assumption of ideality of the solution in the drop. Let us consider a drop of a binary solution that has nucleated in an initially uniform vapor‐gas medium of a passive gas and a two-component mixture of vapors of the same substances as in the drop. After nucleation, the drop grows because of the condensation of each of the two components of the vapor mixture. The amount of the passive gas in the vapor‐gas mixture is assumed to be much larger than the amount of the vapors. The drop grows under diffusion control when the drop radius R noticeably exceeds the free path length λ of molecules of the vapors in the passive gas, i.e., when R ≥ R 0 , where (1) is the drop radius above which the drop grows under diffusion control. The large relative amount of the passive gas in the vapor‐gas medium ensures isothermal conditions of condensation and also allows one to ignore the Stefan flow of the vapor‐gas medium and the effect of the diffusion flows of molecules of the vapors on each other. Let x i , i = 1, 2, be the number of molecules of component i in the drop at a current moment of time and ν i , i = 1, 2, be the partial volume occupied by a molecule of component i in the solution within the drop. As Grinin and Lezova [3], for simplicity, we assume the volumes ν 1 and ν 2 to be constant. It was shown [3] that the solution within the drop is uniform. Obviously,

Improving Estimation of Indoor Exposure to Inhalable Particles for Children in the First Year of Life

There is growing scientific evidence linking early childhood exposure to environmental agents with asthma and other illnesses that may not appear until later in life. Unfortunately the direct measurement of personal exposures of children in the first year of life is not possible by existing methodologies. This study developed and evaluated a new methodology to better assess exposure of children to inhalable particles in the first year of life while involved in floor play in the home. We constructed the Pre-Toddler Inhalable Particulate Environmental Robotic (PIPER) sampler. Two series of measurements of inhalable particles were carried out. One collected filter samples of airborne inhalable particles and a second used a real-time total particle mass concentration monitor. Samples were collected for seven residential locations. Duplicate samples were collected with PIPER 20 cm above the floor and from an identical stationary monitor positioned at a height of 110 cm. The mean observed airborne inhalable particle concentrations measured by PIPER was 98.6 μg/ m3, whereas simultaneously collected stationary samples mean concentration was 49.8 μg/m3. The average observed ratio of PIPER samples to stationary samples was 2.4. A paired t test comparison of the two sampling methods indicated a statistically significant higher level of inhalable particle concentration measured by PIPER in comparison with the fixed sampler (P< 0.0001). Peak concentrations as measured by a real-time monitor were in excess of 3600 μg/m3. The results suggest that children playing on the floor are exposed to a higher concentration of total inhalable particles than previous methodologies estimate.

Control of Actin Assembly Dynamics in Cell Motility

Control of Actin Assembly Dynamics in Cell Motility

Exploitation of the complex chemistry of hindered amine stabilizers in effective plastics stabilization

AbstractHindered amine stabilizers (HAS) remain a prominent class of stabilizers having a fortunate development with continuous interest in shaping the future properties of plastics: increase in polymer durability, application extension, reaching new effects. Commercial tests provided much information. Insufficient mechanistic interpretations of the complex effects of environmental factors (harshness of testing, penetration of radiation and oxygen, superposition of temperature, atmospheric impurities) and those of the microenvironment (morphology of the polymer matrix, physical relations of HAS–polymer, interference between HAS and other additives) are a drawback. Model experiments complement commercial studies and explain some phenomena. A careful transfer of information from model experiments must be done to avoid misinterpretation of mechanisms, particularly of the HAS regenerative cycle. A critical analysis of primary steps of the HAS activity mechanism in the polymer matrix based on HAS‐related primary nitroxides, formation of their stationary concentration and concentration gradients influenced by polymer morphology, spatial competition between autoreactions, and oxidation of polymer‐developed alkyl radicals and their scavenging by nitroxides (the key process of HAS efficiency) is outlined. Cyclic regeneration of nitroxides affected by the structure of the amino moiety in the HAS molecule, influence of acid environment, atmospheric ozone or singlet oxygen, cooperative mixtures of HAS with UV absorbers, combinations with additives increasing the thermal stabilization effect and improving color retention, assessment of the heat stabilization performance of HAS by proper testing, and influence of the molecular weight of HAS are mentioned together with examples of the chemical consumption of HAS in the final phases of their lifetime. lifetime. J. VINYL ADDIT. TECHNOL., 13:119–132, 2007. © 2007 Society of Plastics Engineers

Electric phenomena in multi-bubble cavitation fields

The processes of formation and accumulation of electric charges in the splitting and deformation of cavitation bubbles in an ultrasonic wave field are considered in terms of the local electrification theory. The influence of different factors on the electrification of the bubble-liquid interface is discussed. It is established that, in the splitting of a cavitation bubble and, possibly, in its deformation, the local field strength near the bubble surface dramatically depends on the radius of the neck formed in the bubble. It is shown that, although the stationary concentration of cavitation bubbles may be very high (∼104–105 cm−3), the probability for several deformed cavitation bubbles of “required size” to emit luminescence at a given instant of time depends on the ultrasound intensity and other test conditions, a conclusion supported by experimental data.

Oxidative Dehydrogenation of Propane by Monomeric Vanadium Oxide Sites on Silica Support

We investigate possible mechanisms of oxidative dehydrogenation of propane using density functional theory. Monomeric vanadium oxide species supported on silica are modeled by vanadyl-substituted silsesquioxane. Similarly to other catalysts with transition metal oxo bonds, the initial C−H bond activation step is hydrogen abstraction by the vanadyl (OVV) group yielding a diradical intermediate in which a propyl radical is bound to a HO−VIV site. This is followed by a propyl rebound mechanism yielding alkoxide or alcohol attached to a VIII(OSi)3 surface site from which propene can be formed. Propene is also directly obtained by a second hydrogen abstraction from the diradical intermediate. Desorption of propyl radicals leads to a stationary concentration of propyl in the gas phase and leaves reduced HO−VIV sites on the surface. Due to fast reoxidation their concentration is much smaller than the concentration of OVV sites. Therefore the rate of propene formation after readsorption on OVV sites is much large...

GROWTH AND TOXICITY OFPRYMNESIUM PARVUM(HAPTOPHYTA) AS A FUNCTION OF SALINITY, LIGHT, AND TEMPERATURE1

The growth rate, stationary cell concentration, and toxicity ofPrymnesium parvumN. Carter were measured using a strain isolated from Texas inland waters. We used a multifactor experimental approach with multiple regression analysis to determine the importance of environmental factors, including temperature, light, and salinity to these algal measurements. Exponential growth rate was unimodal in relation to temperature, salinity, and irradiance, with an estimated maximal growth of 0.94 d−1occurring at 27°C, 22 practical salinity units (psu), and 275 μmol photons·m−2·s−1. Stationary cell concentrations also had unimodal responses to temperature and salinity but increased with irradiance. Maximal cell concentrations were estimated to occur at 26°C and 22 psu. Both maximum growth rate and highest stationary cell concentrations were measured at levels of each factor resembling warm, estuarine conditions that differ from the conditions under which blooms occur in inland waters in the southwestern United States. Acute toxicity to fish was highest at the lowest salinity and temperature levels, conditions not optimal for exponential growth but similar to those under which blooms occur in inland waters. Our results imply that summer blooms could occur in inland waters of the southwestern United States. Generally, they have not, suggesting that factors other than those investigated in this research influence bloom dynamics.

Pt Catalyst Supported on Multiwalled Carbon Nanotubes for Hydrogenation-Dearomatization of Toluene

Using homemade multiwalled carbon nanotubes (CNTs) as the support, the Pt/CNTs catalyst was prepared by an incipient wetness method. Performance of the catalyst for hydrogenation-dearomatization (HDA) of toluene was evaluated and compared with the reference catalysts supported on γ-Al2O3 and activated carbon (AC). Over the 1.0%Pt/CNTs catalyst under the reaction conditions of 0.4 MPa, 373 K, PhCH3/H2 = 6/94 (mol/mol), and GHSV = 120 L/(h·g), the observed conversion of toluene HDA reached 100%, and the corresponding specific reaction rate was 0.0523 mmol/(s·m2). This value was 1.17 and 1.18 times that of the 1.4%Pt/γ-Al2O3 and 2.4%Pt/AC catalysts with the respective optimal Pt loading, respectively. It was experimentally found that using CNTs in place of γ-Al2O3 or AC as the support of the catalyst did not cause a significant change in the apparent activation energy for the toluene HDA reaction but led to a slight increase in concentration of catalytically active Pt species (Pt0) at the surface of the functioning catalyst. In addition, the Pt/CNTs catalyst could reversibly adsorb a greater amount of hydrogen under atmospheric pressure at temperatures from room temperature to 573 K. This unique feature would help to generate a microenvironment with higher stationary state concentration of active hydrogen adspecies at the surface of the functioning catalyst. These effects favored the toluene HDA reaction.

Dynamic modelling of the hydrocyclone

In hydrocyclone separation, fluctuating solids contents and size distributions in the feed cause instationarities. Under these conditions, the stationary concentration equilibrium in the apparatus and the separation are affected. Control mechanisms are demanded for stabilization of the separation effect. Designing the control system, knowledge on hydrocyclone dynamics and the transitional behaviour is necessary. To simulate hydrocyclone dynamics, the transport balance considering slip velocity and turbulent particle diffusivity was used. The transitional behaviour of a 40 mm hydrocyclone at special operating conditions has been computed numerically. The following scenario was simulated: a water hydrocyclone at t = 0 is suddenly fed with a 200 g/l-suspension. The transitional period until the concentration equilibrium of all fractions is reached, takes about 2.5 s. Partition curves simulated inside the transitional period indicate a maximum. The major objective of hydrocyclone modelling is estimation of the separation in form of the partition curve. The physics of separation is highly complex because of the turbulent multiphase flow in the apparatus. Basis of modelling is the description of cyclone flow with the Navier–Stokes equations for a suspension and the calculation of the separation with the transport equation. For modelling simplifications are necessary without neglecting the essential physics. Experience show that the separation result tolerates more simplification of the flow model as of the particle transport model.

Stationary concentration establishment in the growing or evaporating droplet of ideal binary solution

The establishment of stationary solution concentration in a growing or evaporating droplet of an ideal binary solution (binary droplet) placed in a vapor mixture of constituting substances and passive gas is described analytically. Relations defining time dependences of solution concentration in a droplet, the number of molecules of each constituting component, and droplet radius are derived at known parameters of the vapor-gas mixture and the initial composition of a binary droplet. The results of calculations of time dependences of aforementioned values are reported for several variants of the initial composition of a droplet and a vapor mixture.

Red Queen strange attractors in host–parasite replicator gene-for-gene coevolution

We study a continuous time model describing gene-for-gene, host–parasite interactions among self-replicating macromolecules evolving in both neutral and rugged fitness landscapes. Our model considers polymorphic genotypic populations of sequences with 3 bits undergoing mutation and incorporating a ‘‘type II’’ non-linear functional response in the host–parasite interaction. We show, for both fitness landscapes, a wide range of chaotic coevolutionary dynamics governed by Red Queen strange attractors. The analysis of a rugged fitness landscape for parasite sequences reveals that fittest genotypes achieve lower stationary concentration values, as opposed to the flattest ones, which undergo a higher stationary concentration. Our model also shows that the increase of parasites pressure (higher self-replication and mutation rates) generically involves a simplification of the host–parasite dynamical behavior, involving the transition from a chaotic to an ordered coevolutionary phase. Moreover, the same transition can also be found when hosts ‘‘run’’ faster through the hypercube. Our results, in agreement with previous studies in host–parasite coevolution, suggest that chaos might be common in coevolutionary dynamics of changing self-replicating entities undergoing a host–parasite ecology.

Effect of uroguanylin on potassium and bicarbonate transport in rat renal tubules

The effect of uroguanylin (UGN) on K+ and H+ secretion in the renal tubules of the rat kidney was studied using in vivo stationary microperfusion. For the study of K+ secretion, a tubule was punctured to inject a column of FDC-green-colored Ringer's solution with 0.5 mmol KCl/L+/-10(-6) mol UGN/L, and oil was used to block fluid flow. K+ activity and transepithelial potential differences (PD) were measured with double microelectrodes (K+ ion-selective resin vs. reference) in the distal tubules of the same nephron. During perfusion, K+ activity rose exponentially, from 0.5 mmol/L to stationary concentration, allowing for the calculation of K+ secretion (JK). JK increased from 0.63+/-0.06 nmol.cm-2.s-1 in the control group to 0.85+/-0.06 in the UGN group (p<0.01). PD was -51.0+/-5.3 mV in the control group and -50.3+/-4.98 mV in the UGN group. In the presence of 10(-7) mol iberiotoxin/L, the UGN effect was abolished: JK was 0.37+/-0.038 nmol.cm-2.s-1 in the absence of, and 0.38+/-0.025 in the presence of, UGN, indicating its action on maxi-K channels. In another series of experiments, renal tubule acidification was studied, using a similar method: proximal and distal tubules were perfused with solutions containing 25 mmol NaHCO3/L. Acidification half-time was increased both in proximal and distal segments and, as a consequence, bicarbonate reabsorption decreased in the presence of UGN (in proximal tubules, from 2.40+/-0.26 to 1.56+/-0.21 nmol.cm-2.s-1). When the Na+/H+ exchanger was inhibited by 10(-4) mol hexamethylene amiloride (HMA)/L, the control and UGN groups were not significantly different. In the late distal tubule, after HMA, UGN significantly reduced JHCO3-, indicating an effect of UGN on H+-ATPase. These data show that UGN stimulated JK+ by acting on maxi-K channels, and decreased JHCO3- by acting on NHE3 in proximal and H+-ATPase in distal tubules.