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Alternating magnetic fields provide a comfortable means for non-intrusive flow control in conductive fluids. However, despite a long history of applications in metallurgy and crystal growth, detailed investigation of the practically important transitional and turbulent flow regimes has become possible only in the last dozen years. The present review gives an overview of this topic with focus on recent experimental and numerical studies of the flow driven by rotating and traveling magnetic fields. We discuss the three-dimensional, instantaneous flow structure as well as the resulting average transport properties for a broad range of parameters, including the superposition of both field types. In addition to the ideal case, the effect of a misalignment of the field with respect to the container axis will be considered, too.

Das Bürogebäude Berliner Bogen mit einer BGF von ca. 52000 m� und Außenabmessungen von ca. 140 m x 70 m wird in städtebaulich zentraler Lage am Berliner Tor in Hamburg errichtet. Im 2. UG des insgesamt 11geschossigen Gebäudes war für die Hamburger Stadtentwässerung ein Mischwasserrückhaltebecken (MRB) zu integrieren. Das Haupttragwerk des Gebäudes besteht aus 22 korbbogenförmigen Stahlbögen, die im Abstand von 12,5 m angeordnet sind. Sie liegen außerhalb der wärmegedämmten Gebäudehaut und tragen zusätzlich zu der Belastung aus Wind, Schnee und Eigengewicht der Glasfassade auch Teile der Gebäudelasten. Für die Zuführung des Abwassers wurde ein ca. 550 m langes Anschlußsiel im Vortriebsverfahren unter schwierigsten Bedingungen aufgefahren.

Principal cells of the Malpighian tubule of the yellow fever mosquito were studied with the methods of two-electrode voltage clamp (TEVC). Intracellular voltage (Vpc) was −86.7 mV, and input resistance (Rpc) was 388.5 kΩ (n= 49 cells). In six cells, Ba2+(15 mM) had negligible effects on Vpc, but it increasedRpcfrom 325.3 to 684.5 kΩ (P< 0.001). In the presence of Ba2+, leucokinin-VIII (1 μM) increased Vpcto −101.8 mV (P< 0.001) and reduced Rpcto 340.2 kΩ (P< 0.002). Circuit analysis yields the following: basolateral membrane resistance, 652.0 kΩ; apical membrane resistance, 340.2 kΩ; shunt resistance (Rsh), 344.3 kΩ; transcellular resistance, 992.2 kΩ. The fractional resistance of the apical membrane (0.35) and the ratio of transcellular resistance and Rsh(3.53) agree closely with values obtained by cable analysis in isolated perfused tubules and confirm the usefulness of TEVC methods in single principal cells of the intact Malpighian tubule. Dinitrophenol (0.1 mM) reversibly depolarizedVpcfrom −94.3 to −10.7 mV (P< 0.001) and reversibly increased Rpcfrom 412 to 2,879 kΩ (P< 0.001), effects that were duplicated by cyanide (0.3 mM). Significant effects of metabolic inhibition on voltage and resistance suggest a role of ATP in electrogenesis and the maintenance of conductive transport pathways.

The omission of sodium from the serosal incubation fluid in isolated frog skins inhibits transcellular Na transport. By the use of intracellular recording with microelectrodes, it has been demonstrated that this inhibition is associated with an increase of the basolateral membrane resistance, resulting in a depolarization of the short-circuited cells. This depolarization in turn accounts for the reduction of Na entry across the apical border. The resistance changes across the outer (apical) border are small in magnitude and unrelated to the inhibition of transcellular transport. The origin of the increase in basolateral membrane resistance, presumably due to decrease of K permeability, is unclear. These data do not support the hypothesis that intracellular Ca regulates the resistance of the apical and basolateral membranes.

The effect of the diterpene, forskolin, on pathways for conductive Cl- transport was analyzed using isolated skins of Bufo viridis. Forskolin did not stimulate the voltage-activated Cl- movement from mucosa to serosa; the Lorentzian component in the power density spectrum, which was present at serosa positive clamp potentials under control conditions, decreased significantly. The observation that stimulation of cytosolic adenosine 3'-5'-cyclic monophosphate (cAMP) by forskolin has no effect on the voltage-activated Cl- transport argues against control of this pathway by cAMP. Our data further demonstrate that the forskolin-activated Cl- conductive pathway is also permeable for NO3-. This pathway was studied in absence of mucosal Cl-, which eliminates Cl- movement through the voltage-activated pathway. With SO4(2-) and Cl- on the mucosal and serosal sides, respectively, this forskolin-induced pathway displayed a linear current-voltage relationship. The associated Lorentzians increased at serosa negative clamp potentials. Transepithelial current and plateau value of the Lorentzian were related by a quadratic function, which suggests voltage-independence of number and open-close probability of these conductance sites. Morphological sites for voltage-activated and forskolin-induced conductive Cl- transport remain to be identified.

Summary In studies of apical membrane current-voltage relationships, in order to avoid laborious intracellular microelectrode techniques, tight epithelia are commonly exposed to high serosal K concentrations. This approach depends on the assumptions that high serosal K reduces the basolateral membrane resistance and potential to insignificantly low levels, so that transepithelial values can be attributed to the apical membrane. We have here examined the validity of these assumptions in frog skins (Rana pipiens pipiens). The skins were equilibrated in NaCl Ringer's solutions, with transepithelial voltageVt clamped (except for brief perturbations ?Vt) at zero. The skins were impaled from the outer surface with 1.5m KCl-filled microelectrodes (Rel>30 MO). The transepithelial (short-circuit) currentli and conductancegt=-?It/?Vt, the outer membrane voltageVo (apical reference) and voltage-divider ratio (Fo=?Vo/?Vt), and the microelectrode resistanceRel were recorded continuously. Intermittent brief apical exposure to 20 µm amiloride permitted estimation of cellular (c) and paracellular (p) currents and conductances. The basolateral (inner) membrane conductance was estimated by two independent means: either from values ofgi andFo before and after amiloride or as the ratio of changes (-?Ic/?Vi) induced by amiloride. On serosal substitution of Na by K, within about 10 min,Ic declined andgt increased markedly, mainly as a consequence of increase ingp. The basolateral membrane voltage (Vi(=-Vo) was depolarized from 75±4 to 2±1 mV [mean±sem (n=6)], and was partially repolarized following amiloride to 5±2 mV. The basolateral conductance increased in high serosal K, as estimated by both methods. Essentially complete depolarization of the basolateral membrane and increase in its conductance in response to high [K] were obtained also when the main serosal anion was SO4 or NO3 instead of Cl. On clampingVt over the range 0 to +125 mV in K2SO4-depolarized skins, the quasi-steady-stateVoVt relationship was linear, with a mean slope of 0.88±0.03. The above results demonstrate that, in a variety of conditions, exposure to high serosal K results in essentially complete depolarization of the basolateral membrane and a large increase in its conductance.

Summary Microelectrodes were used to investigate the effect of 0.5mm mucosal lanthanum (La3+) on the intracellular potential and the resistance of outer and inner isolated frog skin (Rana esculenta) cell membranes. Under short-circuit conditions, the transapical membrane potentialVosc (mean value=-65.4±3.2 mV, inside negative) hyperpolarized to -108.7±2.3 mV in control skins, after addition of the sodium blocker amiloride. Current-voltage curves for the outer and inner membranes were constructed from the amiloride-inhibitable current versus the outer membrane potentialVo or the inner membrane potentialVt. The outer, and to a lesser degree the inner, membrane showed a characteristic nonlinearity with two slope resistances. Addition of La3+ to the outer medium increased the short-circuit current to 190% of the control value.Vosc concomitantly changed to -28±3.5 mV and outer and inner membrane resistances fell, considerably attenuating the nonlinearity seen in control skins. La3+ is suggested to raise the conductance by its effect on the surface potential. A secondary long-term inhibitory effect of La3+ on short-circuit current has been observed. It is ascribed to the penetration of La3+ into the sodium channels.

Summary Intracellular Na+, K+, and Cl− activities (aNai,aKi,aCli) and transapical membrane potentials (Vo) were measured with liquid ion-exchanger and open-tip microelectrodes in isolated short-circuited frog skins (R. pipiens) incubated at 23°C in normal amphibian Ringer's solution. Under control conditionsaNai=14±3mm,aKi=132±10mm andaCli=18±3mm (sd). The value ofaCli is 4.4 times the value corresponding to electrochemical equilibrium for this ion. Thus, Cl− is actively accumulated by epithelial cells of the frog skin. Shortly after addition of amiloride (2–5 μm) to the apical bathing medium,aKi,aNai, andaCli were essentially unchanged althoughVo had hyperpolarized by about 30–40 mV. During long-term exposure to amilorideaKi andaCli did not change significantly,Vo depolarized by about 16 mV from the maximal value andaNai decreased to 8±3mm. Immediately after exposure to amiloride the transmembrane driving force for Na+ increased from 124 to 154 mV. During further exposure to amiloride, despite changes in bothVo andaNai, this driving force remained virtually constant. SinceIsc during this period was close to zero, it is suggested that the observed driving force for Na+ under these conditions approximates the maximal driving force generated by the Na+−K+ ATP-ase pump in the basolateral cell membrane.

Abstract.: The pathway for the voltage-activated chloride current across isolated toad skin was analyzed using a scanning 2D-vibrating voltage probe technique, which permits discrimination of local current peaks if their origins are more than 50 μm apart. The epithelium was separated from the corial connective tissue after enzymatic digestion with collagenase. Cl− current was activated by voltage clamping the transepithelial potential to 60–100 mV, serosa positive. Activated inward current was between 85 and 450 μA/cm2. In more than 25 tissue areas of 150 × 100 μm from 10 animals, which were automatically scanned with the vibrating probe, between 0 and 4 peaks of elevated local current (up to 800 μA/cm2) could be identified in individual fields. The density of current peaks, which were generally located at sites of mitochondria-rich (MR) cells, was less than 10% of the density of microscopically identified MR cells. The total current across individual sites of elevated conductance was 3.9 ± 0.6 nA. Considering the density of peaks, they account for 17 ± 2.5% of the applied transepithelial clamping current. The time course of current activation over previously identified conductive sites was in most cases unrelated to that of the total transepithelial current. Moreover, initially active sites could spontaneously inactivate. The results indicate that detection of elevated current above some MR cells is not sufficient to verify these cells as the pathway for transepithelial voltage-activated Cl− current. Since the major fraction of activated current is apparently not associated with a route through MR cells, channel-like structures in the tight junctions of the paracellular pathway must be considered as an alternative possibility. Current peaks over MR cells could be due to high density of such sites in tight junctions between MR and surrounding principal cells. Improvement of the spatial resolution of the vibrating probe is required to verify this view.

Abstract.: The regulation of the voltage-activated chloride current conductance (G Cl ) in toad skin was investigated by the use of the SH reagents N-ethylmaleimide (NEM) and p-chloro-mercuricbenzenesulfonic acid PCMBS. This anion pathway is controlled by a voltage-sensitive gating regulator. Mucosal application of NEM decreased the voltage-activation in a time and concentration dependent manner, half-maximal inhibition being exerted at a concentration of 30 μm within 20 min. At concentrations higher than 100 μm, the voltage-activated G Cl was near-completely and irreversibly inhibited in less than 10 min. Resting, deactivated conductance was essentially unaffected. NEM had no effect on active sodium transport (measured as I sc ) under conditions, which fully dissipated the voltage-activated G Cl . After complete inhibition of the voltage-activated G Cl with NEM, chloride conductance could still be stimulated by CPT-cAMP as in control tissues. Under these conditions, NEM at concentrations above 1 mm decreased G Cl reversibly. Mucosal application of PCMBS at 500 μm inhibited the activated conductance by 35%, which was slightly reversible. Inhibition of voltage-activated G Cl , which was observed after mucosal addition of the membrane-impermeable NEM analogue, eosin-5-maleimide, was completely reversible after washout. This suggests that the binding site for the maleimide is not accessible from the external face of the apical membrane. Brief application of NEM at lower concentrations (1–3 min, ≤100 μm) led to partial inhibition of G Cl , followed by occasionally complete recovery upon washout of NEM. Recovery of voltage-activated G Cl was progressively attenuated and eventually disappeared after subsequent brief applications of NEM. This could reflect recruitment of permeation/control sites from a finite pool. The data are discussed in the frame of a working model for the voltage-activated Cl−-pathway, that contains two principle components, i.e., an anion-selective permeation path which is controlled by regulatory protein(s).

1. The effects of the phosphodiesterase inhibitors theophylline and isobutylmethylxanthine (IBMX) on baseline and voltage‐activated Cl‐ conductance (gCl) of toad skin were compared with those of the potent 2‐chlorophenylthio analogue of cAMP (CPT‐cAMP). 2. Using intact and split skins of Bufo viridis we confirmed that theophylline and IBMX raised the voltage‐activated gCl with a pattern identical to that seen under control conditions. This effect was small or missing if gCl was already high in the control. 3. CPT‐cAMP, in contrast, increased the Cl(‐)‐specific conductance by up to 6 mS cm‐2 at short circuit. The characteristic time‐dependent, slow activation of gCl by serosa‐positive clamp potentials was completely lost under these conditions. 4. Coinciding with the loss of voltage activation of gCl the plateau value of the Lorentzian component of fluctuation in current at serosa‐positive clamp potentials decreased by almost 50%. The corner frequencies were not notably different. 5. After CPT‐cAMP, the sigmoidal voltage‐conductance relation that is characteristic of control conditions or after theophylline disappeared; the patterns were variable and incompatible with voltage activation. 6. The voltage‐activated gCl under control conditions and with theophylline was blocked by mucosal NO3‐, I‐ or SCN‐, the last two being almost equally effective. In the presence of CPT‐cAMP, mucosal NO3‐ had minimal influence on tissue conductance, whereas the effects of I‐ and SCN‐ were essentially unchanged. Br‐ on the mucosal side could substitute for Cl‐ under all conditions. 7. The results suggest that protein phosphorylation by supramaximal concentrations of cAMP induces maximal conductance through anion‐specific routes, while the voltage sensitivity of this pathway is lost. The effects of theophylline and IBMX on the voltage‐activated Cl‐conductance of toad skin cannot be explained solely by inhibition of the phosphodiesterase.

PAC measurements on the 4.43 MeV12C(2+) state on recoil in magnetized iron at velocitiesvion=2.1v0, 6.0v0, 7.4v0 yield integral precession angles of ?=+0.72(18), +0.94(16) and +0.71(18) mrad, respectively. The results supplementary to existing precession data are interpreted by a distribution of C5+ ions implying a K-shell polarization of ?28% and an effective charge larger than measured after emergence from the solid. The low-velocity precession tends to disagree with the empirical law of linear relationship between transient field and ion velocity. The presence of molecular orbital effects is discussed.

Effects of the divalent heavy metal ions Cd2+, Co2+, Cu2+, Mn2+, Ni2+, and Zn2+ on pathways for sodium and chloride were assessed on isolated amphibian skin (Rana temporaria andesculenta, Bufo marinus andviridis). It was observed that these agents, in addition to the previously reported stimulation of sodium transport, inhibit chloride-related tissue conductance (gCl) in frog skin with spontaneously highgCl when added to the external incubation medium. Serosal application was ineffective. Half-maximal inhibition ofgt occurred at approximately 0.2 mmol/l Ni2+ and Zn2+, 0.5 mmol/l Co2+ and Cd2+, and more than 3 mmol/l Mn2+. The onset of inhibition was rapid, steady state values being reached within 3 min; reversibility was complete with approximately similar time course. Cu2+, which could not be tested at concentrations above 0.1 mmol/l, had only minimal and poorly reversible effect ongCl. Skin ofBufo was virtually insensitive to these metal ions. Microelectrode determinations demonstrate that the decrease of conductance was restricted to a pathway distinct from the principal cells which show, on the contrary, increase of apical membrane conductance originating from stimulation of sodium permeability. The metal ions might be valuable for characterization of the pathway and the mechanism of transepithelial conductive chloride transport.

Homocellular regulation of K+ at increased transcellular Na+ transport implies an increase in K+ exit to match the intracellular K+ load. Increased K+ conductance, gK, was suggested to account for this gain. We tested whether such a mechanism is operational in A6 monolayers. Na+ transport was increased from 5.1±1.0 µA/cm2 to 20.7±1.3 µA/cm2 by preincubation with 0.1 µmol/l dexamethasone for 24 h. Basolateral K+ conductances were derived from transference numbers of K+, tK, and basolateral membrane conductances, gb, using conventional microelectrodes and circuit analysis with application of amiloride. Activation of Na+ transport induced an increase in gb from 0.333±0.067 mS/ cm2 to 1.160±0.196 mS/cm2 and tK was reduced to 0.22±0.01 from a value of 0.70±0.05 in untreated control tissues. As a result, gK remained virtually unchanged at increased Na+ transport rates. The increase in gb after dexamethasone was due to activation of a conductive leak pathway presumably for Cl-. Increased K+ efflux, IK, was a consequence of the larger driving force for K+ exit due to depolarization at an elevated Na+ transport rate. The relationship between calculated K+ fluxes and Na+ transport rate, measured as the Isc, is described by the linear function IK=0.624×INa-0.079, which conforms with a stoichiometry 2:3 for the fluxes of K+ and Na+ in the Na+/K+-ATPase pathway. Our data show that homocellular regulation of K+ in A6 cells is not due to up-regulation of gK.

Conductance of apical and basolateral membranes in short-circuited cultured renal distal cells (A6) was determined using microelectrodes. Epithelia were pre-incubated with 0.1 µmol/l dexamethasone in the presence of 4 µmol/l amiloride to prevent increase in apical Na+ entry. Omission of amiloride increased the ISC from 5.7 to 27.6 µA/cm2 due to the rise in apical membrane conductance from 21 to 595 µS/cm2. Apical fractional resistance decreased from 0.89 to 0.40 and cells depolarized from -52 to -4 mV. Basolateral membrane conductance, which was 320 µS/cm2 at partially inhibited transport, was not significantly altered during the first 2 min following establishment of high transport activity; it started to increase thereafter reaching a more than threefold higher value of 1324 µS/cm2 within 12 min. The gain cannot be explained by increase in partial K+ conductance. Disappearance of the conductance after reduction of basolateral Cl- or in the presence of the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)benzoate indicates a Cl- conductance, which appears to be activated by depolarization.

1. The dependency of the transmembranal potential differences upon the [Na] of the mucosal bathing solution was investigated in frog skin. Semilogarithmic linear correlations were obtained between [na]0 and the transepithelial potential difference (slope: 28‐4 +/‐ 1‐8 mV/dec [Na]0), the potential differences across the outer and the inner membrane under open circuit conditions (slope: 33‐4 +/‐ 1‐8 and 4‐8 +/‐ 1‐5 mV/dec [Na]0, respectively) and the intracellular potential under short circuit conditions (slope: 33‐3 +/‐ 3‐4 mV/dec [Na]0). 2. No difference could be observed between skins incubated in Cl‐ or SO4‐Ringer. 3. The results are not in accordance with the Koefoed‐Johnsen & Ussing hypothesis. Neither the polarity of the postulated Na electrode at the outer border could be obtained nor the expected slope of the dependency between potential gradient and [Na] of the mucosal bathing solution. 4. Current recirculation through paracellular shunt pathways is suggested to explain the deviation, at least in part. In addition, the I‐R‐drop resulting from Na entry across the outer border might account for part of the changes of potential gradients. 5. Under all conditions, Na uptake occurs energetically downhill, but permeability changes of the outer border must be postulated to explain the observed dependency of net Na transport upon [Na]0.

1. Intracellular potentials from frog and toad skins were measured to identify rheogenic components of active Na transport across the basolateral membrane. Transcellular current flow and associated R . I‐drops were blocked with amiloride or Na‐free mucosal solution. 2. The potential difference across the basolateral membrane was found to be hyperpolarized by 18 . 5 +/‐ 1 . 6 mV above the steady‐state value immediately after blockage of apical membrane Na conductance. The hyperpolarization disappeared within 15‐‐25 min. 3. The final steady‐state value of 93 . 1 +/‐ 2 . 5 mV was slightly less than reasonable estimates of the K equilibrium potential. 4. The hyperpolarization could not be observed 3‐‐5 min after addition of ouabain (10(‐4) M). 5. Both the magnitude and duration of the hyperpolarization correlate directly with the amount of Na accumulated in the intracellular space. 6. A fraction of the intracellular potential was missing when Na transport was re‐established after long term blockage of apical membrane Na entry. It reappeared within 10‐‐20 min. 7. It is suggested that the hyperpolarization is due to rheogenic Na transport across the basolateral membranes. This transport mechanism may contribute some 30‐‐50% of the electrical gradient for passive Na entry across the mucosal membrane. 8. A coupling ratio between pumped fluxes of Na and K of about 2:1 is calculated from the data.

In this paper a special class of experimental design problems is looked up which occurusing the family of shrunken least squares estimators. Basing on compromise oriterin a reference to classical problems of experimental design for least squaros estimators is given. Optimal designs for compromise criteria have some robustness properties W.r.t. variatin of asumed prior knowledge about response surface.

In the present paper we mean by weak and fuzzy prior knowledge that we can specify some function of a certain quadratic form of the unknown parameters of the setup, which function is derived from common prior information concerning the unknown response surface. We look for estimators (especially shrunken LSE and preliminary test stimators), which can utilize this prior knowledge to decrease the minimax risk for squared loss.

Signal transduction through phosphoinositide 3-OH kinase (PI 3-kinase) has been implicated in the regulation of lymphocyte adhesion mediated by integrin receptors. Cellular phosphorylation products of PI 3-kinases interact with a subset of pleckstrin homology (PH) domains, a module that has been shown to recruit proteins to cellular membranes. We have recently identified cytohesin-1, a cytoplasmic regulator of beta2 integrin adhesion to intercellular adhesion molecule 1. We describe here that expression of a constitutively active PI 3-kinase is sufficient for the activation of Jurkat cell adhesion to intercellular adhesion molecule 1, and for enhanced membrane association of cytohesin-1. Up-regulation of cell adhesion by PI 3-kinase and membrane association of endogenous cytohesin-1 is abrogated by overexpression of the isolated cytohesin-1 PH domain, but not by a mutant of the PH domain which fails to associate with the plasma membrane. The PH domain of Bruton's tyrosine kinase (Btk), although strongly associated with the plasma membrane, had no effect on either membrane recruitment of cytohesin-1 or on induction of adhesion by PI 3-kinase. Having delineated the critical steps of the beta2 integrin activation pathway by biochemical and functional analyses, we conclude that PI 3-kinase activates inside-out signaling of beta2 integrins at least partially through cytohesin-1.

Elevated levels of metallothionein (MT) found in rapidly growing tissues such as neonatal liver and various types of human tumors have suggested a role for MT in cell proliferation. To further explore this possibility we investigated the concentration of MT in human colonic cancer (HT-29) cells at different stages of proliferation by means of immunocytochemistry and competitive binding. MT is increased in subconfluent proliferating cells relative to growth-inhibited confluent cells, much as it is in growing tissues. Cycling cells synchronized with compactin, an inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, revealed an oscillation of cytoplasmic MT that reached a maximum in successive late G1 phases and at the G1/S transition. Individual phase of the cell cycle were assessed by [3H]thymidine incorporation and by immunofluorescence employing an antibody that detects a nuclear antigen associated with proliferation. An enzyme-linked immunosorbent assay was used to quantify the relative amounts of MT in homogenate supernatants of HT-29 cells. A 2- to 3-fold increase in MT in actively proliferating cells and the regulation of the protein during the mitotic cell cycle point to a physiological role for MT in cellular proliferation and suggest that it may also serve as a proliferation marker.

Abstract: A new approach for the determination of elemental uranium in uranium bearing ore, using high resolution gamma-ray spectrometry, was applied. Using a variant of the enrichment technique an agreement of better than 1% has been obtained between gamma-ray measurement results and a certified value obtained by other analytical methods. For the calibration of the gamma-ray spectrometer uranium reference samples have been used which are made available jointly in Europe and the USA as Certified Reference Materials for Gamma-Ray Spectrometry (EC NRM 171 and NBS SRM 969, respectively). The measured ore has been put in a special designed container which ensured in all directions seen from the radiation window an uniform degree of infinite thickness of about 95%. The results can be taken as an example for the applicability of gamma-ray spectrometry when high accuracy is required and under conditions were homogeneously distributed elemental uranium is embedded in larger amount of matrix material.

A thin section of a fibre system in space is its subset located between two parallel planes The orthogonal projection of a thin section of a statinary spatial fibre process produces a stationary planar fibre jprocess.Its intensity as a function of direction of the section is refered to as rose of sections. With its intensities and the distributions of directions of both the processes can be calculated one from the others. This paper follows the ideas of MECKE/SOTOYAN und MECKE/ NAGEL

Abstract:  The effects of adrenoceptor agonists on the transepithelial Cl– conductance (G Cl) in the skin of several amphibian species, both toads and frogs, were studied. Epinephrine (Epi) from the serosal side selectively and reversibly inhibited the voltage-activated G Cl in toad skin and the short-circuit G Cl in frog skin. The main effects of activation of the adrenoceptors must reside in the skin epithelium and not in the glands, since measurements were made both from intact skins and split epithelia with essentially the same results. Effective concentrations of Epi were variable among individual tissues. G Cl was reduced to 34±17% (n=46) with 1 µmol/l Epi, but in some tissues 0.1 µmol/l inhibited more than 80% of G Cl, whereas some preparations were little influenced at >3 µmol/l Epi. The affected receptor type was identified by the use of the α1-agonist phenylephrine, which mimicked the response of Epi at concentrations above 30 µmol/l, whereas the α2-agonists xylazine and iodoclonidine had no effect at supramaximal concentrations. Prazosin, a specific α1-antagonist, reduced or eliminated the inhibition by Epi, but the response pattern suggests a low affinity. The α2-antagonist yohimbine, at concentrations ≤0.3 µmol/l, had a minimal effect, but reduced the inhibition by Epi at concentrations of 1–10 µmol/l. This might indicate affinity to α1-adrenoceptors in amphibian skin. Activation of β-adrenoceptors by isoproterenol (0.1–5 µmol/l) led to a transient increase of the baseline inactivated component of G Cl with a slight reduction of the voltage-activated G Cl at the higher concentrations, but the inhibitory effect of Epi was not altered. Epi, on the other hand, neither prevented nor reversed the induction of a voltage-insensitive G Cl in toad skin caused by application of cAMP at supramaximal concentrations (>100 µmol/l CPT-cAMP). Preincubation of the serosal medium with Ca2+-free solution (in the presence of 2 mmol/l EGTA) for extended periods of time (>30 min) eliminated the response to Epi. It is concluded that α1-adrenoceptors participate in the physiological control of voltage-activated Cl– conductance in amphibian skin epithelium via modulation of intracellular Ca2+, presumably by efflux from intracellular stores.

An NAD(P)-dependent malic enzyme with a specific activity of 40.6 mumol of NADH/min/mg of protein and an isoelectric point of 5.4 was purified to apparent homogeneity from canine small intestinal mucosal mitochondria. The purification procedure employed ammonium sulfate fractionation, Sepharose CL 6B gel filtration, chromatography on DEAE-cellulose to remove the interfering malate dehydrogenase, and affinity chromatography on 2',5'-ADP-Sepharose and NAD-agarose to take advantage of the dual coenzyme specificity. Antibody prepared from the purified enzyme produced a single peak upon cross-rocket immunoelectrophoresis against the mitochondrial sonicate. Continuous polyacrylamide gel electrophoresis showed NAD and NADP activity co-migrating with the native protein band. A single band of protein having an apparent Mr = 62,000 was seen on sodium dodecyl sulfate electrophoresis. At pH 7.3, gel filtration revealed a single peak of activity with NAD and NADP corresponding to an apparent Mr = 282,000. Gradient gel polyacrylamide electrophoresis at pH 9.0 indicated an additional broad band of activity corresponding to a Mr = 141,000. Under physiological conditions therefore the protein appears to exist as a tetramer of Mr = 282,000 composed of four equal subunits, whereas at elevated pH values during electrophoresis, partial dissociation to a dimeric species occurs.

Transmembrane electrical parameters of the epithelial cells in short-circuited turtle bladders were measured to determine whether those cells participating in Na reabsorption also participate in electrogenic transepithelial acidification and alkalinization. Amiloride-induced increases in intracellular potential (Vsca), apical fractional resistance (FRa), and concomitant decreases in short-circuit current (Isc) denote the participation of the impaled cells in Na reabsorption. In bladders from postabsorptive turtles, amiloride increased Vsca by -45 mV, increased FRa by 37%, and decreased Isc from 36 to -10 microA/cm2. In bladders from NaHCO3-loaded turtles, amiloride increased Vsca by -21 mV, FRa by 21%, and decreased Isc from 22 to 0 microA/cm2. Neither the subsequent inhibition of the negative acidification current in postabsorptive bladders, nor stimulation of positive alkalinization current in bladders from NaHCO3-loaded turtles was associated with any transmembrane electrical change that could be attributed to changes in those transport processes. It is concluded that the electrogenic luminal acidification and alkalinization processes of the turtle bladder are not produced by, or electrically coupled to, those cells that are involved in Na reabsorption.

The new complexes (OC)5MSC(X)Y (8-5) are obtained by reaction of (OC)5MTHF (1) [M = Cr (a), Mo (b), W (c)] with different thiocarbonate, thiourea and thiourethane ligands S = C(X)Y (2a-h). Structure and bonding conditions are discussed on the basis of their IR and 13C NMR spectra. From the spectroscopic data the ligands 2a-h can be arranged in a row with increasing π-acceptor properties.

The effect of aminoperimidine (AP) on transepithelial Na+ transport and Cl– conductance (GCl) of isolated amphibian skin (Bufo viridisand Rana esculenta)was analyzed using transepithelial and intracellular electrophysiological techniques. AP, applied at concentrations between 30 and 100 µMfrom the mucosal side, stimulated Na+ transport rapidly and reversibly by more than 30% of the control value due to an increase in apical membrane Na+ permeability. Influence of AP on basolateral membrane conductance and effective driving force for Na+ were negligible. Voltage-activated GCl of toad skin, but not the resting, deactivated conductance, as well as spontaneously high GCl in frog skin was rapidly inhibited by AP in a concentration-dependent manner. The half-maximal inhibitory concentration of 20 µMis the highest hithero reported inhibitory power for GCl in amphibian skin. The effect of AP on GCl was slowly and incompletely reversible even after brief exposure to the agent. Serosal application of AP had similar, albeit delayed effects on both Na+ and Cl– transport. AP did not interfere with the Cl– pathway after it was opened by 100–300 µMCPT-cAMP, a membrane-permeable, nonhydrolyzed analogue of cAMP. Inhibition of the voltage-activated GCl by AP was attenuated or missing when AP was applied during voltage perturbation to serosa-positive potentials. Since AP is positively charged at physiological pH, it suggests that the affected site is located inside the Cl– pathway at a certain distance from the external surface. AP affects then the Na+ and Cl– transport pathways independent of each other. The nature of chemical interference with AP, which is responsible for the influence on the transport of Na+ and Cl–, remains to be elucidated.

Confluent monolayers of the cultured renal distal tubule cell line (A6) were impaled with microelectrodes under short-circuit conditions. Specific membrane conductances were calculated from equivalent circuit equations. Transport properties of the apical and basolateral membranes were investigated during control conditions and short-term increases in basolateral potassium concentration [K+] from 2.5 to 20 mmol/l, with or without 0.5 mmol/l Ba2+ at the basolateral side. As in most other epithelia, the apical membrane represents the major resistive barrier. Transcellular, apical and basolateral membrane conductances (gc, go and gi respectively), obtained from 22 acceptable microelectrode studies, averaged 61, 80 and 292 µS/cm2, respectively. There was a highly significant correlation between short-circuit current (Isc) and go, whereas gi was unrelated to Isc. The Isc, which averaged 4.1 µA/cm2, was almost completely blocked by amiloride. This was associated with fast hyperpolarization; the intracellular potential (Vsc) increased from -69 to -83 mV and the fractional apical resistance rose to nearly 100%. Using the values of Vsc during amiloride at normal and high [K+], an apparent transference number for K+ at the basolateral membrane of 0.72 can be calculated. This value corresponds with the decrease in gi to about 25% of the control values after blocking the K+ channels with Ba2+. The nature of the remaining conductance is presently unclear. The cellular current decreased during high [K+] and Ba2+, in part resulting from reduction of the electrochemical gradient for apical Na+ uptake due to the depolarization. In addition, go decreased to less than 40%, which is considerably lower than predicted by the constant-field equation; this might indicate voltage sensitivity of the apical Na+ permeability.

The effect on transepithelial Na transport of tizolemide was investigated in isolated frog skin (Rana temporaria). It was found that tizolemide (2–5 mM, serosal side) decreased transepithelial Na transport (measured as short circuit current and as net sodium flux) within 60 min to 25–40% of the control level resulting from reduction of the unidirectional sodium influx. Intracellular recording with microelectrodes revealed that these changes were associated with depolarization of the intracellular space to less than 40% of the control values (averaging -71.7±5.1 mV) which is a consequence of a decrease in conductance of the basolateral border to about 25% of the control values. The conductance of the apical border was only slightly reduced. It is suggested that tizolemde blocks the partial conductance of potassium at the basolateral border which secondarily diminishes trans-epithelial Na transport due to a decrease of the driving force for apical border Na entry. A certain degree of inhibition of the Na-K-ATPase by tizolemide cannot be excluded. When vasopressin (ADH) was added to frog skin after treatment with tizolemide, the response was markedly reduced compared to that of untreated control preparations. Under these conditions, the conductance of the basolateral border increased while the apical border remained little influenced by the hormone — opposite to the response of frog skins under control conditions. It is concluded that the mode of action of ADH is more complex than has been recognized hitherto and includes effects at the basolateral border.

Abstract: Predatory behavior ofMedetera aldrichii Wheeler (Dolichopodidae) larvae was observed in bark-Lucite sandwiches infested with immature broods of the bark beetle preyDendroctonus pseudotsugae Hopkins (Scolytidae). Predator larvae could not penetrate unmined phloem or prey galleries tightly packed with frass, but moved through loose frass and bark-Lucite interspaces formed when the mined inner bark dried. At high prey densities interspace formation and gallerly contiguity enabled the predator to move freely and attack several prey in rapid succession. At low prey densities the predator was frequently isolated from prey by impenetrable strips of phloem. Predator larvae maintained singly in small plastic arenas consumed an average of 14.7 immature prey, but required only 6.2 prey when reared exclusively on large prey.

Summary Knowledge of the voltage dependencies of apical and basolateral conductances is important in determining the factors that regulate transcellular transport. To gain this knowledge it is necessary to distinguish between cellular and paracellular currents and conductances. This is generally done by sequentially measuring transepithelial current/voltage (It/Vt) and conductance/voltage (gt/Vt) relationships before and after the abolition of cellular sodium transport with amiloride. Often, however, there are variable time-dependent and voltage-dependent responses to voltage perturbation both in the absence and presence of amiloride, pointing to effects on the paracellular pathway. We have here investigated these phenomena systematically and found that the difficulties were significantly lessened by the use of an intermittent technique, measuringIt andgt before and after brief (<10 sec) exposure to amiloride at each setting ofVt.I/V relationships were characterized by these means in frog skins (Rana pipiens, Northern variety, andRana temporaria). Cellular current,Ic, decreased with hyperpolarization (larger serosa positive clamps) ofVt. DerivedIc/Vt relationships betweenVt=0 and 175 mV (serosa positive) were slightly concave upwards. Because values of cell conductance,gc, remained finite, it was possible to demonstrate reversal ofIc. Values of the reversal potentialV' averaged 156±14 (sd,n=18) mV. Simultaneous microelectrode measurements permitted also the calculation of apical and basolateral conductances,ga andgb. The apical conductance decreased monotonically with increasing positivity ofVt (andVa). In contrast, in the range in which the basolateral conductance could be evaluated adequately (Vt<125 mV),gb increased with more positive values ofVt (andVb). That is, there was an inverse relation betweengb and cellular current at the quasi-steady state, 10–30 sec after the transepithelial voltage step.

Abstract:  The possible participation of mitochondria-rich cells in transepithelial Na+ transport across frog skin under ”physiological conditions” (low apical [Na+], open circuited) was analysed by recording electrophysiological parameters from principal cells with intracellular microelectrodes and using measurement of Rb+ uptake into the epithelial cells from the serosal side via the Na+/K+-ATPase. It was observed that transport perturbation with amiloride induced changes in the apical potential difference and fractional apical resistance in principal cells, observations which are compatible with the notion that the essential fraction of transcellular current flow occurs across these cells. Amiloride-inhibitable uptake of Rb+ was also restricted to principal cells, the amount being about equivalent to the predicted rate of K+ recycling via the Na+/K+-ATPase. The results indicate that principal cells are responsible for transepithelial Na+ transport irrespective of the experimental conditions. Flow of Na+ across mitochondria-rich cells appears to be negligible.

The effect of loop diuretics on Cl transport was studied on an in vitro preparation of the bullfrog cornea. Bumetanide (10(-4) M) or furosemide (10(-3) M) added to the stromal solution decreased Cl transport measured as the short-circuit current (Isc) to values near zero. Concomitantly, transepithelial conductance (gt) decreased, whereas the intracellular potential (Vo) hyperpolarized and the fractional resistance of the apical membrane (fRo) increased. Substitution of SO4 for Cl in the tear-side solution led to prompt changes in Isc, gt, Vo, and fRo, characteristic of appreciable passive Cl movement across the apical membrane before and after inhibition. Epinephrine (10(-4) M) was similarly effective on apical membrane conductance in inhibited tissues as under control conditions, but the effective electromotive force for transepithelial Cl transport was reduced to approximately 25%. Intracellular Cl activity, measured with ion-selective microelectrodes, decreased so much that the difference in electrochemical Cl potential divided by the Faraday constant (delta mu Cl/F) was close to zero after inhibition of Isc by bumetanide. Apical Cl permeability remained essentially unchanged. Accordingly, loop diuretics inhibit Cl transport in the Cl-secreting cornea epithelium by blocking the Na-Cl symport without secondary apical effects, as believed for other Cl-reabsorbing epithelia.

We investigated the effect of forskolin on Cl- movements across the isolated epithelium of frog skin. With Cl- on both sides, forskolin (50 mumol/l) increased the transepithelial conductance considerably and elicited significant Cl- secretion. Establishing transepithelial Cl- gradients markedly increased the Cl- currents (ICl). During forskolin treatment, the power density spectra (PDS) of the fluctuation in transepithelial current contained a Lorentzian component that depended on the presence of Cl- in the bathing solutions. Mucosal as well as serosal diphenylamine-2-carboxylic acid (DPC; 1 mmol/l) partially depressed ICl as well as the Lorentzian noise component. Microelectrode recordings from cells involved in transepithelial Na+ absorption showed that forskolin activates gated Cl- channels in a cellular pathway in parallel with the Na+-transporting granulosum cells of the frog skin. The activation of the Cl- -dependent currents and Lorentzian noise was rather variable, and adaptation of the animals to solutions that contained 40 or 60 mmol/l NaCl increased the sensitivity to forskolin. In skins of salt-adapted animals, oxytocin (0.1 U/ml) also slightly activated the Cl- pathway. On the other hand, oxytocin and 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP; 1 mmol/l) were without effect in control skins.

An NAD(P)+-dependent ‘malic’ enzyme is shown to be present in mitochondria from small-intestinal mucosa. The intracellular location, activity and regulatory kinetic properties of the enzyme suggest that it participates in the major energy-producing pathway for net oxidation of glutamine-derived tricarboxylic acid-cycle intermediates.

It is shown that the convex polygons are uniquely determined (up to translation and reflection) by their covariograms. The covariogram can be represented by the ‘orientation-dependent chord length distribution', i.e. the distribution of the length of chords which are generated by random lines parallel to fixed directions. Thus the result contributes to answer Blaschke's question about the content of information comprised in chord length distributions.

Three different stereological methods for the determination of second-order quantities of planar fibre processes which have been suggested in the literature are considered. Proofs of the formulae are given (also by using a new integral geometric formula), relations between the methods are derived and the prerequisites are discussed. Furthermore, edge-corrected unbiased estimators for the second-order quantities are given.

Starting from the classical planar Voronoi tesselation for a stationary Poisson point process a model with random disturbance is introduced. While the Voronoi tesselation can be constructed with the perpendicular lines through the centres of the segments linking any pair of points of the generating point process we consider random translations (out of these centres) of the perpendicular lines. The cell to a point is then constructed as the intersection of the half-planes (defined by the perpendicular lines) containing this point - as it is done for the classical Voronoi model.Thus a stationary process of convex nonoverlapping polygons is obtained. For the typical polygon we prove formulae for mean area, perimeter and edge number. Since this model is not a tesselation of the plane it is interesting to investigate the "deficit area" (between the cells). In the present paper we calculate the mean deficit area per unit area and give results for a type of deficit triangles which occur instead of Voronoi nodes. A more sophisticated study of the deficit remains as an open problem.

Studies were done with isolated frog skin to determine the effects of 10(-4) M ouabain on the electrophysiological parameters of outer and inner barriers of the Na-transporting cells. Microelectrodes were used to impale the skins from the outer surface to determine the intracellular voltages (Vsco) under conditions of short-circuiting and under conditions where a voltage clamp was used to vary the transepithelial voltage, VT. From this, the electrical resistances of outer (Rfo) and inner (RI) barriers were estimated. In addition, the driving force for active transepithelial Na transport (ENa = E'1) was estimated from the values of VT when the Vo = 0 mV (Helman and Fisher. 1977. J. Gen. Physiol. 69: 571-604). Studies were done with skins bathed with the usual 2.4 meq/liter [K]i in the inner solution as well as with reduced [K]i of 0.5 and 0 meq/liter. Characteristically, the responses to ouabain could be described by an initial rapid phase (5-10 min) during which time the Ri was increased markedly and the E'1 was decreased from control values. Thereafter, during the slow phases of the response, the resistances of both outer and inner barriers increased continuously and markedly with time leading ultimately to essentially complete inhibition of the short-circuit current. Similar studies were done with skins exposed to 10(-4) M amiloride in the outer solution. Although estimates of Ri could not be obtained under these conditions, the effects on the Vsco and E'1 were similar to those observed for the Na-transporting skins. However, the magnitudes of the effects were less and relatively slower than observed for the Na-transporting skins. The results of these studies were analyzed within the context of a proposed electrical model that takes into account the observation that the magnitude of the voltage at the inner barrier appears to exceed the equilibrium potential for K especially when transepithelial Na transport is inhibited at the apical barrier of the cells.