Bidirectional Movement of γ-Aminobutyric Acid in Rat Spinal Cord Slices

Abstract: The bidirectional movement of GABA (γ-aminobutyric acid) was studied in slices of rat spinal cord which were incubated in small volumes of medium. The appearance in the medium of endogenous GABA and the disappearance from the medium of [¹⁴C]GABA were used to calculate the rates of unidirectional uptake and unidirectional release of GABA. Under these conditions, no net uptake of GABA was observed when slices were incubated in media containing concentrations of GABA as high as 25 μm . Elevated potassium (60 mm ) stimulated the unidirectional release of endogenous GABA from spinal cord slices by a calcium-dependent process. Ouabain (0.1 mm ) more than doubled the unidirectional release of endogenous GABA in a calcium-independent manner, while unidirectional uptake was inhibited by 44%. Nipecotic acid (1.0 mm ) stimulated unidirectional release and inhibited unidirectional uptake of GABA.     

The influence of framework design on the load-bearing capacity of laboratory-made inlay-retained fibre-reinforced composite fixed dental prostheses

Delamination of the veneering composite is frequently encountered with fibre-reinforced composite (FRC) fixed dental prosthesis (FDPs). The aim of this study is to evaluate the influence of framework design on the load-bearing capacity of laboratory-made three-unit inlay-retained FRC-FDPs. Inlay-retained FRC-FDPs replacing a lower first molar were constructed. Seven framework designs were evaluated: PFC, made of particulate filler composite (PFC) without fibre-reinforcement; FRC1, one bundle of unidirectional FRC; FRC2, two bundles of unidirectional FRC; FRC3, two bundles of unidirectional FRC covered by two pieces of short unidirectional FRC placed perpendicular to the main framework; SFRC1, two bundles of unidirectional FRC covered by new experimental short random-orientated FRC (S-FRC) and veneered with 1.5 mm of PFC; SFRC2, completely made of S-FRC; SFRC3, two bundles of unidirectional FRC covered by S-FRC. Load-bearing capacity was determined for two loading conditions (n=6): central fossa loading and buccal cusp loading. FRC-FDPs with a modified framework design made of unidirectional FRC and S-FRC exhibited a significant higher load-bearing capacity (p<0.05) (927±74 N) than FRC-FDPs with a conventional framework design (609±119 N) and PFC-FDPs (702±86 N). Central fossa loading allowed significant higher load-bearing capacities than buccal cusp loading. This study revealed that all S-FRC frameworks exhibited comparable or higher load-bearing capacity in comparison to an already established improved framework design. So S-FRC seems to be a viable material for improving the framework of FRC-FDPs. Highest load-bearing capacity was observed with FRC frameworks made of a combination of unidirectional FRC and S-FRC.     

Feeding and wounding responses in Hydra suggest functional and structural polarization of the tentacle nervous system

The nervous system of Hydra, a freshwater cnidaria, occurs as dispersed, or diffuse, nerve net throughout the animal. It is widely accepted that in a diffuse nervous system an external stimulus is conducted in all directions over the net. Here I report observations that hydra tentacles respond to feeding and wounding stimuli in a unidirectional manner. Upon contact of a tentacle with a brine shrimp larva during feeding, tissue on the proximal side of the point of contact contracted strongly, whereas tissue on the distal side contracted only very weakly. Feeding a tentacle to which a second tentacle was grafted to the proximal end in the reversed orientation showed that unidirectional conduction, once initiated, was blocked by the reversal of polarity, demonstrating that the distal to proximal polarity of tissue is crucial for unidirectional conduction. Unidirectional conduction was obtained also by mechanically pinching the tissue. The response of tentacles devoid of neurons examined was bidirectional, demonstrating that the nervous system is responsible for the unidirectional responses. These observations suggest that polarized property of the nerve net in hydra tentacles is responsible for the unidirectional tentacle contraction.     

Unidirectional Surface Plasmon Polariton Excitation on Single Slit with Oblique Backside Illumination

We have theoretically investigated the unidirectional surface plasmon polariton (SPP) excitation on single slits with oblique backside illumination. An aperture diffraction method is devised, from which the conditions of slit width and beam illumination angle for the unidirectional SPP excitation are formulated analytically. The derived unidirectional conditions are validated with vectorial electromagnetic simulation using the rigorous coupled wave analysis.     

STUDIES ON THE ANOMALOUS CAMBIAL ACTIVITY IN DOXANTHA UNGUIS-CATI (BIGNONIACEAE). II. A CASE OF DIFFERENTIAL PRODUCTION OF SECONDARY TISSUES

The peculiar secondary growth in Doxantha unguis-cati provides several developmental problems concerning cambial activity. One of the most interesting of these problems is the presence of both unidirectional and bidirectional arcs of cambium within the same stem. This investigation reports the ontogenetic development of these two kinds of cambial arcs. The first cambial divisions are observed in the fascicular regions of the 11th to 16th internodes from the shoot tip. This event is initiated after internode elongation is completed. In the initial stages, secondary tissues have a cylindrical configuration, but subsequently four grooves become apparent. These grooves signify the first evidence of unidirectional cambial activity. The four unidirectional arcs occur near the four major vascular strands to which all of the leaf traces connect. As secondary growth continues, the bidirectional and unidirectional arcs of cambium become separated and radial fissues can be seen between the furrows of phloem and the lobes of secondary xylem. Additional furrows originate either as sets of four between the original set of four or as single furrows to either or both sides of an existing furrow. All furrows are bordered by multiseriate rays. The initials of the bidirectional and unidirectional cambial arcs are non-stratified and are similar in size and appearance. The phloem produced within the furrow differs in several respects from that produced by the bidirectional arcs. The two types of cambial activity and the precise locations of the unidirectional cambial arcs in the stem (i.e. near the four major strands) suggests that transported products from the leaves are involved in the control of unidirectional cambial activity.     

Increased flow rate and papaverine increase K+ exchange in perfused rat hind-limb skeletal muscle.

This study tested the hypothesis that increases in perfusate flow rate result in increased rates of unidirectional and net K+ transport in rat hind-limb skeletal muscle at rest. Ten neurally and vascularly isolated hind limbs, with arterial and venous catheters placed proximal to the popliteal region, were perfused for 10-min periods at flow rates (presented in a random order) of 0.27, 0.42, 0.63, 0.84, or 1.05 mL x min(-1) x g(-1). Potassium extraction and unidirectional K+ influx were determined using 42K, and arterial perfusion pressure was measured continuously. Increases in flow rate resulted in decreases in K+ extraction and increases in unidirectional K+ influx, unidirectional K+ efflux, and net K+ efflux. The increases in K+ flux were associated with increases in oxygen uptake, glucose uptake, and lactate release. In separate experiments (n = 5), the vasodilator papaverine (10(-4) M) did not further vasodilate the vasculature of resting hind limbs, suggesting that the hind limbs in this preparation were fully vasodilated. Papaverine, at constant flow, resulted in a nearly 1.5-fold increase in K+ extraction, a doubling of unidirectional K+ influx, and increases in unidirectional K+ efflux and net K+ efflux. It is concluded that physiological increases in flow rate result in increases in K+ transport in isolated, perfused rat hind-limb skeletal muscle. Furthermore, papaverine appeared to induce an increase in skeletal muscle membrane permeability to K+.     

Effect of medial meniscus tear and partial meniscectomy on balancing capacity in response to sudden unidirectional perturbation

Medial meniscus tears and medial partial meniscectomies can damage or remove mechanoreceptors in the meniscus; this inevitably affects knee joint proprioception. Few studies have addressed this subject and none has examined balance in response to sudden perturbation, which requires complex coordination. This study investigated changes in balance in response to sudden unidirectional perturbations after a medial meniscus tear and medial partial meniscectomy in the 3rd and 12th postoperative months. We compared balancing capacity after sudden unidirectional (horizontal) perturbation in 20 control subjects and 20 patients with a medial meniscus tear. Patients were re-examined 3 and 12 months postoperatively. Balancing ability after unidirectional perturbation was assessed by the Lehr's damping ratio in provocation tests. Meniscus tear significantly reduced the Lehr's damping ratio while standing on the affected leg (p=0.0001) and impaired the posture while standing on both legs (p=0.0007). After partial medial meniscectomy, the Lehr's damping ratio was only significantly reduced while standing on the affected side compared to controls (p<0.01). The results indicated that meniscus tears reduced patients' ability to respond to unidirectional perturbation and adapt to environmental changes. Even 1 year postoperatively, balance after sudden unidirectional perturbation on the affected side was weaker than that of controls.     

The effects of unidirectional incompatibility on cytonuclear disequilibria in a hybrid zone

Unidirectional incompatibility selection is examined as an alternate mechanism of natural selection to cytoplasmic male sterility (CMS) for generating cytonuclear disequilibria. Differences in the dynamics and equilibrium behavior of cytonuclear disequilibria between these two cytonuclear selection models may allow for statistical tests of CMS vs. unidirectional incompatibility between mating cytotypes. Unlike CMS without migration, unidirectional incompatibility causes the cytoplasmic allele frequency to change over time rather than remain constant, and the nuclear allele frequencies hitchhike on the cytoplasmic frequencies. The decay of disequilibria is also distinctive in the absence of migration. Furthermore, in comparing both models with migration it is seen that the opportunity for internal equilibrium can be two or three times higher in a unidirectional incompatibility vs. CMS model. An example is presented that shows how unidirectional incompatibility can be statistically eliminated as a possible mechanism of cytonuclear selection. This revised version was published online in July 2006 with corrections to the Cover Date.     

Unidirectional waves on rings: Models for chiral preference of circumnutating plants

Twining plants exhibit a striking oscillation of their stems in their quest for a support. The oscillations, called circumnutation, have periods generally of 1–5 hr, and virtually all species have a preferred direction of twining. I seek to explain these chiral asymmetries in plant behavior by hypothesizing a chiral asymmetry in plant anatomy. Such asymmetries already exist, for example, in phyllotaxis. I explore wave phenomena on asymmetric but isotropic rings, and seek systems which will only support (stable) waves in one direction around the ring, and not in the other. Simulations indicate that (1) oscillatory reaction-diffusion systems do not support unidirectional waves on rings; (2) excitable reaction-diffusion systems do support unidirectional waves on rings; and (3) unidirectional phase-locking (discrete unidirectional waves) occurs in rings of coupled oscillators. Thus, chiral asymmetries of circumnutating plants cannot be explained by continuum oscillator phenomena, but can be explained by general discrete oscillators, or excitable phenomena on the continuum.     

Fourier's law of heat transfer and its implication to cell motility

Fourier's law of heat transfer addressing temperature differences is intrinsically selective in favoring the mitigation of the differences proceeding as fast as possible. We present an experimental demonstration of such selective behavior of material origin. When an actin filament equipped with nano-scale heat acceptors was placed under heat pulsation, it demonstrated a unidirectional movement without the presence of myosin or ATP. The prime factor for the unidirectional movement was the temperature differences between the locally heated portions on the actin filament and the cooler material bodies in the surroundings. The unidirectional movement could be enhanced in the process of mitigating the temperature differences as fast as possible.     

Sugar transport by intestine. Escape of galactose from preloaded mucosa of hamster jejunum.

Everted hamster jejunum was loaded with D-galactose and then escape into an initially galactose-free mucosal solution was followed. Mucosal anaerobiosis greatly increased the rate of escape, an effect which might have been caused by inhibiting reuptake from the unstirred layer and/or by augmenting the ease of unidirectional efflux across the brush border membrane. The former effect was expected because of our previous results from influx studies, and the main object here was to find out if the ease of efflux is affected by anaerobiosis. With phlorizin present in the mucosal solution during escape, information about unidirectional efflux was obtainable. We estimated that 10(-4) M phlorizin inhibited the ease of efflux via the phlorizin-sensitive pathway by about 65%. Apparently the reason why mucosal phlorizin accelerates escape of sugar from loaded mucosa, an effect which has been reported previously by others, is that it inhibits unidirectional efflux less effectively than it inhibits reuptake from the unstirred layer. Residual efflux via the phlorizin-sensitive pathway was markedly increased by mucosal anaerobiosis. This increase did not require an elevation of intracellular Na+ concentration. These results, together with those of our previous study, show that mucosal anaerobiosis abolishes uphill transport of galactose across the brush border of hamster jejunum by inhibiting unidirectional influx and by increasing the ease of unidirectional efflux. Neither of these effects requires a rise in intracellular Na+ concentration.     

Unidirectional sodium and potassium fluxes through the sodium channel of squid giant axons.

Unidirectional 22Na-traced sodium influx or 42K-traced potassium efflux across the membranes of voltage-clamped squid giant axons was measured at various membrane potentials under bi-ionic conditions. Tetrodotoxin almost entirely eliminated the extra K+ efflux induced by short repetitive depolarizations in the presence of tetraethylammonium or 3,4-diaminopyridine. A method of determining the voltage dependence of the unidirectional flux through voltage-gated channels is described. This technique was used to obtain the unidirectional flux-voltage relation for the sodium channel in bi-ionic and single-ion conditions. It allows the determination of the unidirectional flux at the zero-current potential which, for influx, was found to be approximately 20% of the value measured 80 mV negative to the zero-current potential. The unidirectional flux ratio under bi-ionic conditions was also measured and the flux ratio exponent found to average 1.15 with an external sodium and an internal potassium solution. A three-barrier, two-site, multi-occupancy model previously obtained for other conditions was found to predict a similar non-unity average for the flux ratio exponent. It is also shown that some single-occupancy models can predict non-unity values for the flux ratio exponent in bi-ionic conditions.     

Model for RuvAB-mediated branch migration of Holliday junctions

During RuvAB-mediated Holliday-junction migration two opposite arms of double-stranded DNA (dsDNA) are driven to translocate unidirectional by two respective ring-like hexameric RuvB proteins. However, how the RuvB protein, powered by ATP hydrolysis, drives unidirectional translocation of dsDNA is not clear. Here a model is presented for this mechanochemical-coupling mechanism. In the model, the unidirectional translocation is resulted from both the ATP hydrolysis-induced rotation (power stroke) of the RuvB subunits and the passage of the strong DNA binding from the previous to next RuvB subunits during the sequential ATPase activities around the ring. Using the model, the relationship between the power-stroke size, the step size of DNA translocation and the ratio of the rotational rate of DNA over that of RuvB relative to RuvA is predicted.     

Wolbachia-induced unidirectional cytoplasmic incompatibility and speciation: mainland-island model

Bacteria of the genus Wolbachia are among the most common endosymbionts in the world. In many insect species these bacteria induce a sperm-egg incompatibility between the gametes of infected males and uninfected females, commonly called unidirectional cytoplasmic incompatibility (CI). It is generally believed that unidirectional CI cannot promote speciation in hosts because infection differences between populations will be unstable and subsequent gene flow will eliminate genetic differences between diverging populations. In the present study we investigate this question theoretically in a mainland-island model with migration from mainland to island. Our analysis shows that (a) the infection polymorphism is stable below a critical migration rate, (b) an (initially) uninfected "island" can better maintain divergence at a selected locus (e.g. can adapt locally) in the presence of CI, and (c) unidirectional CI selects for premating isolation in (initially) uninfected island populations if they receive migration from a Wolbachia-infected mainland. Interestingly, premating isolation is most likely to evolve if levels of incompatibility are intermediate and if either the infection causes fecundity reductions or Wolbachia transmission is incomplete. This is because under these circumstances an infection pattern with an infected mainland and a mostly uninfected island can persist in the face of comparably high migration. We present analytical results for all three findings: (a) a lower estimation of the critical migration rate in the presence of local adaptation, (b) an analytical approximation for the gene flow reduction caused by unidirectional CI, and (c) a heuristic formula describing the invasion success of mutants at a mate preference locus. These findings generally suggest that Wolbachia-induced unidirectional CI can be a factor in divergence and speciation of hosts.     

促髓细胞分化的锌指基因单向PCR扩增直接测序的研究

锌指基因是一种造血调节基因,编码锌指结构蛋白,主要在髓细胞中表达,促进髓细胞分化,在急性早幼粒白血病维甲酸治疗中,促使病情缓解。本文报道了我们从基因分子上研究锌指基因作用中,探索并建立了单向聚合酶链反应（ＰＣＲ）扩增特定单链ＤＮＡ,直接测序的新方法。它能产生质和量均佳的单链ＤＮＡ,无需纯化即可直接用于测序,使复杂的测序研究简便易行,可在２,３天内完成。这种单向ＰＣＲ扩增特定单链ＤＮＡ直接测序的方法,经对锌指基因的ｃＤＮＡ测序,得到验证。此法不仅适用于疾病研究中的ＤＮＡ测序,还可制各单链ＤＮＡ探针,更利于基因结构组成的研究。     

Sugar transport by intestine. Escape of galactose from preloaded mucosa of hamster jejunum

Everted hamster jejunum was loaded with d-galactose and then escape into an initially galactose-free mucosal solution was followed. Mucosal anaerobiosis greatly increased the rate of escape, an effect which might have been caused by inhibiting reuptake from the unstirred layer and/or by augmenting the ease of unidirectional efflux across the brush border membrane. The former effect was expected because of our previous results from influx studies, and the main object here was to find out if the ease of efflux is affected by anaerobiosis. With phlorizin present in the mucosal solution during escape, information about unidirectional efflux was obtainable. We estimated that 10^?4 M phlorizin inhibited the ease of efflux via the phlorizin-sensitive pathway by about 65%. Apparently the reason why mucosal phlorizin accelerates escape of sugar from loaded mucosa, an effect which has been reported previously by others, is that it inhibits unidirectional efflux less effectively than it inhibits reuptake from the unstirred layer. Residual efflux via the phlorizin-sensitive pathway was markedly increased by mucosal anaerobiosis. This increase did not require an elevation of intracellular Na⁺ concentration. These results, together with those of our previous study, show that mucosal anaerobiosis abolishes uphill transport of galactose across the brush border of hamster jejunum by inhibiting unidirectional influx and by increasing the ease of unidirectional efflux. Neither of these effects requires a rise in intracellular Na⁺ concentration.     

Osteoblasts and osteocytes respond differently to oscillatory and unidirectional fluid flow profiles

Bone cells subjected to mechanical loading by fluid shear stress undergo significant architectural and biochemical changes. The models of shear stress used to analyze the effects of loading bone cells in vitro include both oscillatory and unidirectional fluid shear profiles. Although the fluid flow profile experienced by cells within bone is most likely oscillatory in nature, to date there have been few direct comparisons of how bone cells respond to these two fluid flow profiles. In this study we evaluated morphologic and biochemical responses to a time course of unidirectional and oscillatory fluid flow in two commonly used bone cell lines, MC3T3-E1 osteoblasts and MLO-Y4 osteocytes. We determined that stress fibers formed and aligned within osteoblasts after 1 h of unidirectional fluid flow, but this response was not observed until greater than 5 h of oscillatory fluid flow. Despite the delay in stress fiber formation, oscillatory and unidirectional fluid flow profiles elicited similar temporal effects on the induction of both cyclooxygenase-2 (Cox-2) and osteopontin protein expression in osteoblasts. Interestingly, MLO-Y4 osteocytes formed organized stress fibers after exposure to 24 h of unidirectional shear stress, while the number of dendritic processes per cell increased along with Cox-2 protein levels after 24 h of oscillatory shear stress. Despite these differences, both flow profiles significantly altered osteopontin levels in MLO-Y4 osteocytes. Together these results demonstrate that the profile of fluid shear can induce significantly different responses from osteoblasts and osteocytes.     

Studies on the growth and development of protoplasts of the moss,Physcomitrella patens,and its control by light

Protoplasts prepared from protonemal cultures of the moss Physcomitrella patens begin to regenerate a new cell wall within 1 h of removal from cellulase. The wall is seen as a gradually thickening mat of fibres when examined by scanning electron microscopy. Development of filaments from protoplasts takes place in the majority of cases only after one or more cell divisions have occurred. The direction of emergence of filaments is random in uniform light, but strongly negatively phototropic in bright unidirectional horizotal light. Filament growth is also strongly negatively phototropic. The influence of unidirectional light can be destroyed by incubating protoplasts in the presence of colchicine. Filaments growing in unidirectional light have cytoplasmic microtubules running along their long axes and in close association with large organelles. These results are discussed in terms of the potential for this system for the study of polarity in plants.     

Ouabain stimulates unidirectional and net potassium efflux in resting mammalian skeletal muscle.

The present study compared ouabain-sensitive unidirectional K+ flux into (JinK) and out of (JoutK) perfused rat hindlimb skeletal muscle in situ and mouse flexor digitorum brevis (FDB) in vitro. In situ, 5 mM ouabain inhibited 54 +/- 4% of the total JinK in 28 +/- 1 min, and increased the net and unidirectional efflux of K+ within 4 min. In contrast, 1.8 mM ouabain inhibited 40 +/- 8% of the total JinK in 38 +/- 2 min, but did not significantly affect JoutK. In vitro, 1.8 and 0.2 mM ouabain decreased JinK to a greater extent (83 +/- 5%) than in situ, but did not significantly affect 42K loss rate compared with controls. The increase in unidirectional K+ efflux (JoutK) with 5 mM ouabain in situ was attributed to increased K+ efflux through cation channels, since addition of barium (1 mM) to ouabain-perfused muscles returned JoutK to baseline values within 12 min. Perfusion with 5 mM ouabain plus 2 mM tetracaine for 30 min decreased JinK 46 +/- 9% (0.30 +/- 0.03 to 0.16 +/- 0.02 micromol x min(-1) x g(-1)), however tetracaine was unable to abolish the ouabain-induced increase in unidirectional K+ efflux. In both rat hindlimb and mouse FDB, tetracaine had no effect on JoutK. Perfusion of hindlimb muscle with 0.1 mM tetrodotoxin (TTX, a Na+ channel blocker) decreased JinK by 15 +/- 1%, but had no effect on JoutK; subsequent addition of ouabain (5 mM) decreased JinK a further 32 +/- 2%. The ouabain-induced increase in unidirectional K+ efflux did not occur when TTX was perfused prior to and during perfusion with 5 mM ouabain. We conclude that 5 mM ouabain increases the unidirectional efflux of K+ from skeletal muscle through a barium and TTX-sensitive pathway, suggestive of voltage sensitive Na+ channels, in addition to inhibiting Na+/K+-ATPase activity.     

Unidirectional pulsed-field electrophoresis of single- and double-stranded DNA in agarose gels: analytical expressions relating mobility and molecular length and their application in the measurement of strand breaks

Unidirectional pulsed-field electrophoresis improves the separation of single-stranded DNA molecules longer than 20 kilobases (kb) in alkaline agarose gels compared to static-field electrophoresis. The greatest improvement in separation is for molecules longer than 100 kb. The improved resolution of long molecules with unidirectional pulsed-field electrophoresis makes possible the measurement of lower frequencies of single-strand breaks. The analytical function that relates the length and mobility of single-stranded DNA electrophoresed with a static field also applies to unidirectional pulsed field separations. Thus, the computer programs used to measure single-strand breaks are applicable to both undirectional pulsed- and static-field separations. Unidirectional pulsed-field electrophoresis also improves the separation of double-stranded DNA in neutral agarose gels. The function relating molecular length and mobility for double-stranded DNA separated by unidirectional pulsed-field electrophoresis is a superset of the function for single-stranded DNA. The coefficients of this function can be determined by iterative procedures.