In vitro meristem cloning of Eucalyptus tereticornis Sm.

Rapid multiplication of axillary meristems and direct shoot development occurred from nodal explants of mature Eucalyptus tereticornis Sm. with 5.3 M NAA, 1.1 M IAA and 4.4 M BA in Murashige-Skoog medium. Repeated subcultures of the second generation shoot cultures into low cytokinin-auxin containing media (0.44–0.88 M BA+0.1 M NAA) yielded axillary microshoots in large numbers. Half-strength MS liquid medium with 4.9 M IBA, 5.5 M IAA and 5.3 M NAA for four days, half-strength semi-solid hormonefree MS medium with charcoal, and MS liquid medium without charcoal and hormones, in sequence, induced rooting of shoots in the dark. This system is suitable for the mass propagation of this difficult-to-root eucalypt.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - IBA -indole-3-butyric acid - 2-iP isopentyl adenine - Kn kinetin - MS Murashige-Skoog - NAA -naphthalene acetic acid - PVP polyvinylpyrrolidone     

Der Entwicklungscyclus mit Sexualphase bei der marinen Diatomee Coscinodiscus asteromphalus

Zusammenfassung Die Kultur der großen marinen Diatomee Coscinodiscus asteromphalus wird beschrieben. Die Synchronisation der vegetativen Stadien aus dem Entwicklungscyclus mit Sexualphase wird durch Messung der Valvendurchmesser charakterisiert. Die Art entwickelt sich von Stadien mit 200 m Valvendurchmesser (V.-D.), die nicht sexuell induzierbar sind, zu Stadien mit 80–90 m V.-D. mit einem Optimum der Induzierbarkeit und weiter zu Stadien mit 55–60 m V.-D. Bei dieser Größe ist keine weitere mitotische Zellteilung mehr möglich. Entwicklungsstadien mit 200–190 m, 140–130 m und 100–90 m. V.-D. zeigen bei 24°C und bei 18°C die gleiche Generationszeit im mitotischen Entwicklungscyclus von 1 bzw. 0,6 Zellteilungen pro Tag. Der Valvendurchmesser verringert sich bei dieser Art um 1,5 m bei 24°C und 1,4 m bei 18°C während einer Zellteilung.

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The life cycle with sexual phase in the marine diatom Coscinodiscus asteromphalus I. Culture and synchronisation of developmental stages

Summary Culture-conditions for the large marine centric diatom Coscinodiscus asteromphalus are described. The cells grow in a defined medium in a light-dark regime of 14: 10 h. Synchronization of different stages of the sexual life cycle is characterized by measuring the valve diameter (v.d.) of the cells. The cells develop from stages with 200 m v. d. (not sexually inducible) to stages with 80–90 m v. d. (optimum for sexual induction), and further to stages with 55–60 m v. d., where no following mitotic cell division is possible. The length of the pervalvar axis does not change during this development. Different stages (200–190m, 140–130 m and 100–90 m v. d.) grow with the same doubling time during their mitotic life cycle: 1 cell division per day at 24° C and 0.6 cell divisions per day at 18°C. During one cell division the valve diameter of this species decreases by about 1.5m at 24°C and by 1.4 m at 18°C. Therefore, the development from stages with 200 m v.d. to stages with 60 m v. d. takes between 90 days at 24°C and 165 days at 18°C.

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Teile einer Habilitationsschrift der Naturwissenschaftlichen Fakultät der Universität Marburg (Lahn).     

Localization of sodium absorption and chloride secretion in an intestinal epithelium

Summary Hen coprodeum absorbs sodium electrogenically and, when stimulated by theophylline, secretes chloride. In this study the vibrating microprobe technique was used to localize the transport of these ions to intestinal villi/folds and crypts. With the isolated, stretched epithelium, controlled by light microscopy and scanning electron microscopy, in open circuit, currents were inward, 40±7 A/cm², 50 m vertically above villi, and outward, 36±7 A/cm² above crypts. The currents decayed exponentially to near zero at 300 m with the same length constant. A physical model simulating the observed loci of current sources and sinks predicts potential profiles consistent with our data. Extrapolation of the currents gives a surface potential of 45 V, negative on villi and positive above crypts. Short circuiting increased villus current to 86±27 A/cm² at 50 m, and amiloride treatment reduced it to –8 A/cm²; in both cases crypt currents were abolished. The inward currents are compatible with sodium absorption. Induction of chloride secretion after amiloride treatment, resulted in current circuits similar to those induced by sodium absorption, with villus currents of 23±7 A/cm². This is in accord with chloride secretion at the villi. Quantitative estimates of crypt number (860/cm²) and opening diameter (15 m), in conjunction with isotopic measurements of active and electrical potential-driven ion fluxes demonstrate, however, that only 4% of the potential-driven co-ion transport occurs through the crypts. This indicates that nearly all chloride secretion comes from the sodium-absorbing villar area. Were the chloride secretion to occur solely from the crypts, the current should have been in the opposite direction and 10,000-fold larger.     

Influence of nitrogen on the behaviour of nickel in wheat

A glasshouse experiment was conducted to study the effect of Ni on the growth and nutrients concentration in wheat (Triticum aestivum Cv. WH 291) in the presence and absence of applied N as urea. Responses to N application were observed up to 120 g N g^–1 soil. No response to Ni was observed in the dry matter yield of wheat tops (leaves + stem) in the absence of applied N while in the presence of applied N, significant yield increases were obtained at 12.5g Ni g^–1 soil. Nickel was not toxic to wheat up to 50g Ni g^–1 soil in the presence of 120g N g^–1 soil. Nitrogen and Ni concentration in wheat tops and roots increased with increasing levels of applied N and Ni, respectively. Applied Ni had an antagonistic effect on N concentration. Similarly, N reduced the Ni concentration in the wheat tissues. Positive growth responses to Ni were associated with 22 and 15g Ni g^–1 in wheat tops, in the presence of applied N at 60 and 120g N g^–1 soil, while Ni toxicity was associated with 63, 92.5 and 112.5g Ni g^–1 in wheat tops, in the absence and presence of applied N at 60 and 120g N g^–1 soil, respectively.     

Isolation of thermophilic obligately autotrophic hydrogen-oxidizing bacteria,similar to Hydrogenobacter thermophilus,from Icelandic hot springs

Thermophilic obligately autotrophic hydrogen-oxidizing bacteria were isolated from several alkaline hot springs in Iceland. The bacteria were Gram negative rods, 0.4–0.5 m in diameter and 3–4 m long but 6–7 m long cells without septa were often seen. Long and short laments are formed. Spores, flagella or lipid granules were not observed. Strains H1 and H12 grew optimally at 70° C and pH 6.5 under mixture of air plus 0.6 atm H₂ and 0.1 atm CO₂. The cells contained cytochromes and carotenoid-like pigments. They would not grow on agar or silicia gel plates. The cells would not grow heterotrophically on organic substrates and were inhibited by most of these same organic compounds and agar in low concentrations. They were very sensitive to common antibiotics. The role of these bacteria in the hot spring ecosystem is discussed.     

Adventitious shoot regeneration from in vitro-cultured leaves of Rubus genotypes

Regeneration of adventitious shoots from leaves of several in vitro-cultured Rubus genotypes was affected by media components and incubation conditions. Leaves cultured at 20°C with a photosynthetic photon flux (PPF) of 40 mol m^-2 s^-1 had a higher regeneration frequency and more shoots per regenerating leaf than ones cultured at 25°C with a PPF of either 40 or 80 mol m^-2 s^-1. Thidiazuron (TDZ) was significantly more effective than benzyladenine. Medium containing 1 M TDZ had the highest percentage regeneration for leaves of Autumn Bliss, Canby, Summit and Sentry red raspberries, whereas leaves of MD-ETCE-1 blackberry hybrid responded more to 10 M TDZ. Higher regeneration frequencies were obtained with 0.5 M indolebutyric acid (IBA) than with 1 M, but no significant difference was observed between 0.5 M and no IBA in other experiments. More shoots per regenerating leaf formed on Murashige and Skoog (MS) and N6 media, than on half-strength MS, Anderson, or Woody Plant media for all genotypes tested. The youngest two expanding leaves near the shoot apex were the most regenerative and yielded the highest number of shoots per regenerating leaf.Abbreviations AND Anderson (1980) - BA benzyladenine - IBA indolebutyric acid - MS Murashige & Skoog (1962) - N6 Chu et al. (1975) - NAA naphthaleneacetic acid - PPF photosynthetic photon flux - TDZ thidiazuron (N-phenyl-N'-1, 2, 3-thiadiazol-5-ylurea) - WPM Woody Plant Medium [Lloyd & McCown (1980)]     

Somatic embryogenesis in callus cultures of Rosa hybrida L. cv. Landora

Callus was initiated from immature leaf and stem segments of rose (Rosa hybrida cv. Landora) and subcultured every four weeks on a basal medium of half-strength Murashige & Skoog (1962) salts plus 30 g l^-1 sucrose (1/2 MS) and supplemented with 2.2 M BA, 5.4 M NAA and 2.2–9.0 M 2,4-D. Embryogenic callus and subsequently somatic embryos were obtained from 8-week-old callus culture on 1/2 MS+2.2 M BA+0.05 M NAA+0.3 M GA₃+200–800 mg l^-1 L-proline. Long-term cultures were established and maintained for up to 16 months by repeated subculture of embryogenic callus on L-proline deficient medium. About 12% of cotyledonary stage embryos taken from cultures cold-stored at 8±1°C for 4 days germinated on 1/2 MS+2.2 M BA+0.3 M GA₃+24.7 M adenine sulphate.Abbreviations BA benzyladenine - NAA -naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid     

A lyophilized aqueous extract of<Emphasis Type="Italic"> Maytenus ilicifolia</Emphasis> leaves inhibits histamine-mediated acid secretion in isolated frog gastric mucosa

Lyophilized aqueous extract of Maytenus ilicifolia leaves (LAEMIL) is commonly used in Brazilian folk medicine in the treatment of dyspepsia as well as gastric ulcers. We have investigated the effect and the possible mechanism of action of the LAEMIL on acid secretion in isolated frog gastric mucosa incubated in an Ussing chamber. It was observed that LAEMIL (7–28 mg%) as well as cimetidine (125–4,000 M), a well-known histamine H₂ receptor antagonist, decreased basal acid secretion in a concentration-dependent manner. Similarly to cimetidine (190 M), LAEMIL (21 mg%) also inhibited gastric acid secretion induced by increasing concentrations of histamine (50–800 M). The EC₅₀ values for histamine alone and histamine in the presence of LAEMIL or cimetidine were 94.6 M (71.1–125.9 M), 244.9 M (209.4–286.4 M) and 142.2 M (23.6–855.0 M), respectively. LAEMIL, histamine and cimetidine were effective on acid secretion only when added to the serosal surface of the mucosa. Furthermore, simultaneous addition of LAEMIL and cimetidine at concentrations, per se, ineffective, caused a 16% reduction in the basal acid secretion [from 8.3±0.3 to 6.9±0.2 Eq g^–1 (15 min)^–1, n=4]. Although effects such as inhibition of histamine biosynthesis and/or histamine release can not be ruled out, our data suggest that LAEMIL, like cimetidine, reduces acid secretion in the isolated frog gastric mucosa by antagonising histamine H₂ receptors.Abbreviations LAEMIL Lyophilized aqueous extract of Maytenus ilicifolia leaves - Hist Histamine - Cim Cimetidine     

Grazing by a dominant rotifer Conochilus unicornis Rousselet in a mountain lake: in situ measurements with synthetic microspheres

Grazing rates of zooplankton were analysed in the summer of 1999 in Yellow Belly Lake, an oligotrophic system in the Sawtooth Mountains of Idaho (U.S.A.). The colonial rotifer Conochilus unicornis was a dominant species in the epilimnion, with densities reaching 20 colonies l^–1 (ca. 400 ind. l^–1). Clearance rates were measured with an in situ Haney Grazing chamber and synthetic microspheres 5, 9 and 23m in diameter. At epilimnetic temperatures of around 14 °C, mean clearance rates for 5m particles ranged from 30 to 65 l ind.^–1 h ^–1. Clearance rates were 2–9 times higher on the 5m spheres than on the 9 m spheres, and C. unicornis almost never fed on the 23 m spheres. Grazing rates did not change over the diel cycle. Clearance rates declined more than 10-fold as temperatures declined from 14 °C in the epilimnion to 7 °C in the metalimnion. In the epilimnion, grazing by C. unicornis was more important than grazing by crustaceans in the community, at least on particles 9m. The results show the importance of grazing by rotifers in lakes, and the significance of spatial variations that influence grazing rates.     

Age-Related Erythrocyte Structure and Rheological Blood Properties in Athletes

The relationship between the rheological blood properties and several indices of age-related erythrocyte structure was established in endurance-training athletes (n = 21). Unlike nonathletic subjects, the athletes had a shift in the age-related structure towards younger erythrocyte forms: reticulocytosis, increased erythrocyte resistance, increased percentage of cells with a diameter exceeding 8 m, and decreased percentage of cells with a diameter of less than 7 m. The established correlations between total reticulocyte concentration, mature and immature reticulocyte concentrations, and percentage of cells with a diameter either exceeding 8 m or less than 7 m, on the one hand, and hemorheological parameters (blood viscosity, erythrocyte suspension viscosity, erythrocyte aggregation, and surface/volume ratio) and physical work capacity, on the other hand, revealed a significant effect of younger erythrocyte forms on hemorheological indices in athletes.     

Effect of 2-hydroxybenzoate on the rate of naphthalene mineralization in soil

The effect of 2-hydroxybenzoate (2-OHB, salicylate) on the mineralization rate of [¹⁴C]naphthalene, the population density of naphthalene-degrading bacteria, and the concentration of genes encoding for naphthalene dioxygenase in a soil bacterial community was investigated. Six different concentrations of 2-OHB (10, 20, 50, 100, 150 and 200 g g^–1 soil) were tested in 100-g portions of soil. The addition of 10, 20 or 50 g 2-OHB g^–1 soil produced a general increase in total soil bacterial population density, whereas the addition of 100 g or 200 g 2-OHB g^–1 soil specifically increased the proportion of naphthalene degraders relative to the total population. The addition of 50 g 2-OHB g^–1 soil produced a fourfold increase (the maximum observed) in the rate of naphthalene mineralization relative to the rate in unamended soil. The concentration of 2-OHB ( 100 g/g) added to soil correlated with the population density of naphthalene degraders (r=0.961). Addition of up to 200 g 2-OHB g^–1 correlated with the abundance of DNA sequences homologous to known naphthalene dioxygenase genes (nahAB) (r=0.958). However, mineralization of [¹⁴C]naphthalene was stimulated significantly only by the addition of 50 g 2-OHB g^–1 soil. Results of the mineralization experiments were supported by the detection of nahAB mRNA extracted directly from soil. The specificity of the effect of 2-OHB on naphthalene biodegradation was confirmed in a control experiment using equivalent concentrations of 4-OHB which repressed naphthalene mineralization by about 50%. Addition of ammonium nitrate to the soil also increased the rate of naphthalene mineralization. Ammonium nitrate added together with 2-OHB reduced the mineralization enhancement effect of either compound alone. The study confirmed that specific induction of biodegradative genes can enhance chemical pollutant removal in situ. Correspondence to: O. A. Ogunseitan     

Tissue culture ofKarwinskia humboldtiana—a plant producing toxins with antitumoural effects

Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10^-2 mol l^–1, gibberellic acid (GA₃) 3.10^-2 mol l^–1, and 6-benzylaminopurine (BA) 2 mol l^–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l^–1, GA₃ 14 mol l^–1, and kinetin 5 mol l^–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l^–1 and BA 10 mol l^–1 was induced.Abbreviations BA 6-benzylaminopurine - 2,4-d 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA 1-naphthaleneacetic acid - TEM transmission electron microscopy     

6-Methylpurine-induced inhibition of sclerotia morphogenesis in Sclerotium rolfsii and its reversal by adenosine

In liquid synthetic medium inoculated with Sclerotium rolfsii (SR), addition of 6-methylpurine (MP, 50g/ml) immediately after inoculation led to approximately 100% reduction in sclerotia production. Adenosine, and to a lesser extent guanosine, each at final concentration of 100g/ml significantly reduced inhibition of sclerotia formation by SR in presence of 50g/ml MP. Uridine and cytidine each at 100g/ml had no such effect. The inhibition of sclerotia morphogenesis could be prevented by addition of 800g/ml of adenosine together with 50g/ml MP. Reversal by adenosine of MP-induced inhibition of sclerotia development was concentration dependent.     

Respiration rates of Chiloplacus sp. and other arctic nematodes at low and high temperatures

Summary Respiration of an undescribed species of soil nematode of the genus Chiloplacus from the Canadian High Arctic was measured at 2°, 5°, 10°, 15°, 20° and 25°C. The corresponding metabolic rates were 0.2697×10^-3 l, 0.3406×10^-3 l, 0.8408×10^-3 l, 0.8539×10^-3 l, 1.8420×10^-3 l and 2.9360×10^-3 l O₂ ind^-1 h^-1, respectively, for a nematode of 1.0 g dry weight. The relationship between respiration and dry weight for Chiloplacus sp. at 10°C is described by the function log R=-3.0693+0.8844 log W. Q₁₀ values for the 2°–5°, 5°–10°, 10°–15°, 15°–20° and 20°–25°C temperature intervals were 2.18, 6.09, 1.03, 4.65 and 2.54, respectively. Chiloplacus sp. showed raised metabolic rates at low tempetatures compared with species from warmer environments. Metabolic rates of representative samples of the soil, nematode fauna (dominated by individuals of the genus Plectus) from the same location were 0.1593×10^-3 l, 0.3603×10^-3 l and 0.5332×10^-3 l O₂ ind^-1 h^-1 at 5°, 10° and 15°C for an average nematode of 0.4297 g dry weight.     

High frequency of bulblet regeneration from bulb scale sections of Fritillaria thunbergii

Fritillaria thunbergii Miq. bulb-scale sections were cultured using Murashige and Skoog (MS) medium supplemented with NAA (1.62 M) and KN/2iP/BA (0.47–23.23 M).A high frequency of bulblets was developed from the scale sections and these bulblets have developed leaves and roots in 12 weeks of culture. An optimum of 13.7 bulblets developed from scale sections on solid MS medium supplemented with 1.62 M NAA and 4.65 M KN. Cultures incubated under cycles of 16 h white fluorescent light (40 mol m^–2 s^–1) and 8 h dark at a temperature regime of 25°C have produced optimal bulblets compared to cultures incubated under continuous dark at 25°C. The bulblets were harvested at the end of culture period and were given cold treatment at 5°C for 5 weeks and then transplanted to a potting mixture of peat moss, vermiculite and perlite (1:1:1). The bulblets, which were more than 10 mm in diameter, sprouted (100%) in 5 weeks of transplantation.     

Gamete Structure and Fertilization in the Barents Sea Sponge Leucosolenia complicata

The ultrastructure of male and female gametes of asconoid sponge Leucosolenia complicata(Calcispongiae, Calcaronea), a hermaphrodite species that reproduces in autumn, is described. The mature sponge's oocytes were up to 70 m in diameter, had no coatings, and contained a nucleus about 31 m in diameter with large nucleoli (up to 6.6 m). There were vacuoles with fibrillar contents typical of calcareous sponges in ooplasm. During vitellogenesis, a cluster of a great number of nurse cells developed above each oocyte from transformed choanocytes. Mature spermia of L. complicatalooked like orbicular cells about 2.5 m in diameter, with no acrosome or tail. The spermium nucleus (diameter about 2.2 m) was formed by incompletely condensed chromatin and was surrounded with a thin layer of cytoplasm of nonuniform thickness. In the thick layer of cytoplasm beyond the ribosomes, there were two or three mitochondria, dictyosomes, and electron-dense protein bodies lying freely under the nucleus. Fertilization occurred with the aid of a carrier cell. During spawning (mass release of spermia), any nurse cell complex can seize a spermium and transform into a carrier cell in situ. The transformation of a seized spermium into a spermiocyst was connected with the rapid isolation of the spermium nucleus from the protein body. Fertilization began with the penetration of the protein body into the oocyte cytoplasm. Only after this did the spermium's nucleus penetrate into the oocyte.     

Somatic embryogenesis in Simarouba glauca

Frequency of somatic embryogenesis from callus cultures derived from immature cotyledon explants of Simarouba glauca Linn. was highest on solid MS medium supplemented with 11.1 M benzyladenine and 13.42 M -naphthaleneacetic acid. On transfer of the somatic embryos into maturation medium containing half-strength MS medium supplemented with 1.89 M abscisic acid (ABA) and 2% (w/v)sucrose, 20–25 % of embryos germinated within 20 days of culture with distinct cotyledon, hypocotyl and radicle.     

A catalase microbiosensor for detecting hydrogen peroxide

A microbiosensor for hydrogen peroxide (H₂O₂) was constructed by immobilizing catalase in a polyacrylamide gel on the tip of a Clark-type oxygen microelectrode. The outer tip diameter was 15–40 m. The sensors had response times of 0.7–1.2 s, and could detect as little as 2–4 M H₂O₂. They could measure with a spatial resolution of about 100m and remained operational for up to three weeks.     

Contribution of flow cytometry to estimate picoplankton biomass in estuarine systems

Picoplankton (plankton 3 m) biomass was determined by flow cytometry in three European estuarine systems (Krka Estuary in Croatia, Rhône Delta in France, and Lena Delta and Laptev Sea in Russia). The size of natural phytoplankton groups was obtained by a calibration curve, with different picoplankton's strains (from 1.6 to 3.4 m), measured by a Coulter counter (size) and a flow cytometer (light-scattering). Two natural groups of picoplankton were identified by flow cytometry in the three systems: Synechococcus sp and picoeukaryotes. Picoplankton cells abundance ranged between: 2800 and 42000, 5000 and 37000, 1000 and 50000 cells ml^–1 in the Krka estuary, in the Rhône delta and in the Lena-Laptev system, respectively. In the Krka estuary, picoplankton biomass ranges between 11 and 68 gC l^–1. It can make up as much as 88% of the total photosynthetic plankton population and 50% of total organic particulate carbon. Picoplankton biomass was greater in the summer than in the autumn. At the halocline layer this biomass can attempt ca. 390 gC l^–1during the summer cruise. In the Rhône delta, a lower picoplankton biomass (6–39 gC l^–1) was observed at the end of the winter. These biomass represented between 0.4 and 22% of the particulate organic carbon, which could reach 71% of the total photosynthetic plankton biomass at the marine station. In the Lena-Laptev system, picoplankton biomass varied between 6 and 56 gC l^–1 in surface waters. Picoplankton biomass decreased with depth, but picoeukaryotes were still observed in deep samples (20, 30 m) in the Laptev Sea, showing a considerable autotrophic activity in spite of low temperatures (0–1 °C). Although the widely dispersed estuary geographic distribution and their different estuarine characteristics, the data point out that these small organisms can also play an important role in the transfer of organic carbon from rivers to oceans and that flow cytometry can be able to detect these small cells in turbid systems.     

Asymmetric diffusion into the postsynaptic neuron: An extremely efficient mechanism for removing excess GABA from synaptic clefts on the Deiters' neurone plasma membrane

Microdissected Deiters' neuron plasma membranes have been used for studying the passage of GABA through the membrane both in the inward and outward direction. Working with 0.2 mM GABA in the compartment simulating the outside of the neurone and with 2.0 mM GABA in the one simulating the inside we found a net transport of GABA towards the inside. This mechanism does not require a Na⁺ ion gradient across the membrane. The nature of the transport process involved was studied by determining the rate of [³H]-GABA inward passage as a function of GABA concentration (1 nM–800 M) on the outward side of the membrane. The results have shown that until 50 M a diffusion process (v=D₁×C, where D₁=3.1×10^–11 1/m²×sec) is the sole mechanism involved. Above 50 M a second diffusion process is activated v=D₂×(C–50×10^–6), where D₂=2.8×10^–11 1/m²×sec. Taking in account both inward and outward directed diffusion, one can calculate 16 M as the equilibrium concentration of GABA on the outward side of the membrane. From a kinetic point of view, these diffusion processes are able to reduce GABA concentration in a synaptic cleft from 3 mM to 20 M within 3 sec. These diffusion systems are discussed as extremely efficient in removing the excess of released GABA in the synaptic cleft.