Influence of inorganic microelements on the production of camptothecin with suspension cultures of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis>

The effects of eight microelements (I^–, BO₃ ^3–, MoO₄ ^2–, Co²⁺, Cu²⁺, Mn²⁺, Fe²⁺, Zn²⁺) on the biosynthesis of camptothecin and the growth of suspension cultures of Camptotheca acuminata were studied. The increase of I^– to 25 M l^–1, Cu²⁺ to 1 M l^–1, Co²⁺ to 2 M l^–1 and MoO₄ ^2– to 10 M l^–1 in Murashige and Skoog (MS) medium resulted in 1.66, 2.84, 2.53 and 2.04 times higher of camptothecin yield than that in standard MS medium respectively. Combined treatment of I^– (25 M l^–1), Cu²⁺ (1 M l^–1), Co²⁺ (2 M l^–1) and MoO₄ ^2– (10 M l^–1) lead to improve cell dry weight, camptothecin content, and camptothecin yield to 30.56 g l^–1, 0.0299%, and 9.15 mg l^–1, respectively, which were 20.2, 208.9 and 273.8% increment respectively when compared with those of control.     

Effect of Naloxone on the Activity of Cl–-Activated Mg2+-ATPase from Plasma Membrane Fraction of Bream Brain (Abramis brama L.) in the Presence of GABAa-ergic Substances

We studied the effect of naloxone—an antagonist of the opioid receptors—on sensitivity of Cl^–-activated Mg²⁺-ATPase from the plasma membrane fraction of bream brain (Abramis brama L.) to GABA_a-ergic substances. Preincubation of the plasma membranes with 1–100 M naloxone increased the basal Mg²⁺-ATPase activity and suppressed its activation by chloride ions. The same effects were observed in the presence of the agonists of GABA_a/benzodiazepine receptors: 0.1–100 M GABA, 1–500 M pentobarbital, and 0.1–100 M phenazepam. Naloxone (10 M) inhibited activation of the basal Mg²⁺-ATPase by the studied ligands and restored the enzyme sensitivity to Cl^–. However, the effect of naloxone was not observed in the presence of high concentrations of pentobarbital (500 M) and phenazepam (100 M). The obtained data show that naloxone modulates the activity of Cl^–-activated Mg²⁺-ATPase from the plasma membranes of bream brain and antagonizes the GABA_a receptor ligands.     

Efficiency of photosynthesis in continuous and pulsed light emitting diode irradiation

The light utilization efficiency and relative photon requirement of photosynthesis in pulsed and continuous light from light emitting diodes (LEDs) has been measured. First, we chacterized the photon requirement of photosynthesis from light of LEDs that differ in spectral quality. A photon requirement of 10.3±0.4 was measured using light from a 658 nm peak wavelength (22 nm half band width) LED over the range of 0–50 mol photons m^–2 s^–1 in 2 kPa O₂ in leaves of tomato (Lycopersicon esculentum Mill., cv. VF36). Because the conversion of electrical power to photons increased with wavelength, LED lamps with peak photon output of 668 nm were most efficient for converting electricity to photosynthetically fixed carbon. The effect of pulsed irradiation on photosynthesis was then measured. When all of the light to make the equivalent of 50 mol photons m^–2 s^–1 was provided during 1.5 s pulses of 5000 mol photons m^–2 s^–1 followed by 148.5 s dark periods, photosynthesis was the same as in continuous 50 mol photons m^–2 s^–1. When the pulse light and dark periods were lengthened to 200 s and 19.8 ms, respectively, photosynthesis was reduced, although the averaged photon flux density was unchanged. Under these conditions, the light pulses delivered 10¹⁷ photons m^–2, which we calculate to be equivalent to the capacitance of PS I or PS II. Data support the theory that photons in pulses of 100 s or shorter are absorbed and stored in the reaction centers to be used in electron transport during the dark period. When light/dark pulses were lengthened to 2 ms light and 198 ms dark, net photosynthesis was reduced to half of that measured in continuous light. Pigments of the xanthophyll cycle were not affected by any of these pulsed light treatments even though zeaxanthin formation occurred when leaves were forced to dissipate an equal amount of continuous light.Abbreviations CWF cool white fluorescent - EPS xanthophyll epoxidation state - LED light emitting diode - LUE light utilization efficiency - PFD photon flux density - PR photon requirement (for CO₂ fixation) - PS II primary donor in Photosystem II - RPR relative photon requirement     

The quantitative analysis of chromosome pairing and chiasma formation based on the relative frequencies of M I configurations

Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e ^–2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e ^–2).(1–e ^–2); open bivalents with a frequency (1–e ^–2).e ^–2+(1–e ^–2).e ^–2; univalent pairs with a frequencye ^–2.e ^–2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb _m andb _n of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference.     

Ammonium and nitrate uptake in gap,generalist and understory species of the genus Piper

Summary We studied root net uptake of ammonium (NH ₄ ⁺ ) and nitrate (NO ₃ ^– ) in species of the genus Piper (Piperaceae) under high, intermediate and low photosynthetically active photon flux densities (PFD). Plants were grown hydroponically, and then transferred to temperature controlled (25° C) root cuvettes for nutrient uptake determinations. Uptake solutions provided NH ₄ ⁺ and NO ₃ ^– simultaneously (both) or separately (single). In the first experiment, seven species of Piper, from a broad range of rainforest light habitats ranging from gap to understory, were screened for mineral nitrogen preference (100 M NH ₄ ⁺ and/or 100 M NO ₃ ^– ) at intermediate PFD (100 mol m^–2 s^–1). Preference for NH ₄ ⁺ relative to NO ₃ ^– , defined as the ratio of NH ₄ ⁺ (both):NO ₃ ^– (both) net uptake, was higher in understory species than in gap species. Ammonium repression of NO ₃ ^– uptake, defined as the ratio of NO ₃ ^– (single): NO ₃ ^– (both) net uptake, was also higher in understory species as compared to gap species. In a second set of experiments, we examined the effect of nitrogen concentration (equimolar, 10 to 1000 M) on NH ₄ ⁺ preference and NH ₄ ⁺ repression of NO ₃ ^– net uptake at high (500 mol m^–2 s^–1) and low (50 mol m^–2 s^–1) PFD in a gap (P. auritum), generalist (P. hispidum) and understory species (P. aequale). All species exhibited negligible NH ₄ ⁺ repression of NO ₃ ^– net uptake at high PFD. At low PFD, NH ₄ ⁺ preference and repression of NO ₃ ^– net uptake occurred in all species (understory > generalist > gap), but only at intermediate nitrogen concentrations, i.e. between 10 and 200 M. Ammonium repression of net NO ₃ ^– uptake decreased or increased rapidly (in < 48 h) after transitions from low to high or from high to low PFD respectively. No significant diurnal patterns in NO ₃ ^– or NH ₄ ⁺ net uptake were observed.CIWDPB publication # 1130     

Size-fractionated primary production in the open Southern Ocean in austral spring

Size-fractionated primary production was measured by carbon-14 uptake incubations on three transects between 47°S and 59°30S along 6°W in October/November 1992. Open Antarctic Circumpolar Current and ice-covered Weddell Gyre water showed comparable low productivity (0.3 gCm^–2 day^–1) and size distribution. Picoplankton (<2 m) was the dominant size fraction, contributing approximately half to the total water column production. The significance of larger (>20 m) phytoplankton was only minor. Productivity in the Polar Front Zone north of 50°S, with higher water column stability, was up to 10 times higher with microplankton (>20 m) being predominant. No ice-edge bloom occurred over the 2 months study period; this is explained by non-favourable hydrographic conditions for blooming and the lack of melt-water lenses upon ice retreat. Picoplankton tended to make higher contributions at lower water column stability, and microplankton to make higher contributions at higher stability. Mixing, together with light climate, are discussed as the driving forces for Antarctic primary production and for its size structure.     

Growth inhibition of biomass adapted to the degradation of toluene and xylenes in mixture in a batch reactor with substrates supplied by pulses

A biomass adapted to degrade toluene and xylenes in mixture was grown in a batch reactor with substrates supplied by pulses. The inhibition of biomass growth in the course of substrate degradation was investigated. The maximal biomass concentration of 7 g l^–1 was obtained using 150 l of toluene and 15 l of a mixture of xylenes in one litre of liquid medium, and the maximal biomass productivity and yield were 53 mg l^–1 h^–1 and 0.32 g_DW g _s ^–1 , respectively. Higher quantities of substrate added by pulses, that is 200 l of toluene with 20 l of xylenes and 300 l of toluene with 30 l of xylenes, caused an accumulation of metabolites. These higher quantities of substrates caused inhibition of microbial growth. Among the metabolites produced, 4-methyl catechol was found in large quantities in the culture medium and in the cells.     

The Biogeochemical Cycle of Methane in the Coastal Zone and Littoral of the Kandalaksha Bay of the White Sea

Microbiological and biogeochemical investigations of the processes of methane production (MP) and methane oxidation (MO) in the coastal waters and littoral of the Kandalaksha Bay of the White Sea were carried out. The studies were conducted in the coastal zones and in the water areas of the Kandalaksha Preserve, Moscow State University White Sea Biological Station, and the Zoological Institute (RAS) biological station in August 1999, 2000, and 2001 and in March 2001. The rate of CO₂ assimilation in the shallow and littoral sediments was 35–27800 g C/(dm³ day) in summer and 32.8–88.9 g C/(dm³ day) in winter. The maximal rates of MP were observed in the littoral sediments in the zone of macrophyte decomposition, in local depressions, and in the estuary of a freshwater creek (up to 113 l/(dm³ day)). The maximal level of MO was observed in the shallow estuarine sediments (up to 2450 l/(dm³ day)). During the winter season, at the temperature of –0.5 to 0.5°C, the MP rate in the littoral sediments was 0.02–0.3 l/(dm³ day), while the MO rate was 0.06–0.7 l/(dm³ day). The isotopic data obtained indicate that the C_org of the mats and of the upper sediment layers is enriched with the heavy ¹³C isotope by 1–4 as compared to the C_org of the suspension. A striking difference was found between the levels of methane emission by the typical littoral microlandscapes. In fine sediments, the average emission was 675 l CH₄/(m² day); in stormy discharge stretch sediments, it was 1670 l CH₄/(m² day); and under stones and in silted pits, 1370 l CH₄/(m²day). The calculation, performed with consideration of the microlandscape areas with a high production, allowed the CH₄ production of 1 km² of the littoral to be estimated as 192–300 l CH₄/(km² day).     

Short-term changes in phosphorus storage in an oligotrophic Everglades wetland ecosystem receiving experimental nutrient enrichment

Natural, unenriched Evergladeswetlands are known to be limited by phosphorus(P) and responsive to P enrichment. However,whole-ecosystem evaluations of experimental Padditions are rare in Everglades or otherwetlands. We tested the response of theEverglades wetland ecosystem to continuous,low-level additions of P (0, 5, 15, and30 g L^–1 above ambient) in replicate,100 m flow-through flumes located in unenrichedEverglades National Park. After the first sixmonths of dosing, the concentration andstanding stock of phosphorus increased in thesurface water, periphyton, and flocculentdetrital layer, but not in the soil or macrophytes. Of the ecosystem components measured, total P concentration increased the most in the floating periphyton mat (30 g L^–1: mean = 1916 g P g^–1, control: mean =149 g P g^–1), while the flocculentdetrital layer stored most of the accumulated P(30 g L^–1: mean = 1.732 g P m^–2,control: mean = 0.769 g P m^–2). Significant short-term responsesof P concentration and standing stock wereobserved primarily in the high dose (30 gL^–1 above ambient) treatment. Inaddition, the biomass and estimated P standingstock of aquatic consumers increased in the 30and 5 g L^–1 treatments. Alterationsin P concentration and standing stock occurredonly at the upstream ends of the flumes nearestto the point source of added nutrient. Thetotal amount of P stored by the ecosystemwithin the flume increased with P dosing,although the ecosystem in the flumes retainedonly a small proportion of the P added over thefirst six months. These results indicate thatoligotrophic Everglades wetlands respondrapidly to short-term, low-level P enrichment,and the initial response is most noticeable inthe periphyton and flocculent detrital layer.     

Effect of ammonium on uptake of phosphorus,potassium, calcium and magnesium by intact soybean plants

Summary The effect of a wide range of ammonium concentrations (1.78×10^–5 to 3.57×10^–3 M) on the uptake and tissue content of P, K, Ca and Mg in intact soybean (Glycine max (L.) Merr. Cv. Amsoy) plants at different growth stages was studied. A stimulatory effect of ammonium on the uptake and content of P was observed over the entire concentration range, whereas this effect was observed only up to 500 M of ammonium with respect to K. At higher levels (>500 M), ammonium suppressed the uptake and content of K. Inhibition by high levels (>357 M) of ammonium was also found for the uptake and content of Ca and Mg. Inhibition of uptake of K, Ca and Mg by high levels of ammonium may be an important factor in the mineral nutrition of soybean plants. re]19760420     

The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l^–1 d^–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l^–1 d^–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l^–1 d^–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l^–1 d^-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l^–1 d^–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l^–1 d^–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.     

Establishment and multiplication of colchi-autotetraploids of Rauvolfia serpentina L. Benth. ex Kurz. through tissue culture

A tissue culture procedure was developed for the establishment and propagation of a colchi-autotetraploid of Rauvolfia serpentina for possible commercial exploitation. Multiplication of autotetraploid shoots was obtained either through axillary bud elongation on Murashige and Skoog [1] medium (MS) containing 2.65 M (0.5 mgl^–1) -naphthaleneacetic acid and 0.33 M (0.05 mgl^–1) kinetin, or via multiple shoot formation on MS medium supplemented with 4.44 M (1.0 mgl^–1) 6-benzylaminopurine and 0.53 M (0.1 mgl^–1) -naphthaleneacetic acid. Rooting could be induced by transferring the shoots to MS medium containing 7.95 M (1.5 mgl^–1) -naphthaleneacetic acid alone. The plantlets, thus formed, were tetraploid in nature by cytological observations of the root tips. They exhibited 80–90% success in establishment under glass house and field conditions.     

Distribution of magnesium in wheat (Triticum aestivum L.) in relation to supply

The aims of this study were to describe the distribution of magnesium (Mg) and its retranslocation within wheat, in order to develop diagnostic procedures for Mg deficiency. Plants were grown in solution culture with both constant supply (0, 5, 10, 20, 40, 80, 160 MMg) and discontinued supply (40 M and 160 M decreased to nil).Magnesium was depleted from old leaves when Mg supply to the roots was halted. However, initial deficiency symptoms occurred on young leaves under constant but inadequate supply, contrasting with previous reports. Magnesium concentrations were also lower in young leaves compared to old leaves. Symptoms of yellowing and necrosis occurred if the leaf tissue contained <1194 gg^–1, irrespective of leaf age. The minimum Mg concentration in whole shoots associated with maximum shoot weight was 932 gg^–1; for the youngest emerged blade (YEB) it was 861 gg^–1. Symptoms were apparent on the young leaf before a reduction in shoot weight was measurable. The concentration of Mg in the YEB and whole shoot were better related to solution Mg concentration than was the Mg concentration in the old leaf.     

Rates of nitrification and carbon uptake in the Rhône River plume (northwestern Mediterranean Sea)

Nitrification rates were measured along a salinity gradient in the Rhône River estuary, using specific inhibitors (allylthiourea and chlorate) coupled with the measurement of change in nitrite concentration and inorganic carbon uptake by nitrifiers. Rates of ammonium and nitrite oxidation were similar up to 15 practical salinity units (from 1 to 2 mol N oxidized liter^-1 day^-1). For higher salinities, nitrite and ammonium oxidation rates were 0.14 and 0.23 mol N oxidized liter^-1 day^-1, respectively. Ammonium oxidizers assimilated 19–150 × 10–3 mol C liter^-1 day^-1, while nitrite oxidizers fixed 4.8–72.6 × 10–3 mol C liter^-1 day^-1. The amounts of nitrogen oxidized and C incorporated demonstrated a linear correlation (r ² > 0.99). The ratio of N oxidized to C incorporated ranged between 14.3 to 12.3 for ammonium oxidizers, and between 31.6 and 29 for nitrite oxidizers, the lower values being measured in seawater. Offprint requests to: M. Bianchi.     

Growth and physiology of potassium-limited chemostat cultures of Paracoccus denitrificans

In potassium-limited chemostat cultures of Paracoccus denitrificans the maximum specific growth rate (µ_max) was found to depend on the input potassium concentration: At 0.21mM µ_max was 0.10–0.11 h^-1; at 0.44 mM 0.15–0.16 h^-1 and at 0.66 mM 0.20–0.21 h^-1. The plots of the specific rates of oxygen-, succinate-and potassium consumption against gave straight lines. The intracellular potassium concentration was a linear function of and varied from 1% (0.13 M) at a value of 0.034 h^-1 to 2.2% (0.29 M) at =0.26 h^-1; the potassium concentration gradient and the potassium concentration in the culture fluid in the steady state were dependent on the input potassium concentration. The potassium concentration gradient varied from 8,900-1,200. At all values 20–25% of the total energy production was used for potassium transport. 350,100 and 30 ATP molecules were calculated to be required to maintain one potassium ion intracellular during 1 h at values of 0.034, 0.197 and 0.257 h^-1 respectively. It is concluded that the amount of circulation of potassium is dependent on the potassium concentration gradient or on the potassium concentration in the culture in the steady state. The dependency of µ_max on the input potassium concentration was explained by the assumption that at low input potassium concentrations the net uptake of potassium (influx-efflux) is not rapidly enough to maintain the high potassium gradient in the existing cells and to establish it in the newly formed cells. At high values and at high input potassium concentrations µ_max is limited by the specific rate of oxygen consumption, which was found to be 11–12 mmol O₂ g dry weight^-1 h^-1 at µ_max for potassium-, succinate-and sulphate-limited chemostat cultures.     

Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

Seasonal changes in inorganic and organic phosphorus in the soil of a riparian forest

This study addresses the temporal distribution of forms of phosphorus in the soil of a temporarily flooded riparian forest of the valley of the river Garonne (Southwest of France). A sequential extraction for forms of phosphorus of increasing chemical stability was used. During the study period (13 months), the forest was flooded a few days during March and May. In winter, resin-Pi concentration was high (26 g g^–1) in comparison to spring values (<9 g g^–1). NaHCO₃-Po, NaHCO₃-Pi or NaOH-Pi concentrations increased during winter (up to 74, 124 and 78 g g^–1 respectively) and decreased significantly during spring (32, 44 and 32 g g^–1 respectively). This pattern was attributed to simultaneous mineralization and plant uptake during the growing season and to the flood events (erosional processes and P-release). During summer and fall, resin-Pi concentration increased significantly (up to 26 g g^–1 in October). NaHCO₃-Po concentrations remained low during spring and summer (<33 g g^–1), and increased significantly in fall (>45 g g^–1 NaHCO₃-Pi or NaOH-Pi increased in late spring or summer (90 g g^–1 and 68 g g^–1 respectively). Increasing concentrations of the labile forms during late spring or summer were ascribed to the warm temperature and soil dryness that limited plant growth. HCl-Pi increased regularly after the floods (174 g g^–1 before the flood events to 254 g g^–1 after the floods). Residual P presented a similar pattern i.e. 214 g g^–1 and 279 g g^–1 respectively before and after the flood events. This pattern was attributed to a progressive incorporation of flood deposits to the soil.     

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.     

The in vitro retardation of porcine cataractogenesis by the calpain inhibitor,SJA6017

Calpain inhibitors show the potential to serve as non-surgical alternatives in treating diabetic cataract and other types of these disorders. Here, we have tested the recently developed calpain inhibitor, SJA6017, for its ability to inhibit cataractogenesis in porcine lenses. These lenses were incubated in increasing levels of extralenticular calcium (Ca²⁺; 5–30 mM). Atomic absorption spectroscopy was used to determine total internal lens Ca²⁺ and a correlation between porcine lens Ca²⁺ uptake and levels of lens opacification were found with a total internal lens Ca²⁺ level of 5.8 M Ca²⁺ g^–1 wet lens weight corresponding to the onset of catarctogenesis. A total internal lens Ca²⁺ level of 8.0 M Ca²⁺ g^–1 wet lens weight corresponded to cataract occupying approximately 70% of the lens cell volume. This degree of cataract was reduced by approximately 40%, when SJA6017 (final concentration 0.8 M) was included in the extralenticular medium, suggesting that the Ca²⁺-mediated activation of calpains may be involved in the observed opacification. Supporting this suggestion atomic absorption spectroscopy showed that the effect of SJA6017 (final concentration 0.8 M) on lens opacification was not due to the compound restricting porcine lens Ca²⁺ uptake. The results indicate that calpain-induced cataractogenesis is dependent on extracellular Ca²⁺ and the calpain inhibitor SJA6017 (0.8 M) had no significant effect on Ca²⁺ uptake by lens. Its inhibitory effect on lens opacification may be due to a direct action on the activity of calpain. (Mol Cell Biochem 261: 169–173, 2004)     

Epizooic ciliates (Vorticella sp.) compete for food with their host Daphnia longispina in a small polyhumic lake

Summary Clearance rates of epizooic ciliates (Vorticella sp.) were measured together with their host, a planktonic cladoceran Daphnia longispina by using fluorescent latex beads as tracers of food. Vorticellans and their host graze on food of same size range (nanoplanktonic algae and bacteria). Individual clearance rates of Vorticella averaged 6.9 and 7.0 l ind^-1 h^-1 and those of Daphnia 463 and 708 l ind^-1 h^-1 for beads with diameter 2.00 and 3.92 m. On the average, epizooic vorticellans together on the carapace of Daphnia cleared particles with rates representing 25–33% of that the host cleared, the maximum rates being 50–80%. In a steeply stratified polyhumic lake vorticellans take advantage of following Daphnia to food patches and they can severely compete for food with their host.