Efficiencies and costs of larval growth in different food environments (Asteroidea: Asterina miniata)

The ocean is a nutritionally heterogeneous environment. For feeding larval forms, food variability has significant consequences for growth and later recruitment success. In this study, the physiological and biochemical responses to a range of different food concentrations (unfed, 4, 20, and 40 algal cells μl^− 1) were examined in larvae of the asteroid, Asterina miniata. Measurements of growth, protein synthesis rates, and the energetic cost of protein synthesis were made. Under conditions of rapid growth, protein comprised a larger percent (66%) of a larva's organic biomass compared to similar-aged, slower-growing larvae (26%). Larvae fed at the highest food concentration tested (40 algal cells μl^− 1) had a protein depositional efficiency of 80% (± 16%), a value 3-fold higher than larvae fed 20 algal cells μl^− 1 (28% ± 11%). Also, faster-growing larvae required 3-fold less energy per unit mass of protein growth. Larvae fed 40 algal cells μl^− 1 deposited protein at a respiratory cost of 65 ± 11 pmol O₂ h^− 1 (μg protein)^− 1; larvae fed 20 algal cells μl^− 1 had a cost of 192 ± 47 pmol O₂ h^− 1 (μg protein)^− 1. While there were differences in the cost to deposit protein (i.e., protein growth, the balance of synthesis and degradation), there were no differences in the energetic cost of protein synthesis for all food concentrations tested. The energetic cost of protein synthesis was fixed at 13.8 (± 0.92) Joules (mg protein synthesized)^− 1 and was independent of developmental stage, growth rates, and large changes (58-fold) in protein synthesis rates. A major conclusion from this study is that larvae grown in high-food environments not only grew faster, but did so for considerably less energy. Defining the complex relationships of food availability and metabolic efficiency will provide more accurate predictions of larval growth under variable food conditions in the ocean.     

The calmodulin inhibitor and antipsychotic drug trifluoperazine inhibits voltage-dependent K channels in rabbit coronary arterial smooth muscle cells

We investigated the effect of the calmodulin inhibitor and antipsychotic drug trifluoperazine on voltage-dependent K⁺ (Kv) channels. Kv currents were recorded by whole-cell configuration of patch clamp in freshly isolated rabbit coronary arterial smooth muscle cells. The amplitudes of Kv currents were reduced by trifluoperazine in a concentration-dependent manner, with an apparent IC₅₀ value of 1.58 ± 0.48 μM. The rate constants of association and dissociation by trifluoperazine were 3.73 ± 0.33 μM⁻¹ s⁻¹ and 5.84 ± 1.41 s⁻¹, respectively. Application of trifluoperazine caused a positive shift in the activation curve but had no significant effect on the inactivation curve. Furthermore, trifluoperazine provoked use-dependent inhibition of the Kv current under train pulses (1 or 2 Hz). These findings suggest that trifluoperazine interacts with Kv current in a closed state and inhibits Kv current in the open state in a time- and use-dependent manner, regardless of its function as a calmodulin inhibitor and antipsychotic drug.     

Growth, reproductive and photosynthetic responses to copper in the yellow-horned poppy, Glaucium flavum Crantz.

Glaucium flavum Crantz. is found in an anthropized coastal grassland at the joint estuary of the Tinto and Odiel rivers (SW Spain), growing under the influence of high levels of copper contamination derived from nearby petrochemical industries, with no obvious adverse affects on the performance of the plant. In addition, this species exhibits a series of ecological characteristics which may render it appropriate for use in the phytoremediation of contaminated areas. Nonetheless, the response of G. flavum to elevated copper concentrations has not been studied. A greenhouse experiment was conducted to investigate the effects of a range of Cu concentrations (0 to 47 mmol l⁻¹) on the growth, reproduction and photosynthetic performance of G. flavum, by measuring relative growth rate, fruit and seed production, chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. We also determined total copper, nitrogen, phosphorous, sulphur, calcium and magnesium concentrations. G. flavum survived with concentrations of up to 730 mg Cu kg⁻¹ DW in the leaves, when treated with 30 mmol Cu l⁻¹ (2000 mg l⁻¹). Quantum efficiency of PSII, net photosynthesis rate, as well as leaf Ca and Mg concentrations were all negatively affected by Cu concentrations greater than 9 mmol l⁻¹ in the nutrient solution. Our results indicate that the reduction in photosynthetic performance may be attributed to the adverse effect of excess Cu on the photosynthetic apparatus of the plant, both directly, via a decrease in pigment concentrations, and indirectly, via interference of Cu with Ca ions of PSII. Growth and seed production were only slightly affected by leaf tissue concentrations as high as 230 mg Cu kg⁻¹ dry mass, which suggests that this species could play an important role in phytoremediation of Cu-contaminated soils.     

Denitrifying sulfide removal and carbon methanogenesis in a mesophilic, methanogenic culture

The inhibitory effects of 90-189 mg l⁻¹ of sulfide and 25-75 mg-N l⁻¹ of nitrate on methanogenesis were investigated in a mixed methanogenic culture using butyrate as carbon source. In the initial phase of 90 mg l⁻¹ S²⁻ test, autotrophic denitrification of nitrate occurred with sulfide as the electron donor. Then the sulfate-reducing strains converted the produced sulfur back to sulfide via heterotrophic oxidation pathway. Methanogenesis was not markedly inhibited when 90 mg l⁻¹ of sulfide was dosed alone. When 25-75 mg-N l⁻¹ of nitrate was presented, initiation of methanogenesis was seriously delayed. Nitrogen oxides (NO_x), the intermediates for nitrate reduction via denitrification pathway, inhibited methanogenesis. The 90 mg l⁻¹ of sulfide favored heterotrophic dissimilatory nitrate reduction to ammonia (DNRA) pathway for nitrate reduction. Possible ways of maximizing methane production from an organic carbon-rich wastewater with high levels of sulfide and nitrate were discussed.     

Anaerobic degradation of tetrachlorobisphenol-A in river sediment

This study investigated the anaerobic degradation of tetrachlorobisphenol-A (TCBPA) in sediment samples collected at three sites along the Erren River in southern Taiwan. TCBPA anaerobic degradation half-lives (t_1/2) in the sediment were 12.6, 16.9 and 21.7 d at concentrations of 50, 100, and 250 ??g g⁻¹, respectively. TCBPA (50 ??g g⁻¹) anaerobic degradation half-lives (t_1/2) in the sediment were 10.1, 11.8, 11.0, 11.6, 10.8, 9.1, 8.5, 18.2, 19.3, and 16.1 d by the addition of yeast extract (5 mg l⁻¹), cellulose (0.96 mg l⁻¹), sodium chloride (1%), brij 30 (130 mg l⁻¹), brij 35 (43 mg l⁻¹), rhamnolipid (55 ??M), surfactin (91 ??M), phthalic esters (2 mg l⁻¹), nonylphenol (2 mg l⁻¹), and heavy metals (2 mg l⁻¹), respectively. The degradation rate of TCBPA was enhanced by the addition of yeast extract, cellulose, sodium chloride, brij 30, brij 35, rhamnolipid, or surfactin. However, it was inhibited by the addition of phthalic esters, nonylphenol, or heavy metals. Also noted was the presence of dichlorobisphenol-A and bisphenol-A, two intermediate products resulting from the anaerobic degradation of TCBPA accumulated in the sediments.     

Biogeochemical processes in intensive zero-effluent marine fish culture with recirculating aerobic and anaerobic biofilters

The biogeochemical processes that drive nutrient transformations and recycling in organic marine sediment-water environments were studied for 17 months in a zero-effluent intensive recirculating culture system. The system consisted of a 10 m³ gilthead seabream (Sparus aurata) tank coupled to aerobic and anaerobic water treatment elements. Nutrients and alkalinity were measured in the system to quantify the main biogeochemical processes. Fractions of the carbon fed in feed were found in fish (18.3%) and in sludge (11%); the missing carbon was respired by fish (45%) and by aerobic (8.4%) and anaerobic (7.7%) microorganisms. Fractions of the nitrogen fed in feed were found in fish (15.4%) and in sludge (14.3%); the missing nitrogen was eliminated by nitrification-denitrification. Most of the phosphorus and ash fed in feed and not found in fish accumulated within the sludge in the system. The rates of nitrification, denitrification and sulphate reduction increased with time, reaching 0.3 g N m^− 2 d^− 1, 53 g N m^− 2 d^− 1 and 145 g S m^− 2 d^− 1, respectively. Nitrification developed more rapidly than denitrification, leading at first to nitrate accumulation (to 20 mmol NO₃ l^− 1 by day 200) and a decrease in alkalinity. Once denitrification surpassed nitrification, nitrate concentrations decreased, eventually being reduced to < 0.3 mmol NO₃ l^− 1 by day 510, and alkalinity stabilized. Toxic hydrogen sulphide, generated within the anaerobic sludge, was oxidized by oxygen and nitrate as it diffused through the anaerobic-aerobic sediment-water interface. When nitrate levels in the water above the sludge dropped below 2 mmol l^− 1, sulphide was also oxidized in the fluidized bed reactor. Denitrification reduced nitrate in the water, respired (jointly with sulphate reduction) carbon in the sludge, oxidized the hydrogen sulphide, and contributed to stabilization of alkalinity and accumulation of polyphosphate in bacteria as a major sink of labile P.     

Copper biosorption on Lyngbya putealis: Application of response surface methodology (RSM)

The potential use of biosorbent prepared from an indigenously isolated cyanobacterium, Lyngbya putealis, for the removal of copper from aqueous solution has been investigated under optimized conditions in this study. Batch mode experiments were performed to determine the adsorption equilibrium and kinetic behavior of copper in aqueous solution allowing the computation of kinetic parameters and maximum metal adsorption capacity. Influences of other parameters like initial metal ion concentration (10-100 mg l⁻¹), pH (2-8) and biosorbent dose (0.1-1.0 g/100 ml) on copper adsorption were also examined, using Box-Behnken design matrix. Very high regression coefficient between the variables and the response (R² = 0.9533) indicates excellent evaluation of experimental data by second order polynomial regression model. The response surface method indicated that 40-50 mg l⁻¹ initial copper concentration, 6.0-6.5 pH and biosorbent dose of 0.6-0.8 g/100 ml were optimal for biosorption of copper by biosorbent prepared from L. putealis. On the basis of experimental results and model parameters, it can be inferred that the biosorbent which has quite high biosorption capacity can be utilized for the removal of copper from aqueous solution.     

Neuronal control of the cardiac responses to osmotic stress in the gastropod limpet Patella caerulea

Mediterranean limpets Patella caerulea were exposed to different salinity conditions and treated with drugs interfering with neuronal control of heartbeat. Heart rate was monitored using a non-invasive method. Limpets were superfused with control (33 g l(-1)), hyposaline (0 and 10 g l(-1)) or hypersaline (56 and 66 g l(-1)) artificial seawater. Under osmotic stress the limpets showed an initial increase of heart rate, followed by acardia, particularly under hyposalinity. The tachycardia observed after exposure to 56 g l(-1) was abolished in the animals injected with a selective sodium channel blocker, tetrodotoxin (TTX), or with a serotoninergic antagonist, methysergide. Injection of TTX also partly prevented the acardia occurring at 0 g l(-1). The acardia was completely prevented after injection with atropine and benzoquinonium, two selective cholinergic antagonists. These findings indicate that cardiac responses of P. caerulea to variations in external salinity are regulated by an extrinsic neuronal control involving the serotoninergic and the cholinergic systems in the tachycardic and acardic responses, respectively.     

Comparison and evaluation of RNA quantification methods using viral, prokaryotic, and eukaryotic RNA over a 10 concentration range

Quantification of RNA is essential for various molecular biology studies. In this work, three quantification methods were evaluated: ultraviolet (UV) absorbance, microcapillary electrophoresis (MCE), and fluorescence-based quantification. Viral, bacterial, and eukaryotic RNA were measured in the 500 to 0.05-ng μl⁻¹ range via an ND-1000 spectrophotometer (UV), Agilent RNA 6000 kits (MCE), and Quant-iT RiboGreen assay (fluorescence). The precision and accuracy of each method were assessed and compared with a concentration derived independently using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Cost, operator time and skill, and required sample volumes were also considered in the evaluation. Results indicate an ideal concentration range for each quantification technique to optimize accuracy and precision. The ND-1000 spectrophotometer exhibits high precision and accurately quantifies a 1-μl sample in the 500 to 5-ng μl⁻¹ range. The Quant-iT RiboGreen assay demonstrates high precision in the 1 to 0.05-ng μl⁻¹ range but is limited to lower RNA concentrations and is more costly than the ND-1000 spectrophotometer. The Agilent kits exhibit less precision than the ND-1000 spectrophotometer and Quant-iT RiboGreen assays in the 500 to 0.05-ng μl⁻¹ range. However, the Agilent kits require 1 μl of sample and can determine the integrity of the RNA, a useful feature for verifying whether the isolation process was successful.     

Bioremediation of metal contamination in the Plankenburg River,Western Cape,South Africa

Three bioreactors (two laboratory-scale and one on-site) were evaluated for their efficiency to reduce metal concentrations in water collected from the Plankenburg River, South Africa. Water (bioreactors one, two and on-site) and bioballs (bioreactors two and on-site) collected throughout the study periods were digested and analysed using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Aluminium (Al), nickel (Ni), and zinc (Zn) concentrations decreased from 0.41 mg l^?1 to 0.06 mg l^?1 (85%), 0.2 mg l^?1 to 0.07 mg l^?1 (65%) and 75 mg l^?1 to 0.02 mg l^?1 (97%), respectively (bioreactor one). Aluminium [(1.55–0.38 mg l^?1 (75%)], copper (Cu) [57% (from 0.33 mg l^?1 to 0.14 mg l^?1)], iron (Fe) [71.99–40.4 mg l^?1 (44%)] and manganese (Mn) [57% (0.07–0.03 mg l^?1)] concentrations also decreased in the water samples from bioreactor two. In the on-site, six-tank bioreactor system, concentrations for Fe, Cu, Mn and Ni decreased, while Zn and Al concentrations increased. The concentrations recorded in biofilm samples were higher than the corresponding water samples. The bioballs employed in the bioreactor were thus shown to be efficient attachment surfaces for biofilm development and subsequent metal accumulation. Potentially metal-tolerant organisms (Pseudomonas sp., Sphingomonas sp., and Bacillus sp.) were also identified using phylogeny.     

Quantum dot-based assay for Cu quantification in bacterial cell culture

A simple and sensitive method for quantification of nanomolar copper with a detection limit of 1.2 × 10⁻¹⁰ M and a linear range from 10⁻⁹ to 10⁻⁸ M is reported. For the most useful analytical concentration of quantum dots, 1160 μg/ml, a 1/K_sv value of 11 μM Cu²⁺ was determined. The method is based on the interaction of Cu²⁺ with glutathione-capped CdTe quantum dots (CdTe–GSH QDs) synthesized by a simple and economic biomimetic method. Green CdTe–GSH QDs displayed the best performance in copper quantification when QDs of different sizes/colors were tested. Cu²⁺ quantification is highly selective given that no significant interference of QDs with 19 ions was observed. No significant effects on Cu²⁺ quantification were determined when different reaction matrices such as distilled water, tap water, and different bacterial growth media were tested. The method was used to determine copper uptake kinetics on Escherichia coli cultures. QD-based quantification of copper on bacterial supernatants was compared with atomic absorption spectroscopy as a means of confirming the accuracy of the reported method. The mechanism of Cu²⁺-mediated QD fluorescence quenching was associated with nanoparticle decomposition.     

Sulfide enhances methanogenesis in nitrate-containing methanogenic cultures

The effects of sulfide on nitrate reduction and methanogenesis using butyrate as a carbon source were investigated in a mixed mesophilic, methanogenic culture. In the sulfide-free medium, 25-75 mg l⁻¹ nitrate markedly inhibited the efficiencies of acetogenesis and methanogenesis processes. Adding 25 mg-S l⁻¹ increased methane production in nitrate-amended medium. Low sulfide levels shifted the nitrate reduction pathway from denitrification to dissimilatory nitrate reduction to ammonia (DNRA), thereby reducing the amounts of toxic nitric oxide and nitrous oxide produced that inhibit methanogenesis. The dose of 25 mg l⁻¹ sulfide was oxidized completely, during which heterotrophic DNRA predominated. The oxidized forms of sulfide reformed, limiting induction of the heterotrophic denitrification pathway. The actions of heterotrophic and autotrophic DNRA bacteria, denitrifiers, sulfate-reducing bacteria and methanogens mitigate nitrate toxicity during methanogenesis in an anaerobic process.     

Selectivity and grazing impact of microzooplankton on phytoplankton in two subtropical semi-enclosed bays with different chlorophyll concentrations

Microzooplankton grazing rates were compared between two sites (S1 and S2) in the coastal seas of eastern Hong Kong with similar physio-chemical parameters, but different chlorophyll concentrations. During the period from March 2007 to January 2008, six sets of dilution experiments, combined with high performance liquid chromatography and phytoplankton size fractionation (< 200 μm, < 20 μm and < 5 μm), were carried out to study the microzooplankton grazing rate on phytoplankton of different taxonomic groups and sizes. Although total chlorophyll a concentrations were much higher in S1 (4.98-18.42 μg l^− 1) than in S2 (0.29-1.68 μg l^− 1), size composition of phytoplankton was relatively similar between the two sites. Measured as chlorophyll a, phytoplankton growth rates (− 0.84-1.91 d^− 1 in S1; 0.03-2.85 d^− 1 in S2) and microzooplankton grazing rates (0.00-2.26 d^− 1 in S1; 0.00-1.49 d^− 1 in S2) for all three size fractions were similar between the two bays. Phytoplankton growth rates and microzooplankton grazing rates measured as other pigments for phytoplankton of different size fractions did not show strong variations. Microzooplankton grazing impact, expressed as the ratio of microzooplankton grazing rate to phytoplankton growth rate, was generally higher in S1 than in S2, although the difference was not statistically significant. High microzooplankton grazing impact on alloxanthin (1.00-45.85) suggested strong selection toward cryptophytes. Our results provided no evidence for size selective grazing on phytoplankton by microzooplankton.     

In vitro inhibition of fatty acid synthase by 1,2,3,4,6-penta-O-galloyl-β-d-glucose plays a vital role in anti-tumour activity

1,2,3,4,6-Penta-O-galloyl-β-d-glucose (PGG) inhibits glioma cancer U251 cells, more strongly than MDA-MB-231 and U87 cells. In addition, PGG is transported across cancer cell membrane to further down-regulate FAS and activate caspase-3 in MDA-MB-231 cells. Compared with other FAS inhibitors, including catechin gallate and morin, PGG involves a higher reversible fast-binding inhibition with half-inhibitory concentration value (IC₅₀) of 1.16 μM and an irreversible slow-binding inhibition, i.e. saturation kinetics with a dissociation constant of 0.59 μM and a limiting rate constant of 0.16 min^−l. The major reacting site of PGG is on the β-ketoacyl reduction domain of FAS. PGG exhibits different types of inhibitions against the three substrates in the FAS overall reaction. The higher concentrations of PGG tested (higher than 20 μM) clearly altered the secondary structure of FAS by increasing the α-helix and induced a redshift in the FAS spectra. In addition, only PGG concentrations higher than 20 μM resulted in FAS precipitation.     

An in vitro propagation protocol of two submerged macrophytes for lake revegetation in east China

Thirty-six programs have been set up to revegetate the degraded lake wetlands in east China since 2002. Most projects however faced deficiency of submerged macrophyte propagules. To solve the problem, alternative seedling sources must be found besides traditional field collection. This paper deals with an in vitro propagation protocol for two popularly used submerged macrophytes, Myriophyllum spicatum L. and Potamogeton crispus L. Full strength Murashige and Skoog-based liquid media (MS) plus 3% sucrose in addition to 0–2.0 mg l⁻¹ 6-benzylaminopurine (BA) and 0–1.0 mg l⁻¹ indoleacetic acid (IAA) were tried for shoot regeneration. Meanwhile, full, half or quarter strength MS in addition to 0, 0.1 or 0.2 mg l⁻¹ naphthaleneacetic acid (NAA) were tested for root induction, respectively. Results indicated that both species had the ability of regeneration from stem fragments in MS without further regulators. However, the addition of 2.0 mg l⁻¹ BA with 0.2 or 1.0 mg l⁻¹ IAA in MS drastically stimulated the regeneration efficiency of M. spicatum, while the addition of 2.0 mg l⁻¹ BA with 0.2 or 0.5 mg l⁻¹ IAA in MS significantly stimulated that of P. crispus. For root induction, full strength MS in combination with 0.1or 0.2 mg l⁻¹ NAA was preferred by M. spicatum, and the same MS without or with 0.1 mg l⁻¹ NAA was preferred by P. crispus. Seedlings of each species produced from tissue culture room had a 100% survival rate on clay, sandy loam or their mixture (1:1) in an artificial pond, and phenotypic plasticity was exhibited when the nutrient levels varied among the three types of sediments. This acclimation of seedlings helped develop the shoot and root systems, which ensured seedling quality and facilitated the transplantation. Our study has established an effective protocol to produce high quality seedlings for lake revegetation programs at a larger scale. Since the two species we tested represent different regeneration performances in nature but shared similar in vitro propagation conditions, this study has indicated a potentially wide use of the common media for preparing seedlings of other submerged macrophytes.     

Ethanol production from sweet sorghum juice using very high gravity technology: Effects of carbon and nitrogen supplementations

Ethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP01 was investigated under very high gravity (VHG) fermentation and various carbon adjuncts and nitrogen sources. When sucrose was used as an adjunct, the sweet sorghum juice containing total sugar of 280 g l⁻¹, 3 g yeast extract l⁻¹ and 5 g peptone l⁻¹ gave the maximum ethanol production efficiency with concentration, productivity and yield of 120.68 ± 0.54 g l⁻¹, 2.01 ± 0.01 g l⁻¹ h⁻¹ and 0.51 ± 0.00 g g⁻¹, respectively. When sugarcane molasses was used as an adjunct, the juice under the same conditions gave the maximum ethanol concentration, productivity and yield with the values of 109.34 ± 0.78 g l⁻¹, 1.52 ± 0.01 g l⁻¹ h⁻¹ and 0.45 ± 0.01 g g⁻¹, respectively. In addition, ammonium sulphate was not suitable for use as a nitrogen supplement in the sweet sorghum juice for ethanol production since it caused the reduction in ethanol concentration and yield for approximately 14% when compared to those of the unsupplemented juices.     

P2X7 receptor mediated phosphorylation of p38MAP kinase in the hippocampus

This study was designed to explore the effect of P2X7 receptor (P2X7R) activation on the expression of p38 MAP kinase (p38 MAPK) enzyme in hippocampal slices of wild-type (WT) and P2X7R^−/− mice using the Western blot technique and to clarify its role in P2X7 receptor mediated [³H]glutamate release. ATP (1 mM) and the P2X7R agonist BzATP (100 μM) significantly increased p38 MAPK phosphorylation in WT mice, and these effects were absent in the hippocampal slices of P2X7R^−/− mice. Both ATP- and BzATP-induced p38 MAPK phosphorylations were sensitive to the p38 MAP kinase inhibitor, SB203580 (1 μM). ATP elicited [³H]glutamate release from hippocampal slices, which was significantly attenuated by SB203580 (1 μM) but not by the extracellular signal-regulated kinase (ERK1/2) inhibitor, PD098095 (10 μM). Consequently, we suggest that P2X7Rs and p38 MAPK are involved in the stimulatory effect of ATP on glutamate release in the hippocampal slices of WT mice.     

Effects of acetylcholinesterase inhibitor paraoxon denote the possibility of non-quantal acetylcholine release in myocardium of different vertebrates

Effects of organophosphorous acetylcholinesterase inhibitor paraoxon were studied in the isolated atrial and ventricular myocardium preparations of a fish (cod), an amphibian (frog) and a mammal (rat) using the microelectrode technique. Incubation of isolated atrium with paraoxon (5 × 10⁻⁶–5 × 10⁻⁵ M) caused significant reduction of action potential duration and marked slowing of sinus rhythm. These effects were abolished by muscarinic blocker atropine and therefore are caused by acetylcholine, which accumulates in the myocardium due to acetylcholinesterase inhibition even in the absence of vagal input. Hemicholinium III is a blocker of high affinity choline-uptake transporters, which are believed to mediate non-quantal release of acetylcholine from cholinergic terminals in different tissues. In the atrial myocardium of all the three studied species, hemicholinium III (10⁻⁵ M) significantly suppressed all the effects of paraoxon. Blocker of parasympathetic ganglionic transmission hexamethonium bromide (10⁻⁴ M) and inhibitor of vesicular acetylcholine transporters vesamicol (10⁻⁵ M) failed to attenuate paraoxon effects. Among ventricular myocardium preparations of three species paraoxon provoked marked cholinergic effects only in frog, hemicholinium III abolished these effects effectively. We conclude that paraoxon stops degradation of acetylcholine in the myocardium and helps to reveal the effects of acetylcholine, which is continuously secreted from the cholinergic nerves in non-quantal manner. Thus, non-quantal release of acetylcholine in the heart is not specific only for mammals, but is also present in the hearts of different vertebrates.     

Effects of UV radiation and nitrate limitation on the production of biogenic sulfur compounds by marine phytoplankton

We tested the effects of UV radiation (UVR) and nitrate limitation on the production of dimethylsulfide (DMS), particulate dimethylsulfoniopropionate (DMSPp), and particulate dimethylsulfoxide (DMSOp) in natural seawater from the Gulf of Mexico and in phytoplankton cultures. DMS/Chl a ratios in PAR-only and PAR + UV-exposed seawater were 0.44–2.0 and 0.46–1.9 nmol DMS μg⁻¹ Chl a, respectively, whereas the ratios in cultures of Amphidinium carterae were 1.0–2.2 nmol μg⁻¹ in PAR-exposed samples and 0.91–2.1 nmol μg⁻¹ in PAR + UV-exposed samples. These results suggested that UVR did not substantially affect DMS/Chl a ratios in seawater and A. carterae culture samples. Similarly, UVR had no significant effect on DMSOp/Chl a in seawater samples (0.83–1.6 nmol DMSO μg⁻¹ Chl a for PAR + UV vs. 0.70–1.5 nmol μg⁻¹ for PAR-exposed seawater samples, respectively) or in A. carterae cultures (0.20–1.3 and 0.19–0.88 nmol DMSO μg⁻¹ Chl a in PAR + UV- and PAR-exposed cultures, respectively). In an experiment with the diatom, Thalassiosira oceanica, the culture was grown in high nitrate (30 μM) or low nitrate (6 μM) media and exposed to PAR-only or PAR + UV. The low nitrate, PAR-only samples showed an increase of intracellular dimethylsulfoniopropionate (DMSP) concentration from 2.1 to 15 mmol L⁻¹ in 60 h, but the increase occurred only after cultures reached the stationary phase. Cultures of T. oceanica grown under UVR had lower growth rates than those under PAR-only (μ′ = 0.17 and 0.32 d⁻¹, respectively) and perhaps did not experience severe nitrate limitation even in the low nitrate treatment. These results suggest that the elevated UVR in low nitrate environments could result in reduction of DMSP in some species, whereas DMSP concentrations would not be affected in eutrophic areas.