Effect of hydrolysing and oxidizing agents on the composition and degradation of wheat straw monosaccharides

Summary Wheat straw (WS) was treated with 5% sodium hydroxide, ozone and 5% sulfur dioxide at 70°C for 72 h, and the effect of treatments on monosaccharide composition and in vitro degradability by rumen microorganisms was studied. The major sugars, glucose and xylose, comprising about 90% of the total monosaccharides in the untreated WS were mainly confined to the cell walls. SO₂ exerted the greatest solubilizing effect, followed by ozone and NaOH; the respective values for the solubilized cell wall polysaccharides were: 26, 12 and 4.4%. One third of the total phenolics was oxidized by ozone, whereas, SO₂ exerted mostly a solubilizing effect on this fraction, converting 75% of it into soluble phenolics. In the NaOH treated WS 41% of the total phenolics were soluble, as compared to 22% in the untreated. The in vitro digestibility of monosaccharides in the untreated WS were initially high: 50% and 58% for xylose and glucose, respectively and 63% to 80% for the minor sugars. The SO₂ treatment resulted in an overall increase in digestibility of monosaccharides with values lying in the range of 90%. Sodium hydroxide was more efficient than ozone in enhancing the degradability of xylan and total sugars. The digestibility of cell wall sugars was increased from 52.4% to 84.4%, 63.4% and 72.3% by SO₂, O₃ and NaOH treatments respectively. Based on the present findings, it appears that wheat straw cell wall components are more sensitive to hydrolytic than to oxidative processes aimed at increasing its degradability by rumen microorganisms. SO₂ exerted on WS a multi-effect which was particularly suitable for increasing the digestibility of monosaccharides.     

The degradation and utilization of wheat-straw cell-wall monosaccharide components by defined ruminal cellulolytic bacteria

Cell walls (CW) of untreated wheat straw and sulphur-dioxide (SO₂)-treated wheat straw were used as model substrates for the hydrolysis and utilization of CW carbohydrates by pure cultures or pair-combinations of defined rumen bacterial strains. Fibrobacter succinogenes S85 and BL2 strains and their co-cultures with D1 were the best degraders of CW among ruminal cultures, solubilizing 37.2–39.6% of CW carbohydrates of untreated straw and 62.2–74.5% of SO₂-treated straw. Complementary action between Butyrivibrio fibrisolvens D1 and the F. succinogenes strains was identified with respect to co-culture growth and carbohydrate utilization. However, the extent of CW solubilization was determined mainly by the F. succinogenes strains. In both substrates, utilization of solubilized cellulose by F. succinogenes S85 and BL2 monocultures was higher than that of xylan and hemicellulose: 96.5–98.3%, 34.4–40.5% and 33.5–36.2%, respectively. Under scanning electron microscopy visualization, S85 and BL2 cells of the co-cultures comprised the most dense layer of bacterial cell mass attached to and colonized on straw stems and leaves, whereas D1 cells were always nearby. Stems and leaves of the untreated straw were less crowded by attached bacteria than that of the SO₂-treated straw. In both materials, the cell surface topography of S85 and BL2 bacteria attached to CW particles was specified by a coat of characteristic protuberant structures, polycellulosome complexes.     

Bioconversion of wheat straw to ethanol: Chemical modification,enzymatic hydrolysis,and fermentation

Native wheat straw (WS) was pretreated with various concentrations of H₂SO₄ and NaOH followed by secondary treatments with ethylene diamine (EDA) and NH₄OH prior to enzymatic saccharification. Conversion of the cellulosic component to sugar varied with the chemical modification steps. Treatment solely with alkali yield 51–75% conversion, depending on temperature. Acid treatment at elevated tempeatures showed a substantial decrease in the hemicellulose component, whereas EDA-treated WS (acid pretreated) showed a 69–75% decrease in the lignin component. Acid-pretreated EDA-treated straw yielded a 98% conversion rate, followed by 83% for alkali–NH₄OH treated straws. In other experiments, WS was pretreated with varying concentration of H₂SO₄ or NaOh followed by NH₄OH treatment prior to enzymatic hydrolysis. Pretreatment of straw with 2% NaOH for 4 h coupled to enzymatic hydrolysis yield a 76% conversion of the cellulosic component. Acid–base combination pretreatment yielded only 43% conversions. A reactor column was subsequently used to measure modification–saccharification–fermentation for wheat straw conversion on a larger scale. Thirty percent conversions of wheat straw cellulosics to sugar were observed with subsequent fermentation to alcohol. The crude cellulase preparation yielded considerable quantities of xylose in addition to the glucose. Saccharified materials were fermented directly with actively proliferating proliferating yeast cells without concentration of the sugars.     

Influence of natural magnesium sources on the in vitro fermentation and protozoan population in the rumen fluid collected from sheep

The objective of this experiment was to determine the effect of two types of caustic calcinated magnesite (caustic magnesite (CM) and Agromag (AG)) upon the end products of in vitro fermentation (total gas, methane, total and individual fatty acids, and VFA) and protozoan population in the rumen fluid collected from sheep. Both magnesium additives (CM and AG) as natural products in the dose of 0.01 g were added to the fermentation bottles containing rumen inoculum from sheep and different substrates. Meadow hay (MH), wheat straw (WS), amorphous cellulose (AC) and barley grain (BG) were used as substrates and incubated with the buffered rumen fluid using an in vitro gas measuring technique during 72 h of incubation. The rumen protozoa, Entodinium spp., Trichostomatids and large Entodiniomorphids and the total protozoan concentration were counted after 24 h of incubation. The methane production was significantly decreased with CM or AG, respectively, by 58 or 62% (MH), by 65% (WS), by 52% (AC) and by 58% (BG). The total VFA concentration was significantly lower compared to control for CM plus MH, WS, AC, BG and AG plus WS. The total VFA concentration was significantly higher compared to control for AG plus AC. The effect of the both additives on ciliate population was not uniform and depended on the substrates used and protozoan type. Ciliate population was significantly increased in Entodinium spp. (AG plus BG) and Diploplastron affinae (CM or AG plus BG) compared to control. Tested additives significantly decreased population of Entodinium spp. (AG plus MH or AC), Dasytricha ruminantium (AG plus AC), Ophryoscolex c. tricoronatus, Eremoplastron dilobum and Polyplastron multivesiculatum (CM or AG plus BG). It can be concluded that both natural magnesium sources influenced rumen fermentation patterns and protozoan population in vitro depending on the type of the substrate used; therefore, the relative efficacy of individual tested additive cannot be determined from these experiments. In vivo experiments are required in future.     

Effect of chemical treatments on the degradability of cotton straw by rumen microorganisms and by fungal cellulase

Three different chemical treatments—sulfur dioxide, ozone, and sodium hydroxide—were applied on cotton straw, and the effect on cell-wall degradability was assessed by using rumen microorganism and Trichoderma reesei cellulase. Sulfur dioxide (applied at 70°C for 72 h) did not change the lignin content of cotton straw but reduced the concentration of hemicellulose by 48%. Ozone exerted a dual effect, both on lignin (a 40% reduction) and hemicellulose (a 54% decrease). The treatment with NaOH did not solublize cell-wall components. The in vitro organic matter digestibility with rumen fluid of cotton straw was increased significantly by ozone and SO₂ treatments, by 120% and 50%, respectively, but not by NaOH. T. reesei cellulase was applied on the chemically pretreated cotton straw at a low level (6 filter paper U/g straw, organic matter), and the release of reducing sugars was determined. The highest level of reducing sugars (30.6 g/100 g organic matter) was obtained with the O₃-cellulase combination, which solubilized 64% of the cellulose and 88% of the hemicellulose. the SO₂- and the NaOH-pretreated cotton straw were hydrolyzed by T. reesei cellulase to the same extent (21 g reducing sugars/100 g organic matter). The rumen fluid digestibility of the enzymatic ally hydrolyzed straw was not increased further over the effect already obtained with the chemical pretreatments. However, the fermentability of the combined treatments was increased markedly. In the O₃-cellulase-treated cotton straw, 83% of the rumen fluid digestible material consisted of highly fermentable components. Although ozone proved to be the most potent pretreatment for enzymic saccharification in this study, the absolute result was modest. The limited effect of the combined O₃-cellulase treatment was probably associated with the pretreatment limitations, but not with the enzyme level. Based on the differential response of the chemically treated cotton straw to attack by rumen microorganisms on the one hand, and by T. reesei cellulase on the other hand, a hypothesis has been suggested as to the location of lignin and hemicellulose in the cellwall unit of cotton straw.     

Effects of organic matter incorporation on nitrous oxide emissions from rice-wheat rotation ecosystems in China

Organic matter addition is thought to be an important regulator of nitrous oxide (N₂O) emissions from croplands. Contradictory effects, however, were reported in previous studies. To investigate the effects of crop residue management on N₂O emissions from rice-wheat rotation ecosystems, we conducted field experiments at three sites (Suzhou, Wuxi and Jiangdu) in the Yangtze River Delta, using static chamber and gas chromatography methods. Our data show that N₂O emissions throughout the rice season from plots treated with wheat straw application at a high rate (WS) prior to rice transplanting (1.1–2.0 kg N ha^?1) were significantly lower (P?<?0.05) than those from the control plots without organic matter addition or added with wheat straw at a moderate rate (1.6–2.9 kg N ha^?1). Furthermore, the WS treatments had a residual inhibitory effect on N₂O emissions in the following non-rice season, which consistently resulted in significantly lower emissions (P?<?0.05) compared to the control treatments (2.2–3.1 vs. 3.9–5.6 kg N ha^?1). In comparison to the control treatments, the WS treatments reduced both the seasonal and annual direct emission factors of the applied nitrogen (EF_d) by 50–68% (mean: 57%). The addition of compost (aerobically composted rice or wheat straw harvested in the last rotation) reduced the seasonal and annual EF_ds by 29–32%. Over the entire rice-wheat rotation cycle, annual N₂O emissions from the fertilized fields at the three sites ranged from 3.3?±?0.3 to 16.8?±?0.6 kg N ha^?1, with a coefficient of variation (CV) of 61%. Similarly, the EF_ds during the rice-wheat rotation cycle ranged from 0.4% to 2.5%, with a CV of 67%. These high spatial variations might have been related to: variations in soil properties, such as texture and soil organic carbon; management practices, such as straw treatments (i.e., compost versus fresh straw) and weather conditions, such as precipitation and rainfall distribution. Our results indicate that the incorporation of fresh wheat straw at a high rate during the rice season is an effective management practice for the mitigation of N₂O emissions in rice-wheat rotation systems. Whether this practice is also effective in reducing the overall global warming potential of net N₂O, CH₄ and CO₂ emissions needs to be seen through further studies.     

Diversity of rumen microbiota using metagenome sequencing and methane yield in Indian sheep fed on straw and concentrate diet

An in vivo study aiming to investigate the rumen methanogens community structure was conducted in Mandya sheep fed on straw and concentrate diet. The ruminal fluid samples were collected and processed for unravelling the rumen microbiota and methanogens diversity. Further, the daily enteric methane emission and methane yield was also quantified using the SF₆ tracer technique. Results indicated that the Bacteroidetes (～57%) and Firmicutes (25%) were two prominent affiliates of the bacterial community. Archaea represented about 2.5% of the ruminal microbiota. Methanobacteriales affiliated methanogens were the most prevalent in sheep rumen. The study inveterate that the ruminal archaea community in sheep is composed of 9 genera and 18 species. Methanobrevibacter represented the largest genus of the archaeome, while methylotrophs genera constituted only 13% of the community. Methanobrevibacter gottschalkii was the prominent methanogen, and Methaobrevibacter ruminantium distributed at a lower frequency (～2.5%). Among Methanomassiliicoccales, Group 12 sp. ISO4-H5 constituted the most considerable fraction (～11%). KEGG reference pathway for methane metabolism indicated the formation of methane through hydrogenotrophic and methylotrophic pathways, whereas the acetoclastic pathway was not functional in sheep. The enteric methane emission and methane yield was 19.7 g/d and 20.8 g/kg DMI, respectively. Various species of Methanobrevibacter were differently correlated, and the distribution of hydrogenotrophic methanogens mainly explained the variability in methane yield between the individual sheep. It can be inferred from the study that the hydrogenotrophic methanogens dominate the rumen archaeal community in sheep and methylotrophic/aceticlastic methanogens represent a minor fraction of the community. Further studies are warranted for establishing the metabolic association between the prevalent hydrogenotrophs and methylotrophs to identify the key reaction for reducing methane emission.     

The effect of protein supplement source or supply pattern on the intake,digestibility, rumen kinetics,nitrogen utilisation and growth of Ethiopian Menz sheep fed teff straw

A series of trials were conducted to study the effect of either nitrogen source or supply pattern on the growth, rumen fermentation pattern and utilisation of straw by Ethiopian Menz sheep. All experimental sheep were given teff straw basal diet (CON). Irrespective of the trial, treatment sheep were offered either cottonseed cake (CSC), leucaena (LEU) and sesbania (SESM) in the morning prior to teff straw. Additional treatments with sesbaia were offered either in the evening (SESE) or morning and evening (SESME). Measurements included roughage intake, digestibility, kinetics, rumen fermentation patterns, nitrogen utilisation, microbial protein supply and growth of sheep.Rate of degradation was highest (P < 0.05) when sesbania was offered once a day compared with twice a day, while supplementation produced higher (P < 0.05) liquid passage rates. Diets with sesbania produced higher (P < 0.05) roughage intake compared with leucaena. Microbial protein supply as well as N economy were similar (P > 0.05) among the foliage diets irrespective of source, time or frequency of feeding. Supplementation enhanced (P < 0.001) growth rates in sheep, while cottonseed cake (CSC) diet was superior (P < 0.01) to the fodder trees. Growth rates declined across treatments during the second phase (6–10 weeks) compared with the initial period (1–6 weeks). It is also possible for farmers to feed sesbania supplements in the morning or evening or twice daily without any detrimental effects.     

The effect of combined chemical and enzyme treatments on the saccharification and in vitro digestion rate of wheat straw

Wheat straw was pretreated with sodium hydroxide, ozone, and sulfur dioxide, and subsequently treated with four sources of cellulase, T. reesei, T. reesei, T. viride, A. niger, and Oxyporus sp. The effect of the combined chemical + enzyme treatments on the extent of saccharification and on the digestion rate by rumen microorganisms was studied. Cellulases were applied at an equal but low concentration (0.5 FPU/ml) on the pretreated straw. The combined treatments, SO₂ + T. reesei cellulase nd SO₂ + T. viride cellulase, produced the highest and significant levels of reducing sugars (RS), 577 and 597 mg RS/g straw organic matter. The highest enzyme efficiency, 44.7 mg RS/mg enzyme, was found with T. reesei cellulase when applied on SO₂ pretreated straw. The in vitro organic matter digestibility was affected significantly only by the chemical pretreatments, whereas the effect of the cellulases was expressed mainly in increasing the fermentability of the hydrolyzed straw. The in vitro digestion pattern of the saccharified straw was found to be typical of a highly fermentable feed and comparable to a starchy mixture such as used in concentrate ruminant diets.     

Influence of planting geometry on photosynthetically active radiation interception and dry matter production relationships in pearl millet

A field experiment was conducted at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) Center, Patancheru, India to study photosynthetically active radiation (PAR) interception and dry matter production relationships in pearl millet (Pennisetum americanum (L.) Leeke). Two pearl millet genotypes, BJ 104 (G₁) and ICH 226 (G₂) were sown at three planting geometries obtained by using combinations of row and plant spacings (S₁: 37·5 cm × 26·6 cm; S₂: 75·0 cm × 13·3 cm; S₃: 150·0 cm × 6·6 cm) such that plant population was constant at 100 000 ha⁻¹ in all treatments. Cumulative intercepted PAR was maximum (330 MJ m⁻²) in G₂S₂ and minimum (268 MJ m⁻²) in G₁S₃. Conversion efficiency values ranged from 1·87 g MJ⁻¹ in G₁S₂ to 2·32 g MJ⁻¹ in G₂S₃. Final above-ground dry matter followed the pattern of cumulative intercepted PAR and maximum dry matter (7·22 Mg ha⁻¹) was produced by G₂S₂ while G₁S₃ produced minimum dry matter (4·97 Mg ha⁻¹).     

Effect of refiner defibrizing on the fermentability of ryegrass straw

The effects of two grinding methods, hammer milling and defibrizing by disk refining, on the fermentability of ryegrass straw were investigated. Disk refined or defibrized straw produced more sugar than hammer milled straw. Release of sugar was especially pronounced when H₂SO₄ was added to the straw during the defibrizing process. In vitro rumen digestibility was significantly higher (P < 0.1) for defibrized than for hammer milled straw. With semisolid culture the level of yeast growth was about three times as high on the defibrized as on hammer milled straw. A scanning electron micrograph revealed that defibrizing removed the waxy surface of the straw as well as separating fiber bundles, so that the surface area of the exposed fiber structure was increased.     

Microscopic Studies of Structure and Ruminal Fungal Colonization in Sheep of Wheat Straw Treated with Different Alkalis

The effect of chemically treating wheat straw (straw) with calcium oxide (CaO), Sodium hydroxide (NaOH) and alkaline hydrogen peroxide (AHP) on its subsequent colonization and degradation by rumen fungi was followed in sacco in the rumen of sheep. The colonization of treated straws was compared with untreated counterparts microscopically using a trypan blue lactophenol staining technique to reveal the fungal thalli and rhizoids. Structural disintegration of straw particles caused by chemical treatments was also observed. AHP caused the greatest fragility to straw particles followed respectively by NaOH and CaO treatments. Untreated straw showed relatively less fungal colonization compared with treated straws being heavily colonized by rhizoids and thalli. AHP-treated straw was most extensively colonized with rhizoids observed penetrating deep into straw tissues particularly the bundle sheath cells. The thalli of this study resembled mono- and poly-centric genera of anaerobicChytridiomycete fungi. The pattern of fungal colonization compared well with the previous degradability data on treated straws which demonstrates the value of such treatments to improve degradation of fibrous substrates by rumen micro-organisms, particularly fungi.     

Total mixed ration pellets for light fattening lambs: effects on animal health

Fifty male Merino lambs (6 to 8 weeks, 14.1 kg; n=10 per group) were used to study the effect of feeding system: barley straw in long form and concentrate pellets in separate troughs (Control), ad libitum alfalfa supplemented with concentrate in separate troughs (Alfalfa) or including various levels of ground barley straw in concentrate pellets (B05, B15 and B25 for 50, 150 and 250 g barley straw/kg), on rumen characteristics, acid-base status, blood cell counts and lymphocyte stimulation. Alfalfa lambs had the heaviest digestive tract contents, highest rumen pH values, lowest volatile fatty acid concentration, highest papillae counts and best mucosa colour and the greatest blood pCO₂ values, lowest sodium and chloride and highest potassium concentrations (P<0.05). Including ground barley straw in the concentrate pellet or providing straw in long form separately from the concentrate reduces rumen pH and darkens ruminal mucosa as compared with alfalfa-fed lambs, thus affecting acid-base status.     

Celecoxib and acetylbritannilactone interact synergistically to suppress breast cancer cell growth via COX-2-dependent and -independent mechanisms

The use of celecoxib is associated with a significant decrease in breast cancer risk. However, the long-term use of high-dose celecoxib might be limited owing to cardiovascular side effects. In this study, we found that acetylbritannilactone (ABL), extract from a Chinese medicinal herb, could reduce celecoxib dose and potentiate the growth-inhibitory effect in breast cancer cells. ABL enhanced the apoptotic effect of celecoxib in COX-2-expressing cells, but had little effect in COX-2-negative cells. The apoptosis induced by the combination treatment disappeared when COX-2 was knocked down, whereas the lack of apoptotic effects in COX-2-negative cells was reversed after COX-2 transfection. However, the combination treatment induced a G₀/G₁ phase arrest independent of whether or not the cells expressed COX-2. The G₀/G₁ arrest was attributed to a decreased expression of cyclinD1, cyclinE, CDK2 and CDK6, especially the upregulation of p21. In addition, inhibition of Akt and p38 signaling pathways was required by the synergism, as the constitutively active Akt and p38 protected cells against apoptosis and cell cycle arrest induced by the combination treatment. In vivo, administration of celecoxib and ABL were more effective than the individual agents against xenograft tumor growth. Thus, our data suggested that the combinatorial approach of celecoxib and ABL might be helpful for breast cancer treatment.     

Effect of physicochemical pre-treatment of rice straw on its digestibility by <Emphasis Type="Italic">Clostridium cellulolyticum</Emphasis>

Rice straw (RS) may serve as a low-cost biomass for the production of biofuels and biochemicals, but its native structure is resistant to enzymatic and microbial deconstruction. Therefore, an efficient pre-treatment method is required to modify crystalline cellulose to a more reactive amorphous form. This work investigated pre-treatments of rice straw involving size reduction (S) followed by either sodium hydroxide (NaOH) or diluted sulfuric acid (H₂SO₄) and liquid hot water (LHW). The shrinkage of the vascular bundles in the rice straw structure pre-treated with NaOH–LHW–S was higher than that with LHW–S and H₂SO₄–LHW–S pre-treatments. The highest levels of total fermentative products and residual sugars were obtained at the concentrations of 7.8 ± 0.2 and 2.1 ± 0.3 g/L, respectively, after fermentation by Clostridium cellulolyticum for NaOH–LHW–S pre-treated rice straw at 121 °C for 120 min. Overall, the combined physicochemical pre-treatment of RS led to improved microbial hydrolysis during cellulose degradation at the percentage of 85.5 ± 0.5.     

Optimization of bioleaching and oxidation of gold-bearing pyrite-arsnopyrite ore concentrate in batch mode

Biooxidation of refractory gold-bearing pyrite-arsenopyrite flotation concentrate was optimized and the abundance of predominant groups in the community of thermophilic acidophilic chemolithotrophic microorganisms at various stages of bioleaching was determined. The optimal parameters for growth and leaching/oxidation of the mineral components of the concentrate were pH 1.4–1.8; 47.5°C; and the following salt concentrations in the liquid phase (g/L): K₂HPO₄ · 3H₂O ? 0.53, (NH₄)₂SO₄, 1.6 and MgSO₄ · 7H₂O, 2.5 (or (NH₄)₂SO₄, 1.23; ammophos, 0.41; KOH, 0.1) with 0.03% yeast extract. The optimal conditions resulted in high growth rate, high levels of iron and arsenic leaching, of Fe²⁺ and S^2?/S⁰ oxidation, and predominance of Acidithiobacillus caldus, Sulfobacillus spp., and Ferroplasma spp. in the community.     

Wachstumsuntersuchungen an Bullen des Schwarzbunten Milchrindes (SMR) bei niedrigem Fütterungsniveau

Artificially dried ryegrass, untreated and ammonia‐treated wheat straw were ground and incubated in nylon bags in the rumen of three sheep each fed with diets based on roughage or concentrate. Dry matter degradability, the concentration and the release of the trace elements Cu, Fe, Mn and Zn from the incubated feeds were measured after 0 (washing loss), 6, 12, 24, 48 and 72 h rumen incubation time.

Dry matter degradability, trace element concentration and their release were significantly influenced by the kind of incubated feeds, incubation time and feeding of sheep.

Cu‐ (1.8–6.9 mg kg^?1 DM) and Zn concentrations (36–103 mg kg^?1 DM) of straw residues in the bags were much higher than those of original straw (1.2–1.6 and 8.1–9.9 mg kg^?1 DM resp.).

The inflow of Cu and Zn in the bags containing straw residues was higher than their release. The Cu‐, Fe‐ and Mn‐release from ryegrass was similar to the dry matter degradability, but the Zn‐release was much lower.     

Effect of hydrolytic lignin on formation of protein–lignin complexes and protein degradation by rumen microbes

Several methods have been developed to protect feed protein from rumen microbial degradation. The current study aimed to evaluate the potential use of an industrial lignin, namely hydrolytic lignin, to protect protein from rumen microbial degradation. The hydrolytic lignins assessed in this study were extracted from wheat straw previously subjected to various steam treatment conditions (pressure: 15, 17 and 19 bar; reaction time: 0, 5 and 10 min; use of acidic catalyst: without and with 2% H₂SO₄ on DM basis). Results indicated that hydrolytic lignin can precipitate protein when measured by a standard bovine serum albumin assay. It was also observed that protein-precipitating capacity of lignin increased with increasing harshness of steam treatment until a point from which no further effect was observed. The effect of lignin upon protein degradation in vitro was clearly detected. Both ammonia nitrogen and iso-acid concentration in vitro were significantly decreased (P<0.01) when lignin was added to fermentation flask containing casein. Unlike tannins, hydrolytic lignins do not inhibit rumen microbial activity. Additionally, it was observed that lignin’s ability to bind and protect protein is a pH-dependent reaction. Protein binding to lignin is markedly reduced at pH<3.0.     

Synaptic Electrogenesis in Eel Electroplaques

Whether evoked by neural or by chemical stimulation, the synaptic membrane of eel electroplaques contributes a depolarizing electrogenesis that is due to an increased conductance for Na and K. The reversal potential (E_S) is the same for the two modes of synaptic activation. It is inside-positive by about 30–60 mv, or about midway between the emf's of the ionic batteries for Na (E_Na) and K(E_K). The total conductance contributed by synaptic activity (G_S) varied over a fivefold range, but the individual ionic branches, G_SSNa, and G_SSK, change nearly equally so that the ratio G_SSNa:G_SSK is near unity. G_SSK increases independently of the presence or absence of Na in the bathing medium, and independently of the presence or absence of the electrically excitable G_K channels. When activated, the synaptic membrane appears to be slightly permeable to Ca and Mg. When the membrane is depolarized into inside positivity the conductance of the synaptic components decreases and approaches zero for large inside-positive values. Thus, the synaptic components become electrically excitable when the potential across the membrane becomes inside-positive, responding as do the nonsynaptic components, with depolarizing inactivation.