蓝藻浓缩二氧化碳的机制

综述了蓝藻的CO2逍缩机制研究进展,并简要介绍了一些重要的研究手段。     

Neurons controlling Aplysia feeding inhibit themselves by continuous NO production

Background

Neural activity can be affected by nitric oxide (NO) produced by spiking neurons. Can neural activity also be affected by NO produced in neurons in the absence of spiking?

Methodology/Principal Findings

Applying an NO scavenger to quiescent Aplysia buccal ganglia initiated fictive feeding, indicating that NO production at rest inhibits feeding. The inhibition is in part via effects on neurons B31/B32, neurons initiating food consumption. Applying NO scavengers or nitric oxide synthase (NOS) blockers to B31/B32 neurons cultured in isolation caused inactive neurons to depolarize and fire, indicating that B31/B32 produce NO tonically without action potentials, and tonic NO production contributes to the B31/B32 resting potentials. Guanylyl cyclase blockers also caused depolarization and firing, indicating that the cGMP second messenger cascade, presumably activated by the tonic presence of NO, contributes to the B31/B32 resting potential. Blocking NO while voltage-clamping revealed an inward leak current, indicating that NO prevents this current from depolarizing the neuron. Blocking nitrergic transmission had no effect on a number of other cultured, isolated neurons. However, treatment with NO blockers did excite cerebral ganglion neuron C-PR, a command-like neuron initiating food-finding behavior, both in situ, and when the neuron was cultured in isolation, indicating that this neuron also inhibits itself by producing NO at rest.

Conclusion/Significance

Self-inhibitory, tonic NO production is a novel mechanism for the modulation of neural activity. Localization of this mechanism to critical neurons in different ganglia controlling different aspects of a behavior provides a mechanism by which a humeral signal affecting background NO production, such as the NO precursor L-arginine, could control multiple aspects of the behavior.     

Short- and Long-Term Inhibition of Respiratory Carbon Dioxide Efflux by Elevated Carbon Dioxide

Dark carbon dioxide efflux rates of recently fully expandedleaves and whole plants of Amaranthus hypochondriacus L., Glycinemax (L.) Merr., and Lycopersicon esculentum Mill. grown in controlledenvironments at 35 and 70 Pa carbon dioxide pressure were measuredat 35 and 70 Pa carbon dioxide pressure. Harvest data and whole-plant24-h carbon dioxide exchange were used to determine relativegrowth rates, net assimilation rates, leaf area ratios, andthe ratio of respiration to photosynthesis under the growthconditions. Biomass at a given time after planting was greaterat the higher carbon dioxide pressure in G. max and L. esculentum,but not the C₄ species, A. hypochondriacus. Relative growthrates for the same range of masses were not different betweencarbon dioxide treatments in the two C₃ species, because highernet assimilation rates at the higher carbon dioxide pressurewere offset by lower leaf area ratios. Whole plant carbon dioxideefflux rates per unit of mass were lower in plants grown andmeasured at the higher carbon dioxide pressure in both G. maxand L. esculentum, and were also smaller in relation to daytimenet carbon dioxide influx. Short-term responses of respirationrate to carbon dioxide pressure were found in all species, withcarbon dioxide efflux rates of leaves and whole plants lowerwhen measured at higher carbon dioxide pressure in almost allcases. Amaranthus hypochondriacus L., Glycine max L. Merr., Lycopersicon esculentum Mill., soybean, tomato, carbon dioxide, respiration, growth     

Interspike Interval Fluctuations in Aplysia Pacemaker Neurons

In recent years, several mathematical models have been put forth to explain the time sequence of spike discharges in single neurons, in terms of synaptic inputs or intrinsic mechanisms. All of these models have been hypothetical, in that intracellular events were assumed, and not measured directly. The purpose of the present work was to study the statistics of the discharge from a preparation where intracellular recording was possible, and relate the observed discharge to measurable cell parameters. Regularly firing “pacemaker neurons” in the visceral ganglion of Aplysia californica were studied, using intracellular stimulating and recording techniques. Measurements were obtained of average curves of membrane potential, threshold for spike initiation, membrane resistance, and fluctuations of potential in the intervals between spontanously occurring spikes. The timing of discharges from these neurons was described quantitatively by interspike-interval histograms, mean and standard deviation of intervals, skewness, and serial correlation coefficients. A mathematical model (contained in a simulation program for the IBM 7094 computer) was constructed, based on discrete fluctuations of membrane potential following each spike and other directly observed intracellular events. It was found that the model could quantitatively account for observed spike trains, including variations in the discharge from one cell to another.     

Mechanism of Photosynthetic Carbon Dioxide Uptake by the Red Macroalga, Chondrus crispus

The aim of this study was to determine how Chondrus crispus, a marine red macroalga, acquires the inorganic carbon (C_i) it utilizes for photosynthetic carbon fixation. Analyses of C_i uptake were done using silicone oil centrifugation (using multicellular fragments of thallus), infrared gas analysis, and gas chromatography. Inhibitors of carbonic anhydrase (CA), the band 3 anion exchange protein and Na⁺/K⁺ exchange were used in the study. It was found that: (a) C. crispus does not accumulate C_i internally above the concentration attainable by diffusion; (b) the initial C_i fixtion rate of C. crispus fragments saturates at approximately 3 to 4 millimolar C_i; (c) CA is involved in carbon uptake; its involvement is greatest at high HCO₃⁻ and low CO₂ concentration, suggesting its participation in the dehydration of HCO₃⁻ to CO₂; (d) C. crispus has an intermediate C_i compensation point; and (e) no evidence of any active or facilitated mechanism for the transport of HCO₃⁻ was detected. These data support the view that photosynthetic C_i uptake does not involve active transport. Rather, CO₂, derived from HCO₃⁻ catalyzed by external CA, passively diffuses across the plasma membrane of C. crispus. Intracellular CA also enhances the fixation of carbon in C. crispus.     

Terminal Nerve GnRH3 Neurons Mediate Slow Avoidance of Carbon Dioxide in Larval Zebrafish

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Carbon Dioxide Fixation by Barley Roots

The non-volatile, 80 per cent.ethanol-soluble products of fixationhave been investigated in excised roots, using C^14O₂ and radiochromatography. The main radioactive compounds separated were malic, citric(or iso-citric), aspartic, and glutamic acids, asparagine andglutamine. Less activity was present in serine, tyrosine, -ketoglutaricacid, and alanine, and in a number of unidentified compounds. The uptake of C^14O₂ was inhibited by virtually anaerobic conditions. From the above observations it is considered likely that C¹⁴is transformed through the reactions of the tricarboxylic acidcycle. C¹⁴ in the soluble fraction was markedly increased by maintainingthe root material in water rather than in a nutrient solutionprior to exposure to C^14O₂ This increase was chiefly in malicacid.     

Spontaneous Activity in Isolated Somata of Aplysia Pacemaker Neurons

Somata of pacemaker and nonpacemaker neurons were isolated by ligatures tied around the axons between the somata and the synaptic regions, and the transmembrane potentials of the isolated somata were recorded. Isolated somata of pacemaker neurons had a spontaneous discharge while isolated somata of nonpacemaker neurons were quiescent. In addition, the time course of accommodation in isolated somata of pacemaker and nonpacemaker neurons was found to be different. In pacemaker neurons, injection of current produced a change in rate of discharge sustained for the duration of current injection, while in nonpacemakers, current injection produced only a transient change in discharge rate. Evidence is presented that the pacemaker locus and spike trigger zone in the intact pacemaker neuron are located on the soma.     

二氧化硫体内衍生物对小鼠海马神经元DNA的损伤作用

运用单细胞凝胶电泳技术 (又称彗星实验 )研究了SO2 的体内代谢衍生物———亚硫酸氢钠(NaHSO3 )和亚硫酸钠 (Na2 SO3 )腹腔注射对小鼠海马神经元细胞DNA的损伤 .在衍生物剂量为 0 ,0 1 2 5、0 2 5 0、0 5 0 0、1 0 0 0g kg体重的染毒条件下 ,雄性小鼠海马神经元细胞DNA迁移长度分别为0 4 0、1 1 4、3 6 2、5 0 8、2 9 1 3μm ,雌性小鼠海马神经元细胞DNA迁移长度分别为 0 6 1 ,1 0 4 ,2 75 ,3 6 6 ,2 0 94 μm ,表明SO2 的体内衍生物可以引起小鼠海马神经元细胞DNA损伤 ,且随SO2 衍生物腹腔注射剂量的增加 ,DNA的损伤也加剧 .这意味着SO2 的体内衍生物具有引起哺乳动物海马神经元细胞DNA突变的潜在危险 ,表明SO2 衍生物是一种潜在的神经毒物     

Photoaffinity Labeling of Adenylate Cyclase-Linked Serotonin Receptors in Aplysia Neurons

Serotonin stimulated adenylate cyclase in Aplysia neurons with a Kact of 0.7 microM. Under the same conditions, 1-[2-(4-aminophenyl)ethyl]4-(3-trifluoromethylphenyl)piperazine stimulated adenylate cyclase with a Kact of 20 microM. The azido derivative of this compound, 1-[2-(4-azidophenyl)ethyl]4-(3-trifluoromethylphenyl)piperazine, or of serotonin, (4-amino, 3-nitrophenylazido-serotonin), also stimulated the cyclase in the dark, but with lower efficiency (Kact greater than 10(-4) M). Irradiation of the membranes in the presence of 100 microM 1-[2-(4-azidophenyl)ethyl]4-(3-trifluoromethylphenyl)piperazine abolished 75% of the cyclase activity stimulated by 5 microM serotonin. Under the same conditions, 100 microM 4-amino, 3-nitrophenylazido-serotonin did not inhibit serotonin-stimulated adenylate cyclase activity. When [3H]1-[2-(4-azidophenyl)ethyl]4-(3-trifluoromethylphenyl)piperazine (20 microM) was irradiated with membranes for 5 min at 4 degrees C, a dozen peptides were labeled, as revealed by a fluorogram of sodium dodecyl sulfate-polyacrylamide gels. Among them, the labeling of five polypeptides (molecular weights of 45,000, 55,000, 63,000, 80,000, and 94,000) was protected by the presence of 0.2 mM serotonin during photolysis. These peptides may be related to serotonin receptors.     

N—硝基精氨酸抑制海马神经元兴奋机制

研究N－硝基精氨酸（L－NNA）在青霉素诱发的培养海马CA1区神经元细胞兴奋过程中的抑制机制。用激光扫描共聚焦显微镜观察发现4000IU／ ml的青霉素可诱发一氧化氮（NO）的快速合成模式。L-NNA(0-10μmol/L）呈剂量依赖性抑制NO的合成和青霉素刺激15min后谷氨酸水平的二次升高。同时发现1μmol/L和10μmol/L剂量的L－NNA可显著抑制甲硫氨酸脑啡肽的水平,而10μmol/L剂量的L－NNA还显著升高强啡肽－B的水平。对L－NNA抑制谷氨酸水平二次升高效应,100μmol/L的甲硫氨酸脑啡肽受体抑制剂β－funaltrexamine(β-FNA）可显著协同,而100μmol/L的强啡肽－B受体抑制剂norbinaltorphimine(nor-BIN)则显著逆转。以上结果提示：L－NNA抑制4000IU／ml的青霉素诱导的NO合成,并进而通过抑制氨酸脑啡肽水平,升高强啡肽－B水平来抑制谷氨酸水平,调节神经元的兴奋性。     

Efficient Hydrogen-Dependent Carbon Dioxide Reduction by Escherichia coli

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Differences between Pacemaker and Nonpacemaker Neurons of Aplysia on Voltage Clamping

The responses of pacemaker and nonpacemaker Aplysia neurons to voltage clamp commands of less than 200 msec duration are essentially identical. For moderate depolarizing commands there is an early inward transient current followed by a late outward current and an outward tail current when the membrane is clamped back to resting potential. On long (1–2 sec) commands in pacemakers there is a marked sag in the late current and an inward tail current. E_tail, the potential of the membrane at which there is no net current flow under the conditions prevailing at the end of the clamp, shifts from about -9.0 mv on short commands to +5.0 mv on long commands. In contrast there is no marked sag of the late current or inward tail current on long commands in nonpacemakers, and E_tail is near -9.0 mv for both short and long commands. The current sag and shift in E_tail can be ascribed to a decreased conductance (presumably to K⁺) at the end of the long as compared to the short command in half of the pacemaker neurons. In the remaining cells the essential difference from nonpacemakers appears to be either a greater restricted extracellular space or a more active potential-dependent electrogenic Na⁺ pump in pacemakers.     

Aplysia Ganglia Preparation for Electrophysiological and Molecular Analyses of Single Neurons

A major challenge in neurobiology is to understand the molecular underpinnings of neural circuitry that govern a specific behavior. Once the specific molecular mechanisms are identified, new therapeutic strategies can be developed to treat abnormalities in specific behaviors caused by degenerative diseases or aging of the nervous system. The marine snail Aplysia californica is well suited for the investigations of cellular and molecular basis of behavior because neural circuitry underlying a specific behavior could be easily determined and the individual components of the circuitry could be easily manipulated. These advantages of Aplysia have led to several fundamental discoveries of neurobiology of learning and memory. Here we describe a preparation of the Aplysia nervous system for the electrophysiological and molecular analyses of individual neurons. Briefly, ganglion dissected from the nervous system is exposed to protease to remove the ganglion sheath such that neurons are exposed but retain neuronal activity as in the intact animal. This preparation is used to carry out electrophysiological measurements of single or multiple neurons. Importantly, following the recording using a simple methodology, the neurons could be isolated directly from the ganglia for gene expression analysis. These protocols were used to carry out simultaneous electrophysiological recordings from L7 and R15 neurons, study their response to acetylcholine and quantitating expression of CREB1 gene in isolated single L7, L11, R15, and R2 neurons of Aplysia.