The free amino-acids of invertebrate nerve

Selective Amino Acid-Only in Vivo NMR: A Powerful Tool To Follow Stress Processes

In vivo NMR of small 13C-enriched aquatic organisms is developing as a powerful tool to detect and explain toxic stress at the biochemical level. Amino acids are a very important category of metabolites for stress detection as they are involved in the vast majority of stress response pathways. As such, they are a useful proxy for stress detection in general, which could then be a trigger for more in-depth analysis of the metabolome. 1H-13C heteronuclear single quantum coherence (HSQC) is commonly used to provide additional spectral dispersion in vivo and permit metabolite assignment. While some amino acids can be assigned from HSQC, spectral overlap makes monitoring them in vivo challenging. Here, an experiment typically used to study protein structures is adapted for the selective detection of amino acids inside living Daphnia magna (water fleas). All 20 common amino acids can be selectively detected in both extracts and in vivo. By monitoring bisphenol-A exposure, the in vivo amino acid-only approach identified larger fluxes in a greater number of amino acids when compared to published works using extracts from whole organism homogenates. This suggests that amino acid-only NMR of living organisms may be a very sensitive tool in the detection of stress in vivo and is highly complementary to more traditional metabolomics-based methods. The ability of selective NMR experiments to help researchers to "look inside" living organisms and only detect specific molecules of interest is quite profound and paves the way for the future development of additional targeted experiments for in vivo research and monitoring.

NMR Profiling of Metabolites in Larval and Juvenile Blue Mussels (Mytilus edulis) under Ambient and Low Salinity Conditions

Blue mussels (Mytilus edulis) are ecologically and economically important marine invertebrates whose populations are at risk from climate change-associated variation in their environment, such as decreased coastal salinity. Blue mussels are osmoconfomers and use components of the metabolome (free amino acids) to help maintain osmotic balance and cellular function during low salinity exposure. However, little is known about the capacity of blue mussels during the planktonic larval stages to regulate metabolites during osmotic stress. Metabolite studies in species such as blue mussels can help improve our understanding of the species’ physiology, as well as their capacity to respond to environmental stress. We used 1D ¹H nuclear magnetic resonance (NMR) and 2D total correlation spectroscopy (TOCSY) experiments to describe baseline metabolite pools in larval (veliger and pediveliger stages) and juvenile blue mussels (gill, mantle, and adductor tissues) under ambient conditions and to quantify changes in the abundance of common osmolytes in these stages during low salinity exposure. We found evidence for stage- and tissue-specific differences in the baseline metabolic profiles of blue mussels, which reflect variation in the function and morphology of each larval stage or tissue type of juveniles. These differences impacted the utilization of osmolytes during low salinity exposure, likely stemming from innate physiological variation. This study highlights the importance of foundational metabolomic studies that include multiple tissue types and developmental stages to adequately evaluate organismal responses to stress and better place these findings in a broader physiological context.

Comprehensive multiphase NMR applied to a living organism

Comprehensive multiphase (CMP) NMR is a novel technology that integrates all the hardware from solution-, gel- and solid-state into a single NMR probe, permitting all phases to be studied in intact samples. Here comprehensive multiphase (CMP) NMR is used to study all components in a living organism for the first time. This work describes 4 new scientific accomplishments summarized as: (1) CMP-NMR is applied to a living animal, (2) an effective method to deliver oxygen to the organisms is described which permits longer studies essential for in-depth NMR analysis in general, (3) a range of spectral editing approaches are applied to fully differentiate the various phases solutions (metabolites) through to solids (shell) (4) 13C isotopic labelling and multidimensional NMR are combined to provide detailed assignment of metabolites and structural components in vivo. While not explicitly studied here the multiphase capabilities of the technique offer future possibilities to study kinetic transfer between phases (e.g. nutrient assimilation, contaminant sequestration), molecular binding at interfaces (e.g. drug or contaminant binding) and bonding across and between phases (e.g. muscle to bone) in vivo. Future work will need to focus on decreasing the spinning speed to reduce organism stress during analysis.

Distribution of taurine and other free amino acids in the visual pathway of the crayfish procambarus clarkii

1. Free taurine showed an in homogenous distribution along the neuropiles associated with the visual processing pathway in the eyestalk and brain of the freshwater crayfish Procambarus clarkii.2. Within the eyestalk, taurine was statistically significant (P < 0.001), more Concentrated in the retina(photo reccptor layer) lamina ganglionaris region than in the medulla extema-medulla interna and medulla terminalis regions; 64% of the total content (45% in terms of total concentration) of taurine in the eyestalk was localized in the retina-lamina ganglionaris zone.3. Regarding other free amino acids also identified, and considering the whole eyestalk, taurine concentration was comparable with those of alanine and glycine, but statistically significantly higher than glutamate, GABA and aspartate. In the brain (cerebroid ganglion) taurine, alanine, glycine, glutamate and GABA concentrations, albeit not identical, were not statistically significantly different; only the aspartate concentration was significantly lower (P < 0.001).4. These results show that taurine is a major constituent in the anterior part of the crayfish central nervous system and support the notion that this free amino acid could play a physiologically important role in the crustacean visual pathway.

Cell composition as assessed from osmolality and concentrations of sodium, potassium and chloride: total contributions of other substances to osmolality and charge balance

From published data for various tissues on intracellular Na, K and Cl were calculated the net anionic charge on all other substances present and also the total contribution of these to osmolality, assuming osmotic equilibrium with extracellular fluid. These parameters were compared for muscle and nerve of animals differing widely in osmolality and also for other mammalian cells. Cell volume regulation in some euryhaline species was considered; it is only partly due to ninhydrin-positive materials. In sheep mammary glands K seems to be sequestered with lactose and anion. Changes in mammalian muscle due to adrenalectomy, hypophysectomy, K deficiency, myotonia, acid-base imbalance and treatment with deoxycorticosterone or insulin were discussed.

The composition of animal cells: solutes contributing to osmotic pressure and charge balance

The cytoplasmic solutes of vertebrates and invertebrates, other than Na, K and Cl, are surveyed in relation to their influence on ionic regulation through osmolality and charge balance. The most abundant include MgATP, phosphagens, amino acids, various other nitrogen and phosphorus compounds and sometimes anaerobic end products and antifreeze agents. Differences in muscle osmolality, e.g. between marine and non-marine animals, affect mainly nitrogenous solutes of no net charge, such as certain amino acids, taurine, betaine, trimethylamine oxide and urea. The high osmolality of axoplasm in marine invertebrates is due more to anions such as aspartate, glutamate and isethionate.

Specific glycine uptake by identified neurons of Aplysia californica. I. Autoradiography

The identified giant neurons R3-R14 in the Aplysia parietovisceral ganglion (PVG) have a rapid, Na+-dependent and Hg2+-sensitive uptake system for glycine not found in neighboring neurons. In autoradiographs of PVG incubated in [3H]glycine (glutaraldehyde fix), the cytoplasms of R3-R14 have 3--4 times more silver grains (No./100 sq.micrometer) than other neurons. The glycine uptake system in R3-R14 is selective (alanine, serine, leucine, and proline are taken up equally by all neurons) and is unaffected by reserpine and anisomycin. Neurons R3-R14 contain 2 times less label when ganglia are fixed in formaldehyde than when glutaraldehyde is used as a fixative. Because formaldehyde fixes free amino acids poorly, much of the glycine taken up by R3-R14 is, therefore, not incorporated into protein. In autoradiographs of PVG incubated in [3H]glycine, silver grains are distributed randomly throughout the cytoplasm and nucleus of R3-R14; no association of the grains with the dense core granules characteristic of these neurons7 or other cellular components was found. In contrast, grains in the neurosecretory "bag cells" of the PVG were clustered in numerous discrete areas of the cytoplasm (Golgi complex areas) and the nucleus was only sparsely labeled. The existence of a rapid and selective glycine uptake system in R3-R14, together with their high endogenous glycine concentrations17, suggests that glycine may be a neurotransmitter in these neurons.

Structural determination of three glycoasparagines isolated from the urine of a patient with aspartylglycosaminuria

Three different glycoasparagines have been isolated from the urine of a patient with aspartylglycosaminuria and their structures determined using sugar, amino acid and methylation analysis, enzymic degradation and measurements of the optical rotations. The structures were 2-acetamido-1-N-(4'-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (yield 135 mg/l) beta-D-galactopyranosyl-(1 leads to 4)-2-acetamido-1-N-(4'-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (yield 35 mg/l), and alpha-D-mannopyranosyl-(1 leads to 6)-beta-D-mannopyranosyl-(1 leads to 4)-2-acetamido-2-deoxy-beta-D-glucopyranosyl-(1 leads to 4)-2-acetamido-1-N-(4'-L-aspartyl)-2-deoxy-beta-D-glucopyranosylamine (yield 30 mg/l). The first two compounds have previously been described, whereas the third compound is different from any of the glycoasparagines isolated before.

On the elementary conductance event produced by L-glutamate and quanta of the natural transmitter at the neuromuscular junctions of Maia squinado

1. The membrane potential of giant muscle fibres of Maia squinado was measured with an intracellular wire electrode. On applying L-glutamate to the fibre the cell deplorized and fluctuations of the membrane potential around its mean level--glutamate noise--were seen. 2. The variance of the glutamate voltage noise is proportional to the mean level of depolarization. The noise can be regarded as being caused by numerous exponentially decaying elementary voltage events about 5 X 10(-10) V in amplitude. The miniature excitatory junctional potential (min.e.j.p.) is approximately 6000 times the amplitude of the elementary voltage event produced by L-glutamate. 3. The power spectrum of glutamate voltage noise is a Lorentzian with a half-power frequency of approximately 20 Hz. 4. Min. e.j.p.s. decay exponentially with a time constant that coincides with the average lifetime of the elementary glutamate voltage event. 5. When glutamate is applied locally to a spot where extracellular min. e.j.p.s. can be recorded with a focal glass pipette, extracellular glutamate noise is seen. Glutamate noise could not be detected from elsewhere on the fibre. 6. The variance of the extracellular noise is proportional to the mean extracellular potential, and its power spectrum is a Lorentzian with a half-power frequency of about 110 Hz. 7. The extracellular min. e.j.p.s decay exponentially with a time constant that coincides with average lifetime of the elementary glutamate current event. 8. It is suggested that the decay of the quantal currents flowing at the excitatory junction is limited by the closure of the conductance channels in the post-synaptic membrane and not by the relaxation of the transmitter concentration in the synaptic cleft.

Aspartate: distinct receptors on Aplysia neurons

Aplysia neurons have specific aspartate receptors that are distinct from those to glutamate. In some cells, asparate selectively increases the membrane permeability to chloride, giving rise to a hyperpolarization, while on other cells it increases the permeability to sodium, causing a depolarization. There are also specific receptors for L-glutamate which mediate sodium, chloride, or potassium conductance increases, and another class of receptors activated by both glutamate and aspartate.

Axoplasm chemical composition in Myxicola and solubility properties of its structural proteins

The chemical composition of axoplasm extracted from the giant axon of Myxicola infundibulum has been analysed, and some of the factors which disperse its gel structure have been identified. 2. The axoplasm contains about 3-6% protein, and 0-12% lipid. It is isosmotic with sea water and has a pH near 7-0. 3. Inorganic ions in extracted axoplasm include: Na+, 13m-mole/kg wet wtl; K+, 280; Cl-, 24; Ca2+, 0-3; Mg2+, 3. 4. Free organic ions in axoplasm include: gly, 180 m-mole/kg wet st.; cysteic acid, 120; asp, 75; glu, 10; ala, 7; tau, 5; thr, 2; gln and ser, trace; homarine, 63; isethionate, 0. 5. The gel structure is dispersed by solutions containing 1--10 mM-Ca2+, because this ion activates an endogenous protease. The gel can also be dispersed without proteilysis by solutions containing 0-5 M-KCl, or 0-5 M guanidine hydrochloride, or 3-5 M urea, all of which break down neurofilaments. 6. It is argued that many aspects of the composition and dispersal properties of Myxicola axoplasm are similar to those in other axons.

Content of amino acids in axons from the CNS of the lobster

The contents of alanine, proline, glycine, GABA, glutamate, and aspartate were measured in four bundles of axons (designated areas A through D) from the circumesophageal connective of the lobster (Homarus americanus). The contents of these amino acids were also determined in individual axons within specific bundles and in the external sheath covering the circumesophageal connective. Within the nerve bundles the levels of aspartate were highest of the amino acids measured, ranging from 1.95 +/- 0.12 mumol/mg protein in area C to 7.55 +/- 0.54 mumol/mg protein in area B. On the other hand, GABA had the lowest value in the four bundles; its highest level was found in area C (0.083 +/- 0.006 mu mol/mg protein) and the lowest in area B (none detected). The content of glycine ranged from 1.63 +/- 0.14 (area C) to 2.52 +/- 0.32 mumol/mg protein in area A; that for glutamate ranged from 0.390 +/- 0.019 (area C) to 1.01 +/- 1.03 (area B). The contents of alanine and proline changed relatively little from bundle-to-bundle. The content of aspartate was the highest of any of the amino acids assayed in individual axons (with diameters in the range of 40 to 65 mu) dissected from areas B and C. Glycine had the next highest content followed in order by glutamate, proline, and alanine. GABA was not detected in these axons. With the exception of GABA (which could not be detected), aspartate had the lowest level (0.066 +/- 0.017) and glycine had the highest level (2.00 +/- 0.498 mumol/mg protein) in the external sheath covering the the circumesophageal connective.