Release of exogenously supplied [3H]glutamate and endogenous glutamate from tissue slices of the cestode Hymenolepis diminuta

1988 ◽  
Vol 66 (7) ◽  
pp. 889-894 ◽  
Author(s):  
Rodney A. Webb
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Glutamate Release ◽  
Hymenolepis Diminuta ◽  
Acidic Amino Acid ◽  
Tissue Slices ◽  
Potassium Depolarization ◽  
High Potassium ◽  
Calcium Dependent ◽  
Sodium Dependent

The effect of high potassium depolarization on the release of exogenously supplied [3H]glutamate and endogenous glutamate from tissue slices of the cestode Hymenolepis diminuta was examined. Increasing concentrations of potassium stimulated the release of radiolabel from tissues preloaded with [3H]glutamate. This release was by a partially calcium-dependent, magnesium-antagonized process. In the presence of tetrodotoxin, or absence of sodium, release of radiolabel was depressed, presumably by blockade of sodium-dependent neuronal potentials. The release of glutamate of both exogenous and endogenous origin was specifically and significantly elevated by high potassium; glutamate release was significantly depressed in calcium-free saline. The release of other amino acids of endogenous origin, including aspartate, was not elevated by high potassium. Collectively the data provide strong evidence for glutamate to be viewed as the only acidic amino acid neurotransmitter candidate in the cestodes.

Self-healing hydrogels triggered by amino acids

2016 ◽  
Vol 3 (12) ◽  
pp. 1699-1704 ◽  
Author(s):  
Nicola Zanna ◽  
Andrea Merlettini ◽  
Claudia Tomasini
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Aspartic Acid ◽  
Chemical Properties ◽  
Aromatic Amino Acids ◽  
Self Healing ◽  
Acidic Amino Acid ◽  
Basic Amino Acids

Nine amino acids with different chemical properties have been chosen to promote the formation of hydrogels based on the bolamphiphilic gelator A: three basic amino acids (arginine, histidine and lysine), one acidic amino acid (aspartic acid), two neutral aliphatic amino acids (alanine and serine) and three neutral aromatic amino acids (phenylalanine, tyrosine and tryptophan).

The effect of L-glutamate and related agents on adenylate cyclase in the cestode Hymenolepis diminuta

1991 ◽  
Vol 69 (1) ◽  
pp. 28-36 ◽  
Author(s):  
Harley Eklove ◽  
Rodney A. Webb
Keyword(s):  
Amino Acid ◽  
Adenylate Cyclase ◽  
Hymenolepis Diminuta ◽  
Cyclase Activity ◽  
Adenylate Cyclase Activity ◽  
Tissue Slices ◽  
Basal Activity ◽  
Glutamate Agonists ◽  
Acidic Compounds ◽  
Type Receptor

The effect of the putative amino acid transmitter, L-glutamate, on adenylate cyclase in crude membrane preparations of the rat tapeworm Hymenolepis diminuta was investigated to determine if glutamate effects the generation of the second messenger cAMP. Addition of glutamate at 10−3 and 5.5 × 10−9 M resulted in significant elevations in basal activity of adenylate cyclase, while concentrations in the 10−5–10−7 M range caused significant depressions below basal activity. Assays with glutamate agonists and other acidic compounds showed glutamate to be the only amino acid, dicarboxylic acid, or acidic compound capable of this pattern of stimulation and inhibition. While the response of adenylate cyclase to glutamate agonists suggested that an N-methyl-D-aspartic acid (NMDA) type receptor may be present, glutamate agents acting as NMDA antagonists in vertebrate systems were agonists. Metabolic end products of glycolysis stimulated adenylate cyclase, suggesting that these, along with metabolic glutamate may regulate glycolytic enzymes. Only 10−3 M L-glutamate significantly stimulated adenylate cyclase activity in tissue slices, and this response was restricted to those slices rich in nervous tissues. L-Glutamate eliminated the 5-hydroxytryptamine (5-HT) stimulated adenylate cyclase response suggesting that glutamate can modulate the 5-HT stimulated elevations in adenylate cyclase activity. The data support the hypothesis that L-glutamate is a neurotransmitter–modulator in the cestode.Key words: L-glutamate, cAMP, cestode, modulator.

Characterization of a high-affinity choline uptake mechanism in the cestode Hymenolepis diminuta

1991 ◽  
Vol 69 (3) ◽  
pp. 369-377 ◽  
Author(s):  
Rodney A. Webb
Keyword(s):  
Hymenolepis Diminuta ◽  
Choline Uptake ◽  
Uptake Mechanism ◽  
Tissue Slices ◽  
High Affinity ◽  
Sodium Gradient ◽  
Sodium Dependent ◽  
Wet Weight ◽  
High Affinity Choline Transporter

Radiolabelled choline was taken up by tissue slices of the cestode Hymenolepis diminuta by a sodium-dependent and a sodium-independent mechansim. The sodium-dependent uptake was saturable, against a concentration gradient, displayed structural specificity, and was inhibited, in part, by hemicholinium-3. Kinetic analysis of the sodium-dependent choline uptake showed an apparent Kt = 2.0 μM and a Vmax = 0.146 pmol∙mg−1 wet weight tissue∙min−1, which is consistent with a high-affinity choline uptake (HAChU) mechanism. The rate of uptake or release of choline depended on the magnitude and direction of the sodium gradient, was diminished by high- or low-potassium, but was not chloride or sulphate dependent. A homoexchange mechanism for HAChU was not demonstrated. Evidence was obtained to suggest that HAChU or release of endogenous ACh is regulated by autoreceptors. The choline taken up by the HAChU mechanism was but slowly converted to ACh and other products.Key words: high-affinity sodium-dependent choline uptake, sodium-independent choline uptake, cestode tissue slices, choline metabolism, high-affinity choline transporter.

scholarly journals Steady-state physiological variations across a graded series of Na,K-ATPase-amplified cells.

1989 ◽  
Vol 9 (1) ◽  
pp. 116-123 ◽  
Author(s):  
P G Pauw ◽  
R N Sheck ◽  
J F Ash
Keyword(s):  
Steady State ◽  
Membrane Potential ◽  
Amino Acid ◽  
Lactate Production ◽  
Electrochemical Potential ◽  
Transport Systems ◽  
High Potassium ◽  
System L ◽  
Sodium Dependent ◽  
Dependent Transport

Measurements of internal ion concentrations, amino acid pools, and membrane potential were made across a series of HeLa subclones which are amplified for the genes for the sodium- and potassium-activated ATPase (Na,K-ATPase). These subclones expressed heterogeneous levels of ouabain-binding sites, allowing us to construct a graded amplification series. While [K+]i levels did not vary systematically across the series studied, [Na+]i ranged from 9 to 20 mM as a function of Na,K-ATPase expression. Steady-state accumulation of tetraphenylphosphonium in low versus high potassium was used to measure membrane potential. Values for [Na+]i and the membrane potential were used to calculate the sodium electrochemical potential, which was also found to be a function of Na,K-ATPase expression. Measurements of acid-soluble amino acid pools in cell lysates demonstrated that amino acids which are substrates for sodium-dependent transport systems, or which can potentially exchange through system L for a substrate of a sodium-dependent system, varied as a function of the sodium electrochemical potential. This confirmed our prediction of increased amino acid pool sizes in Na,K-ATPase-amplified lines based on observations of elevated flux through the sodium-independent system L. Finally, we measured lactate production and glycolytic potential in a subset of clones and found that both were reduced in subclones with elevated Na,K-ATPase.

Characterization of Gating and Peptide Block of mSlo, a Cloned Calcium-Dependent Potassium Channel

1997 ◽  
Vol 78 (6) ◽  
pp. 2937-2950 ◽  
Author(s):  
Deirdre A. Sullivan ◽  
Mats H. Holmqvist ◽  
Irwin B. Levitan
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Potassium Channel ◽  
Critical Role ◽  
Single Amino Acid ◽  
Significant Shift ◽  
Triple Mutant ◽  
Calcium Dependent ◽  
Loop Region

Sullivan, Deirdre A., Mats H. Holmqvist, and Irwin B. Levitan. Characterization of gating and peptide block of mSlo, a cloned calcium-dependent potassium channel. J. Neurophysiol. 78: 2937–2950, 1997. The 20 amino acid Shaker inactivation peptide blocks mSlo, a cloned calcium-dependent potassium channel. Changing the charge and degree of hydrophobicity of the peptide alters its blocking kinetics. A “triple mutant” mSlo channel was constructed in which three amino acids (T256, S259, and L262), equivalent to those identified as part of the peptide's receptor site in the S4–S5 cytoplasmic loop region of the Shaker channel, were mutated simultaneously to alanines. These mutations produce only limited changes in the channel's susceptibility to block by a series of peptides of varying charge and hydrophobicity but do alter channel gating. The triple mutant channel shows a significant shift in its calcium-activation curve as compared with the wild-type channel. Analysis of the corresponding single amino acid mutations shows that mutation at position L262 causes the most dramatic change in mSlo gating. These results suggest that the three amino acids mutated in the mSlo S4–S5 loop may contribute to, but are not essential for, peptide binding. On the other hand, they do play a critical role in the channel's calcium-sensing mechanism.

CHARACTERISTICS OF ACIDIC AMINO ACID TRANSPORT IN MAMMALIAN KIDNEY

1963 ◽  
Vol 41 (1) ◽  
pp. 131-137 ◽  
Author(s):  
William A. Webber
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Tubular Reabsorption ◽  
Side Chain ◽  
Acid Transport ◽  
Acidic Amino Acid ◽  
Neutral Amino Acids ◽  
Wide Range ◽  
Renal Tubular

A series of clearance experiments on dogs were carried out which were designed to confirm and characterize the renal tubular reabsorption of glutamic and aspartic acids. Tubular reabsorption was measured and found to reach a maximum of about 100 μmole/minute for L-glutamic and L-aspartic acids and a slightly lower level for D-aspartic. Competitive studies using substituted amino acids were performed and three patterns of inhibition of amino acid reabsorption observed. Acidic amino acids inhibited the reabsorption of each other, while neutral amino acids (and an acidic amino acid substituted so as to have a neutral side chain) inhibited the reabsorption of a wide range of other amino acids. Compounds with the amino group or either carboxyl group substituted or absent, but not resembling neutral amino acids, were not inhibitory. There appears to be a specialized mechanism for acidic amino acid transport which probably requires all three functional groups but which may be interfered with by a compound with alpha carboxyl and amino groups and a neutral side chain.

Binding and Uptake of Amino Acids by Brain Tissue

1973 ◽  
Vol 51 (2) ◽  
pp. 121-128 ◽  
Author(s):  
P. C. Shiu ◽  
K. A. C. Elliott
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Sodium Chloride ◽  
Incubation Medium ◽  
Sucrose Solution ◽  
The Other ◽  
Percentage Increase ◽  
Endogenous Amino Acids ◽  
Sodium Dependent ◽  
Net Uptake

(1) Of the endogenous glutamate, aspartate, alanine, glycine, and γ-aminobutyrate (GABA), 26–37% remains bound in particles when rat brain is homogenized in isosmotic salt-free sucrose solution; a smaller proportion, 16%, of the glutamine is bound. The amounts bound are increased if sodium chloride is present; the percentage increase is greatest in the case of GABA, followed by glutamate, and least with glutamine. When tracer amounts of radioactive amino acids are present in the solution in the absence of salt very little radioactivity appears in bound GABA or glutamine, but appreciable amounts are found in the other amino acids. In the presence of sodium chloride, the total amount of bound amino acid increases as does, to a lesser extent, the radioactivity bound. Ouabain and protoveratrine seem to cause some release of sodium-dependent binding of the amino acids; this is most marked with GABA.(2) Slices incubated in the presence of oxygen and glucose take up each of the amino acids when these are added to the incubation medium. The highest intracellular concentration and the greatest net uptake occur with GABA. The endogenous concentration of glutamate is higher than that of the other amino acids but the net uptake is the least. The highest ratios of uptake to endogenous content occur with alanine and glycine. Determinations of radioactivity indicate that, in the cases of GABA and glycine, the increase in radioactivity in the slices is almost completely accounted for by uptake from the medium with almost no exchange. Some exchange occurs with other amino acids. Protoveratrine inhibits uptake of all the amino acids and actually causes loss of glutamate and aspartate from slices. Ouabain inhibits in all cases; the uptakes of glutamate and aspartate are least affected. Tetrodotoxin, alone or with either of the other two drugs, tends to increase uptake of all the amino acids. When the net uptake is inhibited by drugs considerable exchange of endogenous amino acids with radioactive amino acids in the medium is observed.

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