scholarly journals Output of [14C]adenine nucleotides and their derivatives from cerebral tissues. Tetrodotoxine-resistant and calcium ion-requiring components

1973 ◽  
Vol 136 (4) ◽  
pp. 893-901 ◽  
Author(s):  
Ian Pull ◽  
Henry McIlwain
Keyword(s):  
Electrical Stimulation ◽  
Calcium Ion ◽  
Adenine Nucleotides ◽  
Fold Increase ◽  
Adenosine Kinase ◽  
Electrical Excitation ◽  
Maximal Increase

1. Neocortical tissues, exposed briefly to [14C]adenine and containing over 98% of their14C as adenine nucleotides, when superfused with glucose–bicarbonate salines released about 0.1% of their14C content/min to the superfusate. 2. Addition of unlabelled adenosine to the superfusing fluid increased the14C output three- to four-fold; half-maximal increase was given by about 40μm-adenosine, and reasons are adduced for considering the activity of adenosine kinase to be a major factor in conditioning the14C output. Adenosine similarly increased the enhanced14C output caused by electrical excitation of the superfused tissue; it brought about only a small increase in tissue glycolysis. 3. Output of14C from the [14C]adenine-labelled tissues was increased when Ca2+was omitted from the superfusing fluids, but electrical stimulation did not then liberate more14C. Nevertheless, such tissues still responded to electrical stimulation by increased glycolysis, and their14C output again became susceptible to increase by electrical stimulation when Ca2+was restored. 4. The six-fold increase in tissue glycolysis caused by electrical excitation was almost completely inhibited by tetrodotoxin at 0.1μm and above, but this was associated with about 50% inhibition only in the output of14C from tissues preincubated with [14C]adenine. The14C-labelled compounds of which output was most inhibited by tetrodotoxin were adenosine, inosine and hypoxanthine whereas output in a nucleotide fraction was little affected.

scholarly journals Adenosine as a constituent of the brain and of isolated cerebral tissues, and its relationship to the generation of adenosine 3′:5′-cyclic monophosphate

1977 ◽  
Vol 164 (1) ◽  
pp. 131-137 ◽  
Author(s):  
Michael Newman ◽  
Henry McIlwain
Keyword(s):  
Electrical Stimulation ◽  
Cyclic Amp ◽  
Guinea Pig ◽  
Room Temperature ◽  
Fold Increase ◽  
Electrical Excitation ◽  
Adenosine Concentration ◽  
The Brain ◽  
Guinea Pig Brain

1. Adenosine was determined in rapidly frozen rat and guinea-pig brain and in guinea-pig cerebral tissues after incubation in vitro. Adenosine concentrations were approx. 2nmol/g wet wt. in frozen tissue, diminished at room temperature, and returned to 2nmol/g on incubation in oxygenated glucose/salines. 2. Superfusion with noradrenaline then increased the tissue's adenosine concentration 2.5-fold, and hypoxia caused an 8-fold increase. 3. Electrical stimulation alone or in the presence of noradrenaline or histamine increased the tissue's adenosine and cyclic AMP, but adenosine concentrations reached their peak later and were maintained for longer than those of cyclic AMP. 4. Superfusion with l-glutamate with and without electrical excitation raised adenosine concentrations to 15–34nmol/g. The increases in cyclic AMP on electrical stimulation, superfusion with glutamate or a combination of these treatments were diminished by addition of adenosine deaminase or theophylline. 5. It is concluded that adenosine can be produced endogenously in cerebral systems, in sufficient concentrations to accelerate an adenosine-activated adenylate cyclase, and by this route can contribute to the cerebral actions of electrical stimulation and of the neurohumoral agents. In certain instances cyclic AMP as substrate contributes to an increase in adenosine.

scholarly journals Stimulation of mitochondrial calcium ion efflux by thiol-specific reagents and by thyroxine. The relationship to adenosine diphosphate retention and to mitochondrial permeability

1979 ◽  
Vol 182 (2) ◽  
pp. 455-464 ◽  
Author(s):  
E J Harris ◽  
M Al-Shaikhaly ◽  
H Baum
Keyword(s):  
Thyroid Hormones ◽  
Calcium Ion ◽  
Adenine Nucleotides ◽  
Adenosine Diphosphate ◽  
Ruthenium Red ◽  
Reduced Form ◽  
Factors Affecting ◽  
Ph Values ◽  
Rat Heart Mitochondria ◽  
The Relationship

Respiring rat heart mitochondria were loaded with Ca2+ and then treated with Ruthenium Red. The factors affecting the subsequent Ca2+-efflux were studied. Addition of rotenone or antimycin led to a decline of efflux except at pH values above 7.2, provided the load was less than about 80 nmol per mg of protein. Oligomycin reversed the effect of the respiratory inhibitors. Independently of respiration, efflux was stimulated by the uncoupler trifluoromethyltetrachlorbenzimadazole, by mersalyl and by thyroid hormones. The stimulated efflux could be diminished by ADP, with Mg2+ as cofactor if efflux was rapid. With respiration in progress, efflux could be stimulated by N-ethylmaleimide and 5,5′-dithiobis-(2-nitrobenzoate). The effects of mersalyl and of thyroid hormones could be diminished with dithiothreitol. In the absence of stimulating agents, the Ca2+ efflux was proportional to the load up to some critical amount, this critical amount was decreased by the agents. Thyroxine and mersalyl caused not only loss of Ca2+, but also simultaneous, but not necessarily proportional, loss of internal adenine nucleotides. Both efflux rates were kept at a low value by bongkrekic acid added before the stimulating agent. It is concluded that Ca2+ efflux is a measure of a permeability controlled by the binding of ADP (an Mg2+) to the inner membrane, and that this in turn depends on the maintenance of certain thiol gropus in a reduced form by a reaction that uses NADH and ATP and the energy-linked transhydrogenase.

scholarly journals The mechanism by which adenosine decreases gluconeogenesis from lactate in isolated rat hepatocytes

1987 ◽  
Vol 246 (2) ◽  
pp. 449-454 ◽  
Author(s):  
A Lavoinne ◽  
H A Buc ◽  
S Claeyssens ◽  
M Pinosa ◽  
F Matray
Keyword(s):  
Ketone Body ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Adenosine Kinase ◽  
Isolated Rat Hepatocytes ◽  
Adenosine Deaminase 2 ◽  
Body Production ◽  
Gluconeogenic Substrates ◽  
Isolated Rat ◽  
Stimulation Of

Incubation of hepatocytes from 24 h-starved rats in the presence of 0.5 mM-adenosine decreased gluconeogenesis from lactate, but not from alanine. The inhibition of gluconeogenesis was associated with a stimulation of ketone-body production and an inhibition of pyruvate oxidation. These metabolic changes were suppressed in the presence of iodotubercidin (an inhibitor of adenosine kinase), but were reinforced in the presence of deoxycoformycin (an inhibitor of adenosine deaminase); 2-chloroadenosine induced no change in gluconeogenesis from lactate. These data indicate that the inhibition of gluconeogenesis by adenosine probably results from its conversion into adenine nucleotides. In the presence of lactate or pyruvate, but not with alanine or asparagine, this conversion resulted in a decrease in the [ATP]/[ADP] ratio in both mitochondrial and cytosolic compartments. Adenosine decreased the Pi concentration with all gluconeogenic substrates.

Uptake of adenosine by dispersed chich embryonic cardiac cells

1975 ◽  
Vol 228 (1) ◽  
pp. 62-67 ◽  
Author(s):  
SJ Mustafa ◽  
R Rubio ◽  
RM Berne
Keyword(s):  
Blood Flow ◽  
Coronary Blood Flow ◽  
Adenine Nucleotides ◽  
Cardiac Cells ◽  
Adenosine Kinase ◽  
Heart Cells ◽  
Chick Embryos ◽  
Major Fraction ◽  
Isolated Cells ◽  
Embryo Heart

Adenosine is involved in the regulation of coronary blood flow, but its mechanism of action is not clear. The present investigation is an attempt to understand the mechanism(s) of uptake of adenosine in dispersed chick embryonic cardiac cells and its relationship to the adenosine hypothesis. Adenosine is readily taken up by these cardiac cells, and a small fraction is incorporated into adenine nucleotides, whereas a major fraction is deaminated to inosine. The mechanism of uptake is different in 12- to 15-day-old chick embryos compared to 16- to 22-day-old embryos. The younger embryo heart cells show the incorporation of adenosine into adenine mononucleotides of the incubation medium as well as all the adenine nucleotides of the cells, whereas the older embryo heart cells show incorporation of adenosine only into the adenine nucleotides of the cells. The isolated cells used in the present study do not leak any significant amounts of adenosine kinase and/or nucleotides, and free adenosine was not found in the cells, even with extracellular concentrations as high as 1 mM. The absence of free adenosine in isolated dispersed cells reflects the activities of adenosine kinase and adenosine deaminase and is compatible with the adenosine hypothesis for the regulation of coronary blood flow.

Adenosine transport by the lung

1988 ◽  
Vol 65 (1) ◽  
pp. 297-305 ◽  
Author(s):  
D. K. Das ◽  
H. Steinberg
Keyword(s):  
Pulmonary Artery ◽  
Pulmonary Circulation ◽  
Adenine Nucleotides ◽  
Adenosine Kinase ◽  
Rat Lung ◽  
Potent Vasodilator ◽  
Adenosine Transport ◽  
Rate Limiting ◽  
Isolated Rat Lung ◽  
Isolated Rat

Adenosine, a nucleoside and potent vasodilator, has been found to be taken up by the lung and converted by deamination into inosine and hypoxanthine. In a single circulation through an isolated rat lung, 69.3 +/- 3.3% of infused [14C]adenosine (10 microM) was removed from the circulation. Uptake of [14C]adenosine remained unchanged when deamination of adenosine was inhibited by 8-azaguanine or coformycin. In a single passage of adenosine through the pulmonary artery, very little of the deaminated products appeared in the pulmonary circulation, but when adenosine was recirculated through the pulmonary circulation inosine and hypoxanthine appeared in the venous effluent. These adenosine metabolites were also taken up by the lung. A major portion of the circulating adenosine was transported into the lung, where it was used to synthesize adenine nucleotides. Inhibition of adenosine kinase by iodotubercidin resulted in reduced formation of ATP and ADP. Uptake of adenosine by the lung was saturable on a concentration gradient and was a passive process because it was not affected by the absence of glucose or the presence of ouabain. Km and Vmax for adenosine transport were 0.227 mM and 4.6 mumol.min-1.g lung-1, respectively. Adenosine transport was inhibited by adenosine analogues, and the inhibitions were found to be competitive in nature. These results suggest that a specific and rate-limiting transport system exists in the lung for adenosine.

scholarly journals Laminar Variation in Threshold for Detection of Electrical Excitation of Striate Cortex by Macaques

2005 ◽  
Vol 94 (5) ◽  
pp. 3443-3450 ◽  
Author(s):  
Edgar A. DeYoe ◽  
Jeffrey D. Lewine ◽  
Robert W. Doty
Keyword(s):  
Electrical Stimulation ◽  
Striate Cortex ◽  
Human Subjects ◽  
Human Case ◽  
Constant Current ◽  
Electrical Excitation ◽  
Detection Thresholds ◽  
Current Pulses ◽  
A Site ◽  
Stimulation Of

Macaques were trained to signal their detection of electrical stimulation applied by a movable microelectrode to perifoveal striate cortex. Trains of ≤100 cathodal, 0.2-ms, constant current pulses were delivered at 50 or 100 Hz. The minimum current that could be reliably detected was measured at successive depths along radial electrode penetrations through the cortex. The lowest detection thresholds were routinely encountered when the stimulation was applied to layer 3, particularly just at the juncture between layers 3 and 4A. On the average, there was a twofold variation in threshold along the penetrations, with the highest intracortical thresholds being in layers 4C and 6. Variations as high as 20-fold were obtained in some individual penetrations, whereas relatively little change was observed in others. The minimum detectable current was 1 μA at a site in layer 3, i.e., 10–100 times lower than that for surface stimulation. Because macaques, as do human subjects, find electrical stimulation of striate cortex to be highly similar at all loci (a phosphene in the human case), it is puzzling as to how such uniformity of effect evolves from the exceedingly intricate circuitry available to the effective stimuli. It is hypothesized that the stimulus captures the most excitable elements, which then suppress other functional moieties, producing only the luminance of the phosphene. Lowest thresholds presumably are encountered when the electrode lies among these excitable elements that can, with higher currents, be stimulated directly from some distance or indirectly by the horizontal bands of myelinated axons, the stria of Baillarger.

scholarly journals An Uncharacterized Member of the Ribokinase Family in Thermococcus kodakarensis Exhibits myo-Inositol Kinase Activity

2013 ◽  
Vol 288 (29) ◽  
pp. 20856-20867 ◽  
Author(s):  
Takaaki Sato ◽  
Masahiro Fujihashi ◽  
Yukika Miyamoto ◽  
Keiko Kuwata ◽  
Eriko Kusaka ◽  
...  
Keyword(s):  
Kinase Activity ◽  
Three Dimensional ◽  
Fold Increase ◽  
Adenosine Kinase ◽  
Dimensional Structure ◽  
Uncharacterized Protein ◽  
Thermococcus Kodakarensis ◽  
Sugar Phosphates ◽  
Biochemical Analyses ◽  
Physiological Substrates

Here we performed structural and biochemical analyses on the TK2285 gene product, an uncharacterized protein annotated as a member of the ribokinase family, from the hyperthermophilic archaeon Thermococcus kodakarensis. The three-dimensional structure of the TK2285 protein resembled those of previously characterized members of the ribokinase family including ribokinase, adenosine kinase, and phosphofructokinase. Conserved residues characteristic of this protein family were located in a cleft of the TK2285 protein as in other members whose structures have been determined. We thus examined the kinase activity of the TK2285 protein toward various sugars recognized by well characterized ribokinase family members. Although activity with sugar phosphates and nucleosides was not detected, kinase activity was observed toward d-allose, d-lyxose, d-tagatose, d-talose, d-xylose, and d-xylulose. Kinetic analyses with the six sugar substrates revealed high Km values, suggesting that they were not the true physiological substrates. By examining activity toward amino sugars, sugar alcohols, and disaccharides, we found that the TK2285 protein exhibited prominent kinase activity toward myo-inositol. Kinetic analyses with myo-inositol revealed a greater kcat and much lower Km value than those obtained with the monosaccharides, resulting in over a 2,000-fold increase in kcat/Km values. TK2285 homologs are distributed among members of Thermococcales, and in most species, the gene is positioned close to a myo-inositol monophosphate synthase gene. Our results suggest the presence of a novel subfamily of the ribokinase family whose members are present in Archaea and recognize myo-inositol as a substrate.

Regulation of hepatic gluconeogenesis in newborn rabbit: controlling factors in presuckling period

1985 ◽  
Vol 249 (5) ◽  
pp. E498-E505 ◽  
Author(s):  
W. A. Brennan ◽  
J. R. Aprille
Keyword(s):  
Adenine Nucleotide ◽  
Adenine Nucleotides ◽  
Mitochondrial Protein ◽  
Fold Increase ◽  
Insulin Injection ◽  
Pyruvate Carboxylation ◽  
Glucose Levels ◽  
Newborn Rabbit ◽  
Nucleotide Content

We have previously shown (Comp. Biochem. Physiol. 77B: 35-39, 1984) that a rapid postnatal increase in hepatic mitochondrial adenine nucleotide content activates pyruvate carboxylation and gluconeogenesis in the newborn rabbit. This study investigated factors limiting flux through the gluconeogenic pathway and examined the physiological stimuli responsible for the activation phenomenon. There is a 2.3-fold increase in total mitochondrial adenine nucleotides, along with a threefold increase in the matrix ATP/ADP ratio, by 2 h after birth, resulting overall in a sixfold increase in the amount of ATP/mg mitochondrial protein. Analysis of gluconeogenic intermediates, measured in freeze-clamped livers between birth and 4 h postnatal, suggests that pyruvate carboxylase controls gluconeogenic flux during this period. Newborn rabbits reared in an hypoxic environment (5% O2) exhibited decreased mitochondrial adenine nucleotide content, decreased rates of pyruvate carboxylation, and depressed blood glucose levels compared with littermates reared in room air or 95% O2. Manipulation of the insulin-to-glucagon ratio in vivo by injecting insulin at birth significantly delayed postnatal increases in the mitochondrial adenine nucleotide content and the rate of pyruvate carboxylation. Conversely, glucagon injection produced a supranormal increase in both mitochondrial adenine nucleotide content and pyruvate carboxylation. In addition, insulin injection prevented, whereas glucagon enhanced, the normal postnatal increase in tissue ATP/ADP. These results suggest that tissue oxygenation and a decreased insulin-to-glucagon ratio promote the rapid influx of adenine nucleotides from the liver cytosol into the mitochondrial matrix, thereby activating pyruvate carboxylation and gluconeogenesis during the presuckling period.

The effect of amitriptyline, mianserin, and viloxazine at pre- and post-junctional muscarinic receptors in guinea-pig ileal longitudinal muscle

1982 ◽  
Vol 60 (2) ◽  
pp. 193-200 ◽  
Author(s):  
Y. H. Kwok ◽  
F. Mitchelson
Keyword(s):  
Electrical Stimulation ◽  
Guinea Pig ◽  
Muscarinic Receptors ◽  
Longitudinal Muscle ◽  
Fold Increase ◽  
Selective Inhibition

The antimuscarinic activity of amitriptyline, mianserin, and viloxazine was compared with atropine in guinea-pig ileal longitudinal muscle. The pA2 values obtained using carbachol (CCh) as agonist were as follows: atropine, 9.55; amitriptyline, 7.50; mianserin, 6.40; and viloxazine, 4.91. Responses to transmural electrical stimulation (1–50 Hz) were more resistant than those produced by CCh to inhibition by atropine and the antidepressants. This did not appear to be due to a selective inhibition of prejunctional inhibitory muscarinic receptors, as a pA2 of 8.73 was obtained with atropine for the depression of oxotremorine-induced inhibition of acetylcholine (ACh) output. Amitriptyline (10 μM) caused a 2.4-fold increase in ACh output and was 200-fold weaker than atropine at doubling ACh output in the longitudinal muscle stimulated at 0.3 Hz. Mianserin (10 μM) and viloxazine (1–10 μM) did not significantly affect ACh output. It is suggested that the antidepressants exhibit a greater affinity for the postjunctional muscarinic receptors in the guinea-pig ileal longitudinal muscle.

scholarly journals Homocysteine enhances the inhibitory effect of extracellular adenosine on the synthesis of proteins in isolated rat hepatocytes

1995 ◽  
Vol 310 (3) ◽  
pp. 893-896 ◽  
Author(s):  
S Tinton ◽  
P Buc-Calderon
Keyword(s):  
Protein Synthesis ◽  
Kinase Inhibitor ◽  
Adenine Nucleotides ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Adenosine Kinase ◽  
Isolated Rat Hepatocytes ◽  
Extracellular Adenosine ◽  
Inhibition Of Protein Synthesis ◽  
Isolated Rat

Previous work has shown that extracellular adenosine inhibits the incorporation of radiolabelled leucine into proteins in isolated rat hepatocytes [Tinton, Lefebvre, Cousin and Buc Calderon (1993) Biochim. Biophys. Acta 1176, 1-6]. In this study, we investigated whether its metabolism into adenine nucleotides, inosine or S-adenosylhomocysteine (AdoHcy) is required to induce such an impairment. Incubation of isolated hepatocytes in the presence of adenosine at 0.5 or 1 mM reduces the synthesis of proteins by about 45% after 120 min of incubation. Such an inhibition occurred without cell lysis and was not modified by adding the adenosine kinase inhibitor 5-iodotubercidin (15 microM) or the adenosine deaminase inhibitor coformycin (0.1 microM). It is therefore unlikely that the anabolic and catabolic pathways of adenosine are involved in the inhibition of protein synthesis. Adenosine (1 mM) increased the level of AdoHcy and S-adenosylmethionine by 20- and 5-fold respectively after 60 min of incubation and reduced the methylation index. These events as well as the inhibition of protein synthesis were strongly enhanced in the presence of L-homocysteine (2 mM). It is therefore concluded that the metabolism of adenosine into AdoHcy, which is known to be a potent inhibitor of cellular methylation reactions, may play an important role in the control of translation.

Sign in / Sign up

Export Citation Format

Share Document