Inhibition of Cortical Neurones by Imidazole and Some Derivatives

1973 ◽  
Vol 51 (11) ◽  
pp. 790-797 ◽  
Author(s):  
J. M. Godfraind ◽  
K. Krnjević ◽  
H. Maretić ◽  
R. Pumain
Keyword(s):  
Cyclic Amp ◽  
Cyclic Nucleotide ◽  
Inhibitory Action ◽  
Aminobutyric Acid ◽  
Phosphodiesterase Activity ◽  
Inhibitory Potency ◽  
Imidazole Derivatives ◽  
Propyl Esters ◽  
Relative Potencies ◽  
Acetic Acids

Systematic tests of imidazole and 15 derivatives, applied by microiontophoresis in anesthetized cats, showed a high inhibitory potency of imidazole-4-acetic and imidazole-4-propionic acids and also of their amyl and propyl esters; but imidazole 4-carboxylic and 1-methylimidazole-4-acetic acids were largely inactive. This order of potency is very different from the relative potencies of imidazole derivatives in facilitating cyclic nucleotide phosphodiesterase activity. It is therefore unlikely that their inhibitory action is simply related to changes in cellular levels of cyclic AMP. The characteristics of this action, including lack of antagonism by bicuculline, are consistent with the possibility that it is mediated by γ-aminobutyric acid receptors.

scholarly journals Photoaffinity labelling of central-nervous-system myelin. Evidence for an endogenous type I cyclic AMP-dependent kinase phosphorylating the larger subunit of 2′,3′-cyclic nucleotide 3′-phosphodiesterase

1984 ◽  
Vol 221 (2) ◽  
pp. 361-368 ◽  
Author(s):  
J M Bradbury ◽  
R J Thompson
Keyword(s):  
Central Nervous System ◽  
Nervous System ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
Cyclic Nucleotide ◽  
Type I ◽  
Phosphodiesterase Activity ◽  
Dependent Protein Kinase ◽  
Photoaffinity Labelling ◽  
Dependent Protein

Endogenous cyclic AMP-stimulated phosphorylation of a 49700-Mr Wolfgram protein component in rabbit central nervous system was investigated by using photoaffinity labelling and 2′,3′-cyclic nucleotide 3′-phosphodiesterase activity staining after electroblotting on to nitrocellulose paper. Photoaffinity labelling with 8′-azidoadenosine 3′,5′-cyclic monophosphate showed a cyclic AMP-binding protein that appeared to be intrinsic to the myelin membrane and appeared to represent the R-subunit of a type I cyclic AMP-dependent protein kinase. This photoaffinity-labelled protein was of larger apparent Mr than the protein showing cyclic AMP-stimulated phosphorylation. Blotting of one-dimensional sodium dodecyl sulphate/polyacrylamide-gel electrophoretograms followed by staining for 2′,3′-cyclic nucleotide 3′-phosphodiesterase activity showed two activity bands corresponding to the two components of the Wolfgram protein doublet. Cyclic AMP-stimulated protein phosphorylation corresponded to the upper component of this doublet. Electroblotting of two-dimensional non-equilibrium pH-gradient electrophoretograms also showed co-migration of cyclic AMP-stimulated protein phosphorylation with enzyme activity. It is proposed that central-nervous-system myelin contains an endogenous type I cyclic-AMP dependent protein kinase that phosphorylates the larger subunit of 2′,3′-cyclic nucleotide 3′-phosphodiesterase.

scholarly journals Ontogenetic changes in adenylate cyclase, cyclic AMP phosphodiesterase and calmodulin in chick ventricular myocardium

1987 ◽  
Vol 243 (2) ◽  
pp. 525-531 ◽  
Author(s):  
P M Epstein ◽  
D M Andrenyak ◽  
C J Smith ◽  
A J Pappano
Keyword(s):  
Cyclic Amp ◽  
Embryonic Development ◽  
Adenylate Cyclase ◽  
Cyclic Nucleotide ◽  
Sodium Acetate ◽  
Specific Activity ◽  
Ventricular Myocardium ◽  
Phosphodiesterase Activity ◽  
Ontogenetic Changes ◽  
Cyclic Amp Phosphodiesterase

The activities of cyclic AMP phosphodiesterase (3′,5′-cyclic nucleotide 5′-nucleotidohydrolase, EC 3.1.4.17) and adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] and calmodulin content during development of chick ventricular myocardium were determined. The specific activity of cyclic AMP phosphodiesterase was relatively low in early embryos, increased during embryogenesis by about 4-fold to reach highest values just before hatching, and then decreased by approx. 30% within 1 week after hatching. In contrast, adenylate cyclase did not change during embryonic development, but increased by approx. 50% within 1 week after hatching. Calmodulin content remained constant at 9 micrograms/g wet wt. during embryonic development and decreased to 6 micrograms/g wet wt. by 1 week after hatching. DEAE-Sephacel chromatography of chick ventricular supernatant revealed a single major form of cyclic nucleotide phosphodiesterase activity in early embryonic (9-day E) and hatched (6-day H) chicks. This enzyme form was eluted at approx. 0.27 M-sodium acetate, hydrolysed both cyclic AMP and cyclic GMP, and was sensitive to stimulation by Ca2+-calmodulin, with an apparent Km for calmodulin of approx. 1 nM. In contrast, ventricular supernatant from late-embryonic (18-day E) chicks contained two forms of phosphodiesterase separable on DEAE-Sephacel: the same form as that seen at other ages, plus a cyclic AMP-specific form which was eluted at approx. 0.65 M-sodium acetate and was insensitive to stimulation by Ca2+-calmodulin. The ontogenetic changes in cyclic AMP phosphodiesterase activity in chick ventricular myocardium are consistent with reported ontogenetic changes in the steady-state contents of cyclic AMP in this tissue and suggest that this enzyme may be responsible for the changes that occur in this nucleotide during development of chick myocardium.

scholarly journals Cyclic AMP phosphodiesterase and cyclic GMP phosphodiesterase activities of rat mammary tissue

1984 ◽  
Vol 219 (3) ◽  
pp. 801-809 ◽  
Author(s):  
I Mullaney ◽  
R A Clegg
Keyword(s):  
Cyclic Amp ◽  
Cyclic Gmp ◽  
Cyclic Nucleotide ◽  
Deae Cellulose ◽  
Cyclic Nucleotide Phosphodiesterase ◽  
Mammary Tissue ◽  
Phosphodiesterase Activity ◽  
High Affinity ◽  
Low Concentrations ◽  
Maximal Activation

Cyclic nucleotide phosphodiesterase activity in mammary tissue from rats in midlactation was resolved by DEAE-cellulose chromatography into three functionally distinct fractions: a Ca2+/calmodulin-stimulated cyclic GMP phosphodiesterase, a cyclic GMP-stimulated low-affinity cyclic nucleotide phosphodiesterase, and a high-affinity cyclic AMP-specific phosphodiesterase. The absolute activities and relative proportions of high- and low-affinity enzymes resemble those found, for example, in liver, as distinct from those in excitable tissues. Three functional characteristics are described which are peculiar to mammary-tissue phosphodiesterases. Firstly, the concentration of free Ca2+ required to achieve half-maximal activation of the Ca2+/calmodulin-stimulated phosphodiesterase is somewhat higher than for the analogous enzyme in other tissues; secondly, the activity of this enzyme towards cyclic AMP relative to that towards cyclic GMP is unusually low, and thirdly, the low-affinity cyclic nucleotide phosphodiesterase is inhibited by low concentrations of free Ca2+.

scholarly journals Identification and characterization of a Ca2+-calmodulin-sensitive cyclic nucleotide phosphodiesterase in a human lymphoblastoid cell line

1987 ◽  
Vol 243 (2) ◽  
pp. 533-539 ◽  
Author(s):  
P M Epstein ◽  
S Moraski ◽  
R Hachisu
Keyword(s):  
Cyclic Amp ◽  
Cell Line ◽  
Cyclic Nucleotide ◽  
Sodium Acetate ◽  
Lymphoblastoid Cell Line ◽  
Human Peripheral Blood ◽  
Affinity Column ◽  
Phosphodiesterase Activity ◽  
Linear Kinetics ◽  
Non Linear

This study examines the pattern and regulatory properties of cyclic nucleotide phosphodiesterases in a human lymphoblastoid B-cell line (RPMI 8392) established from a patient with acute lymphocytic leukaemia. In this cell line, phosphodiesterase activity measured at 0.25 microM-cyclic AMP is approx. 7-fold greater than that in isolated human peripheral-blood lymphocytes, and 16% of the phosphodiesterase activity in RPMI 8392 cells is associated with particulate fractions. Phosphodiesterase activity in crude fractions of this cell line is reproducibly stimulated by about 60-80% by Ca2+-calmodulin. In the presence of 20 nM-calmodulin, half-maximal stimulation occurs at 0.7 microM-Ca2+. The cytosolic phosphodiesterase activity of RPMI 8392 cells is separated into two forms by DEAE-Sephacel chromatography. The first form is eluted at approx. 0.2 M-sodium acetate, catalyses the hydrolysis of both cyclic AMP and cyclic GMP, and is stimulated 3-fold by Ca2+-calmodulin. This form exhibits non-linear kinetics for cyclic AMP in the absence of calmodulin, with extrapolated Km values of 0.8 and 4 microM, and non-linear kinetics in the presence of calmodulin, with extrapolated Km values of 0.5 and 1 microM. The Vmax. values are increased approx. 3-fold by calmodulin. The second form is eluted at approx. 0.6 M-sodium acetate, is specific for cyclic AMP, and insensitive to stimulation by Ca2+-calmodulin. The Ca2+-calmodulin-sensitive phosphodiesterase from the DEAE-Sephacel column can be adsorbed to a calmodulin-Sepharose affinity column and eluted with EGTA. This enzymic activity can also be immunoprecipitated by a monoclonal antibody directed against a calmodulin-bovine heart phosphodiesterase complex. This study documents the existence of Ca2+-calmodulin-sensitive phosphodiesterase in a cultured lymphoblastoid cell line derived from a leukaemic patient.

scholarly journals An effect of insulin on adipose-tissue adenosine 3′:5′-cyclic monophosphate phosphodiesterase

1970 ◽  
Vol 120 (1) ◽  
pp. 187-193 ◽  
Author(s):  
E. G. Loten ◽  
J. G. T. Sneyd
Keyword(s):  
Adipose Tissue ◽  
Cyclic Amp ◽  
Cyclic Nucleotide ◽  
Fat Cells ◽  
Maximal Velocity ◽  
Isolated Fat Cells ◽  
Phosphodiesterase Activity ◽  
Cyclic Monophosphate ◽  
Cyclic Nucleotide Phosphodiesterases ◽  
Fat Pads

1. 3′:5′-Cyclic nucleotide phosphodiesterase activity was measured in homogenates prepared from epididymal fat-pads and isolated fat-cells incubated in the absence and presence of insulin. 2. Homogenates of insulin-treated tissues showed an increase in phosphodiesterase activity compared with controls. No effect of insulin was observed when the hormone was added directly to homogenates. 3. There was kinetic evidence for the presence of two 3′:5′-cyclic nucleotide phosphodiesterases in adipose tissue. Insulin raised the maximal velocity of the low-Km enzyme and lowered the Km of the higher-Km enzyme. 4. It is suggested that the effect of insulin on adipose tissue phosphodiesterase accounts for the ability of this hormone to lower cyclic-AMP concentration in the tissue.

scholarly journals Cyclic nucleotide phosphodiesterase of rat pancreatic islets. Effects of Ca2+, calmodulin and trifluoperazine

1981 ◽  
Vol 197 (2) ◽  
pp. 459-464 ◽  
Author(s):  
M C Sugden ◽  
S J Ashcroft
Keyword(s):  
Cyclic Amp ◽  
Pancreatic Islets ◽  
Islets Of Langerhans ◽  
Cyclic Gmp ◽  
Cyclic Nucleotide ◽  
Specific Inhibitor ◽  
Cyclic Nucleotide Phosphodiesterase ◽  
Phosphodiesterase Activity ◽  
Rat Pancreatic Islets ◽  
Rat Islets Of Langerhans

Cyclic nucleotide phosphodiesterase activity towards cyclic AMP and cyclic GMP was studied in extracts of rat islets of Langerhans. Biphasic Eadie plots [Eadie (1942) J. Biol. Chem. 146, 85-93] were obtained with either substrate suggesting the presence of both ‘high’- and ‘low’-Km components. The apparent Km values were 6.2 +/- 0.5 (n = 8) microM and 103.4 +/- 13.5 (6) microM for cyclic AMP and 3.6 +/- 0.3 (12) microM and 61.4 +/- 7.5 (13) microM for cyclic GMP. With cyclic AMP as substrate, phosphodeisterase activity was increased by calmodulin and Ca2+ and decreased by trifluoperazine, a specific inhibitor of calmodulin. With cyclic GMP as substrate, phosphodiesterase activity was decreased by omission of Ca2+ or addition of trifluoperazine. Addition of exogenous calmodulin had no effect on activity. The data suggest that Ca2+ may influence the islet content of cyclic AMP and cyclic GMP via effects on calmodulin-dependent cyclic nucleotide phosphodiesterase(s).

scholarly journals Evidence that the peripheral cyclic AMP phosphodiesterase of rat liver plasma membranes is a metalloenzyme

1985 ◽  
Vol 225 (1) ◽  
pp. 143-147 ◽  
Author(s):  
J Londesborough
Keyword(s):  
Cyclic Amp ◽  
Rat Liver ◽  
Cyclic Nucleotide ◽  
Plasma Membranes ◽  
Metal Chelators ◽  
Phosphodiesterase Activity ◽  
Cyclic Amp Phosphodiesterase ◽  
Liver Plasma Membranes ◽  
Isomer Activity ◽  
Rat Liver Plasma Membranes

Cyclic nucleotide phosphodiesterase activity in salt extracts of rat liver plasma membranes was progressively inactivated by treatment with the metal chelators 8-hydroxyquinoline and o-phenanthroline, but not the non-chelating m-phenanthroline isomer. Activity at 20 microM-cyclic AMP was lost more slowly than activity at 0.4 microM-cyclic AMP. The activity of treated preparations was partially restored by incubation with Zn2+ or Mn2+ ions (in the presence of 1 mM-MgCl2) but not with Ca2+, Cd2+, Co2+, Cu2+ or Fe2+ ions, nor by MgCl2 alone. The results suggest the presence in the membrane extracts of a cyclic AMP phosphodiesterase containing tightly bound metal, possibly Zn or Mn, that affects the enzyme's affinity for cyclic AMP.

scholarly journals Function of calmodulin in postsynaptic densities. I. Presence of a calmodulin-activatable cyclic nucleotide phosphodiesterase activity.

1981 ◽  
Vol 89 (3) ◽  
pp. 433-439 ◽  
Author(s):  
D J Grab ◽  
R K Carlin ◽  
P Siekevitz
Keyword(s):  
Cyclic Amp ◽  
Cyclic Gmp ◽  
Cyclic Nucleotide ◽  
Postsynaptic Density ◽  
Maximal Activity ◽  
Cyclic Nucleotide Phosphodiesterase ◽  
Phosphodiesterase Activity ◽  
Native Structure ◽  
Fraction I ◽  
Two Peaks

The postsynaptic density (PSD) fraction from canine cerebra cortex was found to contain an endogenous cyclic nucleotide-phosphodiesterase activity that was independent on Mn2+ and/or Mg2+ but not on Ca2+. Maximal activity was obtained at 1 micrometer Mn2+. This cyclic nucleotide phosphodiesterase activity was not decreased upon removal of the calmodulin from the PSD fraction, nor was it increased by the addition of calmodulin to a postsynaptic density fraction deficient in calmodulin. The enzymatic activity could be extracted by sonication, with the soluble enzyme having properties similar to those found in the native structure. Two peaks of cyclic nucleotide phosphodiesterase activities could be obtained after S-300 Sephacryl column chromatography of this soluble fraction: fraction I (excluded peak) and fraction II (215,000 mol wt). The fraction I activity preferred cyclic AMP over cyclic GMP and was not activated by calmodulin. The fraction II activity has an approximately fourfold lower Km for cyclic GMP over cyclic AMP. This fraction II activity was activatable by calmodulin, which increased the Vmax and decreased the Km in the case of both cyclic nucleotides. We conclude that two activities are present in the PSD, one activatable, and one not activatable, by calmodulin.

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