Biomedical subjects

C D Bonan

Publications and source records attributed to C D Bonan.

22 records · Page 2Linked to original sources

PubMed1998

Inhibitory avoidance learning inhibits ectonucleotidases activities in hippocampal synaptosomes of adult rats.

Several lines of evidence indicate that ATP may play an important role in Long-Term Potentiation. In this investigation we evaluated the effect of a memory task (step-down inhibitory avoidance) on the synaptosomal ecto-enzymes (ATP diphosphohydrolase and 5'-nucleotidase) involved in the degradation of ATP to adenosine. After the training session, a decrease in the ATPase (40%) and ADPase (29%) activities of ATP diphosphohydrolase as well as was a decrease in 5'-nucleotidase activity (31%) was observed in hippocampal synaptosomes of rats trained and killed immediately after training. In synaptosomes of rats killed 30 minutes after training, a decrease in ATPase activity (28%) was observed. In the test session, no significant changes were observed in the enzyme activities studied. These results provide new information about the activity of ecto-enzymes involved in nucleotide degradation and their possible participation in mechanisms of acquisition and modulation of memory processing.

5'-Nucleotidase↗

PubMed1998

Catabolism of Ap4A and Ap5A by rat brain synaptosomes.

Adenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) and adenosine 5',5"'-P1,P5-pentaphosphate (Ap5A) are stored in and released from rat brain synaptic terminals. In the present study we investigated the hydrolysis of dinucleotides (Ap4A and Ap5A) in synaptosomes from the cerebral cortex of adult rats. Ap4A and Ap5A, but not Ap3A, were hydrolyzed at pH 7.5 in the presence of 20 mM Tris/HCl, 2.0 mM MgCl2, 10 mM glucose and 225 mM sucrose at 37 degrees C. The disappearance of the substrates measured by FPLC on a mono-Q HR column was both time and protein dependent. Since synaptosome integrity was at least 90% at the end of the assay, hydrolysis probably occurred by the action of an ecto-enzyme. Extracellular actions of adenine dinucleotides at central nervous system terminate due to the existence of ecto-nucleotidases which specifically cleave these dinucleotides. These enzymes in association with an ATP diphosphohydrolase and a 5'-nucleotidase are able to promote the complete hydrolysis of dinucleotides to adenosine in the synaptic cleft.

Animals↗

PubMed1997

Effects of 9-amino-1,2,3,4-tetrahydroacridine (THA) on ATP diphosphohydrolase (EC 3.6.1.5) and 5'-nucleotidase (EC 3.1.3.5) from rat brain synaptosomes.

1. 9-Amino-1,2,3,4-tetrahydroacridine (THA), an acetylcholinesterase inhibitor, significantly inhibited in vitro the ATP diphosphohydrolase activity of synaptosomes from the cerebral cortex and hippocampus of adult rats. 2. THA did not inhibit in vitro the 5'-nucleotidase activity of synaptosomes from cerebral cortex and hippocampus of rats. 3. THA exerted an uncompetitive inhibition on ATP diphosphohydrolase activity. This mechanism of inhibition was the same in the 2 different synaptosomal fractions (cerebral cortex and hippocampus) studied. 4. THA, proposed as a drug for the treatment of Alzheimer's disease, can alter in vitro ATP degradation in synaptosomes from the central nervous system.

5'-Nucleotidase↗

PubMed1995

Solubilization and characterization of an ATP diphosphohydrolase (EC 3.6.1.5) from rat brain synaptic plasma membranes.

The effect of different detergents on the ATPase and ADPase activities from synaptic plasma membrane were investigated. Triton X-100, deoxycholate, CHAPS, Nonidet, N-octylglucoside and C12E8, which is commonly used to solubilize plasma membrane proteins, easily inactivated the ATPase and ADPase activities, while digitonin was not harmful to the enzyme. Treatment of the synaptic plasma membrane from rat brain with 0.5% digitonin solubilizes 80% of the proteins and 50% and 60% of ATPase and ADPase, respectively, with the following characteristics: stimulation by Ca2+ in the millimolar range, insensitivity to ATPase inhibitors (ouabain, olygomicyn, orthovanadate), inhibition with sodium azide and NEM and broad substrate specificity for the hydrolysis of nucleoside di- and triphosphate. To further characterize the enzyme solubilized, polyclonal antibodies specific for ATP diphosphohydrolase from potato tuber were tested. Western blot showed that two electrophoretic bands with a molecular mass close to 60-70 kDa had cross-immunoreactivity with antibodies against potato apyrase. The results presented here demonstrate for the first time the solubilization of ATPase and ADPase activities with characteristics of a true ATP diphosphohydrolase from synaptic plasma membrane from rat brain and with cross-immunoreactivity with antibodies against potato apyrase.

Animals↗