NTPDase and 5′-nucleotidase Activities of Synaptosomes from Hippocampus of Rats Subjected to Hyperargininemia

Abstract

ATP is an important excitatory neurotransmitter and adenosine acts as a neuromodulatory structure inhibiting neurotransmitters release in the central nervous system. Since the ecto-nucleotidase cascade that hydrolyzes ATP to adenosine is involved in the control of brain functions and previous studies realized in our laboratory have recently reported that acute administration of Arg decreases the NTPDase and 5'-nucleotidase activities of rat blood serum, in the present study we investigated the effect of arginine administration on NTPDase and 5'-nucleotidase activities by synaptosomes from hippocampus of rats. First, sixty-days-old rats were treated with a single or a triple intraperitoneal injection of arginine (0.8 g/Kg) or an equivalent volume of 0.9% saline solution (control) and were killed 1 h later. Second, rats received an intracerebroventricular injection of 1.5 mM arginine solution or saline (5 microL) and were killed 1 h later. We also tested the in vitro effect of arginine (0.1-1.5 mM) on nucleotide hydrolysis in synaptosomes from rat hippocampus. Results showed that intraperitoneal arginine administration did not alter nucleotide hydrolysis. On the other hand, arginine administered intracerebroventricularly reduced ATP (32%), ADP (30%) and AMP (21%) hydrolysis, respectively. In addition, arginine added to the incubation medium, provoked a decrease on ATP (19%), ADP (17%) and AMP (23%) hydrolysis, respectively. Furthermore, kinetic studies showed that the inhibitory effect of arginine was uncompetitive in relation to ATP, ADP and AMP. In conclusion, according to our results it seems reasonable to postulate that arginine alters the cascade involved in the extracellular degradation of ATP to adenosine.

Effects In Vitro of Guanidinoacetate on Adenine Nucleotide Hydrolysis and Acetylcholinesterase Activity in Tissues from Adult Rats

“…These results differ from previous studies from our laboratory that showed that other guanidine The interaction of GAA with NTPDase and 5 0 -nucleotidase activities was determined using the Lineweaver Burk [41] double reciprocal plot, by plotting 1/V against 1/S analysed over a range of nucleotides concentrations: ATP and ADP (10-1,000 lM) and AMP (20-2,000 lM) in the absence and in the presence of GAA compounds such as N-acetylarginine, arginic acid and homoarginine, which are accumulated in hyperargininemic patients, increased NTPDase and 5 0 -nucleotidase activities in synaptosomes from the cerebral cortex [49]. Taken together, these findings suggest that guanidine compounds have heterogeneously effects in the purinergic signaling in the brain areas, a fact that that can be explained by the different chemical structure of these compounds [49,50]. NTPDase and 5 0 -nucleotidase are the most relevant ectoenzymes involved in adenine extracellular nucleotide hydrolysis [4,6].…”

“…The values of inhibition constant (K i ) were obtained using Cornish-Bowden plots of S/V versus [I] [43]. IC 50 , was estimated at fixed substrate concentration the according to the Dixon and Webb [44] plot using 1/V versus [I].…”

NTPDase and 5'‐nucleotidase activities in physiological and disease conditions: New perspectives for human health

“…In contrast, studies demonstrated that arginine in vitro decreased NTPDase and 5'-nucleotidase activities in rat hippocampus. Rats subjected to intracerebroventricular arginine administration showed a reduction in ATP, ADP and AMP hydrolysis in rat hippocampus and serum and L-NAME, an inhibitor of nitric oxide synthase, prevented such effects [31,34]. Proline, an amino acid accumulated in hyperprolinemia, did not alter nucleotide hydrolysis when added to enzyme assays, but when administered acutely or chronically, it decreased ATP hydrolysis in rat cerebral cortex synaptosomes; ADP and AMP hydrolysis were not altered by proline administration [33].…”