title: Ecto-ATPase inhibition: ATP and adenosine release under physiological and ischemic in vivo conditions in the rat striatum.
abstract: In the central nervous system (CNS) ATP and adenosine act as transmitters and neuromodulators on their own receptors but it is still unknown which part of extracellular adenosine derives per se from cells and which part is formed from the hydrolysis of released ATP. In this study extracellular concentrations of adenosine and ATP from the rat striatum were estimated by the microdialysis technique under in vivo physiological conditions and after focal ischemia induced by medial cerebral artery occlusion. Under physiological conditions, adenosine and ATP concentrations were in the range of 130 nmol/L and 40 nmol/L, respectively. In the presence of the novel ecto-ATPase inhibitor, PV4 (100 nmol/L), the extracellular concentration of ATP increased 12-fold to ~360 nmol/L but the adenosine concentration was not altered. This demonstrates that, under physiological conditions, adenosine is not a product of extracellular ATP. In the first 4h after ischemia, adenosine increased to ~690 nmol/L and ATP to ~50 nmol/L. In the presence of PV4 the extracellular concentration of ATP was in the range of 450 nmol/L and a significant decrease in extracellular adenosine (to ~270 nmol/L) was measured. The contribution of extracellular ATP to extracellular adenosine was maximal in the first 20 min after ischemia onset. Furthermore we demonstrated, by immunoelectron microscopy, the presence of the concentrative nucleoside transporter CNT2 on plasma and vesicle membranes isolated from the rat striatum. These results are in favor that adenosine is transported in vesicles and is released in an excitation-secretion manner under in vivo physiological conditions. Early after ischemia, extracellular ATP is hydrolyzed by ecto-nucleotidases which significantly contribute to the increase in extracellular adenosine. To establish the contribution of extracellular ATP to adenosine might constitute the basis for devising a correct putative purinergic strategy aimed at protection from ischemic damage.
authors: Department of Preclinical and Clinical Pharmacology, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy. alessia.melani@unifi.it
authors: Alessia
authors: A
authors: Melani
authors: Francesca
authors: F
authors: Corti
authors: Holger
authors: H
authors: Stephan
authors: Christa E
authors: CE
authors: Müller
authors: Chiara
authors: C
authors: Donati
authors: Paola
authors: P
authors: Bruni
authors: Maria Giuliana
authors: MG
authors: Vannucchi
authors: Felicita
authors: F
authors: Pedata
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D020244:Infarction, Middle Cerebral Artery / Q000473:pathology*; D008297:Male; D026901:Membrane Transport Proteins / Q000378:metabolism; D017551:Microdialysis; D016253:Microscopy, Immunoelectron; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D016708:Synaptophysin / Q000378:metabolism; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D026901:Membrane Transport Proteins; D016708:Synaptophysin; C065171:cif nucleoside transporter; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; C027201:ectoATPase; D000241:Adenosine