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[ 3 H]Adenosine Transport in Synaptoneurosomes of Postmortem Human Brain
Author(s) -
Gu J. G.,
Kala G.,
Geiger J. D.
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb03509.x
Subject(s) - adenosine , ehna , adenosine kinase , adenosine deaminase , chemistry , adenosine deaminase inhibitor , purine metabolism , hypoxanthine , purine , metabolism , nucleoside , biochemistry , adenine nucleotide , purinergic signalling , adenosine a1 receptor , adenosine receptor , nucleotide , enzyme , receptor , gene , agonist
Abstract: [ 3 H]Adenosine transport was characterized in cerebral cortical synaptoneurosomes prepared from postmortem human brain using an inhibitor‐stop/centrifugation method. The adenosine transport inhibitors dipyridamole and dilazep completely and rapidly blocked transmembrane fluxes of [ 3 H]adenosine. For 5‐s incubations, two kinetically distinguishable processes were identified, i.e., a high‐affinity adenosine transport system with K t and V max values of 89 μ M and 0.98 nmol/min/mg of protein, respectively, and a low‐affinity adenosine transport system that did not appear to be saturable. For incubations with 1 μ M [ 3 H]adenosine as substrate, intrasynaptoneurosomal concentrations of [ 3 H]adenosine were 0.26 μ M at 5 s and 1 μ M at 600 s. Metabolism of accumulated [ 3 H]adenosine to adenine nucleotides was 15% for 5‐s, 23% for 15‐s, 34% for 30‐s, 43% for 60‐s, and 80% for 600‐s incubations. The concentrations (μ M ) of total accumulated 3 H‐purines ([ 3 H]‐adenosine plus metabolites) at these times were 0.3, 0.5, 1.0, 1.3 and 5.6, respectively. These results indicate that in the presence of extensive metabolism, the intrasynaptoneurosomal accumulation of 3 H‐purines was higher than the initial concentration of 1 μ M [ 3 H]adenosine in the reaction medium. For 5‐, 15‐, 30‐, 60‐, and 600‐s incubations in the presence of the adenosine deaminase inhibitor EHNA and the adenosine kinase inhibitor 5′‐iodotubercidin, metabolism of the transported [ 3 H]adenosine was 14, 14, 16, 14, and 38%, respectively. During these times, total 3 H‐purine accumulation was 0.3, 0.5, 0.5, 0.7, and 1.8 μ M , respectively. Thus, the apparently “concentrative'’accumulation of 3 H‐purines can be prevented by inhibition of adenosine metabolism and, taken together, these results suggest that adenosine transport in at least synaptoneurosomes prepared from postmortem human brain is via a nonconcentrative and equilibrative system.