[3H]Adenosine Transport in Synaptoneurosomes of Postmortem Human Brain
Article first published online: 5 OCT 2006
Journal of Neurochemistry
Volume 60, Issue 6, pages 2232–2237, June 1993
How to Cite
Gu, J. G., Kala, G. and Geiger, J. D. (1993), [3H]Adenosine Transport in Synaptoneurosomes of Postmortem Human Brain. Journal of Neurochemistry, 60: 2232–2237. doi: 10.1111/j.1471-4159.1993.tb03509.x
- Issue published online: 5 OCT 2006
- Article first published online: 5 OCT 2006
- Received September 16, 1992; revised manuscript received November 13, 1992; accepted November 13, 1992.
- Adenosine deaminase;
- Adenosine kinase;
- Human brain.
Abstract: Abstract: [3H]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 [3H]adenosine. For 5-s incubations, two kinetically distinguishable processes were identified, i.e., a high-affinity adenosine transport system with Kt and Vmax values of 89 μM 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 μM [3H]adenosine as substrate, intrasynaptoneurosomal concentrations of [3H]adenosine were 0.26 μM at 5 s and 1 μM at 600 s. Metabolism of accumulated [3H]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 (μM) of total accumulated 3H-purines ([3H]-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 3H-purines was higher than the initial concentration of 1 μM [3H]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 [3H]adenosine was 14, 14, 16, 14, and 38%, respectively. During these times, total 3H-purine accumulation was 0.3, 0.5, 0.5, 0.7, and 1.8 μM, respectively. Thus, the apparently “concentrative'’accumulation of 3H-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.