The present address of Dr. J. G. Gu is Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032, U.S.A.
Involvement of Bidirectional Adenosine Transporters in the Release of l-[3H]Adenosine from Rat Brain Synaptosomal Preparations
Version of Record online: 23 NOV 2002
Journal of Neurochemistry
Volume 64, Issue 5, pages 2105–2110, May 1995
How to Cite
Gu, J. G., Foga, I. O., Parkinson, F. E. and Geiger, J. D. (1995), Involvement of Bidirectional Adenosine Transporters in the Release of l-[3H]Adenosine from Rat Brain Synaptosomal Preparations. Journal of Neurochemistry, 64: 2105–2110. doi: 10.1046/j.1471-4159.1995.64052105.x
- Issue online: 23 NOV 2002
- Version of Record online: 23 NOV 2002
- Resubmitted manuscript received June 24, 1994; final revised manuscript received November 3, 1994; accepted November 4, 1994.
- Nucleoside transport inhibitors
Abstract: Adenosine transport inhibitors as enhancers of extracellular levels of endogenous adenosine would, presumably, only be effective if, for example, (1) the inhibitors block influx to a greater degree than efflux (release) of intracellular adenosine or (2) the inhibitors block equally well the influx and efflux of adenosine, but significant amounts of adenosine are formed as a result of dephosphorylation of released adenine nucleotides. Limited information is available regarding the directional symmetry of adenosine transporters in neural cells. Using rat brain crude P2 synaptosomal preparations preloaded with l-[3H]adenosine, our objectives here were to determine (1) if l-[3H]adenosine, a substrate for adenosine transporters that is more metabolically stable than physiological d-adenosine, was being released from synaptosomal preparations, (2) the optimal conditions necessary to observe the release, and (3) the degree to which this release was mediated by efflux through bidirectional nucleoside transporters. l-[3H]Adenosine release was found to be concentration and time dependent, temperature sensitive, and linear with synaptosomal protein. l-[3H]Adenosine release was inhibited dose-dependently by dipyridamole, nitrobenzylthioinosine, and dilazep; at concentrations of 100 µM inhibition was at least 40% for dipyridamole, 52% for nitrobenzylthioinosine, and 49% for dilazep. After loading with l-[3H]adenosine alone or l-[3H]adenosine plus unlabeled l-adenosine, d-adenosine, or uridine, l-[3H]-adenosine release was inhibited 42% by l-adenosine, 69% by uridine, and 81% by d-adenosine. The inhibition of l-[3H]adenosine release from the synaptosomal preparations by substrates for or inhibitors of nucleoside transporters suggests that a portion of the release was mediated by nucleoside transporters. This experimental system may prove useful for evaluating the effects of pharmacological agents on bidirectional transport of adenosine.