Homo- and heteroexchange of adenine nucleotides and nucleosides in rat hippocampal slices by the nucleoside transport system.

(1) Here, we investigated how nucleotides and nucleosides affect the release of tritiated purines and endogenous adenosine 5'-triphosphate (ATP) from superfused rat hippocampal slices. (2) ATP elicited concentration-dependent [(3)H]purine efflux from slices preloaded with [(3)H]adenosine. High-performance liquid chromatography analysis of the effluent showed that the tritium label represented the whole set of adenine nucleotides and nucleosides, and ATP significantly increased the outflow of [(3)H]ATP. (3) Adenosine 5'-diphosphate, adenosine, uridine, uridine 5'-triphosphate, alpha,beta-methylene-ATP and 3'-O-(4-benzoylbenzoyl)-ATP were also active in eliciting [(3)H]purine release. Adenosine (300 micro M) also evoked endogenous ATP efflux from the hippocampal slices. (4) Reverse transcription-coupled-polymerase chain reaction analysis revealed that mRNAs encoding a variety of P2X and P2Y receptor proteins are expressed in the rat hippocampus. Nevertheless, neither P2 receptor (i.e. pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid, 30 micro M, suramin, 300 micro M and reactive blue 2, 10 micro M), nor adenosine receptor (8-cyclopentyl-1,3-dipropylxanthine, 250 nM and dimethyl-1-propargylxanthine, 250 nM) antagonists modified the effect of ATP (300 micro M) to evoke [(3)H]purine release. (5) The nucleoside transport inhibitors, dipyridamole (10 micro M), nitrobenzylthioinosine (10 micro M) and adenosine deaminase (2-10 U ml(-1)), but not the ecto-adenylate kinase inhibitor diadenosine pentaphosphate (200 micro M) significantly reduced ATP-evoked [(3)H]purine efflux. (6) In summary, we found that ATP and other nucleotides and nucleosides promote the release of one another and themselves by the nucleoside transport system. This action could have relevance during physiological and pathological elevation of extracellular purine levels high enough to reverse the nucleoside transporter.