Nucleoside transporter-mediated uptake and release of [³H]L-adenosine in DDT₁ MF-2 smooth muscle cells

[³H]L-Adenosine, an enantiomer of the physiological D-adenosine, was shown previously to be taken up and released, at least in part, through nucleoside transporters in rat brain preparations. In the present study, we used clonal smooth muscle DDT₁ MF-2 cells that contain almost exclusively equilibrative inhibitor-sensitive (es) nucleoside transporters to test the hypothesis that L-adenosine is a permeant for these bidirectional nucleoside transporters. DDT₁ MF-2 cells accumulated approximately 3 times more [³H]D- than [³H]L-adenosine; 10 μM nitrobenzylthioinosine significantly (P < 0.01) inhibited the accumulation of [³H]D-adenosine by 86% and of [³H]L-adenosine by 63%. The IC₅₀ values for the nitrobenzylthioinosine-sensitive portions of [³H]L- and [³H]D-adenosine accumulation were 1.6 and 2.0 nM, respectively. [³H]D-Adenosine accumulation was significantly (P < 0.05) inhibited by up to 72% with L-adenosine and [³H]L-adenosine accumulation was significantly (P < 0.01) inhibited by up to 52% with D-adenosine. Release of accumulated [³H]L-adenosine was temperature- and time-dependent, and was significantly (P < 0.05) reduced by 47% with dipyridamole, 39% with dilazep, and 45% with nitrobenzylthioinosine; the apparent IC₅₀ value for nitrobenzylthioinosine was < 1 nM. These data indicate that a significant proportion of [³H]L-adenosine uptake and release in DDT₁ MF-2 cells is mediated by es nucleoside transporters.