[H-3]adenosine transport in DDT1 MF-2 smooth muscle cells: Inhibition by metabolites of propentofylline

Adenosine receptor signal transduction mechanisms have previously been characterized in Syrian hamster smooth muscle DDT1 MF-2 cells but adenosine transport in these cells has not. DDT1 MF-2 cells possess a high density (370000 sites/cell) of high affinity (K-d value of 0.26 nM) binding sites for [H-3]nitrobenzylthioinosine, a marker for the equilibrative and inhibitor-sensitive subtype of nucleoside transporters. Transport of [H-3]adenosine was insensitive to Na+ and was inhibited by the nucleoside transport inhibitors nitrobenzylthioinosine, dilazep and dipyridamole with IC50 values of 1, 13 and 270 nM, respectively. Propentofylline, a neuroprotective compound that can inhibit nucleoside transporters, is rapidly metabolized in vivo to the racemate (+/-)-A720287. Based on recent findings that some transport inhibitors exhibit marked stereoselectivity, we tested the degree to which individual stereoisomers of (+/-)-A720287 affect adenosine transport. Propentofylline inhibited [H-3]adenosine transport in DDT1 MF-2 cells with an IC50 value of 24 mu M (+/-)-A720287 and the individual stereoisomers (+)-833791 and (-)-844261 had similar potency to propentofylline for inhibition of [H-3]adenosine transport in DDT1 MF-2 cells as well as in clonal mouse leukemia L1210/B23.1 cells, cells which possess only the equilibrative and inhibitor-sensitive subtype of nucleoside transporters. Thus, the neuroprotective effects of propentofylline may be due, in part, to the primary metabolites of propentofylline.