The uptake of [3H] inosine into human CP incubated in aCSF containing 139 mEq Na+ (squares), Na+-free aCSF medium (triangles), and Na+-free aCSF medium containing either 0.5 μM S-(4-Nitrobenzyl)-6-thioinosine (NBMPR) (circle) or 10 μM NBMPR (deltoid). The data are presented as means ± SEM from 3-4 separate experiments. The uptake values for inosine by CP tissue in aCSF (presence of Na+) after 5 and 10 min of incubation were significantly higher than the corresponding uptake values seen in Na+-free aCSF (p < 0.01). Uptake of inosine after 5 min (n = 3) and 10 min (n = 3) of incubation in the presence of 0.5 μM NBMPR in Na+-free aCSF did not differ significantly from the corresponding uptake after incubation in Na+-free aCSF which did not contain NBMPR (p > 0.05). The presence of 10 μM NBMPR in Na+-free aCSF caused significant inhibition of inosine uptake after 5 min (n = 4, p < 0.01) and after 10 min (n = 3, p < 0.001), when compared to the uptake in Na+-free aCSF which did not contain NBMPR.