Abstract
Among cultured cell lines, considerable diversity has been shown in the sensitivity of cellular nucleoside transport (NT) systems to nitrobenzylthioinosine (NBMPR), a potent inhibitor of facilitated diffusion NT systems. In cultured S49 lymphoma cells and human erythrocytes, NT systems are of high NBMPR sensitivity (IC50 1 μM). A number of cell lines, including leukemia L1210, appear to possess NT systems of both high and low sensitivity to NBMPR. We report the joint presence in cultured hepatoma cells (Novikoff UASJ-2.9, Morris 3924A, Reuber H-35) of NT systems with low NBMPR sensitivity and NBMPR binding sites, a finding which suggests that the latter do not interact with the former. Implications of these findings are discussed. Recognition of energy-requiring, concentrative NT systems in several cell types has added to the complexity of this area. We describe studies of formycin B permeation into cultured IEC-6 intestinal epithelial cells, which show the presence of (a) a concentrative NT system of low NBMPR sensitivity that requires an inward Na+ gradient, and (b) an NBMPR-sensitive transporter that mediates formycin B efflux.
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