CSF‐1 stimulates nucleoside transport in S1 macrophages

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Abstract
We have examined nucleoside transport (NT) in a cell line derived from primary day 7 murine bone marrow macrophages (S1 macrophages) in response to the macrophage growth factor, colony-stimulating factor 1 (CSF-1). Adenosine and uridine transport in quiescent S1 macrophages occurred primarily by two facilitated diffusional routes, one that was sensitive and one that was relatively resistant to the inhibitor nitrobenzylthioinosine (NBMPR). Addition of CSF-1 to quiescent cultures resulted in increased adenosine and uridine transport with biphasic kinetics with respect to the cell cycle. Basal NT activity was elevated (about twofold) within 15 min of CSF-1 addition, returned to near basal levels by 1 h, and then increased again (three- to fourfold) 8–12 h later, returning again to basal levels by 48 h post CSF-1 stimulation. We propose that the large increase in NT activity at 8–12 h corresponded with the time when cultures synchronously began to enter the S phase of the cell cycle. In addition to these changes in the absolute rates, the proportions of NBMPR-sensitive and NBMPR-insensitive transport also change after CSF-1 addition. Quiescent cultures exhibited primarily NBMPR-insensitve transport while logrithmically growing cultures exhibited primarily NBMPR-sensitive nucleoside transport activity. The increase in the NBMPR-sensitive component of the transport process paralleled a similar increase in the number of high-affinity NBMPR binding sites, suggesting that the mechanism for upregulating NBMPR-sensitive NT activity involves increases in the number of NBMPR-sensitive transporter sites. Interestingly, we were unable to detect Na+-dependent concentrative uptake of adenosine, uridine, or formycin-B either in the S1 macrophage cell line or in primary (day 7) murine macrophages. Thus these bone marrow derived macrophages did not display the characteristically large Na+-dependent transport systems observed by others in peritoneal macrophages, implying that these two populations of macrophages are, indeed, functionally distinct.