CHARACTERIZATION OF NA+-DEPENDENT, ACTIVE NUCLEOSIDE TRANSPORT IN RAT AND MOUSE PERITONEAL-MACROPHAGES, A MOUSE MACROPHAGE CELL-LINE AND NORMAL RAT-KIDNEY CELLS

Peritoneal rat macrophages expressed solely an Na+-dependent, concentrative nucleoside transporter, which possesses a single Na+-binding site and transports purine nucleosides and uridine but not thymidine or deoxycytidine. The Michaelis-Menten constants for formycin B and Na+ were about 6 μm and 14 mM, respectively, and the estimated Na+:formycin B stoichiometry was 1:1. Rat macrophages accumulated 5 μM formycin B to a steady-state level exceeding that in the medium by about 500-fold during 60 min of incubation at 37° C. Concentrative formycin B transport was resistant to inhibition by nitrobenzylthioinosine, lidoflazine, dilazep and nifedipine, but was slightly inhibited by high concentrations of dipyridamole (> 10 μM) and probenicid (> 100 μM). Mouse peritoneal macrophages and lines of mouse macrophages and normal rat kidney cells expressed Na+-dependent, active nucleoside transport but in addition significant Na+-independent, facilitated nucleoside transport. Facilitated nucleoside transport in these cells was sensitive to inhibition by nitrobenzylthioinosine, dilazep and dipyridamole. The presence of these inhibitors greatly enhanced the concentrative accumulation of formycin B by these cells by inhibiting the efflux via the facilitated transporter of the formycin B actively transported into the cells. Whereas rat macrophages lacked high-affinity nitrobenzylthioinosine-binding sites, mouse macrophages and normal rat kidney cells possessed about 10 000 such sites/cell. Rat and mouse erythrocytes, rat lymphocytes, and lines of Novikoff rat hepatoma cells, Chinese hamster ovary cells, Mus dunni cells and embryonic monkey kidney cells expressed only facilitated nucleoside transport. © 1990.