NA+-DEPENDENT, ACTIVE AND NA+-INDEPENDENT, FACILITATED TRANSPORT OF FORMYCIN-B IN MOUSE SPLEEN LYMPHOCYTES

Na+-dependent, active and Na+-independent facilitated nucleoside transport were characterized in mouse spleen cells using rapid kinetic techniques and formycin B, a metabolically inert analog of inosine, as substrate. The Michaelis-Menten constants for formycin B transport by the two transporters were about 30 and 400 μM, respectively. The firstorder rate constant for Na+-dependent transport was about 4-times higher than that for facilitated formycin B transport. The Na+-dependent carrier is specific for uridine and purine nucleosides and accumulates formycin B concentratively in an unmodified form. Concentration accumulation was inhibited by ATP depletion and gramicidin and ouabain treatment of the cells. Our data indicate a single Na+-binding site on the Na+-dependent nucleoside carrier and a Michaelis-menten constant for Na+ of about 10 mM. This transporter was significantly inhibited by dipyridamole and nitrobenzylthioinosine, inhibitors of the facilitated transporter. The Na+-independent, facilitated nucleoside transporter of spleen cells exhibits properties comparable to those of the carrier present in mammalian cells in general. The B lymphocytes remaining after depletion of spleen cell populations of T lymphocytes by incubation with a combination of T-cell specific monoclonal antibodies plus complement exhibited about the same activities of active and facilitated nucleoside transport as the original suspension. © 1990.