High-affinity [3H]6-nitroquipazine binding to the 5-hydroxytryptamine transport system in rat lung.

[3H]6-Nitroquipazine bound to rat lung membranes at 37 degrees with a dissociation constant (Kd) of 0.310 +/- 0.13 nM and a maximal number of binding sites (Bmax) of 1752 +/- 334 fmol/mg protein (mean +/- SD, N = 4). The binding was saturable, of high affinity and sodium dependent. Drug inhibition studies indicated that [3H]6-nitroquipazine binding in the lung is similar to that already reported in the rat brain and human platelets. Scatchard analysis indicated that 5-hydroxytryptamine (5-HT) inhibited [3H]6-nitroquipazine binding to rat lung membranes in a competitive manner. The present results suggest that [3H]6-nitroquipazine binding sites in the rat lung are associated with the uptake system of 5-HT.