Transport and interaction of drugs in leukocytes

The accumulation of selected CNS drugs by rat leukocytes was previously reported. This paper presents evidence for the transport into leukocytes of additional drugs. Also studied was the inhibition of the latter processes by various structurally related compounds. The markedly rapid and sodium-independent uptakes into rat leukocytes of amphetamine, codeine, methadone and naloxone fulfilled the basic criteria for active transport. The uptake of morphine was apparently accomplished by more than one process. The affinities of the high capacity transport systems (approximate V_max: 100 nmoles/g cells/5sec) varied considerably as reflected by the two extreme K_m values obtained for methadone (20 μM) and morphine (1.8 mM). A variety of amines inhibited the cellular transport of the drugs. Most potent inhibitors were quinacrine (K_i: 0.5 to 3 μM), desipramine (K_i: 6–20 μM) and methadone (K_i: 18–25 μM). Morphine and tryptamine exhibited inhibition constants higher than 1 mM. The cellular transport processes newly described in rat leukocytes apparently represent a novel addition to the heterogenous biological transport of basic amines. The structural specificity of amine transport in various tissues is discussed.