Characterization of melatonin binding sites in human peripheral blood neutrophils.

In this paper we show the presence of 2-[125I]melatonin binding sites in human neutrophils (hN). The specific binding of melatonin to hN cells and hN membranes was dependent on time and temperature, stable, saturable, and reversible. In competition studies, the specific binding of radioactive melatonin to hN cells or hN membranes was inhibited by increasing concentrations of native melatonin. Scatchard analysis showed the existence of a single class of binding sites with a Kd of 2.1 and 7.1 microM for hN cells and hN membranes, respectively. The binding capacity was of 84 and 132 pM for hN cells and hN membranes, respectively. The affinity of the binding sites for melatonin suggests that they may be relevant in studies on the pharmacological properties of melatonin in regulating human neutrophil activity.