Muramyl peptides and serotonin interact at specific binding sites on macrophages and enhance superoxide release.

Serotonin at low micromolar concentrations inhibited binding of two [125I]-labeled muramyl peptides to resident mouse peritoneal cells and to a macrophage-derived cell line, PU5-1.8-F7. Binding of [3H]serotonin was inhibited in parallel fashion. Overnight incubation with serotonin or muramyl peptide enhanced the release of superoxide by both types of cells when later stimulated with phorbol myristate acetate. Serotonin antagonists decreased binding of muramyl peptide and serotonin and diminished the subsequent enhancement of superoxide release. A cell line variant lacking detectable binding sites for muramyl peptide was far less responsive (superoxide release) than the parent line, to either drug. The data are consistent with sharing of a common set of receptors on the macrophage by muramyl peptide and serotonin and with involvement of these receptors in enhancing superoxide release.