Solubilization and characterization of a low-affinity histamine-binding site on human blood mononuclear cells

The extract of human peripheral blood lymphocytes and monocytes treated with Triton X-100, in direct- and competitive-binding studies, with 10(-6)-10(-2) M [14C]histamine contained a low-affinity binding site whose dissociation constant (Kd 1.8 X 10(-4) M) was commensurate with the concns of histamine (10(-6)-10(-3) M) that result from mast cell and basophil degranulation. Binding was enhanced by millimolar concns of divalent cations and by raising the incubation temp from 4 to 37 degrees C. It was inhibited by trypsin, EDTA, agents interacting with thiol groups, and by Triton X-100 concns greater than 0.2%. Thus a low-affinity histamine receptor that maintains its ligand-binding properties after solubilization from the cell surface was identified.