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

Abstract 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 [ 14 C]histamine contained a low-affinity binding site whose dissociation constant ( K d 1.8 × 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°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.