Analysis of 3H-histamine interaction with lymphocytes: receptor binding or uptake?

The immunoregulatory role of histamine is presumably mediated by specific receptors on the plasma membrane of lymphocytes. However, using murine spleen cells and a whole cell assay commonly applied in hormone receptor studies, specific histamine receptors with an affinity higher than that of non-specific binding could not be identified. Nevertheless, approximately 30% of the totally bound histamine was undissociable over a range of added histamine concentrations (9 X 10(-6)-1 X 10(-2) M). Lectin stimulation of spleen cells caused an additional two-fold increase of undissociable histamine. The H1 receptor antagonist, diphenhydramine, blocked histamine uptake, whereas the H2 receptor antagonist, cimetidine, had no effect. Binding experiments carried out at 4 degrees C demonstrated that the amount of undissociable histamine was much reduced. Even at 4 degrees C, evidence for specific membrane associated histamine receptor could not be obtained. It was therefore concluded that lymphocytes take up histamine by an energy-dependent mechanism inhibitable by diphenhydramine but not cimetidine, and that the usual hormone receptor methodology did not allow the identification of specific membrane associated histamine receptors.