Lysosomotropic behavior of adrenergic antagonists in interactions with human neutrophils

Abstract Autonomic neurohormones affect the secretory activity of neutrophils by modulating release of lysosomal enzymes in response to immunologie stimuli. Autonomic agents are also weak bases which might modify cell function by accumulating in the acidic interior of the lysosome, in addition to their receptor-mediated activity. We examined the association of the beta-adrenergic antagonist [ 3 H]dihydroalprenolol with human neutrophils and lysosome and membrane fractions derived from neutrophils, and the subcellular distribution of the photoaffinity-labeled beta-adrenergic ligand [ 3 H]azidobenzylcarazolol after incubation with intact cells. Isolated neutrophil lysosomes accumulated significantly more [ 3 H]dihydroalprenolol than isolated membrane preparations. Decreasing the transmembrane pH gradient markedly reduced [ 3 H]dihydroalprenolol accumulation by intact cells or lysosomes but not by membranes. Since [ 3 H]dihydroalprenolol accumulated by intact cells remained rapidly exchangeable, the photoaffinity ligand [ 3 H]azidobenzylcarazolol was used to assess ligand distribution after association with whole cells. After cell disruption, 18.5 ± 1.3% of this ligand appeared in the lysosome fraction as compared to 2.2 ± 0.6% in the membrane fraction. The secretagogue phorbol myristate acetate caused release of the ligand as well as lysosomal enzymes from cells. These findings suggest that there is significant pH-dependent lysosomal accumulation of beta-antagonists. This lysosomotropic interaction may be important both as it affects the sequestration and redistribution of the drugs, and as it might in some circumstances affect host defense functions of the neutrophil.