Diazepam stimulates migration and phagocytosis of human neutrophils: Possible contribution of peripheral-type benzodiazepine receptors and intracellular calcium

In isolated human neutrophils, diazepam (10 nmol/l to 10 mu mol/l) concentr ation-dependently increased migration and phagocytosis. Diazepam-induced mi gration and phagocytosis were inhibited by the peripheral benzodiazepine re ceptor (PER) antagonist PK11195 (10 mu mol/l). The PER agonist Ro5-4864 (10 nmol/l to 10 mu mol/l) did not affect migration but slightly enhanced phag ocytosis, while clonazepam, which binds to the central-type benzodiazepine receptors but has no affinity for PBRs, was ineffective on both parameters up to 10 mu mol/l. Phagocytosis induced by diazepam or Ro5-4864 was inhibit ed by the Ca2+ channel blocker L-verapamil (10 mu mol/l), which however did not affect the action of diazepam on migration. Competition binding experi ments performed by fluorescent staining of PBRs showed that diazepam direct ly interacts with PBRs on human neutrophils. Both diazepam and Ro5-4864 (10 nmol/l to 10 mu mol/l) induced a rise of intracellular free Ca2+ concentra tions ([Ca2+](i)), which was inhibited by PK11195 (10 mu mol/l) and L-verap amil (10 mu mol/l) and prevented by extracellular Ca2+ chelation with EGTA (5 mmol/l). In conclusion, experimental evidence indicates that in human ne utrophils diazepam stimulates both migration and phagocytosis through activ ation of PBRs. Diazepam-induced [Ca2+](i) changes depend on a PER-operated, L-verapamil-sensitive increase in the plasma membrane permeability and sub sequent extracellular Ca2+ entry, and contribute to diazepam-induced phagoc ytosis. On the contrary, the effect of diazepam on migration seems to occur through Ca2+-independent mechanisms. Copyright (C) 2001 S.Karger AG, Basel .