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Activation of mast cells (MCs) can be achieved by the high-affinity receptor for IgE (FceRI) as well as by additional receptors such as the lipopolysaccharide (LPS) receptor and the receptor tyrosine kinase Kit (stem cell factor [SCF] receptor). Thus, pharmacological interventions which stabilize MCs in response to different receptors would be preferable in diseases with pathological systemic MC activation such as systemic mastocytosis. 1,4-Benzodiazepines (BDZs) have been reported to suppress MC effector functions. In the present study, our aim was to analyze molecularly the effects of BDZs on MC activation by comparison of the effects of the two BDZs Ro5-4864 and clonazepam, which markedly differ in their affinities for the archetypical BDZ recognition sites, i.e., the GABAA receptor and TSPO (previously termed peripheral-type BDZ receptor). Ro5-4864 is a selective agonist at TSPO, whereas clonazepam is a selective agonist at the GABAA receptor. Ro5-4864 suppressed pro-inflammatory MC effector functions in response to antigen (Ag) (degranulation/cytokine production) and LPS and SCF (cytokine production), whereas clonazepam was inactive. Signaling pathway analyses revealed inhibitory effects of Ro5-4864 on Ag-triggered production of reactive oxygen species, calcium mobilization and activation of different downstream kinases. The initial activation of Src family kinases was attenuated by Ro5-4864 offering a molecular explanation for the observed impacts on various downstream signaling elements. In conclusion, BDZs structurally related to Ro5-4864 might serve as multifunctional MC stabilizers without the sedative effect of GABAA receptorinteracting BDZs. [ABSTRACT FROM AUTHOR]