In neutrophils, activation of the beta2-adrenergic receptor (beta2AR), a Gs-coupled receptor,
inhibits inflammatory responses, which could be therapeutically exploited. The aim of this study was to
evaluate the effects of various beta2AR ligands on adenosine-3',5'-cyclic monophosphate (cAMP)
accumulation and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced superoxide anion
(O2*-) production in human neutrophils and to probe the concept of ligand-specific receptor
conformations (also referred to as functional selectivity or biased signaling) in a native cell system.
cAMP concentration was determined by HPLC/tandem mass spectrometry, and O2*- formation was
assessed by superoxide dismutase-inhibitable reduction of ferricytochrome c. beta2AR agonists were
generally more potent in inhibiting fMLP-induced O2*- production than in stimulating cAMP
accumulation. (-)-Ephedrine and dichloroisoproterenol were devoid of any agonistic activity in the
cAMP assay, but partially inhibited fMLP-induced O2*- production. Moreover, (-)-adrenaline was equiefficacious
in both assays whereas the efficacy of salbutamol was more than two-fold higher in the O2*-
assay. In contrast to the agonists, the effects of beta2AR antagonists were comparable between the two
parameters on neutrophils. Differences between the data from neutrophils and recombinant test
systems were observed for the beta2AR agonists as well as for the beta2AR antagonists. Lastly, we
obtained no evidence for an involvement of protein kinase A in the inhibition of fMLP-induced O2*-
production after beta2AR-stimulation, although, in principle, cAMP-increasing substances can inhibit
O2*- production. Taken together, our data corroborate the concept of ligand-specific receptor
conformations with unique signaling capabilities and suggest that the beta2AR inhibits O2*-
production in a cAMP-independent manner.