Differential inhibition and potentiation by cell-permeant analogues of cyclic AMP and cyclic GMP and NO-containing compounds of exocytosis in human neutrophils

Summary

The chemoattractants, N-formyl-L-methio-nyl-L-leucyl-L-phenylalanine (fMet-Leu-Phe), complement C5a and platelet-activating factor (PAF), induce ß-glucuronidase release and aggregation and an increase in cytosolic Ca²⁺ [Ca²⁺]_i in human neutrophils. We studied the roles of cAMP and cGMP in neutrophil avtivation, using their cell-permeant analogues, N⁶,2′-O-dibutyryl adenosine 3′:5′-cyclic monophosphate (Bt2cAMP) and N² ,2′-O-dibutyryl guanosine 3′:5′-cyclic monophosphate (Bt₂cGMP) and the NO-containing compounds, sodium nitroprusside (SNP), 3-morpholino-sydnonimine (SIN-1) and its prodrug, molsidomine (SIN-10). Bt₂cAMP, Bt₂cGMP, SIN-1 and SIN-10 but not SNP inhibited exocytosis induced by fMet-Leu-Phe. Superoxide dismutase potentiated the inhibitory effect of SIN-1. Bt₂cGMP and SNP potentiated C5a-induced ß-glucuronidase release, Bt₂cAMP, KCN, SIN-1 and SIN-10 being ineffective. KCN partially reversed the stimulatory effect of SNP, and in the presence of superoxide dismutase, SIN-1 potentiated C5a-induced exocytosis. PAF-induced ß-glucuronidase release was not affected by Bt₂cAMP, Bt₂cGMP, SNP and SIN-1. Bt₂cGMP was more effective than Bt2cAMP to inhibit aggregation and the increase in [Ca²⁺]_i induced by fet-Leu-Phe at submaximally effective concentrations. C5a-induced rises in [Ca²⁺]_i were not affected by Bt₂cAMP and Bt₂cGMP. Bt₂cAMP but not Bt₂cGMP inhibited the effect of PAF at submaximally effective concentrations on [Ca²⁺]_i. Our data suggest (I) that Bt2cGMP and Bt2cAMP differentially modulate neutrophil activation, that (II) NO-containing compounds partially mimick the effects of Bt₂cGMP on exocytosis and that (III) cGMP plays an inhibitory role in fMet-Leu-Phe- and a stimulatory role in C5a-induced ß-glucuronidase release.