Effect of colforsin on human neutrophil superoxide production and intracellular calcium mobilization

1. The effects of dibutyryl cyclic AMP (cAMP), isoproterenol and colforsin (forskolin) were evaluated on respiratory burst in human polymorphonuclear neutrophils (PMN). 2. Dibutyryl cAMP showed a dose-dependent inhibition of n-formyl-methionyl-leucyl-phenylalanine (FMLP)-induced superoxide production by human PMN. 3. Administration of isoproterenol induced a dose-dependent inhibition of FMLP-induced superoxide production by human PMN, and the inhibition was blocked by propranolol. 4. Administration of colforsin induced a dose-dependent inhibition of FMLP-induced superoxide production by human PMN, and the inhibition could not be blocked by propranolol. 5. Incubation with colforsin caused a significant increase in the cAMP level in human PMN. 6. Pretreatment with colforsin caused a dose-dependent inhibition in the elevation of intracellular free calcium (monitored by fura-2 fluorescence), which was observed in human PMN stimulated with FMLP. 7. These results suggest that cAMP is an inhibitory factor of superoxide production and intracellular calcium mobilization in human PMN stimulated with FMLP.