Effect of rolipram and dibutyryl cyclic AMP on resequestration of cytosolic calcium in FMLP-activated human neutrophils

1. We have investigated the effects of the selective phosphodiesterase (PDE) type 4 inhibitor, rolipram (0.01–1 μM) on cytosolic Ca²⁺ fluxes in FMLP-activated human neutrophils, as well as on superoxide production by, and release of elastase from, these cells.
2. Cytosolic Ca²⁺ fluxes were measured by use of fura-2 spectrofluorimetry in combination with a radiometric procedure that enables distinction between net efflux and influx of the cation. Superoxide production and elastase release were measured by lucigenin-enhanced chemiluminescence and a colorimetric procedure, respectively.
3. Pretreatment of neutrophils with rolipram did not affect the FMLP-activated release of Ca²⁺ from intracellular stores, but was associated with dose-related acceleration of the rate of decline in fura-2 fluorescence and with decreased efflux, as well as store-operated influx of ⁴⁵Ca²⁺, indicative of enhancement of resequestration of the cation by the endo-membrane Ca²⁺-ATPase.
4. Inhibition of superoxide production and elastase release was observed at concentrations of rolipram which accelerated the clearance of Ca²⁺ from the cytosol of FMLP-activated neutrophils.
5. These effects of rolipram on FMLP-activated Ca²⁺ fluxes, superoxide generation and elastase release were mimicked by pretreatment of neutrophils with dibutyryl cyclic AMP (0.5–4 mM), while theophylline (10–150 μM), a non-specific PDE inhibitor, as well as the β₂-agonist, salbutamol, were less effective.
6. We conclude that rolipram deactivates FMLP-stimulated human neutrophils by enhancement of cyclic AMP-dependent resequestration of cytosolic Ca²⁺.