Mobilization of Ca²⁺ plays an important role in the degranulation of mast cells. Although events upstream of Ca²⁺ mobilization in the regulation of degranulation are relatively well characterized, the downstream mediators of Ca²⁺ remain largely unknown.

We sought to characterize the downstream signaling mechanism by which Ca²⁺ mobilization mediates degranulation in antigen-stimulated mast cells.

The effect of various inhibitors was examined in the antigen-induced or Ca²⁺ ionophore A23187–induced degranulation process, and the effect of inhibitors on histamine release was tested in the mouse model of asthma.

The δ isoform of protein kinase C (PKC) functions downstream of Ca²⁺ in the signaling pathway from FcεRI to degranulation in RBL-2H3 mast cells. Stimulation of cells with either antigen or the Ca²⁺ ionophore A23187 induced a rapid translocation of PKC-δ from the cytosol to the cellular membranes, and either treatment with the PKC-δ–specific inhibitor rottlerin or infection with an adenovirus encoding a dominant negative mutant of PKC-δ markedly inhibited degranulation induced with antigen or A23187. Furthermore, both the translocation of PKC-δ and degranulation induced by A23187 were inhibited by prevention of the accumulation of reactive oxygen species normally elicited by the ionophore. Finally, intraperitoneal injection of rottlerin prevented the increase in the concentration of histamine in bronchoalveolar lavage fluid induced by means of antigen challenge in a mouse model of allergic asthma.

PKC-δ plays an essential downstream mediatory role in the degranulation elicited by Ca²⁺ mobilization, and reactive oxygen species mediate the activation of PKC-δ by Ca²⁺ in the regulation of degranulation.