Protoporphyrin and Long-Wave Ultraviolet Light Modulate Metabolic Events in Rat Peritoneal Mast Cells

We have previously shown that protoporphyrin (PP) plus long-wave ultraviolet light (UVA) has an inhibitory effect on the release of histamine from rat peritoneal mast cells in response to various stimuli, without compromising cell viability. In the present study, we observed that protoporphyrin at a noncytolytic dose (3 ng/ml) plus UVA irradiation (0.038 J/cm2) is also able to suppress prostaglandin D2 generation by rat peritoneal mast cells in response to calcium ionophore A23187, compound 48/80, or anti-IgE antibody by 64%, 92%, and 100%, respectively. Because of the participation of protein kinase C in stimulus-secretion coupling in mast cells, we also investigated the effect of PP plus UVA on the release of histamine induced by the protein kinase C activator, phorbol 12-myristate 13-acetate (PMA). PP plus UVA inhibited histamine release induced by PMA. The release of histamine induced by the synergistic combination of PMA (50 nM) and a low dose of calcium ionophore A23187 (0.1 μM) was also inhibited. PP plus UVA inhibited the release of histamine induced by the non-fluorescent calcium ionophore, 4-Br-A23187, by 47.8%, but had essentially no effect on changes in intracellular calcium induced by this stimulus. In contrast, both the release of histamine and changes in intracellular calcium stimulated by compound 48/80 were inhibited. We conclude from these results that PP plus UVA may affect both early and late biochemical events involved in mast cell mediator release