Inhibition of mast cell mediator secretion induced by protoporphyrin plus long-wave ultraviolet light: a morphometric and ultrastructural analysis.

It has been shown that treatment of rat peritoneal mast cells with protoporphyrin plus long-wave ultraviolet light (UVA) irradiation can suppress mediator secretion. In this study we conducted a morphometric and ultrastructural analysis of rat peritoneal mast cells to investigate possible alterations produced by this treatment before or after stimulation with calcium ionophore. Protoporphyrin plus UVA, at doses causing inhibition of mediator release, had no effect on either cell size or viability but increased cellular sphericity. There was a 43% reduction of the cell surface area, and qualitative inspection of the cells revealed that this change was associated with a reduction in microfolds on the cell surface. After 1 minute of incubation with calcium ionophore A23187 (1 mumol/L), both cells that were pretreated with protoporphyrin plus UVA and control cells showed dramatic changes in granule structure. Although treated cells had an unchanged tendency to have granules that closely approached the plasma membrane, there was an inhibition of granule extrusion in response to ionophore stimulation. These observations may be relevant to the inhibitory effect of protoporphyrin plus UVA on the generation and release of mast cell mediators.