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 pro toporphyrin plus long-wave ultraviolet light (UVA) irradiation can sup press mediator secretion. In this study we conducted a morphometric an d ultrastructural analysis of rat peritoneal mast cells to investigate possible alterations produced by this treatment before or after stimu lation with calcium ionophore. Protoporphyrin plus UVA, at doses causi ng inhibition of mediator release, had no effect or, either cell size or viability but increased cellular sphericity. There was a 43% reduct ion of the cell surface area, and qualitative inspection of the cells revealed that this change was associated with a reduction in microfold s on the cell surface. After 1 minute of incubation with calcium ionop hore A23187 (1 mu mol/L), both cells that were pretreated with protopo rphyrin plus UVA and control cells showed dramatic changes in granule structure. Although treated cells had an unchanged tendency to have gr anules that closely approached the plasma membrane, there was an inhib ition of granule extrusion in response to ionophore stimulation. These observations may be relevant to the inhibitory effect of protoporphyr in plus UVA on the generation and release of mast cell mediators.