Photolysis of mast cells in presence of protoporphyrin.

The effects of ultraviolet and visible irradiation in presence of protoporhyrin upon mast cells were investigated. Rat peritoneal mast cells were suspended in a medium containing varying concentrations of protoporphyrin and were irradiated using a mercury vapor lamp. The release of histamine is related to both the concentrations of protoporphyrin and the period of irradiation. Comparatively negligible amounts of histamine were released when the cells were irradiated in absence of protophyrin or when the cells were incubated in the dark in presence of protoporphyrin. When 51Cr-labelled cells were employed, the release of histamine was paralleled by the release of 51Cr. These results suggest that the release of histamine was due to the lysis of cells. It was found that 2-deoxyglucose, iodoacetate and carbonyl cyanide, m-chlorophenyl hydrazone at concentrations which are known to inhibit the secretory release of histamine or uncouple oxidative phosphorylation, had no effect on the photolysis of mast cells. When mast cells were irradiated in presence of protoporphyrin for 5 to 10 minutes and then kept in the dark, the release of histamine was greater than when the cells were irradiated but not subsequently kept in the dark. It is suggested that the initial site of photochemical lysis is at or near the cell surface.