THE EFFECT OF PROTOPORPHYRIN ON HISTAMINE-SECRETION BY RAT PERITONEAL MAST-CELLS - A DUAL PHOTO-TOXIC REACTION

Protoporphyrin[PP]-induced phototoxicity in rat peritoneal mast cells was manifested by inhibition of 48/80-stimulated histamine secretion or by cell lysis. At a protoporphyrin concentration of 100 ng/m (0.17 .mu.M), histamine secretion was completely inhibited after 30 min illumination. After initiation the inhibited state progressed in the dark. H was irreversible, but did not develop into cell lysis. More severe phototoxic reactions in mast cells were not produced by increasing the PP concentration or the incubation time; cell lysis was evoked by increasing the light intensity between 180-950 W/m2, using a light source with emission maxima in the 350-470 nm region. Dual phototoxic effects were demonstrated in erythrocytes by manipulating the illumination conditions. Increased resistance to osmotic lysis was seen under moderate conditions. Decreased resistance and cell lysis were seen under severe conditions. In the absence of protoporphyrin the effect of only light on mast cells was similar to protoporphyrin-phototoxicity, although the light intensities required were higher for inhibition (60-130 W/m2) and lysis (280-950 W/m2). Certain cell functions apparently are specifically disrupted by non cytotoxic phototoxic reactions; phototoxic reactions leading to severe membrane protein denaturation and cell lysis occur. The manifestation of these dual effects depends on the intensity of illumination in the 350-470 nm region.