Photohemolysis sensitized by psoralen: reciprocity law is not fulfilled.

The effect of the intensity of ultraviolet-A (UV-A) radiation (366 nm) on delayed photohemolysis sensitized by psoralen (PUV-A hemolysis) was studied. It was shown that PUV-A hemolysis induced by UV-A radiation at low fluence rate (20 W m-2) develops according to the well-known colloid-osmotic mechanism: there was no threshold dose of PUV-A treatment. After irradiation all the cells were hemolysed. The rate of PUV-A hemolysis was proportional to the square of the fluence. Hemolysis was delayed in the presence of sucrose. When the fluence rate of UV-A radiation was increased to 150 W m-2, the character of PUV-A hemolysis changed drastically. A threshold fluence appeared, below which PUV-A hemolysis was not induced. At fluences slightly exceeding the threshold, only part of the cells in the suspension were lysed. The dependence of the portion of hemolysing cells on fluence was S-shaped. Increasing the fluence resulted in complete (100%) hemolysis. The rate of complete hemolysis decreased at higher fluences, but was many-fold higher than the rate of low-intensity PUV-A hemolysis at equal fluences. The main features of high intensity PUV-A hemolysis (dependences on fluence and temperature, effect of sucrose) were the same for the hemolysis induced by the addition of previously photooxidized psoralen. We suggest that high intensity PUV-A hemolysis is induced with participation of photooxidized psoralen as an intermediate.