MODES OF PHOTODYNAMIC VS SONODYNAMIC CYTOTOXICITY

We compared effects of ultrasound-induced vs. photodynamic cytotoxicit y in cell culture. The photodynamic effects mediated by mesoporphyrin caused a delayed toxic reaction, the presence of a ''shoulder'' on the dose-response curve, indicating the capacity for limited repair of ph otodamage. In contrast, ultrasound-induced loss of viability resulted from rapid cell destruction and was proportional to the time of sonica tion. Photodynamic damage to cells before exposure to ultrasound poten tiated cell breakage but did not affect the clonogenicity of the survi ving cell population. Photodamage after exposure to ultrasound decreas ed the viability of cells which had survived ultrasonic treatment.