Modes of photodynamic vs. sonodynamic cytotoxicity.

We compared effects of ultrasound-induced vs. photodynamic cytotoxicity 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 photodamage. In contrast, ultrasound-induced loss of viability resulted from rapid cell destruction and was proportional to the time of sonication. Photodynamic damage to cells before exposure to ultrasound potentiated cell breakage but did not affect the clonogenicity of the surviving cell population. Photodamage after exposure to ultrasound decreased the viability of cells which had survived ultrasonic treatment.