[Hematoporphyrin derivative (HPD) plus light on transcription activity in the nucleus]

To elucidate the mechanism of photodynamic damage of cells, the effect of HPD plus light on transcription activity in the nucleus isolated from the normal rat liver was studied in vitro by 3H-UTP incorporation into RNA. Measurement of fluorescence spectrum showed that HPD was bound to the nucleus and its fluorescence intensity increased with HPD concentration. The nuclear transcription activity was found to be inhibited significantly and the degree of inhibition was dependent on HPD concentration and the time of exposure to light. After treatment by 3 micrograms/ml HPD, the inhibition rate of the nuclear transcription activity was 23%, 45%, 69%, 80% and 90%, respectively for light exposure of 2, 5, 10, 20 and 30 minutes.