Toelucidatethemechanismofphotodynamicdamageofcells,theeffectofHPDpluslightontranscriptlonalectlvltyInthemucleusIsolatefromthenormalratliverwasstudiedinvitorby3H-UTPincorporationintoRNA.MeasurementsoffluorescencespectrumshowedthatHPDwasboundtothenucleusanditsfluorescenceIntensityIncreasedwiththeIncreaseofHPDconcentration.TheexperimentalresultsIndicatedthatnochangescouldbeobservedwheneitherHPDorlightwasusedalone.WhereasthenucleartranscriptionactivitywasfoundtobeinhibitedsignificantlybybothHPDandlighttreatment,andthedegreeofInhibitionwasdependentontheHPDconcentrationandthetimeofexposuretolight.Aftertreatmentby3μg/mlHPD,theinhibitionrateofthenucleartranscriptionactivitywas23%,45%,69%,80%and90%,respectivelyforlightexposureof2,5,10,20and30minutes.Ourresultssuggestedthatdose-dependentdecreasesinthenucleartranscriptionactivity,andmarkedinhibitionofthe
