ALTERATIONS IN PLASMA-MEMBRANE OF GLIOBLASTOMA CELLS BY PHOTODYNAMIC-ACTION OF MEROCYANINE-540

Photodynamic action of merocyanine 540 (MC540) on the plasma membrane of human glioblastoma (U-87MG) cells has been investigated. Plasma mem brane was labeled with lipid specific probe (4-trimethylammonium),6-di phenyl-1,3,5-hexatriene. Steady-state anisotropy, decay time and time- dependent anisotropy of TMA-DPH in U-87MG cells have been measured as a function of light dose. A decrease in the steady-state anisotropy an d decay time of TMA-DPH in MC540-treated cells was observed upon light irradiation. The time-dependent anisotropy measurements showed a decr ease in the limiting anisotropy (r(infinity)) and an increase in the r otational relaxation time (phi) of the probe upon photosensitization o f cells. Analysis of these data using wobbling in cone model for probe rotation in the membrane indicated an increase in the cone angle (the ta(c)) and a decrease in the order parameter (S). Protein specific pro be N-(1-pyrene)-maleimide was used to study the effect of photosensiti zation on the plasma membrane proteins. An increase in the rotational relaxation time and a decrease in the ratio of excimer to monomer fluo rescence intensity of PM was observed on photosensitization. Photodyna mic action of MC540 also caused an inhibition of protein SH groups and Na+-K+-ATPase activity of plasma membrane. Our results demonstrate th at the photodynamic action of MC540 decreases the order of the lipid b ilayer and reduces the mobility of the proteins in the plasma membrane of cells.