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 membrane was labeled with lipid specific probe 1,(4-trimethylammonium),6-diphenyl-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 and decay time of TMA-DPH in MC540-treated cells was observed upon light irradiation. The time-dependent anisotropy measurements showed a decrease in the limiting anisotropy (r infinity) and an increase in the rotational relaxation time (phi) of the probe upon photosensitization of cells. Analysis of these data using wobbling in cone model for probe rotation in the membrane indicated an increase in the cone angle (theta c) and a decrease in the order parameter (S). Protein specific probe N-(1-pyrene)-maleimide was used to study the effect of photosensitization on the plasma membrane proteins. An increase in the rotational relaxation time and a decrease in the ratio of excimer to monomer fluorescence intensity of PM was observed on photosensitization. Photodynamic action of MC540 also caused an inhibition of protein SH groups and Na(+)-K(+)-ATPase activity of plasma membrane. Our results demonstrate that the photodynamic action of MC540 decreases the order of the lipid bilayer and reduces the mobility of the proteins in the plasma membrane of cells.