Ca2+ INFLUX INDUCED BY PHOTODYNAMIC ACTION IN HUMAN CEREBRAL GLIOMA (U-87 MG) CELLS: POSSIBLE INVOLVEMENT OF A CALCIUM CHANNEL

Abstract The plasma membrane has been implicated as a critical target of photodynamic action on cells. We have observed that the photosensitization of human cerebral glioma (U-87 MG) cells by hematoporphyrin derivative (HpD) causes a large increase in intracellular calcium [Ca²⁺]. This increase in [Ca²⁺]_i was solely due to the influx of extracellular Ca²⁺ through the plasma membrane and showed a dependence on HpD concentration, light dose and concentration of calcium in the extracellular medium. The magnitude of the Ca²⁺ influx decreased with increasing postirradiation time, which suggests that the cell membrane partially recovers from the photodynamic injury. The photoinduced Ca²⁺ influx was inhibited by the Ca²⁺ channel blocker diltiazem and the reducing agent dithioerythritol. These findings are discussed in terms of possible activation of a Ca²⁺ channel as a result of photosensitization.     

The annealing of radical species in γ-irradiated cesium nitrate

The kinetics of thermal annealing of radical species /equivalent nitrite (NO ₂ ^– )', NO ₂ ^– and their difference, (NO ₂ ^– )/ in -irradiated CsNO₃ has been investigated. The data have been nalyzed on the basis of models for vacancy interstititial combination and also on the basis of conventional chemical kinetics.     

BINDING OF HEMATOPORPHYRIN DERIVATIVE TO BRAIN TUMOR CELLS—A FLUORESCENCE SPECTROSCOPIC STUDY

The binding of hematoporphyrin derivative (HpD) to brain tumor cells and their photosensitivity was studied as a function of HpD concentration, time of incubation and growth phase of cells. Upon binding to cells, HpD showed three fluorescence bands at 616, 636 and 678 nm. In plateau phase cells a fluorescence band at 636 nm was predominant, which was further enhanced by increasing HpD concentration and/or increasing incubation time. In exponential phase cells the maximum fluorescence was exhibited at 616 nm. After 1 h incubation of exponential phase cells with increasing HpD concentration an overall intensity enhancement occurred with no change in the distribution of bands, whereas longer incubation time caused an increase in relative intensity of the 636 nm band similar to that observed in plateau phase cells. After 1 h incubation with HpD plateau phase cells were more photosensitive than exponential phase cells, although cell bound HpD was much less in the former case. Incubation of cells for 24 h drastically enhanced the photosensitivity irrespective of the growth phase. Our results suggest a relationship between the fluorescence emission band of HpD at 636 nm and photosensitivity of cells.     

The annealing of chemical radiation damage in acetatopentamminecobalt/III/nitrate

The kinetics of isothermal annealing of NO ₂ ⁻ in γ-irradiated acetatopentamminecobalt/III/ nitrate in the range 95–115 °C is a combination of a first order process affecting 28% of the damage fragments and a second order process, governing the behaviour of the remainder. The annealing data have also been analyzed on the basis of models developed by Fletcher and Brown and by Waite.