GH₃ Cells, Ionic Currents and Cell Killing: Photomodification Sensitized by Rose Bengal

Photosensitization using Rose Bengal (RB) modifies membrane ionic currents and kills cultured mouse pituitary, GH(3), cells. Here we investigate the dose-response relationship for ionic current modification and for cell killing to assess a possible causal link. When exposed to 0.5 mu M RE and 6.5 mW/cm(2) of visible light, calcium current was blocked in 1.9 +/- 0.2 min (mean a SEM; 0.74 +/- 0.08 J/cm(2); n = 18), a transient component of potassium current, tentatively identified as a delayed-rectifier potassium current, disappeared in 52 +/- 8 s (0.34 +/- 0.05 J/cm(2); n = 10) and a steady-state component of potassium current, largely a calcium-activated potassium current, disappeared in 3.5 +/- 0.4 min (1.37 +/- 0.16 J/cm(2); n = 11), conversely, the background leak current increased in magnitude, At 5 min of illumination, the longest time studied here, it continued to increase nearly linearly, making it the only current component studied that is still changing after 5 min of light. Under the conditions used, cell killing increased to 100% in the exposure range of 4-10 min of illumination (1.6 J/cm(2) to 3.9 J/cm(2)) when assessed using fluorescent markers, ethidium homodimer and calcein and required slightly longer exposure times when assessed using trypan blue. Thus, it is difficult to ascribe a causal role in cell killing by photosensitization to alterations of standard ion channels and known ionic currents. However, the increase in leak current has the correct dose-response characteristics to be involved.