Fig. 1. The electrical-field-induced Ca²⁺ response in multicellular prostate tumor spheroids. (A) Image gallery of representative multicellular tumor spheroids treated with a single electrical field pulse (750 Vm^-1, 60 seconds). Images were recorded from the start point of the Ca²⁺ response, which occurred approximately 40 seconds after the onset of the electrical field. Tumor spheroids were loaded with the fluorescent Ca²⁺ indicator fluo-3. The Ca²⁺ response started at the anode-facing side and propagated towards the cathode-facing side. Images were recorded in 3 second intervals. Bar, 50 µm. (B) Representative tracings of the electrical-field-treated Ca²⁺ response recorded in single cells at the anode- as well as the cathode-facing side of the tumor spheroid. (C) Ca²⁺ responses in single cells of multicellular tumor spheroids after repetitive treatment with electrical field pulses (750 Vm^-1, 60 seconds). Note that repetitive treatment with the electrical field decreased the amplitude as well as the duration of the Ca²⁺ response.