Intracellular free calcium mediates glioma cell detachment and cytotoxicity after photodynamic therapy

Photofrin photodynamic therapy (PDT) caused a dose-dependent decrease of enzymatic cell detachment by trypsin/ethylenediamine tetra-acetic acid (EDTA) in human glioma U251n and U87 cells. This happened coincidently with the increase of intracellular free calcium ([Ca²⁺]_i). Thapsigargin, which increased [Ca²⁺]_i, induced further decrease in enzymatic cell detachment and increased cytotoxicity. Opposite effects were observed when 1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetra-acetic acid tetrakis, an intracellular Ca²⁺ chelator, was used. PDT-induced changes in [Ca²⁺]_i and cell detachment were not blocked by calcium channel antagonists nickel (Ni²⁺) or nimodipine, nor were they altered when cells were irradiated in a buffer free from Ca²⁺ and magnesium (Mg²⁺), suggesting that [Ca²⁺]_i is derived from the internal calcium stores. Decreased cell migration was observed after PDT, as assessed by chemotactic and wound-healing assays. Our findings indicated that internal calcium store-derived [Ca²⁺]_i plays an important role in PDT-induced enzymatic cell detachment decrease and cytotoxicity. Cell migration may be affected by these changes.