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.