Ca(2+) chelating agents are widely used in biological research for Ca(2+) buffering. Here we report that BAPTA, EDTA and HEDTA produce fast, reversible, voltage-dependent inhibition of swelling-activated Cl(-) current (I(Cl,swell)) in LNCaP prostate cancer epithelial cells that is unrelated to their Ca(2+) binding. BAPTA was the most effective (maximal blockade 67%, IC(50)=70 microM, at +100 mV) followed by EDTA and HEDTA. I(Cl,swell) blockade by EDTA was pH-dependent. BAPTA blocked I(Cl,swell) also in other cell types. We conclude that Ca(2+) chelating agents block I(Cl,swell) by acting directly on the underlying channel, and that the negative charge of the free chelator form is critical for the blockade.