Sulphonic acid derivatives as probes of pore properties of volume-regulated anion channels in endothelial cells

1 We have used the whole-cell patch-clamp technique to study the effects of 4-sulphonic-calixarenes and some other poly-sulphonic acid agents, such as suramin and basilen blue, on volume-regulated anion channel (VRAC:) curren ts in cultured endothelial cells (CPAE cells). 2 The 4-sulphonic-calixarenes induced a fast inhibition at positive potenti als but were ineffective at negative potentials. At small positive potentia ls, 4-sulphonic-calix[4]arene was a more effective inhibitor than 4-sulphon ic-calix[6]arene and -calix[8]arene, which became more effective at more po sitive potentials. 3 Also suramin and basilen blue induced a voltage dependent current inhibit ion, reaching a maximum around +40 mV and declining at more positive potent ials. 4 The voltage dependence of inhibition was modelled by assuming that these negatively charged molecules bind to a site inside VRAC that senses a fract ion delta of the applied electrical field, ranging beween 0.16 to 0.32. 4-S ulphonic-calix[4]arene, suramin and basilen blue bind and occlude VRAC at m oderate potentials, but permeate the channel at more positive potentials. 4 -Sulphonic-calix[6]arene and -calix[8]arene however do not permeate the cha nnel. From the structural information of the calixarenes, we estimate a low er and upper limit of 11*12 and 17*12 Angstrom(2) respectively for the cros s-sectional area of the pore.