Inhibition of volume-regulated anion channels in cultured endothelial cells by the anti-oestrogens clomiphene and nafoxidine

1 We have used the whole-cell patch clamp technique to study the effect of the partial antioestrogens clomiphene and nafoxidine, the pure anti-oestrogens ICI 182,780 and RU 58,668 and the oestrogen beta -estradiol, on the volume-regulated anion channel (VRAC) in cultured pulmonary artery endothelial (CPAE) cells. 2 In contrast to the pure anti-oestrogens and beta -estradiol, clomiphene and nafoxidine potently inhibited the volume-sensitive chloride current, I-Cl,I-swell, activated by challenging CPAE cells with a 25% hypotonic solution. For clomiphene, the estimated IC50 and Hill coefficient were 1.03+/-0.14 muM and 1.40+/-0.21 respectively. In the case of nafoxidine, these values were 1.61+/-0.29 muM and 1.24+/-0.19. 3 The inhibition induced by the pure enantiomers of clomiphene, zuclomiphene and enclomiphene, was not different from that of the racemic mixture, indicating that the interaction between clomiphene and VRAC is not stereoselective. 4 Clomiphene and nafoxidine inhibited proliferation of CPAE cells. Half-maximal inhibition was found at 1.98+/-0.17 and 1.66+/-0.21 muM respectively, concentrations similar to those for half-maximal block of VRAC. 5 In conclusion, the nonsteroidal partial anti-oestrogens nafoxidine and clomiphene are potent inhibitors of volume-regulated anion channels. The inhibition by clomiphene is not stereoselective and occurs at concentrations close to therapeutically relevant concentrations. Finally, both drugs inhibit the proliferation of endothelial cells.