Résumé
1 To characterize the volume-sensitive, osmolyte permeable anion channels responsible for the osmodependent release of taurine from supraoptic nucleus (SON) astrocytes, we investigated the pharmacological properties of the [ 3 H]-taurine eux from acutely isolated SON. 2 Taurine release induced by hypotonic stimulus (250 mosmol l 71) was not antagonized by the taurine transporter blocker guanidinoethyl sulphonate, con®rming the lack of implication of the transporter. 3 The osmodependent release of taurine was blocked by a variety of Cl 7 channel inhibitors with the order of potency: NPPB4ni¯umic acid4DPC4DIDS4ATP. On the other hand, release of taurine was only weakly aected by other compounds (dideoxyforskolin, 4-bromophenacyl bromide, mibefradil) known to block volume-activated anion channels in other cell preparations, and was completely insensitive to tamoxifen, a broad inhibitor of these channels. 4 Although the molecular identity of volume-sensitive anion channels is not ®rmly established, a few genes have been postulated as potential candidates to encode such channels. We checked the expression in the SON of three of them, ClC 3 , phospholemman and VDAC 1 , and found that the transcripts of these genes are found in SON neurons, but not in astrocytes. Similar observation was previously reported for ClC 2. 5 In conclusion, the osmodependent taurine permeable channels of SON astrocytes display a particular pharmacological pro®le, suggesting the expression of a particular type or subtype of volume-sensitive anion channel, which is likely to be formed by yet unidenti®ed proteins.