Pharmacological characterization of volume-sensitive, taurine permeable anion channels in rat supraoptic glial cells

1 To characterize the volume-sensitive, osmolyte permeable anion channels r esponsible for the osmodependent release of taurine from supraoptic nucleus (SON) astrocytes, we investigated the pharmacological properties of the [H -3]-taurine efflux from acutely isolated SON. 2 Taurine release induced by hypotonic stimulus (250 mosmol l(-1)) was not antagonized by the taurine transporter blocker guanidinoethyl sulphonate, c onfirming the lack of implication of the transporter. 3 The osmodependent release of taurine was blocked by a variety of Cl- chan nel inhibitors with the order of potency: NPPB > niflumic acid > DPC > DIDS >ATP. On the other hand, release of taurine was only weakly affected by ot her compounds (dideoxyforskolin, 4-bromophenacyl bromide, mibefradil) known to block volume-activated anion channels in other cell preparations, and w as completely insensitive to tamoxifen, a broad inhibitor of these channels . 4 Although the molecular identity of volume-sensitive anion channels is not firmly established, a few genes have been postulated as potential candidat es to encode such channels. We checked the expression in the SON of three o f them, ClC3, phospholemman and VDAC(1), and found that the transcripts of these genes are found in SON neurons, but not in astrocytes. Similar observ ation was previously reported for ClC2. 5 In conclusion, the osmodependent taurine permeable channels of SON astroc ytes display a particular pharmacological profile, suggesting the expressio n of a particular type or subtype of volume-sensitive anion channel, which is likely to be formed by yet unidentified proteins.