Interaction of stilbene disulphonates with cloned K-ATP channels

1 In this study, we tested the effects of the stilbene disulphonates DIDS a nd SITS on three different types of cloned K-ATP channel (Kir6.2/SUR1, Kir6 .2/SUR2A and Kir6.2 DeltaC) heterologously expressed in Xenopus oocytes, wi th the aim of identifying the part of the channel which is involved in medi ating disulphonate inhibition. 2 We found that the inhibitory site(s) for these drugs lies within the Kir6 .2 subunit of the channel, although its properties are further modulated by the sulphonylurea (SUR) subunit. In particular, SUR2A reduces both the rat e and extent of block, by impairing the ability of DIDS binding to produce channel closure. 3 The disulphonate-binding site interacts with the ATP inhibitory site on K ir6.2 because ATP is able to protect against irreversible channel inhibitio n by disulphonates. This effect is not mimicked by tolbutamide (at a concen tration that interacts with Kir6.2) and is abolished by mutations that rend er the channel ATP insensitive. 4 A number of point mutations in both the N and C termini of Kir6.2 reduced the extent and reversibility of channel inhibition by SITS. The results ar e consistent with the idea that residue C42 of Kir6.2 is likely to be invol ved in covalently linking of SITS to the channel. 5 Other types of Kir channel (Kir1.1, Kir2.1 and Kir4.1) were also irrevers ibly blocked by DIDS, suggesting that these channels may share common bindi ng sites for these stilbene disulphonates.