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ATP-sensitive potassium channels (K(ATP)) are formed from four pore-forming Kir6.2 subunits complexed with four regulatory sulfonylurea receptor subunits (SUR1 in pancreatic beta-cells, SUR2A in heart). The sensitivity of the channel to different sulfonylureas depends on the SUR isoform. In particular, Kir6.2-SUR1 but not Kir6.2-SUR2A channels are blocked by tolbutamide with high affinity. We made chimeras between SUR1 and SUR2A to identify the region of the protein involved in high-affinity tolbutamide block. Chimeric SURs were coexpressed with Kir6.2 in Xenopus oocytes, and macroscopic currents were measured in inside-out membrane patches. High-affinity tolbutamide inhibition could be conferred on SUR2A by replacing transmembrane domains (TMs) 14-16 with the corresponding region of SUR1. Conversely, high-affinity tolbutamide inhibition of SUR1 was abolished by replacing TMs 13-16 with the corresponding SUR2A sequence, or by mutating a single serine residue within this region to tyrosine (S1237Y). Binding of [3H]glibenclamide to membranes expressing SUR1 was abolished concomitantly with the loss of high-affinity tolbutamide block. These results suggest that a site in the COOH-terminal set of TMs of the SUR1 subunit of the K(ATP) channel is involved in the binding of tolbutamide and glibenclamide.

Type

Journal article

Journal

Diabetes

Publication Date

06/1999

Volume

48

Pages

1341 - 1347

Keywords

ATP-Binding Cassette Transporters, Adenosine Diphosphate, Amino Acid Substitution, Animals, Binding Sites, COS Cells, Glyburide, Hypoglycemic Agents, Potassium Channels, Potassium Channels, Inwardly Rectifying, Rats, Receptors, Drug, Sulfonylurea Compounds, Sulfonylurea Receptors, Tolbutamide, Transfection, Xenopus