Identification of the high-affinity tolbutamide site on the SUR1 subunit of the K(ATP) channel.

Journal article

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.

Authors: Ashfield, R; Gribble, F; Ashcroft, S; Ashcroft, F

• Publication status: Published
• Journal: Diabetes
• Volume: 48
• Issue: 6
• Pages: 1341-1347
• Publication date: 1999-06-01
• DOI: 10.2337/diabetes.48.6.1341
• EISSN: 1939-327X
• ISSN: 0012-1797
• Language: English
• Keywords: Amino Acid Substitution; Sulfonylurea Compounds; COS Cells; Animals; Glyburide; Tolbutamide; Rats; ATP-Binding Cassette Transporters; Receptors, Drug; Xenopus; Transfection; Potassium Channels; Potassium Channels, Inwardly Rectifying; Hypoglycemic Agents; Adenosine Diphosphate; Binding Sites