ATP4- mediates closure of pancreatic beta-cell ATP-sensitive potassium channels by interaction with 1 of 4 identical sites

• Published in: Diabetes (New York, N.Y.) Vol. 49; no. 9; pp. 1413 - 1418
• Main Authors: MARKWORTH, E, SCHWANSTECHER, C, SCHWANSTECHER, M
• Format: Journal Article
• Language: English
• Published: Alexandria, VA American Diabetes Association 01.09.2000
• Subjects: Adenosine Triphosphate - pharmacology; Adenosine Triphosphate - physiology; Amino Acid Substitution; Animals; Biological and medical sciences; COS Cells; Cricetinae; Diabetes; Endocrine pancreas; Fundamental and applied biological sciences. Psychology; Islets of Langerhans - physiology; Kinetics; Macromolecular Substances; Membrane Potentials; Mice; Morphology. Functional localizations; Mutagenesis, Site-Directed; Potassium; Potassium Channels - chemistry; Potassium Channels - drug effects; Potassium Channels - physiology; Potassium Channels, Inwardly Rectifying; Protein Structure, Quaternary; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Transfection; Vertebrates: endocrinology; Stoichiometry; Cell line; B-Cell; Langerhans islet; Electrophysiology; Ionic channel; ATP; Potassium; Endocrine pancreas
• ISSN: 0012-1797; 1939-327X
• DOI: 10.2337/diabetes.49.9.1413

ATP4- mediates closure of pancreatic beta-cell ATP-sensitive potassium channels by interaction with 1 of 4 identical sites. E Markworth , C Schwanstecher and M Schwanstecher Institute of Pharmacology and Toxicology, University of Braunschweig, Germany. Abstract In pancreatic beta-cells, cytosolic [ATP(4-)] critically controls insulin secretion via inhibition of ATP-sensitive potassium (KATP) channels. These channels are heteromultimers composed with a 4:4 stoichiometry of an inwardly rectifying K+ channel subunit (Kir6.2) plus a regulatory sulfonylurea receptor. To elucidate stoichiometry of ATP(4-) action, we analyzed ATP(4-) sensitivity of channels coassembled from wild-type Kir6.2 and a loss of ATP(4-) sensitivity mutant (G334D). Concentration-inhibition curves for cDNA ratios of 1:1 or 1:10 resembled those for channel block resulting from interaction with 1 of 4 sites, whereas models for inhibition requiring occupation of 2, 3, or 4 sites were incongruous. Random assembly of wild-type Kir6.2 with the G334D mutant was confirmed by controls, which assessed the effect of an additional mutation that induced strong rectification (N160D). We conclude 4 identical noncooperative ATP(4-) sites to be grouped within 1 KATP channel complex, with occupation of 1 site being sufficient to induce channel closure. This architecture might facilitate coupling of [ATP(4-)] to insulin secretion and may protect against diabetic dysregulation resulting from heterozygous mutations in Kir6.2.