ATP4- mediates closure of pancreatic beta-cell ATP-sensitive potassium channels by interaction with 1 of 4 identical sites.
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.
Markworth
E
E
Institute of Pharmacology and Toxicology, University of Braunschweig, Germany.
Schwanstecher
C
C
Schwanstecher
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M
D000255:Adenosine Triphosphate / Q000494:pharmacology* / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D006224:Cricetinae; D007515:Islets of Langerhans / Q000502:physiology*; D007700:Kinetics; D046911:Macromolecular Substances; D008564:Membrane Potentials; D051379:Mice; D016297:Mutagenesis, Site-Directed; D015221:Potassium Channels / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection
D046911:Macromolecular Substances; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate